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Journal Cover Global Change Biology
  [SJR: 5.379]   [H-I: 167]   [123 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1354-1013 - ISSN (Online) 1365-2486
   Published by John Wiley and Sons Homepage  [1579 journals]
  • Experimental warming alters spring phenology of certain plant functional
           groups in an early-successional forest community
    • Authors: C.R. Rollinson; M.W. Kaye
      Abstract: Experimental study of the effects of projected climate change on plant phenology allows us to isolate effects of warming on life history events such as leaf out. We simulated a 2°C temperature increase and 20% precipitation increase in a recently harvested temperate deciduous forest community in central Pennsylvania, USA, and observed the leaf out phenology of all species in 2009 and 2010. Over 130 plant species were monitored weekly in study plots, but due to high variability in species composition among plots, species were grouped into five functional groups: short forbs, tall forbs, shrubs, small trees, and large trees. Tall forbs and large trees, which usually emerge in the late spring, advanced leaf out 14-18 days in response to warming. Short forbs, shrubs, and small trees emerge early in spring and did not alter their phenology in response to warming or increased precipitation treatments. Earlier leaf out of tall forbs and large trees coincided with almost three weeks of increased community-level leaf area index (LAI), indicating greater competition and a condensed spring green-up period. While phenology of large trees and tall forbs appears to be strongly influenced by temperature-based growth cues, our results suggest that photoperiod and chilling cues more strongly influence the leaf out of other functional groups. Reduced freeze events and warmer temperatures from predicted climate change will interact with non-temperature growth cues to have cascading consequences throughout the ecosystem.
      PubDate: 2012-01-06T15:46:14.502111-05:
      DOI: 10.1111/j.1365-2486.2012.02612.x
  • Yield vs. quality trade-offs for wheat in response to carbon dioxide and
    • Authors: Håkan Pleijel; Johan Uddling
      Abstract: Although it is established that there exist potential trade-offs between grain yield and grain quality in wheat exposed to elevated carbon dioxide (CO2) and ozone (O3), their underlying causes remain poorly explored. To investigate the processes affecting grain quality under altered CO2 and O3, we analysed 57 experiments with CO2 or O3 exposure in different exposure systems. The study covered 24 cultivars studied in 112 experimental treatments from 11 countries. A significant growth dilution effect on grain protein was found: a change in grain yield of 10% by O3 was associated with a change in grain protein yield of 8.1% (R2=0.96), while a change in yield effect of 10% by CO2 was linked to a change in grain protein yield effect of 7.5% (R2=0.74). Superimposed on this effect, elevated CO2, but not O3, had a significant negative effect on grain protein yield also in the absence of effects on grain yield, indicating that there exists a process by which CO2 restricts grain protein accumulation, which is absent for O3. Grain mass, another quality trait, was more strongly affected by O3 than grain number, while the opposite was true for CO2. Harvest index was strongly and negatively influenced by O3, but was unaffected by CO2.We conclude that yield vs. protein trade-offs for wheat in response to CO2 and O3 are constrained by close relationships between effects on grain biomass and less than proportional effects on grain protein. An important and novel finding was that elevated CO2 has a direct negative effect on grain protein accumulation independent of the yield effect, supporting recent evidence of CO2-induced impairment of nitrate uptake/assimilation. Finally, our results demonstrated that processes underlying responses of grain yield vs. quality trade-offs are very different in wheat exposed to elevated O3 compared to elevated CO2.
      PubDate: 2011-07-06T02:52:44.55371-05:0
      DOI: 10.1111/j.1365-2486.2011.02489.x
  • Spring fasting behavior in a marine apex predator provides an index of
           ecosystem productivity
    • Abstract: The effects of declining Arctic sea ice on local ecosystem productivity are not well understood but have been shown to vary inter‐specifically, spatially, and temporally. Because marine mammals occupy upper trophic‐levels in Arctic food webs, they may be useful indicators for understanding variation in ecosystem productivity. Polar bears (Ursus maritimus) are apex predators that primarily consume benthic and pelagic‐feeding ice‐associated seals. As such, their productivity integrates sea ice conditions and the ecosystem supporting them. Declining sea ice availability has been linked to negative population effects for polar bears but does not fully explain observed population changes. We examined relationships between spring foraging success of polar bears and sea ice conditions, prey productivity, and general patterns of ecosystem productivity in the Beaufort and Chukchi Seas. Fasting status (≥ 7 days) was estimated using serum urea and creatinine levels of 1,448 samples collected from 1,177 adult and subadult bears across three subpopulations. Fasting increased in the Beaufort Sea between 1983‐1999 and 2000‐2016 and was related to an index of ringed seal body condition. This change was concurrent with declines in body condition of polar bears and observed changes in the diet, condition and/or reproduction of four other vertebrate consumers within the food chain. In contrast, fasting declined in Chukchi Sea polar bears between periods and was less common than in the two Beaufort Sea subpopulations consistent with studies demonstrating higher primary productivity and maintenance or improved body condition in polar bears, ringed seals, and bearded seals despite recent sea ice loss in this region. Consistency between regional and temporal variation in spring polar bear fasting and food web productivity suggest that polar bears may be a useful indicator species. Further, our results suggest that spatial and temporal ecological variation is important in affecting upper trophic level productivity in these marine ecosystems.This article is protected by copyright. All rights reserved.
  • Responses of phenology and biomass production of boreal fens to climate
           warming under different water‐table level regimes
    • Abstract: Climate change affects peatlands directly through increased air temperatures and indirectly through changes in water‐table level (WL). The interactions of these two still remain poorly known. We determined experimentally the separate and interactive effects of temperature and WL regime on factors of relevance for the inputs to the carbon cycle: plant community composition, phenology, biomass production and shoot:root allocation in two wet boreal sedge‐dominated fens, ‘southern’ at 62°Ν and ‘northern’ at 68°Ν. Warming (1.5 °C higher average daily air temperature) was induced with open‐top chambers and WL drawdown (WLD; 3‐7 cm on average) by shallow ditches. Total biomass production varied from 250 to 520 g m−2, with belowground production comprising 25–63%. Warming was associated with minor effects on phenology and negligible effects on community composition, biomass production and allocation. WLD clearly affected the contribution of different plant functional types (PFTs) in the community and the biomass they produced: shrubs benefited while forbs and mosses suffered. These responses did not depend on the warming treatment. Following WLD, aboveground biomass production decreased mainly due to reduced growth of mosses in the southern fen. Aboveground vascular plant biomass production remained unchanged but the contribution of different PFTs changed. The observed changes were also reflected in plant phenology, with different PFTs showing different responses. Belowground production increased following WLD in the northern fen only, but an increase in the contributions of shrubs and forbs was observed in both sites, while sedge contribution decreased. Moderate warming alone seems not able to drive significant changes in plant productivity or community composition in these wet ecosystems. However, if warming is accompanied by even modest WL drawdown, changes should be expected in the relative contribution of PFTs, which could lead to profound changes in the function of fens. Consequently, hydrological scenarios are of utmost importance when estimating their future function.This article is protected by copyright. All rights reserved.
  • Why decadal to century timescale paleoclimate data is needed to explain
           present‐day patterns of biological diversity and change
    • Abstract: The current distribution of species, environmental conditions and their interactions represent only one snapshot of a planet that is continuously changing, in part due to human influences. To distinguish human impacts from natural factors, the magnitude and pace of climate shifts since the Last Glacial Maximum are often used to determine whether patterns of diversity today are artefacts of past climate change. In the absence of high‐temporal‐resolution paleoclimate reconstructions, this is generally done by assuming that past climate change occurred at a linear pace between widely spaced (usually, ≥ 1,000 years) climate snapshots. We show here that this is a flawed assumption, because regional climates have changed significantly across decades and centuries during glacial/interglacial cycles, likely causing rapid regional replacement of biota. We demonstrate how recent atmosphere‐ocean general circulation model (AOGCM) simulations of the climate of the past 21,000 years can provide credible estimates of the details of climate change on decadal to centennial time scales, showing that these details differ radically from what might be inferred from longer time scale information. High temporal resolution information can provide more meaningful estimates of the magnitude and pace of climate shifts, the location and timing of drivers of physiological stress, and the extent of novel climates. They also produce new opportunities to directly investigate whether short‐term climate variability is more important in shaping biodiversity patterns, rather than gradual changes in long‐term climatic means. Together these more accurate measures of past climate instability are likely to bring about a better understanding of the role of paleoclimatic change and variability in shaping current macro‐ecological patterns in many regions of the world.This article is protected by copyright. All rights reserved.
  • Land use of drained peatlands: greenhouse gas fluxes, plant production,
           and economics
    • Abstract: Drained peatlands are hotspots for greenhouse gas (GHG) emissions, which could be mitigated by rewetting and land use change. We performed an ecological/economic analysis of rewetting drained fertile peatlands in a hemiboreal climate using different land use strategies over 80 years. Vegetation, soil processes, and total GHG emissions were modeled using the CoupModel for four scenarios: 1) business as usual – Norway spruce with average soil water table of ‐40 cm; 2) willow with groundwater at ‐20 cm; 3) reed canary grass with groundwater at ‐10 cm; and 4) a fully rewetted peatland. The predictions were based on previous model calibrations with several high‐resolution datasets consisting of water, heat, carbon, and nitrogen cycling. Spruce growth was calibrated by tree‐ring data that extended the time period covered. The GHG balance of four scenarios, including vegetation and soil, were 4.7, 7.1, 9.1, and 6.2 Mg CO2eq ha−1 yr−1, respectively. The total soil emissions (including litter and peat respiration CO2 + N2O + CH4) were 33.1, 19.3, 15.3, and 11.0 Mg CO2eq ha−1 yr−1, respectively, of which the peat loss contributed 35%, 24%, and 7% of the soil emissions for the three drained scenarios, respectively. No peat was lost for the wet peatland. It was also found that draining increases vegetation growth, but not as drastically as peat respiration does. The cost benefit analysis (CBA) is sensitive to time frame, discount rate, and carbon price. Our results indicate that the net benefit was greater with a somewhat higher soil water table and when the peatland was vegetated with willow and reed canary grass (Scenario 2 and 3). We conclude that saving peat and avoiding methane release using fairly wet conditions can significantly reduce GHG emissions, and that this strategy should be considered for land use planning and policy‐making.This article is protected by copyright. All rights reserved.
  • Disentangling the mechanisms behind winter snow impact on vegetation
           activity in northern ecosystems
    • Abstract: While seasonal snow is recognized as an important component in the global climate system, the ability of snow to affect plant production remains an important unknown for assessing climate‐change impacts on vegetation dynamics at high‐latitude ecosystems. Here we compile data on satellite observation of vegetation greenness and spring onset date, satellite‐based soil moisture, passive microwave snow water equivalent (SWE) and climate data to show that winter SWE can significantly influence vegetation greenness during the early growing season (the period between spring onset date and peak photosynthesis timing) over nearly one‐fifth of the land surface in the region north of 30 degrees, but the magnitude and sign of correlation exhibits large spatial heterogeneity. We then apply an assembled path model to disentangle the two main processes (via changing early growing season soil moisture, and via changing the growth period) in controlling the impact of winter SWE on vegetation greenness, and suggest that the “moisture” and “growth period” effect, to a larger extent, results in positive and negative snow–productivity associations, respectively. The magnitude and sign of snow–productivity association is then dependent upon the relative dominance of these two processes, with the “moisture” effect and positive association predominating in Central, western North America and Greater Himalaya, and the “growth period” effect and negative association in Central Europe. We also indicate that current state‐of‐the‐art models in general reproduce satellite‐based snow–productivity relationship in the region north of 30 degrees, and do a relatively better job of capturing the “moisture” effect than the “growth period” effect. Our results therefore work towards an improved understanding of winter snow impact on vegetation greenness in northern ecosystems, and provide a mechanistic basis for more realistic terrestrial carbon cycle models that consider the impacts of winter snow processes.This article is protected by copyright. All rights reserved.
  • Tipping point effect in plant‐fungal interactions under severe drought
           causes abrupt rise in peatland ecosystem respiration
    • Abstract: Ecosystems are increasingly prone to climate extremes, such as drought, with long lasting effects on both plant and soil communities and, subsequently, on carbon (C) cycling. However, recent studies underlined the strong variability in ecosystem's response to droughts, raising the issue of non‐linear responses in plant and soil communities. The conundrum is what causes ecosystems to shift in response to drought. Here, we investigated the response of plant and soil fungi to drought of different intensities using a water table gradient in peatlands – a major C sink ecosystem. Using moving window structural equation models, we show that substantial changes in ecosystem respiration, plant and soil fungal communities occurred when the water level fell below a tipping point of ‐24 cm. As a corollary, ecosystem respiration was the greatest when graminoids and saprotrophic fungi became prevalent as a response to the extreme drought. Graminoids indirectly influenced fungal functional composition and soil enzyme activities through their direct effect on dissolved organic matter quality, while saprotrophic fungi directly influenced soil enzyme activities. In turn, increasing enzyme activities promoted ecosystem respiration. We show that functional transitions in ecosystem respiration critically depends on the degree of response of graminoids and saprotrophic fungi to drought. Our results represent a major advance in understanding the non‐linear nature of ecosystem properties to drought and pave the way towards a truly mechanistic understanding of the effects of drought on ecosystem processes.This article is protected by copyright. All rights reserved.
  • Improving models of photosynthetic thermal acclimation: which parameters
           are most important and how many should be modified'
    • Abstract: Photosynthetic temperature acclimation could strongly affect coupled vegetation‐atmosphere feedbacks in the global carbon cycle, especially as the climate warms. Thermal acclimation of photosynthesis can be modelled as changes in the parameters describing the direct effect of temperature on photosynthetic capacity (i.e. activation energy, Ea; deactivation energy, Hd; entropy parameter, ΔS) or the basal value of photosynthetic capacity (i.e. photosynthetic capacity measured at 25 °C). However, the impact of acclimating these parameters (individually or in combination) on vegetative carbon gain is relatively unexplored. Here we compare the ability of 66 photosynthetic temperature acclimation scenarios to improve the ability of a spatially explicit canopy carbon flux model, MAESTRA, to predict eddy covariance data from a loblolly pine forest. We show that: 1) incorporating seasonal temperature acclimation of basal photosynthetic capacity improves the model's ability to capture seasonal changes in carbon fluxes and outperforms acclimation of other single factors (i.e. Ea or ΔS alone); 2) multifactor scenarios of photosynthetic temperature acclimation provide minimal (if any) improvement in model performance over single factor acclimation scenarios; 3) acclimation of Ea should be restricted to the temperature ranges of the data from which the equations are derived; and 4) model performance is strongly affected by the Hd parameter. We suggest that a renewed effort be made into understanding whether basal photosynthetic capacity, Ea, Hd and ΔS co‐acclimate across broad temperature ranges to determine whether and how multifactor thermal acclimation of photosynthesis occurs.This article is protected by copyright. All rights reserved.
  • Soil carbon cycling proxies: Understanding their critical role in
           predicting climate change feedbacks
    • Abstract: The complexity of processes and interactions that drive soil C dynamics necessitate the use of proxy variables to represent soil characteristics that cannot be directly measured (correlative proxies), or that aggregate information about multiple soil characteristics into one variable (integrative proxies). These proxies have proven useful for understanding the soil C cycle, which is highly variable in both space and time, and are now being used to make predictions of the fate and persistence of C under future climate scenarios. However, the C pools and processes that proxies represent must be thoughtfully considered in order to minimize uncertainties in empirical understanding. This is necessary to capture the full value of a proxy in model parameters and in model outcomes. Here, we provide specific examples of proxy variables that could improve decision‐making, and modeling skill, while also encouraging continued work on their mechanistic underpinnings. We explore the use of three common soil proxies used to study soil C cycling: metabolic quotient, clay content, and physical fractionation. We also consider how emerging data types, such as genome‐sequence data, can serve as proxies for microbial community activities. By examining some broad assumptions in soil C cycling with the proxies already in use, we can develop new hypotheses and specify criteria for new and needed proxies.This article is protected by copyright. All rights reserved.
  • How much does climate change threaten European forest tree species
    • Abstract: Although numerous species distribution models have been developed, most were based on insufficient distribution data or used older climate change scenarios. We aimed to quantify changes in projected ranges and threat level by the years 2061‐2080, for 12 European forest tree species under three climate change scenarios. We combined tree distribution data from the Global Biodiversity Information Facility, EUFORGEN and forest inventories, and we developed species distribution models using MaxEnt and 19 bioclimatic variables. Models were developed for three climate change scenarios – optimistic (RCP2.6), moderate (RCP4.5) and pessimistic (RPC8.5) – using three General Circulation Models, for the period 2061‐2080. Our study revealed different responses of tree species to projected climate change. The species may be divided into three groups: “winners” – mostly late‐successional species: Abies alba, Fagus sylvatica, Fraxinus excelsior, Quercus robur and Q. petraea; “losers” – mostly pioneer species: Betula pendula, Larix decidua, Picea abies and Pinus sylvestris and alien species – Pseudotsuga menziesii, Q. rubra and Robinia pseudoacacia, which may be also considered as “winners”. Assuming limited migration, most of the species studied would face significant decrease of suitable habitat area. The threat level was highest for species that currently have the northernmost distribution centers. Ecological consequences of the projected range contractions would be serious for both forest management and nature conservation.This article is protected by copyright. All rights reserved.
  • Decoupling the direct and indirect effects of climate on plant litter
           decomposition and terrestrial nutrient cycling
    • Abstract: Decomposition of plant litter is a fundamental ecosystem process that can act as a feedback to climate change by simultaneously influencing both the productivity of ecosystems and the flux of carbon dioxide from the soil. The influence of climate on decomposition from a post‐senescence perspective is relatively well known; in particular, climate is known to regulate the rate of litter decomposition via its direct influence on the reaction kinetics and microbial physiology on processes downstream of tissue senescence. Climate can alter plant metabolism during the formative stage of tissues and could shape the final chemical composition of plant litter, and thus indirectly influence decomposition; however, these indirect effects are relatively poorly understood. Climatic stress disrupts cellular homeostasis in plants and results in the reprogramming of primary and secondary metabolic pathways, which leads to changes in the quantity, composition and organization of small molecules and recalcitrant heteropolymers, including lignins, tannins, suberins and cuticle within the plant tissue matrix. Furthermore, by regulating metabolism during tissue senescence, climate influences the resorption of nutrients from senescing tissues. Thus, the final composition of plant litter that forms the substrate of decomposition is a combined product of pre‐senescence physiological processes through the production and resorption of metabolites. The changes in quantity, composition and localization of the molecular construct of the litter could influence tissue decomposition and soil nutrient cycling by altering the recalcitrance of the lignocellulose matrix, the composition of microbial communities and the activity of microbial exo‐enzymes via various complexation reactions. Compared with temperate ecosystems, the indirect effects of climate on litter decomposition in the tropics are not well understood, which underscores the need to conduct additional studies in tropical biomes. We also emphasize the need to focus on how climatic stress affects the root chemistry as roots contribute significantly to biogeochemical cycling, and on utilizing more robust analytical approaches to capture the molecular composition of tissue matrix that fuel microbial metabolism.This article is protected by copyright. All rights reserved.
  • Climate change impacts on the conservation outlook of populations on the
           poleward periphery of species ranges: A case study of Canadian
           black‐tailed prairie dogs (Cynomys ludovicianus)
    • Abstract: Given climate change, species’ climatically suitable habitats are increasingly expected to shift poleward. Some imperiled populations towards the poleward edge of their species’ range might therefore conceivably benefit from climate change. Interactions between climate and population dynamics may be complex, however, with climate exerting effects both indirectly via influence over food availability and more directly, via effects on physiology and its implications for survival and reproduction. A thorough understanding of these interactions is critical for effective conservation management. We therefore examine the relationship between climate, survival and reproduction in Canadian black‐tailed prairie dogs, a threatened keystone species in an imperiled ecosystem at the northern edge of the species’ range. Our analyses considered eight years of annual mark‐recapture data (2007 – 2014) in relation to growing degree days, precipitation, drought status and winter severity, as well as year, sex, age, and body mass. Survival was strongly influenced by the interaction of drought and body mass class and winter temperature severity. Female reproductive status was associated with the interaction of growing degree days and growing season precipitation, with spring precipitation and with winter temperature severity. Results related to body mass suggested that climatic variables exerted their effects via regulation of food availability with potential linked effects of food quality, immunological and behavioural implications, and predation risk. Predictions of future increases in drought conditions in North America's grassland ecosystems has raised concerns for the outlook of Canadian black‐tailed prairie dogs. Insights gained from the analyses, however, point to mitigating species management options targeted at decoupling the mechanisms by which climate exerts its negative influence. Our approach highlights the importance of understanding the interaction between climate and population dynamics in peripheral populations whose viability might ultimately determine their species’ ability to track climatically suitable space.This article is protected by copyright. All rights reserved.
  • Forest bees are replaced in agricultural and urban landscapes by native
           species with different phenologies and life history traits
    • Abstract: Anthropogenic landscapes are associated with biodiversity loss and large shifts in species composition and traits. These changes predict the identities of winners and losers of future global change, and also reveal which environmental variables drive a taxon's response to land use change. We explored how the biodiversity of native bee species changes across forested, agricultural, and urban landscapes. We collected bee community data from 36 sites across a 75,000 km2 region, and analyzed bee abundance, species richness, composition, and life history traits. Season‐long bee abundance and richness were not detectably different between natural and anthropogenic landscapes, but community phenologies differed strongly, with an early spring peak followed by decline in forests, and a more extended summer season in agricultural and urban habitats. Bee community composition differed significantly between all three land use types, as did phylogenetic composition. Anthropogenic land use had negative effects on the persistence of several life history strategies, including early spring flight season and brood parasitism, which may indicate adaptation to conditions in forest habitat. Overall, anthropogenic communities are not diminished subsets of contemporary natural communities. Rather, forest species do not persist in anthropogenic habitats, but are replaced by different native species and phylogenetic lineages pre‐adapted to open habitats. Characterizing compositional and functional differences is crucial for understanding land use as a global change driver across large regional scales.This article is protected by copyright. All rights reserved.
  • El Niño Southern Oscillation influences the abundance and movements of a
           marine top predator in coastal waters
    • Abstract: Large‐scale climate modes such as El Niño Southern Oscillation (ENSO) influence population dynamics in many species, including marine top predators. However, few quantitative studies have investigated the influence of large‐scale variability on resident marine top predator populations. We examined the effect of climate variability on the abundance and temporary emigration of a resident bottlenose dolphin (Tursiops aduncus) population off Bunbury, Western Australia (WA). This population has been studied intensively over six consecutive years (2007–2013), yielding a robust dataset that captures seasonal variations in both abundance and movement patterns. In WA, ENSO affects the strength of the Leeuwin Current (LC), the dominant oceanographic feature in the region. The strength and variability of the LC affects marine ecosystems and distribution of top predator prey. We investigated the relationship between dolphin abundance and ENSO, Southern Annular Mode, austral season, rainfall, sea surface salinity and sea surface temperature (SST). Linear models indicated that dolphin abundance was significantly affected by ENSO, and that the magnitude of the effect was dependent upon season. Dolphin abundance was lowest during winter 2009, when dolphins had high temporary emigration rates out of the study area. This coincided with the single El Niño event that occurred throughout the study period. Coupled with this event, there was a negative anomaly in SST and an above average rainfall. These conditions may have affected the distribution of dolphin prey, resulting in the temporary emigration of dolphins out of the study area in search of adequate prey. This study demonstrated the local effects of large‐scale climatic variations on the short‐term response of a resident, coastal delphinid species. With a projected global increase in frequency and intensity of extreme climatic events, resident marine top predators may not only have to contend with increasing coastal anthropogenic activities, but also have to adapt to large‐scale climatic changes.We examined the effect of El Niño Southern Oscillation (ENSO) on the abundance and temporary emigration of a resident bottlenose dolphin (Tursiops aduncus) population off south‐west Australia. Models indicated that abundance was significantly affected by ENSO, and that the magnitude was dependent upon season. Abundance was lowest during winter 2009, when dolphins had high temporary emigration rates out of the study area. During this time, there was an El Niño event, negative anomaly in SST and an above average rainfall. These conditions may have affected the distribution of dolphin prey, resulting in the movement of dolphins out of the area.
  • Networking our science to characterize the state, vulnerabilities, and
           management opportunities of soil organic matter
    • Abstract: Soil organic matter (SOM) supports the Earth's ability to sustain terrestrial ecosystems, provide food and fiber, and retains the largest pool of actively cycling carbon. Over 75% of the soil organic carbon (SOC) in the top meter of soil is directly affected by human land use. Large land areas have lost SOC as a result of land use practices, yet there are compensatory opportunities to enhance productivity and SOC storage in degraded lands through improved management practices. Large areas with and without intentional management are also being subjected to rapid changes in climate, making many SOC stocks vulnerable to losses by decomposition or disturbance. In order to quantify potential SOC losses or sequestration at field, regional, and global scales, measurements for detecting changes in SOC are needed. Such measurements and soil‐management best practices should be based on well established and emerging scientific understanding of processes of C stabilization and destabilization over various timescales, soil types, and spatial scales. As newly engaged members of the International Soil Carbon Network, we have identified gaps in data, modeling, and communication that underscore the need for an open, shared network to frame and guide the study of SOM and SOC and their management for sustained production and climate regulation.
  • Clarifying the landscape approach: A Letter to the Editor on “Integrated
           landscape approaches to managing social and environmental issues in the
    • Abstract: Objectives, assumptions, and methods for landscape restoration and the landscape approach. World leaders have pledged 350 Mha for restoration using a landscape approach. The landscape approach is thus poised to become one of the most influential methods for multi‐functional land management. Reed et al (2016) meaningfully advance scholarship on the landscape approach, but they incorrectly define the approach as it exists within their text. This Letter to the Editor clarifies the landscape approach as an ethic for land management, demonstrates how it relates to landscape restoration, and motivates continued theoretical development and empirical assessment of the landscape approach.
  • Proper estimate of residue input as condition for understanding drivers of
           soil carbon dynamics
  • Land use for animal production in global change studies: Defining and
           characterizing a framework
    • Abstract: Land use for animal production influences the earth system in a variety of ways, including local‐scale modification to biodiversity, soils, and nutrient cycling; regional changes in albedo and hydrology; and global‐scale changes in greenhouse gas and aerosol concentrations. Pasture is furthermore the single most extensive form of land cover, currently comprising about 22–26% of the earth's ice‐free land surface. Despite the importance and variable expressions of animal production, distinctions among different systems are effectively absent from studies of land use and land cover change. This deficiency is improving; however, livestock production system classifications are rarely applied in this context, and the most popular global land cover inventories still present only a single, usually poorly defined category of “pasture” or “rangeland” with no characterization of land use. There is a marked lack of bottom‐up, evidence‐based methodology, creating a pressing need to incorporate cross‐disciplinary evidence of past and present animal production systems into global change studies. Here, we present a framework, modified from existing livestock production systems, that is rooted in sociocultural, socioeconomic, and ecological contexts. The framework defines and characterizes the range of land usage pertaining to animal production, and is suitable for application in land use inventories and scenarios, land cover modeling, and studies on sustainable land use in the past, present, and future.Animal production is the single most extensive form of land use globally, and influences the earth system in a variety of ways, including local‐scale modification to biodiversity, soils, and nutrient cycling; regional changes in albedo and hydrology; and global changes in greenhouse gas and aerosol concentrations. Despite its importance, distinctions among different systems of animal production are effectively absent from studies of land use and cover change, and the most popular global land cover inventories present only a single, usually poorly defined category of “pasture” or “rangeland” with no characterization of land use. Given the marked lack of bottom‐up, evidence‐based methodology, we present a cross‐disciplinary framework, rooted in socioeconomic and ecological contexts, that defines and characterizes the land usage pertaining to animal production, and is suitable for application in land use inventories and scenarios, land cover modeling, and studies on sustainable land use in the past, present, and future.
  • Widespread production of nonmicrobial greenhouse gases in soils
    • Abstract: Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the three most important greenhouse gases (GHGs), and all show large uncertainties in their atmospheric budgets. Soils of natural and managed ecosystems play an extremely important role in modulating their atmospheric abundance. Mechanisms underlying the exchange of these GHGs at the soil–atmosphere interface are often assumed to be exclusively microbe‐mediated (M‐GHGs). We argue that it is a widespread phenomenon for soil systems to produce GHGs through nonmicrobial pathways (NM‐GHGs) based on a review of the available evidence accumulated over the past half century. We find that five categories of mechanistic process, including photodegradation, thermal degradation, reactive oxidative species (ROS) oxidation, extracellular oxidative metabolism (EXOMET), and inorganic chemical reactions, can be identified as accounting for their production. These pathways are intricately coupled among themselves and with M‐GHGs production and are subject to strong influences from regional and global change agents including, among others, climate warming, solar radiation, and alterations of atmospheric components. Preliminary estimates have suggested that NM‐GHGs could play key roles in contributing to budgets of GHGs in the arid regions, whereas their global importance would be enhanced with accelerated global environmental changes. Therefore, more research should be undertaken, with a differentiation between NM‐GHGs and M‐GHGs, to further elucidate the underlying mechanisms, to investigate the impacts of various global change agents, and to quantify their contributions to regional and global GHGs budgets. These efforts will contribute to a more complete understanding of global carbon and nitrogen cycling and a reduction in the uncertainty of carbon‐climate feedbacks in the Earth system.It is a widespread phenomenon for soils (plant residues) to produce GHGs through nonmicrobial pathways (NM‐GHGs). Five categories of mechanistic process (photodegradation, thermal degradation, reactive oxidative species oxidation, extracellular oxidative metabolism, and inorganic chemical reactions) are currently identified. Preliminary estimates have suggested that these pathways could play key roles in regulating the regional budget of GHGs. Their global importance would be enhanced with accelerated global environmental changes.
  • Avoiding a crisis of motivation for ocean management under global
           environmental change
    • Abstract: Climate change and ocean acidification are altering marine ecosystems and, from a human perspective, creating both winners and losers. Human responses to these changes are complex, but may result in reduced government investments in regulation, resource management, monitoring and enforcement. Moreover, a lack of peoples’ experience of climate change may drive some towards attributing the symptoms of climate change to more familiar causes such as management failure. Taken together, we anticipate that management could become weaker and less effective as climate change continues. Using diverse case studies, including the decline of coral reefs, coastal defences from flooding, shifting fish stocks and the emergence of new shipping opportunities in the Arctic, we argue that human interests are better served by increased investments in resource management. But greater government investment in management does not simply mean more of “business‐as‐usual.” Management needs to become more flexible, better at anticipating and responding to surprise, and able to facilitate change where it is desirable. A range of technological, economic, communication and governance solutions exists to help transform management. While not all have been tested, judicious application of the most appropriate solutions should help humanity adapt to novel circumstances and seek opportunity where possible.Using five diverse case studies, ranging from climate impacts on coral reefs to shifts in fisheries distributions to opening of the Arctic for shipping, we reveal the rational drivers that might generate reductions in management regardless of whether global change is providing benefits or costs to human society. We argue that better outcomes will follow from greater management investment. We then discuss the key challenges to make management more effective and flexible.
  • Climate change is predicted to alter the current pest status of Globodera
           pallida and G. rostochiensis in the United Kingdom
    • Abstract: The potato cyst nematodes Globodera pallida and G. rostochiensis are economically important plant pathogens causing losses to UK potato harvests estimated at £50 m/ year. Implications of climate change on their future pest status have not been fully considered. Here, we report growth of female G. pallida and G. rostochiensis over the range 15 to 25°C. Females per plant and their fecundity declined progressively with temperatures above 17.5°C for G. pallida, whilst females per plant were optimal between 17.5 and 22.5°C for G. rostochiensis. Relative reproductive success with temperature was confirmed on two potato cultivars infected with either species at 15, 22.5 and 25°C. The reduced reproductive success of G. pallida at 22.5°C relative to 15°C was also recorded for a further seven host cultivars studied. The differences in optimal temperatures for reproductive success may relate to known differences in the altitude of their regions of origin in the Andes. Exposure of G. pallida to a diurnal temperature stress for one week during female growth significantly suppressed subsequent growth for one week at 17.5°C but had no effect on G. rostochiensis. However, after two weeks of recovery, female size was not significantly different from that for the control treatment. Future soil temperatures were simulated for medium‐ and high‐emission scenarios and combined with nematode growth data to project future implications of climate change for the two species. Increased soil temperatures associated with climate change may reduce the pest status of G. pallida but benefit G. rostochiensis especially in the southern United Kingdom. We conclude that plant breeders may be able to exploit the thermal limits of G. pallida by developing potato cultivars able to grow under future warm summer conditions. Existing widely deployed resistance to G. rostochiensis is an important characteristic to retain for new potato cultivars.The potato cyst nematodes Globodera pallida and G. rostochiensis are economically important plant pathogens causing losses to UK potato harvests estimated at £50 m/year. These nematodes are potato's main pests and alien species introduced to many potato‐growing countries from different altitudes in the Andes. Implications of climate change on their future pest status have not been fully considered. Here, we combine nematode growth data collected from the glasshouse with future soil temperatures simulated for medium‐ and high‐emission scenarios to project future implications of climate change for the two species. For the first time, we establish soil temperatures associated with climate change may reduce G. pallida's pest status in southern United Kingdom but not the more readily controlled G. rostochiensis. Breeding potato plants suited to future warm conditions that suppress G. pallida would offset its currently inadequate control by resistant cultivars.
  • Scale‐dependent complementarity of climatic velocity and environmental
           diversity for identifying priority areas for conservation under climate
    • Abstract: As most regions of the earth transition to altered climatic conditions, new methods are needed to identify refugia and other areas whose conservation would facilitate persistence of biodiversity under climate change. We compared several common approaches to conservation planning focused on climate resilience over a broad range of ecological settings across North America and evaluated how commonalities in the priority areas identified by different methods varied with regional context and spatial scale. Our results indicate that priority areas based on different environmental diversity metrics differed substantially from each other and from priorities based on spatiotemporal metrics such as climatic velocity. Refugia identified by diversity or velocity metrics were not strongly associated with the current protected area system, suggesting the need for additional conservation measures including protection of refugia. Despite the inherent uncertainties in predicting future climate, we found that variation among climatic velocities derived from different general circulation models and emissions pathways was less than the variation among the suite of environmental diversity metrics. To address uncertainty created by this variation, planners can combine priorities identified by alternative metrics at a single resolution and downweight areas of high variation between metrics. Alternately, coarse‐resolution velocity metrics can be combined with fine‐resolution diversity metrics in order to leverage the respective strengths of the two groups of metrics as tools for identification of potential macro‐ and microrefugia that in combination maximize both transient and long‐term resilience to climate change. Planners should compare and integrate approaches that span a range of model complexity and spatial scale to match the range of ecological and physical processes influencing persistence of biodiversity and identify a conservation network resilient to threats operating at multiple scales.There is a pressing need for comparisons of approaches to identifying refugia and other areas whose conservation would facilitate persistence of biodiversity under climate change. We compared a range of approaches to identifying refugia across North America to ascertain how metric performance varies with ecological context and scale. Our results indicate that priority areas based on different environmental diversity metrics differed substantially from each other and from priorities based on more complex metrics such as climatic velocity. Our results suggest guidelines for when and how to use simple and complex metrics for identifying refugia. Planners should compare and integrate approaches that span a spectrum of model complexity and spatial scale to match the range of ecological and physical processes influencing persistence of biodiversity.
  • Mule deer and energy development—Long‐term trends of
           habituation and abundance
    • Abstract: As the extent and intensity of energy development in North America increases, so do disturbances to wildlife and the habitats they rely upon. Impacts to mule deer are of particular concern because some of the largest gas fields in the USA overlap critical winter ranges. Short‐term studies of 2–3 years have shown that mule deer and other ungulates avoid energy infrastructure; however, there remains a common perception that ungulates habituate to energy development, and thus, the potential for a demographic effect is low. We used telemetry data from 187 individual deer across a 17‐year period, including 2 years predevelopment and 15 years during development, to determine whether mule deer habituated to natural gas development and if their response to disturbance varied with winter severity. Concurrently, we measured abundance of mule deer to indirectly link behavior with demography. Mule deer consistently avoided energy infrastructure through the 15‐year period of development and used habitats that were an average of 913 m further from well pads compared with predevelopment patterns of habitat use. Even during the last 3 years of study, when most wells were in production and reclamation efforts underway, mule deer remained >1 km away from well pads. The magnitude of avoidance behavior, however, was mediated by winter severity, where aversion to well pads decreased as winter severity increased. Mule deer abundance declined by 36% during the development period, despite aggressive onsite mitigation efforts (e.g. directional drilling and liquid gathering systems) and a 45% reduction in deer harvest. Our results indicate behavioral effects of energy development on mule deer are long term and may affect population abundance by displacing animals and thereby functionally reducing the amount of available habitat.We used telemetry data from 187 deer across a 17‐year period, including 2 years predevelopment and 15 years during development, to determine whether mule deer habituated to energy development and if abundance decreased through time. Mule deer did not habituate to disturbance and the population size declined by 36%. Our results indicate behavioral effects of energy development on mule deer are long term and can affect population abundance by displacing animals and thereby functionally reducing the amount of available habitat.
  • Future warmer seas: increased stress and susceptibility to grazing in
           seedlings of a marine habitat‐forming species
    • Abstract: Increases in seawater temperature are expected to have negative consequences for marine organisms. Beyond individual effects, species‐specific differences in thermal tolerance are predicted to modify species interactions and increase the strength of top‐down effects, particularly in plant–herbivore interactions. Shifts in trophic interactions will be especially important when affecting habitat‐forming species such as seagrasses, as the consequences on their abundance will cascade throughout the food web. Seagrasses are a major component of coastal ecosystems offering important ecosystem services, but are threatened by multiple anthropogenic stressors, including warming. The mechanistic understanding of seagrass responses to warming at multiple scales of organization remains largely unexplored, especially in early‐life stages such as seedlings. Yet, these early‐life stages are critical for seagrass expansion processes and adaptation to climate change. In this study, we determined the effects of a 3 month experimental exposure to present and predicted mean summer SST of the Mediterranean Sea (25°C, 27°C, and 29°C) on the photophysiology, size, and ecology (i.e., plant‐herbivore interactions) of seedlings of the seagrass Posidonia oceanica. Warming resulted in increased mortality, leaf necrosis, and respiration as well as lower carbohydrate reserves in the seed, the main storage organ in seedlings. Aboveground biomass and root growth were also limited with warming, which could hamper seedling establishment success. Furthermore, warming increased the susceptibility to consumption by grazers, likely due to lower leaf fiber content and thickness. Our results indicate that warming will negatively affect seagrass seedlings through multiple direct and indirect pathways: increased stress, reduced establishment potential, lower storage of carbohydrate reserves, and increased susceptibly to consumption. This work provides a significant step forward in understanding the major mechanisms that will drive the capacity of seagrass seedlings to adapt and survive to warming, highlighting the potential additive effects that herbivory will have on ultimately determining seedling success.This work analyzes the major mechanisms that will drive the capacity of seagrass seedlings to adapt and survive to warming, highlighting the potential additive effects that herbivory will have on ultimately determining seedling success. Warming will negatively affect seagrass seedlings through multiple direct and indirect pathways: increased stress, reduced establishment potential, lower storage of carbohydrate reserves, and increased susceptibly to consumption.
  • Soil carbon sequestration potential of permanent pasture and continuous
           cropping soils in New Zealand
    • Abstract: Understanding soil organic carbon (SOC) sequestration is important to develop strategies to increase the SOC stock and, thereby, offset some of the increases in atmospheric carbon dioxide. Although the capacity of soils to store SOC in a stable form is commonly attributed to the fine (clay + fine silt) fraction, the properties of the fine fraction that determine the SOC stabilization capacity are poorly known. The aim of this study was to develop an improved model to estimate the SOC stabilization capacity of Allophanic (Andisols) and non‐Allophanic topsoils (0–15 cm) and, as a case study, to apply the model to predict the sequestration potential of pastoral soils across New Zealand. A quantile (90th) regression model, based on the specific surface area and extractable aluminium (pyrophosphate) content of soils, provided the best prediction of the upper limit of fine fraction carbon (FFC) (i.e. the stabilization capacity), but with different coefficients for Allophanic and non‐Allophanic soils. The carbon (C) saturation deficit was estimated as the difference between the stabilization capacity of individual soils and their current C concentration. For long‐term pastures, the mean saturation deficit of Allophanic soils (20.3 mg C g−1) was greater than that of non‐Allophanic soils (16.3 mg C g−1). The saturation deficit of cropped soils was 1.14–1.89 times that of pasture soils. The sequestration potential of pasture soils ranged from 10 t C ha−1 (Ultic soils) to 42 t C ha−1 (Melanic soils). Although meeting the estimated national soil C sequestration potential (124 Mt C) is unrealistic, improved management practices targeted to those soils with the greatest sequestration potential could contribute significantly to off‐setting New Zealand's greenhouse gas emissions. As the first national‐scale estimate of SOC sequestration potential that encompasses both Allophanic and non‐Allophanic soils, this serves as an informative case study for the international community.A quantile regression model was developed and used to estimate the soil C stabilization capacity and saturation deficit for a wide range of New Zealand pasture and cropping soils. The overall mean saturation deficit for these soils was 15.1 ± 0.8 mg C g−1 soil. Accounting for differences in bulk density and land area, the mean saturation deficit of each major soil Order was used to estimate a national C sequestration potential of 124 ± 37 Mt C.
  • Ecological regime shift drives declining growth rates of sea turtles
           throughout the West Atlantic
    • Abstract: Somatic growth is an integrated, individual‐based response to environmental conditions, especially in ectotherms. Growth dynamics of large, mobile animals are particularly useful as bio‐indicators of environmental change at regional scales. We assembled growth rate data from throughout the West Atlantic for green turtles, Chelonia mydas, which are long‐lived, highly migratory, primarily herbivorous mega‐consumers that may migrate over hundreds to thousands of kilometers. Our dataset, the largest ever compiled for sea turtles, has 9690 growth increments from 30 sites from Bermuda to Uruguay from 1973 to 2015. Using generalized additive mixed models, we evaluated covariates that could affect growth rates; body size, diet, and year have significant effects on growth. Growth increases in early years until 1999, then declines by 26% to 2015. The temporal (year) effect is of particular interest because two carnivorous species of sea turtles—hawksbills, Eretmochelys imbricata, and loggerheads, Caretta caretta—exhibited similar significant declines in growth rates starting in 1997 in the West Atlantic, based on previous studies. These synchronous declines in productivity among three sea turtle species across a trophic spectrum provide strong evidence that an ecological regime shift (ERS) in the Atlantic is driving growth dynamics. The ERS resulted from a synergy of the 1997/1998 El Niño Southern Oscillation (ENSO)—the strongest on record—combined with an unprecedented warming rate over the last two to three decades. Further support is provided by the strong correlations between annualized mean growth rates of green turtles and both sea surface temperatures (SST) in the West Atlantic for years of declining growth rates (r = −.94) and the Multivariate ENSO Index (MEI) for all years (r = .74). Granger‐causality analysis also supports the latter finding. We discuss multiple stressors that could reinforce and prolong the effect of the ERS. This study demonstrates the importance of region‐wide collaborations.Somatic growth is an integrated, individual‐based response to environmental conditions, especially in ectotherms. The authors compiled extensive growth data for green sea turtles throughout the West Atlantic from 30 sites from Bermuda to Uruguay from 1973 to 2015. Growth rates declined significantly from 1999 to the present. Synchronous declines in growth rates among three sea turtle species across a trophic spectrum provide strong evidence that the ecological regime shift (ERS) that occurred in the late 1990s in the Atlantic is driving growth dynamics. The ERS combined with an unprecedented warming rate over the last two to three decades and cumulative impacts of ongoing anthropogenic degradation of foraging habitats in the region slowed growth in these mega‐consumers. The summary conclusion that productivity of sea turtles is lower at warmer temperatures is not good news in an age of warming seas.
  • Asymmetric effects of cooler and warmer winters on beech phenology last
           beyond spring
    • Abstract: In temperate trees, the timings of plant growth onset and cessation affect biogeochemical cycles, water, and energy balance. Currently, phenological studies largely focus on specific phenophases and on their responses to warming. How differently spring phenology responds to the warming and cooling, and affects the subsequent phases, has not been yet investigated in trees. Here, we exposed saplings of Fagus sylvatica L. to warmer and cooler climate during the winter 2013–2014 by conducting a reciprocal transplant experiment between two elevations (1,340 vs. 371 m a.s.l., ca. 6°C difference) in the Swiss Jura mountains. To test the legacy effects of earlier or later budburst on the budset timing, saplings were moved back to their original elevation shortly after the occurrence of budburst in spring 2014. One degree decrease in air temperature in winter/spring resulted in a delay of 10.9 days in budburst dates, whereas one degree of warming advanced the date by 8.8 days. Interestingly, we also found an asymmetric effect of the warmer winter vs. cooler winter on the budset timing in late summer. Budset of saplings that experienced a cooler winter was delayed by 31 days compared to the control, whereas it was delayed by only 10 days in saplings that experienced a warmer winter. Budburst timing in 2015 was not significantly impacted by the artificial advance or delay of the budburst timing in 2014, indicating that the legacy effects of the different phenophases might be reset during each winter. Adapting phenological models to the whole annual phenological cycle, and considering the different response to cooling and warming, would improve predictions of tree phenology under future climate warming conditions.Using an original transplant experiment from a 1,000‐m elevation gradient allowing to induce natural warming and cooling to European beech saplings, we showed that spring budburst phenology has a significant but different response to warming and cooling. In particular, we found that beech trees had a greater budburst response to cooling than to warming, that is, 11‐day delay vs. 9‐day advance per degree cooling and warming, respectively. Interestingly, the induced advance or delay in the budburst due to the downward or upward transplantation significantly affects the budset timing in the following autumn. Additionally, this asymmetric effect of warming and cooling is also found on the growing season length (GSL), where cooling reduced the GSL by 14 days whereas warming increased GSL by 28 days. Our study provides evidences in natural conditions of the carryover effect of spring phenophases over following phenophases in a temperate tree.
  • Pan‐Arctic sea ice‐algal chl a biomass and suitable habitat are
           largely underestimated for multiyear ice
    • Abstract: There is mounting evidence that multiyear ice (MYI) is a unique component of the Arctic Ocean and may play a more important ecological role than previously assumed. This study improves our understanding of the potential of MYI as a suitable habitat for sea ice algae on a pan‐Arctic scale. We sampled sea ice cores from MYI and first‐year sea ice (FYI) within the Lincoln Sea during four consecutive spring seasons. This included four MYI hummocks with a mean chl a biomass of 2.0 mg/m2, a value significantly higher than FYI and MYI refrozen ponds. Our results support the hypothesis that MYI hummocks can host substantial ice‐algal biomass and represent a reliable ice‐algal habitat due to the (quasi‐) permanent low‐snow surface of these features. We identified an ice‐algal habitat threshold value for calculated light transmittance of 0.014%. Ice classes and coverage of suitable ice‐algal habitat were determined from snow and ice surveys. These ice classes and associated coverage of suitable habitat were applied to pan‐Arctic CryoSat‐2 snow and ice thickness data products. This habitat classification accounted for the variability of the snow and ice properties and showed an areal coverage of suitable ice‐algal habitat within the MYI‐covered region of 0.54 million km2 (8.5% of total ice area). This is 27 times greater than the areal coverage of 0.02 million km2 (0.3% of total ice area) determined using the conventional block‐model classification, which assigns single‐parameter values to each grid cell and does not account for subgrid cell variability. This emphasizes the importance of accounting for variable snow and ice conditions in all sea ice studies. Furthermore, our results indicate the loss of MYI will also mean the loss of reliable ice‐algal habitat during spring when food is sparse and many organisms depend on ice‐algae.We sampled sea ice from the so‐called Last Ice Area, an under‐represented region home to the last remaining really thick, old Arctic sea ice. We measured ice algae biomass values among the highest ever reported for old Arctic sea ice. This was attributed to the typically low‐snow cover of hummocks resulting from wind‐induced snow redistribution, which allowed for continuously suitable light conditions for algal growth despite ice thicknesses over 4 m. Hummocks were identified as common suitable MYI habitat features with an average coverage of 33%. Accounting for the spatial variability of hummocks within a pan‐Arctic habitat classification resulted in nearly 30 times more suitable habitat. This is likely a conservative estimate because we did not consider the potential of horizontal light scattering around hummocks, which would further increase the coverage of suitable habitat. Our findings indicate that losing “the Last Ice Area” will have profound ecological consequences far exceeding our current projections.
  • Non‐additive effects of simulated heat waves and predators on prey
           phenotype and transgenerational phenotypic plasticity
    • Abstract: Understanding the effects of extreme climatic events on species and their interactions is of paramount importance for predicting and mitigating the impacts of climate change on communities and ecosystems. However, the joint effects of extreme climatic events and species interactions on the behaviour and phenotype of organisms remain poorly understood, leaving a substantial gap in our knowledge on the impacts of climatic change on ecological communities. Using an aphid–ladybeetle system, we experimentally investigated the effects of predators and heat shocks on prey body size, microhabitat use, and transgenerational phenotypic plasticity (i.e., the asexual production of winged offspring by unwinged mothers). We found that (i) aphids were smaller in the presence of predators but larger when exposed to frequent heat shocks; (ii) frequent heat shocks shifted aphid distribution towards the plant's apex, but the presence of predators had the opposite effect and dampened the heat‐shock effects; and (iii) aphids responded to predators by producing winged offspring, but heat shocks strongly inhibited this transgenerational response to predation. Overall, our experimental results show that heat shocks inhibit phenotypic and behavioural responses to predation (and vice versa) and that such changes may alter trophic interactions, and have important consequences on the dynamics and stability of ecological communities. We conclude that the effects of extreme climatic events on the phenotype and behaviour of interacting species should be considered to understand the effects of climate change on species interactions and communities.The joint effects of extreme climatic events and species interactions on the behaviour and phenotype of organisms remain poorly understood, leaving a substantial gap in our knowledge on the impacts of climatic change on ecological communities. Using an aphid–ladybeetle system, we experimentally investigated the effects of predators and heat shocks on prey phenotypic traits. We found that (i) aphids were smaller in the presence of predators but larger when exposed to heat shocks; (ii) heat shocks shifted aphid distribution towards the plant's apex, but the presence of predators had the opposite effect and dampened the heat‐shock's effects; and (iii) aphids responded to predators by producing winged offspring, but heat shocks strongly inhibited this transgenerational response. Overall, our experimental results show that heat shocks inhibit phenotypic and behavioural responses to predation and that such changes may alter trophic interactions and have important consequences on the dynamics and stability of ecological communities.
  • Seasonal associations with urban light pollution for nocturnally migrating
           bird populations
    • Abstract: The spatial extent and intensity of artificial light at night (ALAN) has increased worldwide through the growth of urban environments. There is evidence that nocturnally migrating birds are attracted to ALAN, and there is evidence that nocturnally migrating bird populations are more likely to occur in urban areas during migration, especially in the autumn. Here, we test if urban sources of ALAN are responsible, at least in part, for these observed urban associations. We use weekly estimates of diurnal occurrence and relative abundance for 40 nocturnally migrating bird species that breed in forested environments in North America to assess how associations with distance to urban areas and ALAN are defined across the annual cycle. Migratory bird populations presented stronger than expected associations with shorter distances to urban areas during migration, and stronger than expected association with higher levels of ALAN outside and especially within urban areas during migration. These patterns were more pronounced during autumn migration, especially within urban areas. Outside of the two migration periods, migratory bird populations presented stronger than expected associations with longer distances to urban areas, especially during the nonbreeding season, and weaker than expected associations with the highest levels of ALAN outside and especially within urban areas. These findings suggest that ALAN is associated with higher levels of diurnal abundance along the boundaries and within the interior of urban areas during migration, especially in the autumn when juveniles are undertaking their first migration journey. These findings support the conclusion that urban sources of ALAN can broadly effect migratory behavior, emphasizing the need to better understand the implications of ALAN for migratory bird populations.There is evidence that nocturnally migrating birds are attracted to artificial light sources, and there is evidence that migratory bird populations are more likely to occur in urban areas during migration. In this study, we use bird observations from the eBird citizen‐science database to explore the associations between nighttime light pollution and the abundance of migratory birds. Our results indicate that nighttime light pollution emanating from urban areas is associated with higher levels of abundance along the boundaries and within the interior of urban areas during migration, supporting the conclusion that urban sources of nighttime light pollution broadly affects migratory behavior.
  • Life history tactics shape amphibians’ demographic responses to the
           North Atlantic Oscillation
    • Abstract: Over the last three decades, climate abnormalities have been reported to be involved in biodiversity decline by affecting population dynamics. A growing number of studies have shown that the North Atlantic Oscillation (NAO) influences the demographic parameters of a wide range of plant and animal taxa in different ways. Life history theory could help to understand these different demographic responses to the NAO. Indeed, theory states that the impact of weather variation on a species’ demographic traits should depend on its position along the fast–slow continuum. In particular, it is expected that NAO would have a higher impact on recruitment than on adult survival in slow species, while the opposite pattern is expected occur in fast species. To test these predictions, we used long‐term capture–recapture datasets (more than 15,000 individuals marked from 1965 to 2015) on different surveyed populations of three amphibian species in Western Europe: Triturus cristatus, Bombina variegata, and Salamandra salamandra. Despite substantial intraspecific variation, our study revealed that these three species differ in their position on a slow–fast gradient of pace of life. Our results also suggest that the differences in life history tactics influence amphibian responses to NAO fluctuations: Adult survival was most affected by the NAO in the species with the fastest pace of life (T. cristatus), whereas recruitment was most impacted in species with a slower pace of life (B. variegata and S. salamandra). In the context of climate change, our findings suggest that the capacity of organisms to deal with future changes in NAO values could be closely linked to their position on the fast–slow continuum.Our study revealed that Triturus cristatus, Bombina variegata, and Salamandra salamandra differ in their position on a slow–fast gradient of pace of life. Our results also suggest that the differences in life history tactics could influence amphibian responses to North Atlantic Oscillation (NAO) fluctuations: Survival was most affected by the NAO in the species with the fastest pace of life (T. cristatus), whereas recruitment was most impacted in species with a slower pace of life (B. variegata and S. salamandra). In the context of climate change, our findings suggest that the capacity of organisms to deal with future changes in NAO values could be closely linked to their position on the fast–slow continuum.
  • Climatic changes can drive the loss of genetic diversity in a Neotropical
           savanna tree species
    • Abstract: The high rates of future climatic changes, compared with the rates reported for past changes, may hamper species adaptation to new climates or the tracking of suitable conditions, resulting in significant loss of genetic diversity. Trees are dominant species in many biomes and because they are long‐lived, they may not be able to cope with ongoing climatic changes. Here, we coupled ecological niche modelling (ENM) and genetic simulations to forecast the effects of climatic changes on the genetic diversity and the structure of genetic clusters. Genetic simulations were conditioned to climatic variables and restricted to plant dispersal and establishment. We used a Neotropical savanna tree as species model that shows a preference for hot and drier climates, but with low temperature seasonality. The ENM predicts a decreasing range size along the more severe future climatic scenario. Additionally, genetic diversity and allelic richness also decrease with range retraction and climatic genetic clusters are lost for both future scenarios, which will lead genetic variability to homogenize throughout the landscape. Besides, climatic genetic clusters will spatially reconfigure on the landscape following displacements of climatic conditions. Our findings indicate that climate change effects will challenge population adaptation to new environmental conditions because of the displacement of genetic ancestry clusters from their optimal conditions.The high rates of future climatic changes, compared with the rates reported for past changes, may hamper species adaptation to new climates or the tracking of suitable conditions, resulting in significant loss of genetic diversity. Our findings, using a Neotropical savanna tree species, indicate that climate change effects will challenge population adaptation to new environmental conditions because of the displacement of genetic ancestry clusters from their optimal conditions. The ENM predicts a decreasing range size along the more severe future climatic scenario, that is 8.5 RCP, and genetic diversity and allelic richness also decrease with range retraction and climatic genetic clusters are lost for both future scenarios (4.5 and 8.5 RCP), which will lead genetic variability to homogenize throughout the landscape.
  • Surfing parameter hyperspaces under climate change scenarios to design
           future rice ideotypes
    • Abstract: Growing food crops to meet global demand and the search for more sustainable cropping systems are increasing the need for new cultivars in key production areas. This study presents the identification of rice traits putatively producing the largest yield benefits in five areas that markedly differ in terms of environmental conditions in the Philippines, India, China, Japan and Italy. The ecophysiological model WARM and sensitivity analysis techniques were used to evaluate phenotypic traits involved with light interception, photosynthetic efficiency, tolerance to abiotic stressors, resistance to fungal pathogens and grain quality. The analysis involved only model parameters that have a close relationship with phenotypic traits breeders are working on, to increase the in vivo feasibility of selected ideotypes. Current climate and future projections were considered, in the light of the resources required by breeding programs and of the role of weather variables in the identification of promising traits. Results suggest that breeding for traits involved with disease resistance, and tolerance to cold‐ and heat‐induced spikelet sterility could provide benefits similar to those obtained from the improvement of traits involved with canopy structure and photosynthetic efficiency. In contrast, potential benefits deriving from improved grain quality traits are restricted by weather variability and markedly affected by G × E interactions. For this reason, district‐specific ideotypes were identified using a new index accounting for both their productivity and feasibility.The ecophysiological model WARM and sensitivity analysis techniques were used to evaluate rice phenotypic traits involved with light interception, photosynthetic efficiency, tolerance to abiotic stressors, resistance to fungal pathogens and grain quality. Current conditions and climate change projections were considered in five rice production areas differing in terms of environmental conditions in the Philippines, India, China, Japan and Italy. Strong G × E interactions affected results, thus leading to define rice district‐specific ideotypes via a new index accounting for both their productivity and feasibility.
  • Legacy introductions and climatic variation explain spatiotemporal
           patterns of invasive hybridization in a native trout
    • Abstract: Hybridization between invasive and native species, a significant threat to worldwide biodiversity, is predicted to increase due to climate‐induced expansions of invasive species. Long‐term research and monitoring are crucial for understanding the ecological and evolutionary processes that modulate the effects of invasive species. Using a large, multidecade genetics dataset (N = 582 sites, 12,878 individuals) with high‐resolution climate predictions and extensive stocking records, we evaluate the spatiotemporal dynamics of hybridization between native cutthroat trout and invasive rainbow trout, the world's most widely introduced invasive fish, across the Northern Rocky Mountains of the United States. Historical effects of stocking and contemporary patterns of climatic variation were strongly related to the spread of hybridization across space and time. The probability of occurrence, extent of, and temporal changes in hybridization increased at sites in close proximity to historical stocking locations with greater rainbow trout propagule pressure, warmer water temperatures, and lower spring precipitation. Although locations with warmer water temperatures were more prone to hybridization, cold sites were not protected from invasion; 58% of hybridized sites had cold mean summer water temperatures (
  • Rapid thermal adaptation in photosymbionts of reef‐building corals
    • Abstract: Climate warming is occurring at a rate not experienced by life on Earth for 10 s of millions of years, and it is unknown whether the coral‐dinoflagellate (Symbiodinium spp.) symbiosis can evolve fast enough to ensure coral reef persistence. Coral thermal tolerance is partly dependent on the Symbiodinium hosted. Therefore, directed laboratory evolution in Symbiodinium has been proposed as a strategy to enhance coral holobiont thermal tolerance. Using a reciprocal transplant design, we show that the upper temperature tolerance and temperature tolerance range of Symbiodinium C1 increased after ~80 asexual generations (2.5 years) of laboratory thermal selection. Relative to wild‐type cells, selected cells showed superior photophysiological performance and growth rate at 31°C in vitro, and performed no worse at 27°C; they also had lower levels of extracellular reactive oxygen species (exROS). In contrast, wild‐type cells were unable to photosynthesise or grow at 31°C and produced up to 17 times more exROS. In symbiosis, the increased thermal tolerance acquired ex hospite was less apparent. In recruits of two of three species tested, those harbouring selected cells showed no difference in growth between the 27 and 31°C treatments, and a trend of positive growth at both temperatures. Recruits that were inoculated with wild‐type cells, however, showed a significant difference in growth rates between the 27 and 31°C treatments, with a negative growth trend at 31°C. There were no significant differences in the rate and severity of bleaching in coral recruits harbouring wild‐type or selected cells. Our findings highlight the need for additional Symbiodinium genotypes to be tested with this assisted evolution approach. Deciphering the genetic basis of enhanced thermal tolerance in Symbiodinium and the cause behind its limited transference to the coral holobiont in this genotype of Symbiodinium C1 are important next steps for developing methods that aim to increase coral bleaching tolerance.The rate of climate warming is unprecedented. Coral thermal tolerance is partly dependent on the symbiotic microalgae, Symbiodinium, that they host. We show that after 80 asexual generations (~2.5 years) of laboratory temperature selection, the derived Symbiodinium cells had superior photophysiological performance and growth rate under heat stress with low levels of oxidative stress relative to the nonselected Symbiodinium. However, the enhanced thermal tolerance acquired was much reduced when Symbiodinium cells were harboured within the coral host.
  • Pinus taeda forest growth predictions in the 21st century vary with site
           mean annual temperature and site quality
    • Abstract: Climate projections from 20 downscaled global climate models (GCMs) were used with the 3‐PG model to predict the future productivity and water use of planted loblolly pine (Pinus taeda) growing across the southeastern United States. Predictions were made using Representative Concentration Pathways (RCP) 4.5 and 8.5. These represent scenarios in which total radiative forcing stabilizes before 2100 (RCP 4.5) or continues increasing throughout the century (RCP 8.5). Thirty‐six sites evenly distributed across the native range of the species were used in the analysis. These sites represent a range in current mean annual temperature (14.9–21.6°C) and precipitation (1,120–1,680 mm/year). The site index of each site, which is a measure of growth potential, was varied to represent different levels of management. The 3‐PG model predicted that aboveground biomass growth and net primary productivity will increase by 10%–40% in many parts of the region in the future. At cooler sites, the relative growth increase was greater than at warmer sites. By running the model with the baseline [CO2] or the anticipated elevated [CO2], the effect of CO2 on growth was separated from that of other climate factors. The growth increase at warmer sites was due almost entirely to elevated [CO2]. The growth increase at cooler sites was due to a combination of elevated [CO2] and increased air temperature. Low site index stands had a greater relative increase in growth under the climate change scenarios than those with a high site index. Water use increased in proportion to increases in leaf area and productivity but precipitation was still adequate, based on the downscaled GCM climate projections. We conclude that an increase in productivity can be expected for a large majority of the planted loblolly pine stands in the southeastern United States during this century.An increase in productivity can be expected for a large majority of the planted loblolly pine stands in the southeastern United States during this century. At cooler sites, the relative growth increase will be greater than at warmer sites. Stands at a high site index in the warmest areas tended to have little or no increase in productivity, but these stands are already highly productive. Water use increased in proportion to increases in leaf area and productivity but precipitation will be still adequate, based on the GCM climate projections.
  • Interannual variation in methane emissions from tropical wetlands
           triggered by repeated El Niño Southern Oscillation
    • Abstract: Methane (CH4) emissions from tropical wetlands contribute 60%–80% of global natural wetland CH4 emissions. Decreased wetland CH4 emissions can act as a negative feedback mechanism for future climate warming and vice versa. The impact of the El Niño–Southern Oscillation (ENSO) on CH4 emissions from wetlands remains poorly quantified at both regional and global scales, and El Niño events are expected to become more severe based on climate models’ projections. We use a process‐based model of global wetland CH4 emissions to investigate the impacts of the ENSO on CH4 emissions in tropical wetlands for the period from 1950 to 2012. The results show that CH4 emissions from tropical wetlands respond strongly to repeated ENSO events, with negative anomalies occurring during El Niño periods and with positive anomalies occurring during La Niña periods. An approximately 8‐month time lag was detected between tropical wetland CH4 emissions and ENSO events, which was caused by the combined time lag effects of ENSO events on precipitation and temperature over tropical wetlands. The ENSO can explain 49% of interannual variations for tropical wetland CH4 emissions. Furthermore, relative to neutral years, changes in temperature have much stronger effects on tropical wetland CH4 emissions than the changes in precipitation during ENSO periods. The occurrence of several El Niño events contributed to a lower decadal mean growth rate in atmospheric CH4 concentrations throughout the 1980s and 1990s and to stable atmospheric CH4 concentrations from 1999 to 2006, resulting in negative feedback to global warming.CH4 emissions from tropical wetlands respond strongly to repeated ENSO events. An approximately 8‐month time‐lag was detected between tropical wetland CH4 emissions and ENSO events and the ENSO can explain 49% of inter‐annual variations for tropical wetland CH4 emissions. The occurrence of several El Niño events contributed to a lower decadal mean growth rate in atmospheric CH4 concentrations throughout the 1980s and 1990s and to stable atmospheric CH4 concentrations from 1999 to 2006.
  • Disentangling species and functional group richness effects on soil N
           cycling in a grassland ecosystem
    • Abstract: Species richness (SR) and functional group richness (FGR) are often confounded in both observational and experimental field studies of biodiversity and ecosystem function. This precludes discernment of their separate influences on ecosystem processes, including nitrogen (N) cycling, and how those influences might be moderated by global change factors. In a 17‐year field study of grassland species, we used two full factorial experiments to independently vary SR (one or four species, with FGR = 1) and FGR (1–4 groups, with SR = 4) to assess SR and FGR effects on ecosystem N cycling and its response to elevated carbon dioxide (CO2) and N addition. We hypothesized that increased plant diversity (either SR or FGR) and elevated CO2 would enhance plant N pools because of greater plant N uptake, but decrease soil N cycling rates because of greater soil carbon inputs and microbial N immobilization. In partial support of these hypotheses, increasing SR or FGR (holding the other constant) enhanced total plant N pools and decreased soil nitrate pools, largely through higher root biomass, and increasing FGR strongly reduced mineralization rates, because of lower root N concentrations. In contrast, increasing SR (holding FGR constant and despite increasing total plant C and N pools) did not alter root N concentrations or net N mineralization rates. Elevated CO2 had minimal effects on plant and soil N metrics and their responses to plant diversity, whereas enriched N increased plant and soil N pools, but not soil N fluxes. These results show that functional diversity had additional effects on both plant N pools and rates of soil N cycling that were independent of those of species richness.Increasing SR or FGR (holding the other constant) enhanced total plant N pools and decreased soil nitrate pools, and increasing FGR strongly reduced mineralization rates. In contrast, increasing SR (holding FGR constant and despite increasing total plant C and N pools) did not alter root N concentrations or net N mineralization rates. Elevated CO2 had minimal effects on plant and soil N metrics and their responses to plant diversity, whereas enriched N increased plant and soil N pools, but not soil N fluxes. These results show that functional diversity had additional effects on both plant N pools and rates of soil N cycling that were independent of those of species richness.
  • Higher yields and lower methane emissions with new rice cultivars
    • Abstract: Breeding high‐yielding rice cultivars through increasing biomass is a key strategy to meet rising global food demands. Yet, increasing rice growth can stimulate methane (CH4) emissions, exacerbating global climate change, as rice cultivation is a major source of this powerful greenhouse gas. Here, we show in a series of experiments that high‐yielding rice cultivars actually reduce CH4 emissions from typical paddy soils. Averaged across 33 rice cultivars, a biomass increase of 10% resulted in a 10.3% decrease in CH4 emissions in a soil with a high carbon (C) content. Compared to a low‐yielding cultivar, a high‐yielding cultivar significantly increased root porosity and the abundance of methane‐consuming microorganisms, suggesting that the larger and more porous root systems of high‐yielding cultivars facilitated CH4 oxidation by promoting O2 transport to soils. Our results were further supported by a meta‐analysis, showing that high‐yielding rice cultivars strongly decrease CH4 emissions from paddy soils with high organic C contents. Based on our results, increasing rice biomass by 10% could reduce annual CH4 emissions from Chinese rice agriculture by 7.1%. Our findings suggest that modern rice breeding strategies for high‐yielding cultivars can substantially mitigate paddy CH4 emission in China and other rice growing regions.We present evidence from three independent but complementary experiments that high‐yielding cultivars actually reduce CH4 emissions from typical rice paddies. Our results suggest that the larger and more porous root systems of high‐yielding cultivars facilitate CH4 oxidation by promoting O2 transport to soils. Meta‐analysis indicates that a 10% increase in biomass reduces CH4 emissions from Chinese rice agriculture by 7.1%, confirming that the use of high‐yielding cultivars can substantially mitigate anthropogenic greenhouse gas emissions.
  • Climate‐driven geographic distribution of the desert locust during
           recession periods: Subspecies’ niche differentiation and relative risks
           under scenarios of climate change
    • Abstract: The desert locust is an agricultural pest that is able to switch from a harmless solitarious stage, during recession periods, to swarms of gregarious individuals that disperse long distances and affect areas from western Africa to India during outbreak periods. Large outbreaks have been recorded through centuries, and the Food and Agriculture Organization keeps a long‐term, large‐scale monitoring survey database in the area. However, there is also a much less known subspecies that occupies a limited area in Southern Africa. We used large‐scale climatic and occurrence data of the solitarious phase of each subspecies during recession periods to understand whether both subspecies climatic niches differ from each other, what is the current potential geographical distribution of each subspecies, and how climate change is likely to shift their potential distribution with respect to current conditions. We evaluated whether subspecies are significantly specialized along available climate gradients by using null models of background climatic differences within and between southern and northern ranges and applying niche similarity and niche equivalency tests. The results point to climatic niche conservatism between the two clades. We complemented this analysis with species distribution modeling to characterize current solitarious distributions and forecast potential recession range shifts under two extreme climate change scenarios at the 2050 and 2090 time horizon. Projections suggest that, at a global scale, the northern clade could contract its solitarious recession range, while the southern clade is likely to expand its recession range. However, local expansions were also predicted in the northern clade, in particular in southern and northern margins of the current geographical distribution. In conclusion, monitoring and management practices should remain in place in northern Africa, while in Southern Africa the potential for the subspecies to pose a threat in the future should be investigated more closely.Here, we study the climatic niche and recession range of the two subspecies of desert locust, a widespread agricultural pest that is widely known for its impressive large outbreaks in northern Africa, the Middle East, and Asia, but that is also present in southern Africa. We found that, although the two subspecies occupy different climates during recession periods, their environmental niches have been conserved. However, because of the differences in climate change projections between the two regions it occupies, the northern clade is likely to contract its recession range, at least at a global scale, while the southern clade is likely to expand its recession range in the face of climate change. In conclusion, monitoring and management practices should remain in place in northern Africa, and in Southern Africa, the potential for the subspecies to pose a threat in the future should be investigated more closely.
  • Global evaluation of a semiempirical model for yield anomalies and
           application to within‐season yield forecasting
    • Abstract: Quantifying the influence of weather on yield variability is decisive for agricultural management under current and future climate anomalies. We extended an existing semiempirical modeling scheme that allows for such quantification. Yield anomalies, measured as interannual differences, were modeled for maize, soybeans, and wheat in the United States and 32 other main producer countries. We used two yield data sets, one derived from reported yields and the other from a global yield data set deduced from remote sensing. We assessed the capacity of the model to forecast yields within the growing season. In the United States, our model can explain at least two‐thirds (63%–81%) of observed yield anomalies. Its out‐of‐sample performance (34%–55%) suggests a robust yield projection capacity when applied to unknown weather. Out‐of‐sample performance is lower when using remote sensing‐derived yield data. The share of weather‐driven yield fluctuation varies spatially, and estimated coefficients agree with expectations. Globally, the explained variance in yield anomalies based on the remote sensing data set is similar to the United States (71%–84%). But the out‐of‐sample performance is lower (15%–42%). The performance discrepancy is likely due to shortcomings of the remote sensing yield data as it diminishes when using reported yield anomalies instead. Our model allows for robust forecasting of yields up to 2 months before harvest for several main producer countries. An additional experiment suggests moderate yield losses under mean warming, assuming no major changes in temperature extremes. We conclude that our model can detect weather influences on yield anomalies and project yields with unknown weather. It requires only monthly input data and has a low computational demand. Its within‐season yield forecasting capacity provides a basis for practical applications like local adaptation planning. Our study underlines high‐quality yield monitoring and statistics as critical prerequisites to guide adaptation under climate change.We applied a semiempirical model to quantify weather impacts on yields globally and to forecast yields within the growing season. Our model robustly explains weather‐related yield variability and is able to forecast yields up to two months before harvest in several countries. Our study also underlines high‐quality yield monitoring and statistics as critical prerequisites to guide adaptation under climate change.
  • Enhanced decomposition of stable soil organic carbon and microbial
           catabolic potentials by long‐term field warming
    • Abstract: Quantifying soil organic carbon (SOC) decomposition under warming is critical to predict carbon–climate feedbacks. According to the substrate regulating principle, SOC decomposition would decrease as labile SOC declines under field warming, but observations of SOC decomposition under warming do not always support this prediction. This discrepancy could result from varying changes in SOC components and soil microbial communities under warming. This study aimed to determine the decomposition of SOC components with different turnover times after subjected to long‐term field warming and/or root exclusion to limit C input, and to test whether SOC decomposition is driven by substrate lability under warming. Taking advantage of a 12‐year field warming experiment in a prairie, we assessed the decomposition of SOC components by incubating soils from control and warmed plots, with and without root exclusion for 3 years. We assayed SOC decomposition from these incubations by combining inverse modeling and microbial functional genes during decomposition with a metagenomic technique (GeoChip). The decomposition of SOC components with turnover times of years and decades, which contributed to 95% of total cumulative CO2 respiration, was greater in soils from warmed plots. But the decomposition of labile SOC was similar in warmed plots compared to the control. The diversity of C‐degradation microbial genes generally declined with time during the incubation in all treatments, suggesting shifts of microbial functional groups as substrate composition was changing. Compared to the control, soils from warmed plots showed significant increase in the signal intensities of microbial genes involved in degrading complex organic compounds, implying enhanced potential abilities of microbial catabolism. These are likely responsible for accelerated decomposition of SOC components with slow turnover rates. Overall, the shifted microbial community induced by long‐term warming accelerates the decomposition of SOC components with slow turnover rates and thus amplify the positive feedback to climate change.The decomposition of SOC components with turnover times of years and decades, which contributed to 95% of total cumulative CO2 respiration, was greater in soils from warmed plots compared to the control. But the decomposition of labile SOC was similar in warmed plots compared to the control. The diversity of C‐degradation microbial genes generally declined with time during the incubation in all the soils from control and warmed plots, with and without root exclusion. Meanwhile, compared to the control, soils from warmed plots showed significant increase in the signal intensities of microbial genes involved in degrading complex organic compounds, implying enhanced potential abilities of microbial catabolism. Taken together, this study highlights changes in soil microbial community functions induced by long‐term warming. The shifted microbial community accelerates the decomposition of SOC components with slow turnover rates and thus amplify the positive feedback to climate change.
  • Global climate change will increase the abundance of symbiotic
           nitrogen‐fixing trees in much of North America
    • Abstract: Symbiotic nitrogen (N)‐fixing trees can drive N and carbon cycling and thus are critical components of future climate projections. Despite detailed understanding of how climate influences N‐fixation enzyme activity and physiology, comparatively little is known about how climate influences N‐fixing tree abundance. Here, we used forest inventory data from the USA and Mexico (>125,000 plots) along with climate data to address two questions: (1) How does the abundance distribution of N‐fixing trees (rhizobial, actinorhizal, and both types together) vary with mean annual temperature (MAT) and precipitation (MAP)' (2) How will changing climate shift the abundance distribution of N‐fixing trees' We found that rhizobial N‐fixing trees were nearly absent below 15°C MAT, but above 15°C MAT, they increased in abundance as temperature rose. We found no evidence for a hump‐shaped response to temperature throughout the range of our data. Rhizobial trees were more abundant in dry than in wet ecosystems. By contrast, actinorhizal trees peaked in abundance at 5–10°C MAT and were least abundant in areas with intermediate precipitation. Next, we used a climate‐envelope approach to project how N‐fixing tree relative abundance might change in the future. The climate‐envelope projection showed that rhizobial N‐fixing trees will likely become more abundant in many areas by 2080, particularly in the southern USA and western Mexico, due primarily to rising temperatures. Projections for actinorhizal N‐fixing trees were more nuanced due to their nonmonotonic dependence on temperature and precipitation. Overall, the dominant trend is that warming will increase N‐fixing tree abundance in much of the USA and Mexico, with large increases up to 40° North latitude. The quantitative link we provide between climate and N‐fixing tree abundance can help improve the representation of symbiotic N fixation in Earth System Models.Symbiotic nitrogen‐fixing trees can drive nitrogen and carbon cycling and thus are critical components of future climate projections. Global warming will increase nitrogen‐fixing tree abundance in much of the USA and Mexico, with large increases up to 40° North latitude.
  • Climate variability drives recent tree mortality in Europe
    • Abstract: Tree mortality is an important process in forest ecosystems, frequently hypothesized to be highly climate sensitive. Yet, tree death remains one of the least understood processes of forest dynamics. Recently, changes in tree mortality have been observed in forests around the globe, which could profoundly affect ecosystem functioning and services provisioning to society. We describe continental‐scale patterns of recent tree mortality from the only consistent pan‐European forest monitoring network, identifying recent mortality hotspots in southern and northern Europe. Analyzing 925,462 annual observations of 235,895 trees between 2000 and 2012, we determine the influence of climate variability and tree age on interannual variation in tree mortality using Cox proportional hazard models. Warm summers as well as high seasonal variability in precipitation increased the likelihood of tree death. However, our data also suggest that reduced cold‐induced mortality could compensate increased mortality related to peak temperatures in a warming climate. Besides climate variability, age was an important driver of tree mortality, with individual mortality probability decreasing with age over the first century of a trees life. A considerable portion of the observed variation in tree mortality could be explained by satellite‐derived net primary productivity, suggesting that widely available remote sensing products can be used as an early warning indicator of widespread tree mortality. Our findings advance the understanding of patterns of large‐scale tree mortality by demonstrating the influence of seasonal and diurnal climate variation, and highlight the potential of state‐of‐the‐art remote sensing to anticipate an increased likelihood of tree mortality in space and time.We identified recent tree mortality hotspots using more than 200.000 forest monitoring observations from across Europe. Seasonal variability in summer and winter temperatures as well as shifts of precipitation between seasons enhance the mortality risk, while increasing tree age reduces the likelihood for tree death. In a warming climate elevated mortality due to high peak temperatures could be offset by reduced cold‐induced mortality. Remotely sensed productivity can be used to foresee future mortality events.
  • Attribution of seasonal leaf area index trends in the northern latitudes
           with “optimally” integrated ecosystem models
    • Abstract: Significant increases in remotely sensed vegetation indices in the northern latitudes since the 1980s have been detected and attributed at annual and growing season scales. However, we presently lack a systematic understanding of how vegetation responds to asymmetric seasonal environmental changes. In this study, we first investigated trends in the seasonal mean leaf area index (LAI) at northern latitudes (north of 30°N) between 1982 and 2009 using three remotely sensed long‐term LAI data sets. The most significant LAI increases occurred in summer (0.009 m2 m−2 year−1, p 
  • The phenology of leaf quality and its within‐canopy variation is
           essential for accurate modeling of photosynthesis in tropical evergreen
    • Abstract: Leaf quantity (i.e., canopy leaf area index, LAI), quality (i.e., per‐area photosynthetic capacity), and longevity all influence the photosynthetic seasonality of tropical evergreen forests. However, these components of tropical leaf phenology are poorly represented in most terrestrial biosphere models (TBMs). Here, we explored alternative options for the representation of leaf phenology effects in TBMs that employ the Farquahar, von Caemmerer & Berry (FvCB) representation of CO2 assimilation. We developed a two‐fraction leaf (sun and shade), two‐layer canopy (upper and lower) photosynthesis model to evaluate different modeling approaches and assessed three components of phenological variations (i.e., leaf quantity, quality, and within‐canopy variation in leaf longevity). Our model was driven by the prescribed seasonality of leaf quantity and quality derived from ground‐based measurements within an Amazonian evergreen forest. Modeled photosynthetic seasonality was not sensitive to leaf quantity, but was highly sensitive to leaf quality and its vertical distribution within the canopy, with markedly more sensitivity to upper canopy leaf quality. This is because light absorption in tropical canopies is near maximal for the entire year, implying that seasonal changes in LAI have little impact on total canopy light absorption; and because leaf quality has a greater effect on photosynthesis of sunlit leaves than light limited, shade leaves and sunlit foliage are more abundant in the upper canopy. Our two‐fraction leaf, two‐layer canopy model, which accounted for all three phenological components, was able to simulate photosynthetic seasonality, explaining ~90% of the average seasonal variation in eddy covariance‐derived CO2 assimilation. This work identifies a parsimonious approach for representing tropical evergreen forest photosynthetic seasonality in TBMs that utilize the FvCB model of CO2 assimilation and highlights the importance of incorporating more realistic phenological mechanisms in models that seek to improve the projection of future carbon dynamics in tropical evergreen forests.Tropical leaf phenology largely regulates the carbon assimilation of tropical evergreen forests; however, the leaf phenology effects are still poorly represented in most terrestrial biosphere models (TBMs). Here, we explored alternative options for the representation of leaf phenology effects in TBMs, by assessing the three components of phenological variations (i.e., leaf quantity, quality, and the within‐canopy variation). Our work demonstrates that the phenology of leaf quality and its within‐canopy variation is essential for accurate modeling in tropical evergreen forests, explaining ~90% of local eddy covariance‐derived photosynthetic seasonality; our work also identifies a parsimonious approach for representing tropical evergreen forest photosynthetic seasonality in TBMs and highlights the importance of incorporating more realistic phenological mechanisms in models that seek to improve the projection of future carbon dynamics in tropical evergreen forests.
  • Acclimation of bloom‐forming and perennial seaweeds to elevated pCO2
           conserved across levels of environmental complexity
    • Abstract: Macroalgae contribute approximately 15% of the primary productivity in coastal marine ecosystems, fix up to 27.4 Tg of carbon per year, and provide important structural components for life in coastal waters. Despite this ecological and commercial importance, direct measurements and comparisons of the short‐term responses to elevated pCO2 in seaweeds with different life‐history strategies are scarce. Here, we cultured several seaweed species (bloom forming/nonbloom forming/perennial/annual) in the laboratory, in tanks in an indoor mesocosm facility, and in coastal mesocosms under pCO2 levels ranging from 400 to 2,000 μatm. We find that, across all scales of the experimental setup, ephemeral species of the genus Ulva increase their photosynthesis and growth rates in response to elevated pCO2 the most, whereas longer‐lived perennial species show a smaller increase or a decrease. These differences in short‐term growth and photosynthesis rates are likely to give bloom‐forming green seaweeds a competitive advantage in mixed communities, and our results thus suggest that coastal seaweed assemblages in eutrophic waters may undergo an initial shift toward communities dominated by bloom‐forming, short‐lived seaweeds.Macroalgae are primary productivity in coastal marine ecosystems and provide important structural components for life in coastal waters. Despite their ecological and commercial importance, direct measurements and comparisons of variability in the short‐term responses of different macroalgal species to elevated pCO2 are scarce and often carried out in the laboratory, where it is unclear how the results translate into more natural settings. We found that ephemeral species of the genus Ulva increased their photosynthesis and growth rates the most, whereas longer‐lived perennial species showed a smaller increase or a decrease in photosynthesis and growth rates. Our results suggest that coastal seaweed assemblages in eutrophic waters may undergo an initial shift toward bloom‐forming seaweed‐dominated communities and that short‐term laboratory measurements can predict the direction and shape of the response in more complex settings well, but the magnitude is modulated by temperature fluctuations in the outdoor and indoor mesocosm facilities.
  • Short‐term acclimation to warmer temperatures accelerates leaf carbon
           exchange processes across plant types
    • Abstract: While temperature responses of photosynthesis and plant respiration are known to acclimate over time in many species, few studies have been designed to directly compare process‐level differences in acclimation capacity among plant types. We assessed short‐term (7 day) temperature acclimation of the maximum rate of Rubisco carboxylation (Vcmax), the maximum rate of electron transport (Jmax), the maximum rate of phosphoenolpyruvate carboxylase carboxylation (Vpmax), and foliar dark respiration (Rd) in 22 plant species that varied in lifespan (annual and perennial), photosynthetic pathway (C3 and C4), and climate of origin (tropical and nontropical) grown under fertilized, well‐watered conditions. In general, acclimation to warmer temperatures increased the rate of each process. The relative increase in different photosynthetic processes varied by plant type, with C3 species tending to preferentially accelerate CO2‐limited photosynthetic processes and respiration and C4 species tending to preferentially accelerate light‐limited photosynthetic processes under warmer conditions. Rd acclimation to warmer temperatures caused a reduction in temperature sensitivity that resulted in slower rates at high leaf temperatures. Rd acclimation was similar across plant types. These results suggest that temperature acclimation of the biochemical processes that underlie plant carbon exchange is common across different plant types, but that acclimation to warmer temperatures tends to have a relatively greater positive effect on the processes most limiting to carbon assimilation, which differ by plant type. The acclimation responses observed here suggest that warmer conditions should lead to increased rates of carbon assimilation when water and nutrients are not limiting.We examined temperature acclimation of photosynthetic and leaf respiratory processes across 22 plant species from a variety of plant functional types. Acclimation to warmer temperatures was manifested in an increase in photosynthetic and respiratory processes. The photosynthetic allocation patterns tended to favor processes that limited photosynthesis, which differed by plant type.
  • Global forest carbon uptake due to nitrogen and phosphorus deposition from
           1850 to 2100
    • Abstract: Spatial patterns and temporal trends of nitrogen (N) and phosphorus (P) deposition are important for quantifying their impact on forest carbon (C) uptake. In a first step, we modeled historical and future change in the global distributions of the atmospheric deposition of N and P from the dry and wet deposition of aerosols and gases containing N and P. Future projections were compared between two scenarios with contrasting aerosol emissions. Modeled fields of N and P deposition and P concentration were evaluated using globally distributed in situ measurements. N deposition peaked around 1990 in European forests and around 2010 in East Asian forests, and both increased sevenfold relative to 1850. P deposition peaked around 2010 in South Asian forests and increased 3.5‐fold relative to 1850. In a second step, we estimated the change in C storage in forests due to the fertilization by deposited N and P (∆Cν dep), based on the retention of deposited nutrients, their allocation within plants, and C:N and C:P stoichiometry. ∆Cν dep for 1997–2013 was estimated to be 0.27 ± 0.13 Pg C year−1 from N and 0.054 ± 0.10 Pg C year−1 from P, contributing 9% and 2% of the terrestrial C sink, respectively. Sensitivity tests show that uncertainty of ∆Cν dep was larger from P than from N, mainly due to uncertainty in the fraction of deposited P that is fixed by soil. ∆CP dep was exceeded by ∆CN dep over 1960–2007 in a large area of East Asian and West European forests due to a faster growth in N deposition than P. Our results suggest a significant contribution of anthropogenic P deposition to C storage, and additional sources of N are needed to support C storage by P in some Asian tropical forests where the deposition rate increased even faster for P than for N.We estimate the historical and future change in global distributions of the atmospheric deposition of N and P. We apply a stoichiometric mass‐balance approach to estimate the change in C storage in forests due to the fertilization by deposited N and P. We find that the effect of P is exceeded by N in East Asian and West European forests due to a faster growth in N deposition than P, and that there is a significant contribution of anthropogenic P deposition to C storage in some Asian tropical forests where the deposition increased even faster for P than for N.
  • Optimal climate for large trees at high elevations drives patterns of
           biomass in remote forests of Papua New Guinea
    • Abstract: Our ability to model global carbon fluxes depends on understanding how terrestrial carbon stocks respond to varying environmental conditions. Tropical forests contain the bulk of the biosphere's carbon. However, there is a lack of consensus as to how gradients in environmental conditions affect tropical forest carbon. Papua New Guinea (PNG) lies within one of the largest areas of contiguous tropical forest and is characterized by environmental gradients driven by altitude; yet, the region has been grossly understudied. Here, we present the first field assessment of aboveground biomass (AGB) across three main forest types of PNG using 193 plots stratified across 3,100‐m elevation gradient. Unexpectedly, AGB had no direct relationship to rainfall, temperature, soil, or topography. Instead, natural disturbances explained most variation in AGB. While large trees (diameter at breast height > 50 cm) drove altitudinal patterns of AGB, resulting in a major peak in AGB (2,200–3,100 m) and some of the most carbon‐rich forests at these altitudes anywhere. Large trees were correlated to a set of climatic variables following a hump‐shaped curve. The set of “optimal” climatic conditions found in montane cloud forests is similar to that of maritime temperate areas that harbor the largest trees in the world: high ratio of precipitation to evapotranspiration (2.8), moderate mean annual temperature (13.7°C), and low intra‐annual temperature range (7.5°C). At extreme altitudes (2,800–3,100 m), where tree diversity elsewhere is usually low and large trees are generally rare or absent, specimens from 18 families had girths >70 cm diameter and maximum heights 20–41 m. These findings indicate that simple AGB‐climate‐edaphic models may not be suitable for estimating carbon storage in forests where optimal climate niches exist. Our study, conducted in a very remote area, suggests that tropical montane forests may contain greater AGB than previously thought and the importance of securing their future under a changing climate is therefore enhanced.Montane cloud forests are often thought to be squat and gnarly with little carbon benefit, a misconception we show in this study. Optimal climate conditionsfor large trees drive forest biomass patterns along a 3000m elevation gradient in Papua New Guinea. These optimal climate niches, similar to those also found in the temperate coastal climates that are home to the largest trees in the world, are also found at high elevations in remote tropical forests of Papua New Guinea.
  • Methane emission from feather moss stands
    • Abstract: Data from remote sensing and Eddy towers indicate that forests are not always net sinks for atmospheric CH4. However, studies describing specific sources within forests and functional analysis of microorganisms on sites with CH4 turnover are scarce. Feather moss stands were considered to be net sinks for carbon dioxide, but received little attention to their role in CH4 cycling. Therefore, we investigated methanogenic rates and pathways together with the methanogenic microbial community composition in feather moss stands from temperate and boreal forests. Potential rates of CH4 emission from intact moss stands (n = 60) under aerobic conditions ranged between 19 and 133 pmol CH4 h−1 gdw−1. Temperature and water content positively influenced CH4 emission. Methanogenic potentials determined under N2 atmosphere in darkness ranged between 22 and 157 pmol CH4 h−1 gdw−1. Methane production was strongly inhibited by bromoethane sulfonate or chloroform, showing that CH4 was of microbial origin. The moss samples tested contained fluorescent microbial cells and between 104 and 105 copies per gram dry weight moss of the mcrA gene coding for a subunit of the methyl CoM reductase. Archaeal 16S rRNA and mcrA gene sequences in the moss stands were characteristic for the archaeal families Methanobacteriaceae and Methanosarcinaceae. The potential methanogenic rates were similar in incubations with and without methyl fluoride, indicating that the CH4 was produced by the hydrogenotrophic rather than aceticlastic pathway. Consistently, the CH4 produced was depleted in 13C in comparison with the moss biomass carbon and acetate accumulated to rather high concentrations (3–62 mM). The δ13C of acetate was similar to that of the moss biomass, indicating acetate production by fermentation. Our study showed that the feather moss stands contained active methanogenic microbial communities producing CH4 by hydrogenotrophic methanogenesis and causing net emission of CH4 under ambient conditions, albeit at low rates.Depth profile of O2 concentrations in different feather moss stands sampled from Marburg and Sweden. (a) Swedish feather moss; (b) Swedish feather moss O2 depth profile and (c) Marburg feather moss O2 depth profile.
  • Shifting Pacific storm tracks as stressors to ecosystems of western North
    • Abstract: Much of the precipitation delivered to western North America arrives during the cool season via midlatitude Pacific storm tracks, which may experience future shifts in response to climate change. Here, we assess the sensitivity of the hydroclimate and ecosystems of western North America to the latitudinal position of cool‐season Pacific storm tracks. We calculated correlations between storm track variability and three hydroclimatic variables: gridded cool‐season standardized precipitation‐evapotranspiration index, April snow water equivalent, and water year streamflow from a network of USGS stream gauges. To assess how historical storm track variability affected ecosystem processes, we derived forest growth estimates from a large network of tree‐ring widths and land surface phenology and wildfire estimates from remote sensing. From 1980 to 2014, cool‐season storm tracks entered western North America between approximately 41°N and 53°N. Cool‐season moisture supply and snowpack responded strongly to storm track position, with positive correlations to storm track latitude in eastern Alaska and northwestern Canada but negative correlations in the northwestern U.S. Ecosystems of the western United States were greener and more productive following winters with south‐shifted storm tracks, while Canadian ecosystems were greener in years when the cool‐season storm track was shifted to the north. On average, larger areas of the northwestern United States were burned by moderate to high severity wildfires when storm tracks were displaced north, and the average burn area per fire also tended to be higher in years with north‐shifted storm tracks. These results suggest that projected shifts of Pacific storm tracks over the 21st century would likely alter hydroclimatic and ecological regimes in western North America, particularly in the northwestern United States, where moisture supply and ecosystem processes are highly sensitive to the position of cool‐season storm tracks.We investigated how recent variation in storm track position and intensity has affected the hydroclimate and ecosystems of western North America. When storm tracks were positioned anomalously far north, the northwestern United States was drier than normal while western Canada was wetter than normal. Results indicate that reduced vegetative growth and increased wildfire risk follow the drier conditions in the northwestern United States associated with north‐shifted storm tracks.
  • Does climate variability influence the demography of wild primates'
           Evidence from long‐term life‐history data in seven species
    • Abstract: Earth's rapidly changing climate creates a growing need to understand how demographic processes in natural populations are affected by climate variability, particularly among organisms threatened by extinction. Long‐term, large‐scale, and cross‐taxon studies of vital rate variation in relation to climate variability can be particularly valuable because they can reveal environmental drivers that affect multiple species over extensive regions. Few such data exist for animals with slow life histories, particularly in the tropics, where climate variation over large‐scale space is asynchronous. As our closest relatives, nonhuman primates are especially valuable as a resource to understand the roles of climate variability and climate change in human evolutionary history. Here, we provide the first comprehensive investigation of vital rate variation in relation to climate variability among wild primates. We ask whether primates are sensitive to global changes that are universal (e.g., higher temperature, large‐scale climate oscillations) or whether they are more sensitive to global change effects that are local (e.g., more rain in some places), which would complicate predictions of how primates in general will respond to climate change. To address these questions, we use a database of long‐term life‐history data for natural populations of seven primate species that have been studied for 29–52 years to investigate associations between vital rate variation, local climate variability, and global climate oscillations. Associations between vital rates and climate variability varied among species and depended on the time windows considered, highlighting the importance of temporal scale in detection of such effects. We found strong climate signals in the fertility rates of three species. However, survival, which has a greater impact on population growth, was little affected by climate variability. Thus, we found evidence for demographic buffering of life histories, but also evidence of mechanisms by which climate change could affect the fates of wild primates.We use long‐term life‐history data for natural populations of seven primate species representing the four major radiations of primates to investigate associations between vital rate variation, local climate variability, and global climate oscillations. We ask whether primates are sensitive to global changes that are universal (e.g., higher temperature, large‐scale climate oscillations) or whether they are more sensitive to global change effects that are local (e.g., more rain in some places), which would complicate predictions of how primates in general will respond to climate change. We found strong climate signals in the fertility rates of three species, but most survival rates were little affected by climate variability. These findings indicate demographic buffering of life histories and provide new insights into the implications of climate change for the fates of wild primates.
  • Climate change and temperature‐linked hatchling mortality at a globally
           important sea turtle nesting site
    • Abstract: The study of temperature‐dependent sex determination (TSD) in vertebrates has attracted major scientific interest. Recently, concerns for species with TSD in a warming world have increased because imbalanced sex ratios could potentially threaten population viability. In contrast, relatively little attention has been given to the direct effects of increased temperatures on successful embryonic development. Using 6603 days of sand temperature data recorded across 6 years at a globally important loggerhead sea turtle rookery—the Cape Verde Islands—we show the effects of warming incubation temperatures on the survival of hatchlings in nests. Incorporating published data (n = 110 data points for three species across 12 sites globally), we show the generality of relationships between hatchling mortality and incubation temperature and hence the broad applicability of our findings to sea turtles in general. We use a mechanistic approach supplemented by empirical data to consider the linked effects of warming temperatures on hatchling output and on sex ratios for these species that exhibit TSD. Our results show that higher temperatures increase the natural growth rate of the population as more females are produced. As a result, we project that numbers of nests at this globally important site will increase by approximately 30% by the year 2100. However, as incubation temperatures near lethal levels, the natural growth rate of the population decreases and the long‐term survival of this turtle population is threatened. Our results highlight concerns for species with TSD in a warming world and underline the need for research to extend from a focus on temperature‐dependent sex determination to a focus on temperature‐linked hatchling mortalities.Using empirical data from one of the world's largest sea turtle populations, we address whether warming temperatures will drive a species that exhibits temperature‐dependent sex determination (TSD) to extinction. Our results show that higher temperatures increase the population growth rate of our model species as more females are produced due to TSD. However, as temperatures reach the lethal limit for embryonic development, the long‐term survival of this endangered species is threatened. (Photographic credit: Kostas Papafitsoros)
  • Phenological responses of Icelandic subarctic grasslands to short‐term
           and long‐term natural soil warming
    • Abstract: The phenology of vegetation, particularly the length of the growing season (LOS; i.e., the period from greenup to senescence), is highly sensitive to climate change, which could imply potent feedbacks to the climate system, for example, by altering the ecosystem carbon (C) balance. In recent decades, the largest extensions of LOS have been reported at high northern latitudes, but further warming‐induced LOS extensions may be constrained by too short photoperiod or unfulfilled chilling requirements. Here, we studied subarctic grasslands, which cover a vast area and contain large C stocks, but for which LOS changes under further warming are highly uncertain. We measured LOS extensions of Icelandic subarctic grasslands along natural geothermal soil warming gradients of different age (short term, where the measurements started after 5 years of warming and long term, i.e., warmed since ≥50 years) using ground‐level measurements of normalized difference vegetation index. We found that LOS linearly extended with on average 2.1 days per °C soil warming up to the highest soil warming levels (ca. +10°C) and that LOS had the potential to extend at least 1 month. This indicates that the warming impact on LOS in these subarctic grasslands will likely not saturate in the near future. A similar response to short‐ and long‐term warming indicated a strong physiological control of the phenological response of the subarctic grasslands to warming and suggested that genetic adaptations and community changes were likely of minor importance. We conclude that the warming‐driven extension of the LOSs of these subarctic grasslands did not saturate up to +10°C warming, and hence that growing seasons of high‐latitude grasslands are likely to continue lengthening with future warming (unless genetic adaptations or species shifts do occur). This persistence of the warming‐induced extension of LOS has important implications for the C‐sink potential of subarctic grasslands under climate change.The length of the growing season (LOS) is highly sensitive to climate change, and could in its turn induce powerful feedback mechanisms to the climate system. There are indications, however, that the temperature sensitivity of LOS has recently been declining. We found that Icelandic subarctic grasslands can still extend their growing season for more than one month under warming. This persistence of warming‐induced LOS extension has important implications for the C‐sink potential of subarctic grasslands under climate change.
  • A global synthesis of the effects of diversified farming systems on
           arthropod diversity within fields and across agricultural landscapes
    • Abstract: Agricultural intensification is a leading cause of global biodiversity loss, which can reduce the provisioning of ecosystem services in managed ecosystems. Organic farming and plant diversification are farm management schemes that may mitigate potential ecological harm by increasing species richness and boosting related ecosystem services to agroecosystems. What remains unclear is the extent to which farm management schemes affect biodiversity components other than species richness, and whether impacts differ across spatial scales and landscape contexts. Using a global metadataset, we quantified the effects of organic farming and plant diversification on abundance, local diversity (communities within fields), and regional diversity (communities across fields) of arthropod pollinators, predators, herbivores, and detritivores. Both organic farming and higher in‐field plant diversity enhanced arthropod abundance, particularly for rare taxa. This resulted in increased richness but decreased evenness. While these responses were stronger at local relative to regional scales, richness and abundance increased at both scales, and richness on farms embedded in complex relative to simple landscapes. Overall, both organic farming and in‐field plant diversification exerted the strongest effects on pollinators and predators, suggesting these management schemes can facilitate ecosystem service providers without augmenting herbivore (pest) populations. Our results suggest that organic farming and plant diversification promote diverse arthropod metacommunities that may provide temporal and spatial stability of ecosystem service provisioning. Conserving diverse plant and arthropod communities in farming systems therefore requires sustainable practices that operate both within fields and across landscapes.Organic farming and on‐farm plant diversification can reduce biodiversity loss and boost‐related ecosystem services like pollination and pest control. Using a global dataset, we found that both management schemes enhanced richness at local and regional scales, mainly by promoting rare taxa that are critical for ecosystem resilience. Positive effects were greatest for two groups of beneficial insects: pollinators and predators. We also found stronger impacts of farm management for fields embedded in complex landscapes.
  • Continental impacts of water development on waterbirds, contrasting two
           Australian river basins: Global implications for sustainable water use
    • Abstract: The world's freshwater biotas are declining in diversity, range and abundance, more than in other realms, with human appropriation of water. Despite considerable data on the distribution of dams and their hydrological effects on river systems, there are few expansive and long analyses of impacts on freshwater biota. We investigated trends in waterbird communities over 32 years, (1983–2014), at three spatial scales in two similarly sized large river basins, with contrasting levels of water resource development, representing almost a third (29%) of Australia: the Murray–Darling Basin and the Lake Eyre Basin. The Murray–Darling Basin is Australia's most developed river basin (240 dams storing 29,893 GL) while the Lake Eyre Basin is one of the less developed basins (1 dam storing 14 GL). We compared the long‐term responses of waterbird communities in the two river basins at river basin, catchment and major wetland scales. Waterbird abundances were strongly related to river flows and rainfall. For the developed Murray–Darling Basin, we identified significant long‐term declines in total abundances, functional response groups (e.g., piscivores) and individual species of waterbird (n = 50), associated with reductions in cumulative annual flow. These trends indicated ecosystem level changes. Contrastingly, we found no evidence of waterbird declines in the undeveloped Lake Eyre Basin. We also modelled the effects of the Australian Government buying up water rights and returning these to the riverine environment, at a substantial cost (>3.1 AUD billion) which were projected to partly (18% improvement) restore waterbird abundances, but projected climate change effects could reduce these benefits considerably to only a 1% or 4% improvement, with respective annual recovery of environmental flows of 2,800 GL or 3,200 GL. Our unique large temporal and spatial scale analyses demonstrated severe long‐term ecological impact of water resource development on prominent freshwater animals, with implications for global management of water resources.Long‐term declining trends in waterbird numbers, at the total numbers, different species and functional response groups, were detected in the Murray–Darling Basin, with its rivers developed by dams. In comparison, there were few trends in the similarly sized but undeveloped Lake Eyre Basin. These two river basins cover near one‐third of the Australian continent. These trends in waterbird numbers were consistent at the scale of the entire basin, the two main rivers in each basin and for ten of the most important wetlands in each river basin. These results were from surveys over more than three decades and indicate the long‐term impacts of water resource developments on ecosystems, critical for rehabilitation and development of rivers around the world.
  • The future distribution of river fish: The complex interplay of climate
           and land use changes, species dispersal and movement barriers
    • Abstract: The future distribution of river fishes will be jointly affected by climate and land use changes forcing species to move in space. However, little is known whether fish species will be able to keep pace with predicted climate and land use‐driven habitat shifts, in particular in fragmented river networks. In this study, we coupled species distribution models (stepwise boosted regression trees) of 17 fish species with species‐specific models of their dispersal (fish dispersal model FIDIMO) in the European River Elbe catchment. We quantified (i) the extent and direction (up‐ vs. downstream) of predicted habitat shifts under coupled “moderate” and “severe” climate and land use change scenarios for 2050, and (ii) the dispersal abilities of fishes to track predicted habitat shifts while explicitly considering movement barriers (e.g., weirs, dams). Our results revealed median net losses of suitable habitats of 24 and 94 river kilometers per species for the moderate and severe future scenarios, respectively. Predicted habitat gains and losses and the direction of habitat shifts were highly variable among species. Habitat gains were negatively related to fish body size, i.e., suitable habitats were projected to expand for smaller‐bodied fishes and to contract for larger‐bodied fishes. Moreover, habitats of lowland fish species were predicted to shift downstream, whereas those of headwater species showed upstream shifts. The dispersal model indicated that suitable habitats are likely to shift faster than species might disperse. In particular, smaller‐bodied fish (
  • Restless roosts: Light pollution affects behavior, sleep, and physiology
           in a free‐living songbird
    • Abstract: The natural nighttime environment is increasingly polluted by artificial light. Several studies have linked artificial light at night to negative impacts on human health. In free‐living animals, light pollution is associated with changes in circadian, reproductive, and social behavior, but whether these animals also suffer from physiologic costs remains unknown. To fill this gap, we made use of a unique network of field sites which are either completely unlit (control), or are artificially illuminated with white, green, or red light. We monitored nighttime activity of adult great tits, Parus major, and related this activity to within‐individual changes in physiologic indices. Because altered nighttime activity as a result of light pollution may affect health and well‐being, we measured oxalic acid concentrations as a biomarker for sleep restriction, acute phase protein concentrations and malaria infection as indices of immune function, and telomere lengths as an overall measure of metabolic costs. Compared to other treatments, individuals roosting in the white light were much more active at night. In these individuals, oxalic acid decreased over the course of the study. We also found that individuals roosting in the white light treatment had a higher probability of malaria infection. Our results indicate that white light at night increases nighttime activity levels and sleep debt and affects disease dynamics in a free‐living songbird. Our study offers the first evidence of detrimental effects of light pollution on the health of free‐ranging wild animals.The nighttime environment is increasingly polluted by artificial light at night. We show that white light at night increases activity at night, making birds more restless. This increase in activity translates into increased sleep debt and decreases in immune function.
  • Moisture‐induced greening of the South Asia over the past three
    • Abstract: South Asia experienced a weakening of summer monsoon circulation in the past several decades, resulting in rainfall decline in wet regions. In comparison with other tropical ecosystems, quantitative assessments of the extent and triggers of vegetation change are lacking in assessing climate‐change impacts over South Asia dominated by crops. Here, we use satellite‐based Normalized Difference Vegetation Index (NDVI) to quantify spatial–temporal changes in vegetation greenness, and find a widespread annual greening trend that stands in contrast to the weakening of summer monsoon circulation particularly over the last decade. We further show that moisture supply is the primary factor limiting vegetation activity during dry season or in dry region, and cloud cover or temperature would become increasingly important in wet region. Enhanced moisture conditions over dry region, coinciding with the decline in monsoon, are mainly responsible for the widespread greening trend. This result thereby cautions the use of a unified monsoon index to predict South Asia's vegetation dynamics. Current climate–carbon models in general correctly reproduce the dominant control of moisture in the temporal characteristics of vegetation productivity. But the model ensemble cannot exactly reproduce the spatial pattern of satellite‐based vegetation change mainly because of biases in climate simulations. The moisture‐induced greening over South Asia, which is likely to persist into the wetter future, has significant implications for regional carbon cycling and maintaining food security.Spatial distributions of GIMMS NDVI trends over the South Asia during the three periods: 1982–2014 (first row), 1982–2001 (second row), and 2002–2014 (third row). The trends are estimated on the annual (a, d, and g), wet season (b, e, and h), and dry season basis (c, f, and i), respectively. The inset panels show the pixels where NDVI trends are statistically significant at p 
  • High Arctic summer warming tracked by increased Cassiope tetragona growth
           in the world's northernmost polar desert
    • Abstract: Rapid climate warming has resulted in shrub expansion, mainly of erect deciduous shrubs in the Low Arctic, but the more extreme, sparsely vegetated, cold and dry High Arctic is generally considered to remain resistant to such shrub expansion in the next decades. Dwarf shrub dendrochronology may reveal climatological causes of past changes in growth, but is hindered at many High Arctic sites by short and fragmented instrumental climate records. Moreover, only few High Arctic shrub chronologies cover the recent decade of substantial warming. This study investigated the climatic causes of growth variability of the evergreen dwarf shrub Cassiope tetragona between 1927 and 2012 in the northernmost polar desert at 83°N in North Greenland. We analysed climate–growth relationships over the period with available instrumental data (1950–2012) between a 102‐year‐long C. tetragona shoot length chronology and instrumental climate records from the three nearest meteorological stations, gridded climate data, and North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) indices. July extreme maximum temperatures (JulTemx), as measured at Alert, Canada, June NAO, and previous October AO, together explained 41% of the observed variance in annual C. tetragona growth and likely represent in situ summer temperatures. JulTemx explained 27% and was reconstructed back to 1927. The reconstruction showed relatively high growing season temperatures in the early to mid‐twentieth century, as well as warming in recent decades. The rapid growth increase in C. tetragona shrubs in response to recent High Arctic summer warming shows that recent and future warming might promote an expansion of this evergreen dwarf shrub, mainly through densification of existing shrub patches, at High Arctic sites with sufficient winter snow cover and ample water supply during summer from melting snow and ice as well as thawing permafrost, contrasting earlier notions of limited shrub growth sensitivity to summer warming in the High Arctic.Rapid climate warming has resulted in shrub expansion, mainly in the Low Arctic, but the cold and dry High Arctic is generally considered to remain resistant to such shrub expansion in the next decades. This study investigated the climatic causes of growth variability of the evergreen dwarf shrub Cassiope tetragona between 1927 and 2012 in the polar desert of North Greenland, at 83°N. We observed a rapid growth increase of C. tetragona shrubs in response to recent High Arctic summer warming, which shows that recent and future warming might promote an expansion of this evergreen dwarf shrub at High Arctic sites with sufficient winter snow cover and ample water supply during summer from melting snow and ice as well as thawing permafrost.
  • Differentiating drought legacy effects on vegetation growth over the
           temperate Northern Hemisphere
    • Abstract: In view of future changes in climate, it is important to better understand how different plant functional groups (PFGs) respond to warmer and drier conditions, particularly in temperate regions where an increase in both the frequency and severity of drought is expected. The patterns and mechanisms of immediate and delayed impacts of extreme drought on vegetation growth remain poorly quantified. Using satellite measurements of vegetation greenness, in‐situ tree‐ring records, eddy‐covariance CO2 and water flux measurements, and meta‐analyses of source water of plant use among PFGs, we show that drought legacy effects on vegetation growth differ markedly between forests, shrubs and grass across diverse bioclimatic conditions over the temperate Northern Hemisphere (NH). Deep−rooted forests exhibit a drought legacy response with reduced growth during up to 4 years after an extreme drought, whereas shrubs and grass have drought legacy effects of approximately 2 years and 1 year, respectively. Statistical analyses partly attribute the differences in drought legacy effects among PFGs to plant eco‐hydrological properties (related to traits), including plant water use and hydraulic responses. These results can be used to improve the representation of drought response of different PFGs in land surface models, and assess their biogeochemical and biophysical feedbacks in response to a warmer and drier climate.This article is protected by copyright. All rights reserved.
  • Enhanced‐efficiency fertilizers are not a panacea for resolving the
           nitrogen problem
    • Abstract: Improving nitrogen (N) management for greater agricultural output while minimizing unintended environmental consequences is critical in the endeavor of feeding the growing population sustainably amid climate change. Enhanced‐efficiency fertilizers (EEFs) have been developed to better synchronize fertilizer N release with crop uptake, offering the potential for enhanced N use efficiency (NUE) and reduced losses. Can EEFs play a significant role in helping address the N management challenge' Here we present a comprehensive analysis of worldwide studies published in 1980‐2016 evaluating four major types of EEFs (polymer‐coated fertilizers PCF, nitrification inhibitors NI, urease inhibitors UI, and double inhibitors DI, i.e. urease and nitrification inhibitors combined) regarding their effectiveness in increasing yield and NUE and reducing N losses. Overall productivity and environmental efficacy depended on the combination of EEF type and cropping systems, further affected by biophysical conditions. Best scenarios include: (i) DI used in grassland (n=133), averaging 11% yield increase, 33% NUE improvement, and 47% decrease in aggregated N loss (sum of NO3‐, NH3, and N2O, totaling 84 kg N ha−1); (ii) UI in rice‐paddy systems (n=100), with 9% yield increase, 29% NUE improvement, and 41% N‐loss reduction (16 kg N ha−1). EEF efficacies in wheat and maize systems were more complicated and generally less effective. In‐depth analysis indicated that the potential benefits of EEFs might be best achieved when a need is created, for example, by downward adjusting N application from conventional rate. We conclude that EEFs can play a significant role in sustainable agricultural production but their prudent use requires firstly eliminating any fertilizer mismanagement plus the implementation of knowledge‐based N management practices.This article is protected by copyright. All rights reserved.
  • Projecting the future of an alpine ungulate under climate change scenarios
    • Abstract: Climate change represents a primary threat to species persistence and biodiversity at a global scale. Cold adapted alpine species are especially sensitive to climate change and can offer key “early warning signs” about deleterious effects of predicted change. Among mountain ungulates, survival, a key determinant of demographic performance, may be influenced by future climate in complex, and possibly opposing ways. Demographic data collected from 447 mountain goats in 10 coastal Alaska, USA, populations over a 37 year time span indicated that survival is highest during low snowfall winters and cool summers. However, General Circulation Models (GCMs) predict future increase in summer temperature and decline in winter snowfall. To disentangle how these opposing climate‐driven effects influence mountain goat populations, we developed an age‐structured population model to project mountain goat population trajectories for 10 different GCM/emissions scenarios relevant for coastal Alaska. Projected increases in summer temperature had stronger negative effects on population trajectories than the positive demographic effects of reduced winter snowfall. In 5 of the 10 GCM/RCP scenarios, the net effect of projected climate change was extinction over a 70 year time window (2015–2085); smaller initial populations were more likely to go extinct faster than larger populations. Using a resource selection modeling approach, we determined that distributional shifts to higher elevation (i.e. “thermoneutral”) summer range was unlikely to be a viable behavioral adaptation strategy; due to the conical shape of mountains, summer range was expected to decline by 17–86% for 7 of the 10 GCM/RCP scenarios. Projected declines of mountain goat populations are driven by climate‐linked bottom‐up mechanisms and may have wide ranging implications for alpine ecosystems. These analyses elucidate how projected climate change can negatively alter population dynamics of a sentinel alpine species and provide insight into how demographic modeling can be used to assess risk to species persistence.This article is protected by copyright. All rights reserved.
  • Clarifying the landscape approach: A response to the Editor
    • Abstract: We welcome the insightful critiques and specific concerns raised by Erbaugh & Agrawal (2017) of our recent treatise on landscape approaches (Reed et al. 2016). Their contribution provides an opportunity to clarify and advance an important debate about both the nature and future of multi‐functional land management.This article is protected by copyright. All rights reserved.
  • Variation in bulk‐leaf 13C discrimination, leaf traits and water‐use
           efficiency‐trait relationships along a continental‐scale climate
           gradient in Australia
    • Abstract: Large spatial and temporal gradients in rainfall and temperature occur across Australia. This heterogeneity drives ecological differentiation in vegetation structure and ecophysiology. We examined multiple leaf‐scale traits, including foliar 13C isotope discrimination (Δ13C), rates of photosynthesis and foliar N concentration and their relationships with multiple climate variables. 55 species across 27 families were examined across eight sites spanning contrasting biomes.Key questions addressed include: 1) Does Δ 13C and intrinsic water use efficiency (WUEi) vary with climate at a continental scale' 2) What are the seasonal and spatial patterns in Δ13C / WUEi across biomes and species' 3) To what extent does Δ13C reflect variation in leaf structural, functional and nutrient traits across climate gradients' and 4) Does the relative importance of assimilation and stomatal conductance in driving variation in Δ13C differ across seasons'We found that MAP, temperature seasonality, isothermality and annual temperature range exerted independent effects on foliar Δ13C / WUEi. Temperature‐related variables exerted larger effects than rainfall‐related variables. The relative importance of photosynthesis and stomatal conductance (gs) in determining Δ13C differed across seasons: Δ13C was more strongly regulated by gs during the dry season and by photosynthetic capacity during the wet‐season.Δ13C was most strongly correlated, inversely, with leaf mass area ratio among all leaf attributes considered.Leaf Nmass was significantly and positively correlated with MAP during dry‐ and wet‐ seasons and with moisture index (MI) during the wet‐season but was not correlated with Δ13C. Leaf Pmass showed significant positive relationship with MAP and Δ13C only during the dry‐season. For all leaf nutrient‐related traits, the relationships obtained for Δ13C with MAP or MI indicated that Δ13C at the species level reliably reflects the water status at the site level. Temperature and water availability, not foliar nutrient content, are the principal factors influencing Δ13C across Australia.This article is protected by copyright. All rights reserved.
  • A decline in primary production in the North Sea over twenty‐five years,
           associated with reductions in zooplankton abundance and fish stock
    • Abstract: Phytoplankton primary production is at the base of the marine food web; changes in primary production have direct or indirect effects on higher trophic levels, from zooplankton organisms to marine mammals and seabirds. Here we present a new time‐series on gross primary production in the North Sea, from 1988 to 2013, estimated using in situ measurements of chlorophyll and underwater light. This shows that recent decades have seen a significant decline in primary production in the North Sea. Moreover, primary production differs in magnitude between six hydrodynamic regions within the North Sea. Sea surface warming and reduced riverine nutrient inputs are found to be likely contributors to the declining levels of primary production. In turn, significant correlations are found between observed changes in primary production and the dynamics of higher trophic levels including (small) copepods and a standardised index of fish recruitment, averaged over 7 stocks of high commercial significance in the North Sea. Given positive (bottom‐up) associations between primary production, zooplankton abundance and fish stock recruitment, this study provides strong evidence that if the decline in primary production continues, knock‐on effects upon the productivity of fisheries are to be expected unless these fisheries are managed effectively and cautiously.This article is protected by copyright. All rights reserved.
  • Prioritizing forest fuels treatments based on the probability of
           high‐severity fire restores adaptive capacity in Sierran forests
    • Abstract: In frequent fire forests of the western US a legacy of fire suppression coupled with increases in fire weather severity have altered fire regimes and vegetation dynamics. When coupled with projected climate change, these conditions have the potential to lead to vegetation type change and altered carbon (C) dynamics. In the Sierra Nevada, fuels reduction approaches that include mechanical thinning followed by regular prescribed fire are one approach to restore the ability of the ecosystem to tolerate episodic fire and still sequester C. Yet, the spatial extent of the area requiring treatment makes widespread treatment implementation unlikely. We sought to determine if a priori knowledge of where uncharacteristic wildfire is most probable could be used to optimize the placement of fuels treatments in a Sierra Nevada watershed. We developed two treatment placement strategies: the naive strategy, based on treating all operationally available area and the optimized strategy, which only treated areas where crown‐killing fires were most probable. We ran forecast simulations using projected climate data through 2100 to determine how the treatments differed in terms of C sequestration, fire severity, and C emissions relative to a no‐management scenario. We found that in both the short (20 years) and long (100 years) term, both management scenarios increased C stability, reduced burn severity, and consequently emitted less C as a result of wildfires than no‐management. Across all metrics, both scenarios performed the same, but the optimized treatment required significantly less C removal (naive = 0.42 Tg C, optimized = 0.25 Tg C) to achieve the same treatment efficacy. Given the extent of western forests in need of fire restoration, efficiently allocating treatments is a critical task if we are going to restore adaptive capacity in frequent‐fire forests.This article is protected by copyright. All rights reserved.
  • Complex effect of projected sea temperature and wind change on flatfish
    • Abstract: Climate change not only alters ocean physics and chemistry but also affects the biota. Larval dispersal patterns from spawning to nursery grounds and larval survival are driven by hydrodynamic processes and shaped by (a)biotic environmental factors. Therefore, it is important to understand the impacts of increased temperature rise and changes in wind speed and direction on larval drift and survival. We apply a particle‐tracking model coupled to a 3D‐hydrodynamic model of the English Channel and the North Sea to study the dispersal dynamics of the exploited flatfish (common) sole (Solea solea). We first assess model robustness and interannual variability of larval transport over the period 1995‐2011. Then, using a subset of representative years (2003‐2011), we investigate the impact of climate change on larval dispersal, connectivity patterns and recruitment at the nursery grounds. The impacts of five scenarios inspired by the 2040 projections of the Intergovernmental Panel on Climate Change are discussed and compared with interannual variability. The results suggest that 33% of the year‐to‐year recruitment variability is explained at a regional scale and that a 9‐year period is sufficient to capture interannual variability in dispersal dynamics. In the scenario involving a temperature increase, early spawning and a wind change, the model predicts that (i) dispersal distance (+70%) and pelagic larval duration (+22%) will increase in response to the reduced temperature (–9%) experienced by early hatched larvae, (ii) larval recruitment at the nursery grounds will increase in some areas (36%) and decrease in others (‐58%), and (iii) connectivity will show contrasting changes between areas. At the regional scale, our model predicts considerable changes in larval recruitment (+9%) and connectivity (retention ‐4% and seeding +37%) due to global change. All of these factors affect the distribution and productivity of sole and therefore the functioning of the demersal ecosystem and fisheries management.This article is protected by copyright. All rights reserved.
  • Phenological and distributional shifts in ichthyoplankton associated with
           recent warming in the northeast Pacific Ocean
    • Abstract: Understanding changes in the migratory and reproductive phenology of fish stocks in relation to climate change is critical for accurate ecosystem‐based fisheries management. Relocation and changes in timing of reproduction can have dramatic effects upon the success of fish populations and throughout the food web. During anomalously warm conditions (1–4°C above normal) in the northeast Pacific Ocean during 2015–2016, we documented shifts in timing and spawning location of several pelagic fish stocks based on larval fish samples. Total larval concentrations in the northern California Current (NCC) during winter (January–March) 2015 and 2016 were the highest observed since annual collections first occurred in 1998, primarily due to increased abundances of Engraulis mordax (northern anchovy) and Sardinops sagax (Pacific sardine) larvae, which are normally summer spawning species in this region. Sardinops sagax and Merluccius productus (Pacific hake) exhibited an unprecedented early and northward spawning expansion during 2015–16. In addition, spawning duration was greatly increased for E. mordax, as the presence of larvae was observed throughout the majority of 2015–16, indicating prolonged and nearly continuous spawning of adults throughout the warm period. Larvae from all three of these species have never before been collected in the NCC as early in the year. In addition, other southern species were collected in the NCC during this period. This suggests that the spawning phenology and distribution of several ecologically and commercially important fish species dramatically and rapidly changed in response to the warming conditions occurring in 2014–2016, and could be an indication of future conditions under projected climate change. Changes in spawning timing and poleward migration of fish populations due to warmer ocean conditions or global climate change will negatively impact areas that were historically dependent on these fish, and change the food web structure of the areas that the fish move into with unforeseen consequences.During anomalously warm conditions (1–4°C above normal) in the northeastern Pacific Ocean during 2015–2016, we documented shifts in timing and spawning location of several pelagic fish stocks based on larval fish samples. Total larval concentrations in the northern California Current (NCC) during winter (January–March) 2015 and 2016 were the highest observed since annual collections first occurred in 1998, which was primarily due to increased abundances of Engraulis mordax (northern anchovy), Sardinops sagax (Pacific sardine), and Merluccius productus (Pacific hake) larvae. Sardinops sagax and M. productus historically spawn south of the NCC region, but exhibited an unprecedented early and northward spawning expansion during 2015–16, while spawning duration was greatly increased for E. mordax, as the presence of larvae was observed throughout the majority of 2015–16.
  • Using fuzzy logic to determine the vulnerability of marine species to
           climate change
    • Abstract: Marine species are being impacted by climate change and ocean acidification, although their level of vulnerability varies due to differences in species' sensitivity, adaptive capacity and exposure to climate hazards. Due to limited data on the biological and ecological attributes of many marine species, as well as inherent uncertainties in the assessment process, climate change vulnerability assessments in the marine environment frequently focus on a limited number of taxa or geographic ranges. As climate change is already impacting marine biodiversity and fisheries, there is an urgent need to expand vulnerability assessment to cover a large number of species and areas. Here, we develop a modelling approach to synthesize data on species‐specific estimates of exposure, and ecological and biological traits to undertake an assessment of vulnerability (sensitivity and adaptive capacity) and risk of impacts (combining exposure to hazards and vulnerability) of climate change (including ocean acidification) for global marine fishes and invertebrates. We use a fuzzy logic approach to accommodate the variability in data availability and uncertainties associated with inferring vulnerability levels from climate projections and species' traits. Applying the approach to estimate the relative vulnerability and risk of impacts of climate change in 1074 exploited marine species globally, we estimated their index of vulnerability and risk of impacts to be on average 52 ± 19 SD and 66 ± 11 SD, scaling from 1 to 100, with 100 being the most vulnerable and highest risk, respectively, under the ‘business‐as‐usual' greenhouse gas emission scenario (Representative Concentration Pathway 8.5). We identified 157 species to be highly vulnerable while 294 species are identified as being at high risk of impacts. Species that are most vulnerable tend to be large‐bodied endemic species. This study suggests that the fuzzy logic framework can help estimate climate vulnerabilities and risks of exploited marine species using publicly and readily available information.We develop fuzzy logic expert system to synthesize data on species‐specific estimates of exposure, and ecological and biological traits to undertake assessment of risk of climate change for marine fishes and invertebrates. We apply this approach to study 1074 exploited marine species globally. We identify 294 species being at high risk to climate change impacts. We show that the analytical framework presented here can be useful to tell us about the vulnerability of marine species to climate change using readily available biological and ecological information
  • Human activities as a driver of spatial variation in the trophic structure
           of fish communities on Pacific coral reefs
    • Abstract: Anthropogenic activities such as land‐use change, pollution and fishing impact the trophic structure of coral reef fishes, which can influence ecosystem health and function. Although these impacts may be ubiquitous, they are not consistent across the tropical Pacific Ocean. Using an extensive database of fish biomass sampled using underwater visual transects on coral reefs, we modelled the impact of human activities on food webs at Pacific‐wide and regional (1,000s–10,000s km) scales. We found significantly lower biomass of sharks and carnivores, where there were higher densities of human populations (hereafter referred to as human activity); however, these patterns were not spatially consistent as there were significant differences in the trophic structures of fishes among biogeographic regions. Additionally, we found significant changes in the benthic structure of reef environments, notably a decline in coral cover where there was more human activity. Direct human impacts were the strongest in the upper part of the food web, where we found that in a majority of the Pacific, the biomass of reef sharks and carnivores were significantly and negatively associated with human activity. Finally, although human‐induced stressors varied in strength and significance throughout the coral reef food web across the Pacific, socioeconomic variables explained more variation in reef fish trophic structure than habitat variables in a majority of the biogeographic regions. Notably, economic development (measured as GDP per capita) did not guarantee healthy reef ecosystems (high coral cover and greater fish biomass). Our results indicate that human activities are significantly shaping patterns of trophic structure of reef fishes in a spatially nonuniform manner across the Pacific Ocean, by altering processes that organize communities in both “top‐down” (fishing of predators) and “bottom‐up” (degradation of benthic communities) contexts.There are now very few (if any) places where human activities do not have an impact on coral reef ecosystems. Direct human impacts are the strongest in the upper part of the food web. Moreover, the importance of human populations as structuring forces within reef ecosystems is demonstrated by socioeconomic variables of human populations explaining as much or more variation in the trophic structure of reef fishes than habitat in a majority of the biogeographic regions. Our study highlights the need to tune management approaches regionally to not only account for account for differences in habitat and biogeography, but also for the socioeconomic factors of resident human populations.
  • Climate mitigation by dairy intensification depends on intensive use of
           spared grassland
    • Abstract: Milk and beef production cause 9% of global greenhouse gas (GHG) emissions. Previous life cycle assessment (LCA) studies have shown that dairy intensification reduces the carbon footprint of milk by increasing animal productivity and feed conversion efficiency. None of these studies simultaneously evaluated indirect GHG effects incurred via teleconnections with expansion of feed crop production and replacement suckler‐beef production. We applied consequential LCA to incorporate these effects into GHG mitigation calculations for intensification scenarios among grazing‐based dairy farms in an industrialized country (UK), in which milk production shifts from average to intensive farm typologies, involving higher milk yields per cow and more maize and concentrate feed in cattle diets. Attributional LCA indicated a reduction of up to 0.10 kg CO2e kg−1 milk following intensification, reflecting improved feed conversion efficiency. However, consequential LCA indicated that land use change associated with increased demand for maize and concentrate feed, plus additional suckler‐beef production to replace reduced dairy‐beef output, significantly increased GHG emissions following intensification. International displacement of replacement suckler‐beef production to the “global beef frontier” in Brazil resulted in small GHG savings for the UK GHG inventory, but contributed to a net increase in international GHG emissions equivalent to 0.63 kg CO2e kg−1 milk. Use of spared dairy grassland for intensive beef production can lead to net GHG mitigation by replacing extensive beef production, enabling afforestation on larger areas of lower quality grassland, or by avoiding expansion of international (Brazilian) beef production. We recommend that LCA boundaries are expanded when evaluating livestock intensification pathways, to avoid potentially misleading conclusions being drawn from “snapshot” carbon footprints. We conclude that dairy intensification in industrialized countries can lead to significant international carbon leakage, and only achieves GHG mitigation when spared dairy grassland is used to intensify beef production, freeing up larger areas for afforestation.Previous studies have shown that the carbon footprint of milk declines as dairy farming intensifies, owing to improved feed conversion efficiency. For the first time, we demonstrate that direct greenhouse gas (GHG) mitigation achieved by intensification of UK dairy farms is outweighed by GHG emissions from land use change driven by increased demand for maize and concentrate feed, plus additional suckler‐beef production required to replace reduced dairy‐beef output. Dairy intensification can cause international carbon leakage, and may only achieve net GHG mitigation when spared dairy grassland is used to intensify beef production, freeing up larger areas for afforestation
  • Continental‐extent patterns in amphibian malformations linked to
           parasites, chemical contaminants and their interactions
    • Abstract: Widespread observations of malformed amphibians across North America have generated both concern and controversy. Debates over the causes of such malformations—which can affect >50% of animals in a population—have continued, likely due to involvement of multiple causal factors. Here, we used a 13‐year dataset encompassing 53,880 frogs and toads from 422 wetlands and 42 states in the conterminous USA to test hypotheses relating abnormalities and four categories of potential drivers: (1) chemical contaminants, (2) land use practices, (3) parasite infection, and (4) targeted interactions between parasites and pesticides. By using a hierarchically‐nested, competing‐model approach, we further examined how these associations varied spatially among geographic regions. Although malformations were rare overall (average = 1.6%), we identified 96 hotspot sites with 5 to 25% abnormal individuals. Using the full dataset of 934 collections (without data on parasite infection), malformation frequency was best predicted by the presence of oil and gas wells within the watershed. Among collections also examined for parasite infection (n=154), average parasite load and its interaction with pesticide application positively predicted malformations: wetlands with a greater abundance of the trematode Ribeiroia ondatrae were more likely to have malformed amphibians, but these effects were strongest when pesticide application was also high, consistent with prior experimental research. Importantly, however, the influence of these factors also varied regionally, helping explain divergent results from previous studies at local scales; parasite infection was more influential in the West and Northeast, whereas pesticide application and oil/gas wells correlated with abnormalities in the Northeast, Southeast and western regions of the USA. These results, based on the largest systematic sampling of amphibian malformations, suggest that increased observations of abnormal amphibians are associated with both parasite infection and chemical contaminants, but that their relative importance and interaction strength varied with the spatial extent of the analysis.This article is protected by copyright. All rights reserved.
  • Increased resource use efficiency amplifies positive response of aquatic
           primary production to experimental warming
    • Abstract: Climate warming is affecting the structure and function of river ecosystems, including their role in transforming and transporting carbon (C), nitrogen (N), and phosphorus (P). Predicting how river ecosystems respond to warming has been hindered by a dearth of information about how otherwise well‐studied physiological responses to temperature scale from organismal to ecosystem levels. We conducted an ecosystem‐level temperature manipulation to quantify how coupling of stream ecosystem metabolism and nutrient uptake responded to a realistic warming scenario. A ~3.3°C increase in mean water temperature altered coupling of C, N, and P fluxes in ways inconsistent with single‐species laboratory experiments. Net primary production tripled during the year of experimental warming, while whole‐stream N and P uptake rates did not change, resulting in 289% and 281% increases in autotrophic dissolved inorganic N and P use efficiency (UE), respectively. Increased ecosystem production was a product of unexpectedly large increases in mass‐specific net primary production and autotroph biomass, supported by (a) combined increases in resource availability (via N mineralization and N2 fixation) and (b) elevated resource use efficiency, the latter associated with changes in community structure. These large changes in C and nutrient cycling could not have been predicted from the physiological effects of temperature alone. Our experiment provides clear ecosystem‐level evidence that warming can shift the balance between C and nutrient cycling in rivers, demonstrating that warming will alter the important role of in‐stream processes in C, N, and P transformations. Moreover, our results reveal a key role for nutrient supply and use efficiency in mediating responses of primary producers to climate warming.This article is protected by copyright. All rights reserved.
  • Vegetation Demographics in Earth System Models: a review of progress and
    • Abstract: Numerous current efforts seek to improve the representation of ecosystem ecology and vegetation demographic processes within Earth System Models (ESMs). These developments are widely viewed as an important step in developing greater realism in predictions of future ecosystem states and fluxes. Increased realism, however, leads to increased model complexity, with new features raising a suite of ecological questions that require empirical constraints. Here, we review the developments that permit the representation of plant demographics in ESMs, and identify issues raised by these developments that highlight important gaps in ecological understanding. These issues inevitably translate into uncertainty in model projections but also allow models to be applied to new processes and questions concerning the dynamics of real‐world ecosystems. We argue that stronger and more innovative connections to data, across the range of scales considered, are required to address these gaps in understanding. The development of first‐generation land surface models as a unifying framework for ecophysiological understanding stimulated much research into plant physiological traits and gas exchange. Constraining predictions at ecologically relevant spatial and temporal scales will require a similar investment of effort and intensified inter‐disciplinary communication.This article is protected by copyright. All rights reserved.
  • Functional traits determine tree growth and ecosystem productivity of a
           tropical montane forest: Insights from a long‐term nutrient manipulation
    • Abstract: Trait response‐effects are critical to forecast community structure and biomass production in highly diverse tropical forests. Ecological theory and few observation studies indicate that trees with acquisitive functional traits would respond more strongly to higher resource availability than those with conservative traits. We assessed how long‐term tree growth in experimental nutrient addition plots (N, P and N+P) varied as a function of morphological traits, tree size and species identity. We also evaluated how trait‐based responses affected stand scale biomass production considering the community structure. We found that tree growth depended on interactions between functional traits and the type or combination of nutrients added. Common species with acquisitive functional traits responded more strongly to nutrient addition, mainly to N+P. Phosphorous enhanced the growth rates of species with acquisitive and conservative traits, had mostly positive effects on common species and neutral or negative effects in rare species. Moreover, trees receiving N+P grew faster irrespective of their initial size relative to control or to other treatment plots. Finally, species responses were highly idiosyncratic suggesting that community processes including competition and niche dimensionality may be altered under increased resource availability. We found no statistically significant effects of nutrient additions on aboveground biomass productivity because acquisitive species had a limited potential to increase their biomass, possibly due to their generally lower wood density. In contrast, P addition increased the growth rates of species characterized by more conservative resource strategies (with higher wood density) that were poorly represented in the plant community. We provide the first long‐term experimental evidence that trait‐based responses, community structure, and community processes modulate the effects of increased nutrient availability on biomass productivity in a tropical forest.This article is protected by copyright. All rights reserved.
  • A Large‐Area, Spatially Continuous Assessment of Land Cover Map Error
           and Its Impact on Downstream Analyses
    • Abstract: Land cover maps increasingly underlie research into socioeconomic and environmental patterns and processes, including global change. It is known that map errors impact our understanding of these phenomena, but quantifying these impacts is difficult because many areas lack adequate reference data. We used a highly accurate, high‐resolution map of South African cropland to assess 1) the magnitude of error in several current generation land cover maps, and 2) how these errors propagate in downstream studies. We first quantified pixel‐wise errors in the cropland classes of four widely used land cover maps at resolutions ranging from 1 to 100 km, then calculated errors in several representative “downstream” (map‐based) analyses, including assessments of vegetative carbon stocks, evapotranspiration, crop production, and household food security. We also evaluated maps’ spatial accuracy based on how precisely they could be used to locate specific landscape features. We found that cropland maps can have substantial biases and poor accuracy at all resolutions (e.g. at 1 km resolution, up to ∼45% underestimates of cropland (bias) and nearly 50% mean absolute error (MAE, describing accuracy); at 100 km, up to 15% underestimates and nearly 20% MAE). National‐scale maps derived from higher resolution imagery were most accurate, followed by multi‐map fusion products. Constraining mapped values to match survey statistics may be effective at minimizing bias (provided the statistics are accurate). Errors in downstream analyses could be substantially amplified or muted, depending on the values ascribed to cropland‐adjacent covers (e.g. with forest as adjacent cover, carbon map error was 200‐500% greater than in input cropland maps, but ∼40% less for sparse cover types). The average locational error was 6 km (600%). These findings provide deeper insight into the causes and potential consequences of land cover map error, and suggest several recommendations for land cover map users.This article is protected by copyright. All rights reserved.
  • On the causes of trends in the seasonal amplitude of atmospheric CO2
    • Abstract: No consensus has yet been reached on the major factors driving the observed increase in the seasonal amplitude of atmospheric CO2 in the northern latitudes. In this study, we used atmospheric CO2 records from 26 northern hemisphere stations with a temporal coverage longer than 15 years, and an atmospheric transport model prescribed with net biome productivity (NBP) from an ensemble of nine terrestrial ecosystem models, to attribute change in the seasonal amplitude of atmospheric CO2. We found significant (P50°N), consistent with previous observations that the amplitude increased faster at Barrow (Arctic) than at Mauna Loa (subtropics). The multi‐model ensemble mean (MMEM) shows that the response of ecosystem carbon cycling to rising CO2 concentration (eCO2) and climate change are dominant drivers of the increase in AMPP‐T and AMPT‐P in the high latitudes. At the Barrow station, the observed increase of AMPP‐T and AMPT‐P over the last 33 years is explained by eCO2 (39% and 42%) almost equally than by climate change (32% and 35%). The increased carbon losses during the months with a net carbon release in response to eCO2 are associated with higher ecosystem respiration due to the increase in carbon storage caused by eCO2 during carbon uptake period. Air‐sea CO2 fluxes (10% for AMPP‐T and 11% for AMPT‐P) and the impacts of land‐use change (marginally significant 3% for AMPP‐T and 4% for AMPT‐P) also contributed to the CO2 measured at Barrow, highlighting the role of these factors in regulating seasonal changes in the global carbon cycle.This article is protected by copyright. All rights reserved.
  • Forest biomass, productivity and carbon cycling along a rainfall gradient
           in West Africa
    • Abstract: Net primary productivity (NPP) is one of the most important parameters in describing the functioning of any ecosystem and yet it arguably remains a poorly quantified and understood component of carbon cycling in tropical forests, especially outside of the Americas. We provide the first comprehensive analysis of NPP and its carbon allocation to woody, canopy and root growth components at contrasting lowland West African forests spanning a rainfall gradient. Using a standardised methodology to study evergreen (EF), semi‐deciduous (SDF), dry forests (DF) and woody savanna (WS), we find that (i) climate is more closely related with above and belowground C stocks than with NPP (ii) total NPP is highest in the SDF site, then the EF followed by the DF and WS and that (iii) different forest types have distinct carbon allocation patterns whereby SDF allocate in excess of 50% to canopy production and the DF and WS sites allocate 40‐50% to woody production. Furthermore, we find that (iv) compared with canopy and root growth rates the woody growth rate of these forests is a poor proxy for their overall productivity and that (v) residence time is the primary driver in the productivity‐allocation‐turnover chain for the observed spatial differences in woody, leaf and root biomass across the rainfall gradient. Through a systematic assessment of forest productivity we demonstrate the importance of directly measuring the main components of above and belowground NPP and encourage the establishment of more permanent carbon intensive monitoring plots across the tropics.This article is protected by copyright. All rights reserved.
  • Nutrients and temperature additively increase stream microbial respiration
    • Abstract: Rising temperatures and nutrient enrichment are co‐occurring global‐change drivers that stimulate microbial respiration of detrital carbon (C), but nutrient effects on the temperature dependence of respiration in aquatic ecosystems remain uncertain. We measured respiration rates associated with leaf litter, wood, and fine benthic organic matter (FBOM) across seasonal temperature gradients before (PRE) and after (ENR1, ENR2) experimental nutrient (nitrogen [N] and phosphorus [P]) additions to five forest streams. Nitrogen and P were added at different N:P ratios using increasing concentrations of N (~80‐650 μg/L) and corresponding decreasing concentrations of P (~90‐11 μg/L). We assessed the temperature dependence, and microbial (i.e., fungal) drivers of detrital mass‐specific respiration rates using the metabolic theory of ecology, before vs. after nutrient enrichment, and across N and P concentrations. Detrital mass‐specific respiration rates increased with temperature, exhibiting comparable activation energies (E, electronvolts [eV]) for all substrates (FBOM E = 0.43 [95% CI = 0.18‐0.69] eV, leaf litter E = 0.30 [95% CI =0.072‐0.54] eV, wood E = 0.41 [95% CI = 0.18‐0.64] eV) close to predicted MTE values. There was evidence that temperature‐driven increased respiration occurred via increased fungal biomass (wood) or increased fungal biomass‐specific respiration (leaf litter). Respiration rates increased under nutrient‐enriched conditions on leaves (1.32×) and wood (1.38×), but not FBOM. Respiration rates responded weakly to gradients in N or P concentrations, except for positive effects of P on wood respiration. The temperature dependence of respiration was comparable among years, and across N or P concentration for all substrates. Responses of leaf litter and wood respiration to temperature and the combined effects of N and P were similar in magnitude. Our data suggest that the temperature dependence of stream microbial respiration is unchanged by nutrient enrichment, and that increased temperature and N+P availability have additive and comparable effects on microbial respiration rates.This article is protected by copyright. All rights reserved.
  • Multi‐model comparison highlights consistency in predicted effect of
           warming on a semi‐arid shrub
    • Abstract: A number of modeling approaches have been developed to predict the impacts of climate change on species distributions, performance and abundance. The stronger the agreement from models that represent different processes and are based on distinct and independent sources of information, the greater the confidence we can have in their predictions. Evaluating the level of confidence is particularly important when predictions are used to guide conservation or restoration decisions. We used a multi‐model approach to predict climate change impacts on big sagebrush (Artemisia tridentata), the dominant plant species on roughly 43 million hectares in the western United States and a key resource for many endemic wildlife species. To evaluate the climate sensitivity of A. tridentata, we developed four predictive models, two based on empirically‐derived spatial and temporal relationships, and two that applied mechanistic approaches to simulate sagebrush recruitment and growth. This approach enabled us to produce an aggregate index of climate change vulnerability and uncertainty based on the level of agreement between models. Despite large differences in model structure, predictions of sagebrush response to climate change were largely consistent. Performance, as measured by change in cover, growth, or recruitment, was predicted to decrease at the warmest sites, but increase throughout the cooler portions of sagebrush's range. A sensitivity analysis indicated that sagebrush performance responds more strongly to changes in temperature than precipitation. Most of the uncertainty in model predictions reflected variation among the ecological models, raising questions about the reliability of forecasts based on a single modeling approach. Our results highlight the value of a multi‐model approach in forecasting climate change impacts and uncertainties, and should help land managers to maximize the value of conservation investments.This article is protected by copyright. All rights reserved.
  • CO2 evasion from boreal lakes: revised estimate, drivers of spatial
           variability, and future projections
    • Abstract: Lakes (including reservoirs) are an important component of the global carbon (C) cycle, as acknowledged by the 5th assessment report of the IPCC. In the context of lakes, the boreal region is disproportionately important contributing to 27% of the worldwide lake area, despite representing just 14% of global land surface area. In this study, we used a statistical approach to derive a prediction equation for the partial pressure of CO2 (pCO2) in lakes as a function of lake area, terrestrial net primary productivity (NPP) and precipitation (r2 = 0.56), and to create the first high resolution, circumboreal map (0.5) of lake pCO2. The map of pCO2 was combined with lake area from the recently published GLOWABO database and three different estimates of the gas transfer velocity k to produce a resulting map of CO2 evasion (FCO2). For the boreal region we estimate an average, lake area weighted,pCO2 of 966 (678‐ 1325) μatm and a total FCO2 of 189 (74‐347) Tg C yr−1, and evaluate the corresponding uncertainties based on Monte Carlo simulation. Our estimate of FCO2 is approximately twofold greater than previous estimates, as a result of methodological and data source differences. We use our results along with published estimates of the other C fluxes through inland waters to derive a C budget for the boreal region, and find that FCO2 from lakes is the most significant flux of the land‐ocean aquatic continuum, and of a similar magnitude as emissions from forest fires. Using the model and applying it to spatially resolved projections of terrestrial NPP and precipitation while keeping everything else constant, we predict a 107% increase in boreal lake FCO2 under emission scenario RCP8.5 by 2100. Our projections are largely driven by increases in terrestrial NPP over the same period, showing the very close connection between the terrestrial and aquatic C cycle.This article is protected by copyright. All rights reserved.
  • Analysis of climate signals in the crop yield record of Sub‐Saharan
    • Abstract: Food security and agriculture productivity assessments in sub‐Saharan Africa (SSA) require a better understanding of how climate and other drivers influence regional crop yields. In this paper, our objective was to identify the climate signal in the realized yields of maize, sorghum, and groundnut in SSA. We explored the relation between crop yields and scale‐compatible climate data for the 1962‐2014 period using Random Forest, a diagnostic machine learning technique. We found that improved agricultural technology and country fixed effects are three times more important than climate variables for explaining changes in crop yields in SSA. We also found that increasing temperatures reduced yields for all three crops in the temperature range observed in SSA, while precipitation increased yields up to a level roughly matching crop evapotranspiration. Crop yields exhibited both linear and nonlinear responses to temperature and precipitation, respectively. For maize, technology steadily increased yields by about 1% (13 kg/ha) per year while increasing temperatures decreased yields by 0.8% (10 kg/ha) per °C. This study demonstrates that although we should expect increases in future crop yields due to improving technology, the potential yields could be progressively reduced due to warmer and drier climates.This article is protected by copyright. All rights reserved.
  • Ungulates increase forest plant species richness to the benefit of
           non‐forest specialists
    • Abstract: Large wild ungulates are a major biotic factor shaping plant communities. They influence species abundance and occurrence directly by herbivory and plant dispersal, or indirectly by modifying plant‐plant interactions and through soil disturbance. In forest ecosystems, researchers’ attention has been mainly focused on deer overabundance. Far less is known about the effects on understory plant dynamics and diversity of wild ungulates where their abundance is maintained at lower levels to mitigate impacts on tree regeneration. We used vegetation data collected over ten years on 82 pairs of exclosure (excluding ungulates) and control plots located in a nation‐wide forest monitoring network (Renecofor). We report the effects of ungulate exclusion on (i) plant species richness and ecological characteristics, (ii) and cover percentage of herbaceous and shrub layers. We also analysed the response of these variables along gradients of ungulate abundance, based on hunting statistics, for wild boar (Sus scrofa), red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Outside the exclosures, forest ungulates maintained a higher species richness in the herbaceous layer (+15%), while the shrub layer was 17% less rich, and the plant communities became more light‐demanding. Inside the exclosures, shrub cover increased, often to the benefit of bramble (Rubus fruticosus agg.). Ungulates tend to favour ruderal, hemerobic, epizoochorous and non‐forest species. Among plots, the magnitude of vegetation changes was proportional to deer abundance. We conclude that ungulates, through the control of the shrub layer, indirectly increase herbaceous plant species richness by increasing light reaching the ground. However, this increase is detrimental to forest‐specialist species, and contributes to a landscape‐level biotic homogenisation. Even at population density levels considered to be harmless for overall plant species richness, ungulates remain a conservation issue for plant community composition.This article is protected by copyright. All rights reserved.
  • What type of rigorous experiments are needed to investigate the impact of
           artificial light at night on individuals and populations'
    • Abstract: In our recent paper on how artificial light at night (ALAN) affects within‐individual changes in physiology, we used a unique experimental setup of colored LED lights to show effects on nighttime activity levels and physiology in free‐living great tits, Parus major (Ouyang et al., 2017). Raap et al's response, entitled: “Rigorous field experiments are essential to understand the genuine severity of light pollution and to identify possible solutions” lists issues with our analyses (Raap et al., 2017). Rather than go into a detailed response, we use this forum to address the major critiques by answering the bigger question of what types of rigorous field experiments are needed to evaluate ALAN's impact.This article is protected by copyright. All rights reserved.
  • Assessment of ecosystem resilience to hydroclimatic disturbances in India
    • Abstract: Recent studies have shown an increasing trend in hydroclimatic disturbances like droughts, which are anticipated to become more frequent and intense under global warming and climate change. Droughts adversely affect the vegetation growth and crop yield, which enhances the risks to food security for a country like India with over 1.2 billion people to feed. Here, we compared the response of terrestrial net primary productivity (NPP) to hydroclimatic disturbances in India at different scales (i.e., at river basins, land covers, and climate types) to examine the ecosystems’ resilience to such adverse conditions. The ecosystem water use efficiency (WUEe: NPP/Evapotranspiration) is an effective indicator of ecosystem productivity, linking carbon (C) and water cycles. We found a significant difference (p 
  • Large soil organic carbon increase due to improved agronomic management in
           the North China Plain from 1980s to 2010s
    • Abstract: Agricultural soils are widely recognized to be capable of carbon sequestration that contributes to mitigating CO2 emissions. To better understand soil organic carbon (SOC) stock dynamics and its driving and controlling factors corresponding with a period of rapid agronomic evolution from the 1980s to the 2010s in the North China Plain (NCP), we collected data from two region‐wide soil sampling campaigns (in the 1980s and 2010s) and conducted an analysis of the controlling factors using the Random Forest model. Between the 1980s and 2010s, environmental (i.e. soil salinity/fertility) and societal (i.e. policy/techniques) factors both contributed to adoption of new management practices (i.e. chemical fertilizer application/mechanization). Results of our work indicate that SOC stocks in the NCP croplands increased significantly, which also closely related to soil total nitrogen (TN) changes. Samples collected near the surface (0‐20 cm) and deeper (20‐40 cm) both increased by an average of 9.4 and 5.1 Mg C ha−1, respectively, which are equivalent to increases of 73% and 56% compared with initial SOC stocks in the 1980s. The annual carbon sequestration amount in surface soils reached 10.9 Tg C yr−1, which contributed an estimated 43% of total carbon sequestration in all of China's cropland on just 27% of its area. Successful desalinization and the subsequent increases in carbon (C) inputs, induced by agricultural projects and policies intended to support crop production (i.e. reconstruction of low yield farmland, and agricultural subsidies), combined with improved cultivation practices (i.e. fertilization, and straw return) since the early 1980s were the main drivers for the SOC stock increase. This study suggests that rehabilitation of NCP soils to reduce salinity and increase crop yields have also served as a pathway for substantial soil C sequestration.This article is protected by copyright. All rights reserved.
  • Natural disturbances are spatially diverse but temporally synchronized
           across temperate forest landscapes in Europe
    • Abstract: Natural disturbance regimes are changing substantially in forests around the globe. However, large‐scale disturbance change is modulated by a considerable spatiotemporal variation within biomes. This variation remains incompletely understood particularly in the temperate forests of Europe, for which consistent large‐scale disturbance information is lacking. Here our aim was to quantify the spatiotemporal patterns of forest disturbances across temperate forest landscapes in Europe using remote sensing data, and determine their underlying drivers. Specifically, we tested two hypotheses: (1) Topography determines the spatial patterns of disturbance, and (2) climatic extremes synchronize natural disturbances across the biome. We used novel Landsat‐based maps of forest disturbances 1986‐2016 in combination with landscape analysis to compare spatial disturbance patterns across five unmanaged forest landscapes with varying topographic complexity. Furthermore, we analyzed annual estimates of disturbance change for synchronies and tested the influence of climatic extremes on temporal disturbance patterns. Spatial variation in disturbance patterns was substantial across temperate forest landscapes. With increasing topographic complexity, natural disturbance patches were smaller, more complex in shape, more dispersed, and affected a smaller portion of the landscape. Temporal disturbance patterns, however, were strongly synchronized across all landscapes, with three distinct waves of high disturbance activity between 1986 and 2016. All three waves followed years of pronounced drought and high peak wind speeds. Natural disturbances in temperate forest landscapes of Europe are thus spatially diverse but temporally synchronized. We conclude that the ecological effect of natural disturbances (i.e., whether they are homogenizing a landscape or increasing its heterogeneity) is strongly determined by the topographic template. Furthermore, as the strong biome‐wide synchronization of disturbances was closely linked to climatic extremes, large‐scale disturbance episodes are likely in Europe's temperate forests under climate changes.This article is protected by copyright. All rights reserved.
  • Towards physiologically meaningful water‐use efficiency estimates
           from eddy covariance data
    • Abstract: Intrinsic water‐use efficiency (iWUE) characterizes the physiological control on the simultaneous exchange of water and carbon dioxide in terrestrial ecosystems. Knowledge of iWUE is commonly gained from leaf‐level gas exchange measurements, which are inevitably restricted in their spatial and temporal coverage. Flux measurements based on the eddy covariance (EC) technique can overcome these limitations, as they provide continuous and long‐term records of carbon and water fluxes at the ecosystem scale. However, vegetation gas exchange parameters derived from EC data are subject to scale‐dependent and method‐specific uncertainties that compromise their ecophysiological interpretation as well as their comparability among ecosystems and across spatial scales. Here, we use estimates of canopy conductance and gross primary productivity (GPP) derived from EC data to calculate a measure of iWUE (G1,”stomatal slope”) at the ecosystem level at six sites comprising tropical, Mediterranean, temperate, and boreal forests. We assess the following six mechanisms potentially causing discrepancies between leaf and ecosystem‐level estimates of G1: 1) non‐transpirational water fluxes; 2) aerodynamic conductance; 3) meteorological deviations between measurement height and canopy surface; 4) energy balance non‐closure; 5) uncertainties in NEE partitioning; and 6) physiological within‐canopy gradients. Our results demonstrate that an unclosed energy balance caused the largest uncertainties, in particular if it was associated with erroneous latent heat flux estimates. The effect of aerodynamic conductance on G1 was sufficiently captured with a simple representation. G1 was found to be less sensitive to meteorological deviations between canopy surface and measurement height and, given that data are appropriately filtered, to non‐transpirational water fluxes. Uncertainties in the derived GPP and physiological within‐canopy gradients and their implications for parameter estimates at leaf and ecosystem level are discussed. Our results highlight the importance of adequately considering the sources of uncertainty outlined here when EC‐derived WUE is interpreted in an ecophysiological context.This article is protected by copyright. All rights reserved.
  • Detection of climate change‐driven trends in phytoplankton phenology
    • Abstract: The timing of the annual phytoplankton spring bloom is likely to be altered in response to climate change. Quantifying that response has however been limited by the typically coarse temporal resolution (monthly) of global climate models. Here we use higher resolution model output (maximum 5 days) to investigate how phytoplankton bloom timing changes in response to projected 21st century climate change, and how the temporal resolution of data influences the detection of long‐term trends. We find that bloom timing generally shifts later at mid‐latitudes and earlier at high and low latitudes by ~ 5 days per decade to 2100. The spatial patterns of bloom timing are similar in both low (monthly) and high (5 day) resolution data, although initiation dates are later at low resolution. The magnitude of the trends in bloom timing from 2006‐2100 is very similar at high and low resolution, with the result that the number of years of data needed to detect a trend in phytoplankton phenology is relatively insensitive to data temporal resolution. We also investigate the influence of spatial scales on bloom timing and find that trends are generally more rapidly detectable after spatial averaging of data. Our results suggest that, if pinpointing the start date of the spring bloom is the priority, the highest possible temporal resolution data should be used. However, if the priority is detecting long‐term trends in bloom timing, data at a temporal resolution of 20 days is likely to be sufficient. Further, our results suggest that data sources which allow for spatial averaging will promote more rapid trend detection.This article is protected by copyright. All rights reserved.
  • The origin of soil organic matter controls its composition and
           bioreactivity across a mesic boreal forest latitudinal gradient
    • Abstract: Warmer climates have been associated with reduced bioreactivity of soil organic matter (SOM) typically attributed to increased diagenesis; the combined biological and physiochemical transformation of SOM. Additionally, cross site studies have indicated that ecosystem regime shifts, associated with long‐term climate warming, can affect SOM properties through changes in vegetation and plant litter production thereby altering the composition of soil inputs. The relative importance of these two controls, diagenesis and inputs, on SOM properties as ecosystems experience climate warming, however, remains poorly understood. To address this issue we characterized the elemental, chemical (nuclear magnetic resonance spectroscopy and total hydrolysable amino acids analysis), and isotopic composition of plant litter and SOM across a well‐constrained mesic boreal forest latitudinal transect in Atlantic Canada. Results across forest sites within each of three climate regions indicated that (1) climate history and diagenesis affect distinct parameters of SOM chemistry, (2) increases in SOM bioreactivity with latitude were associated with elevated proportions of carbohydrates relative to plant waxes and lignin, and (3) despite the common forest type across regions, differences in SOM chemistry by climate region were associated with chemically distinct litter inputs and not different degrees of diagenesis. The observed climate effects on vascular plant litter chemistry, however, explained only part of the regional differences in SOM chemistry, most notably the higher protein content of SOM from warmer regions. Greater proportions of lignin and aliphatic compounds and smaller proportions of carbohydrates in warmer sites’ soils were explained by the higher proportion of vascular plant relative to moss litter in the warmer relative to cooler forests. These results indicate that climate change induced decreases in the proportion of moss inputs not only impacts SOM chemistry but also increases the resistance of SOM to decomposition, thus significantly altering SOM cycling in these boreal forest soils.This article is protected by copyright. All rights reserved.
  • Quality‐assured long‐term satellite‐based leaf area
           index product
    • Abstract: Global long‐term Satellite‐based leaf area index (LAI) products have been generated and applied widely for understanding the feedbacks between climate and terrestrial vegetation. However, these long‐term LAI products are not internally consistent over time and also not consistent with each other, which means they might be not suitable for serving as reference datasets in long‐term global change research. Therefore, there is a strong need for a quality‐assured long‐term LAI product with reliable, traceable and understandable quality information. The Quality Assurance for Essential Climate Variables (QA4ECV) project is developing a quality assurance framework to provide understandable and traceable quality information for ECVs such as LAI. The LAI produced from this framework will add greater transparency and openness between ECV producers and end users, and facilitate the application of a long‐term LAI product for global change research.This article is protected by copyright. All rights reserved.
  • Biogeographic responses of the copepod Calanus glacialis to a changing
           Arctic marine environment
    • Abstract: Dramatic changes have occurred in the Arctic Ocean over the past few decades, especially in terms of sea ice loss and ocean warming. Those environmental changes may modify the planktonic ecosystem with changes from lower to upper trophic levels. This study aimed to understand how the biogeographic distribution of a crucial endemic copepod species, Calanus glacialis, may respond to both abiotic (ocean temperature) and biotic (phytoplankton prey) drivers. A copepod individual‐based model coupled to an ice‐ocean‐biogeochemical model was utilized to simulate temperature‐ and food‐dependent life cycle development of C. glacialis annually from 1980 to 2014. Over the 35‐year study period, the northern boundaries of modeled diapausing C. glacialis expanded poleward and the annual success rates of C. glacialis individuals attaining diapause in a circumpolar transition zone increased substantially. Those patterns could be explained by a lengthening growth season (during which time food is ample) and shortening critical development time (the period from the first feeding stage N3 to the diapausing stage C4). The biogeographic changes were further linked to large scale oceanic processes, particularly diminishing sea ice cover, upper ocean warming, and increasing and prolonging food availability, which could have potential consequences to the entire Arctic shelf/slope marine ecosystems.This article is protected by copyright. All rights reserved.
  • Climate change alters stability and species potential interactions in a
           large marine ecosystem
    • Abstract: We have little empirical evidence of how large‐scale overlaps between large numbers of marine species may have altered in response to human impacts. Here, we synthesized all available distribution data (>1 million records) since 1992 for 61 species of the East Australian marine ecosystem, a global hot spot of ocean warming and continuing fisheries exploitation. Using a novel approach, we constructed networks of the annual changes in geographical overlaps between species. Using indices of changes in species overlap, we quantified changes in the ecosystem stability, species robustness, species sensitivity and structural keystone species. We then compared the species overlap indices with environmental and fisheries data to identify potential factors leading to the changes in distributional overlaps between species. We found that the structure of the ecosystem has changed with a decrease in asymmetrical geographical overlaps between species. This suggests that the ecosystem has become less stable and potentially more susceptible to environmental perturbations. Most species have shown a decrease in overlaps with other species. The greatest decrease in species overlap robustness and sensitivity to the loss of other species has occurred in the pelagic community. Some demersal species have become more robust and less sensitive. Pelagic structural keystone species, predominately the tunas and billfish, have been replaced by demersal fish species. The changes in species overlap were strongly correlated with regional oceanographic changes, in particular increasing ocean warming and the southward transport of warmer and saltier water with the East Australian Current (EAC), but less correlated with fisheries catch. Our study illustrates how large‐scale multispecies distribution changes can help identify structural changes in marine ecosystems associated with climate change.This article is protected by copyright. All rights reserved.
  • Individual fitness and the effects of a changing climate on the cessation
           and length of the breeding period using a 34‐year study of a temperate
    • Abstract: Studies of the phenological responses of animals to climate change typically emphasize the initiation of breeding, even though climatic effects on the cessation and length of the breeding period may be as or more influential of fitness. We quantified links between climate, the cessation and length of the breeding period, and individual survival and reproduction using a 34 year study of a resident song sparrow (Melospiza melodia) population subject to dramatic variation in climate. We show that the cessation and length of the breeding period varied strongly across years, and predicted female annual fecundity but not survival. Breeding period length was more influential of fecundity than initiation or cessation of breeding alone. Warmer annual temperature and drier winters and summers predicted an earlier cessation of breeding. Population density, the date breeding was initiated, a female's history of breeding success, and the number of breeding attempts initiated previously also predicted the cessation of breeding annually, indicating that climatic, population, and individual factors may interact to affect breeding phenology. Linking climate projections to our model results suggests that females will both initiate and cease breeding earlier in the future; this will have opposite effects on individual reproductive rate because breeding earlier is expected to increase fecundity, whereas ceasing breeding earlier should reduce it. Identifying factors affecting the cessation and length of the breeding period in multiparous species may be essential to predicting individual fitness and population demography. Given a rich history of studies on the initiation of breeding in free‐living species, re‐visiting those data to estimate climatic effects on the cessation and length of breeding should improve our ability to predict the impacts of climate change on multiparous species.This article is protected by copyright. All rights reserved.
  • Cocoa agroforestry is less resilient to sub-optimal and extreme climate
           than cocoa in full sun
    • Abstract: Cocoa agroforestry is perceived as potential adaptation strategy to sub-optimal or adverse environmental conditions such as drought. We tested this strategy over wet, dry and extremely dry periods comparing cocoa in full sun with agroforestry systems: shaded by (i) a leguminous tree species, Albizia ferruginea and (ii) Antiaris toxicaria, the most common shade tree species in the region. We monitored micro-climate, sap flux density, throughfall and soil water content from November 2014 to March 2016 at the forest-savannah transition zone of Ghana with climate and drought events during the study period serving as proxy for projected future climatic conditions in marginal cocoa cultivation areas of West Africa. Combined transpiration of cocoa and shade trees was significantly higher than cocoa in full sun during wet and dry periods. During wet period, transpiration rate of cocoa plants shaded by A. ferruginea was significantly lower than cocoa under A. toxicaria and full sun. During the extreme drought of 2015/16, all cocoa plants under A. ferruginea died. Cocoa plants under A. toxicaria suffered 77% mortality and massive stress with significantly reduced sap flux density of 115 gcm−2d−1 whereas cocoa in full sun maintained higher sap flux density of 170 gcm−2d−1. Moreover, cocoa sap flux recovery after the extreme drought was significantly higher in full sun (163 gcm−2d−1) than under A. toxicaria (37 g cm−2 d−1). Soil water content in full sun was higher than in shaded systems suggesting that cocoa mortality in the shaded systems was linked to strong competition for soil water. The present results have major implications for cocoa cultivation under climate change. Promoting shade cocoa agroforestry as drought resilient system especially under climate change needs to be carefully reconsidered as shade tree species such as the recommended leguminous A. ferruginea constitute major risk to cocoa functioning under extended severe drought.This article is protected by copyright. All rights reserved.
  • Mycorrhizal fungi enhance plant nutrient acquisition and modulate nitrogen
           loss with variable water regimes
    • Abstract: Climate change will alter both the amount and pattern of precipitation and soil water availability, which will directly affect plant growth and nutrient acquisition, and potentially, ecosystem functions like nutrient cycling and losses as well. Given their role in facilitating plant nutrient acquisition and water stress resistance, arbuscular mycorrhizal (AM) fungi may modulate the effects of changing water availability on plants and ecosystem functions. The well-characterized mycorrhizal tomato (Solanum lycopersicum L.) genotype 76R (referred to as MYC+) and the mutant mycorrhiza-defective tomato genotype rmc were grown in microcosms in a glasshouse experiment manipulating both the pattern and amount of water supply in unsterilized field soil. Following 4 weeks of differing water regimes, we tested how AM fungi affected plant productivity and nutrient acquisition, short-term interception of a 15NH4+ pulse, and inorganic nitrogen (N) leaching from microcosms. AM fungi enhanced plant nutrient acquisition with both lower and more variable water availability, for instance increasing plant P uptake more with a pulsed water supply compared to a regular supply and increasing shoot N concentration more when lower water amounts were applied. Although uptake of the short-term 15NH4+ pulse was higher in rmc plants, possibly due to higher N demand, AM fungi subtly modulated NO3- leaching, decreasing losses by 54% at low and high water levels in the regular water regime, with small absolute amounts of NO3- leached (
  • Role of Population Genetics in Guiding Ecological Responses to Climate
    • Abstract: Population responses to climate were assessed using 3-7 yr height growth data gathered for 266 populations growing in 12 common gardens established in the 1980s as part of 5 disparate studies of Pinus contorta var. latifolia. Responses are interpreted according to three concepts: the ecological optimum, the climate where a population is competitively exclusive and in which, therefore, it occurs naturally; the physiological optimum, the climate where a population grows best but is most often competitively excluded; and growth potential, the innate capacity for growth at the physiological optimum. Statistical analyses identified winter cold, measured by the square root of negative degree-days calculated from the daily minimum temperature (MINDD01/2), as the climatic effect most closely related to population growth potential; the colder the winter inhabited by a population, the lower its growth potential, a relationship presumably molded by natural selection. By splitting the data into groups based on population MINDD01/2 and using a function suited to skewed normal distributions, regressions were developed for predicting growth from the distance in climate space (MINDD01/2) populations had been transferred from their native location to a planting site. The regressions were skewed, showing that the ecological optimum of most populations is colder than the physiological optimum and that the discrepancy between the two increases as the ecological optimum becomes colder. Response to climate change is dependent on innate growth potential and the discrepancy between the two optima and, therefore, is population-specific, developing out of genotype-environment interactions. Response to warming in the short-term can be either positive or negative, but long term responses will be negative for all populations, with the timing of the demise dependent on the amount of skew. The results pertain to physiological modeling, species distribution models, and climate-change adaptation strategies.This article is protected by copyright. All rights reserved.
  • Leap-frog in slow-motion: divergent responses of tree species and life
           stages to climatic warming in Great Basin sub-alpine forests
    • Abstract: In response to climate warming, subalpine treelines are expected to move up in elevation since treelines are generally controlled by growing season temperature. Where treeline is advancing, dispersal differences and early life stage environmental tolerances are likely to affect how species expand their ranges. Species with an establishment advantage will colonize newly available habitat first, potentially excluding species that have slower establishment rates. Using a network of plots across five mountain ranges, we described patterns of upslope elevational range shift for the two dominant Great Basin sub-alpine species, limber pine and Great Basin bristlecone pine. We found that the Great Basin treeline for these species is expanding upslope with a mean vertical elevation shift of 19.1 m since 1950, which is lower than what we might expect based on temperature increases alone. The largest advances were on limber pine-dominated granitic soils, on west aspects, and at lower latitudes. Bristlecone pine juveniles establishing above treeline share some environmental associations with bristlecone adults. Limber pine above-treeline juveniles, in contrast, are prevalent across environmental conditions and share few environmental associations with limber pine adults. Strikingly, limber pine is establishing above treeline throughout the region without regard to site characteristic such as soil type, slope, aspect, or soil texture. Though limber pine is often rare at treeline where it coexists with bristlecone pine, limber pine juveniles dominate above treeline even on calcareous soils that are core bristlecone pine habitat. Limber pine is successfully “leap-frogging” over bristlecone pine, probably because of its strong dispersal advantage and broader tolerances for establishment. This early-stage dominance indicates the potential for the species composition of treeline to change in response to climate change. More broadly, it shows how species differences in dispersal and establishment may result in future communities with very different specific composition.This article is protected by copyright. All rights reserved.
  • Long-term Ecological Changes in Marine Mammals Driven by Recent Warming in
           Northwestern Alaska
    • Abstract: Carbon and nitrogen isotope analyses were performed on marine mammal bone collagen from three archaeological sites (A.D. 1170-1813) on Cape Espenberg (Kotzebue Sound, northwestern Alaska) as well as modern animals harvested from the same area to examine long-term trends in foraging ecology and sea ice productivity. We observed significant and dramatic changes in ringed seal stable isotope values between the early 19th and early 21st centuries, likely due to changing sea ice productivity and reduced delivery of organic matter to the benthos driven by recent warming in the Arctic. These data highlight the importance of the archaeological record for providing a long-term perspective on environmental variation and interpreting recent changes driven by anthropogenic processes.This article is protected by copyright. All rights reserved.
  • Simulating plant invasion dynamics in mountain ecosystems under global
           change scenarios
    • Abstract: Across the globe, invasive alien species cause severe environmental changes, altering species composition and ecosystem functions. So far, mountain areas have mostly been spared from large-scale invasions. However, climate change, land-use abandonment, the development of tourism and the increasing ornamental trade will weaken the barriers to invasions in these systems. Understanding how alien species will react and how native communities will influence their success is thus of prime importance in a management perspective. Here, we used a spatially and temporally explicit simulation model to forecast invasion risks in a protected mountain area in the French Alps under future conditions. We combined scenarios of climate change, land-use abandonment and tourism-linked increases in propagule pressure to test if the spread of alien species in the region will increase in the future. We modelled already naturalized alien species and new ornamental plants, accounting for interactions among global change components, but also competition with the native vegetation. Our results show that propagule pressure and climate change will interact to increase overall species richness of both naturalized aliens and new ornamentals, as well as their upper elevational limits and regional range-sizes. Under climate change, woody aliens are predicted to more than double in range-size and herbaceous species to occupy up to 20% of the park area. In contrast, land-use abandonment will open new invasion opportunities for woody aliens, but decrease invasion probability for naturalized and ornamental alien herbs as a consequence of colonization by native trees. This emphasises the importance of interactions with the native vegetation either for facilitating or potentially for curbing invasions. Overall, our work highlights an additional and previously underestimated threat for the fragile mountain flora of the Alps already facing climate changes, land-use transformations and overexploitation by tourism.This article is protected by copyright. All rights reserved.
  • Climate change and Saharan dust drive recent cladoceran and primary
           production changes in remote alpine lakes of Sierra Nevada, Spain
    • Abstract: Recent anthropogenic climate change and the exponential increase over the past few decades of Saharan dust deposition, containing ecologically important inputs of phosphorus (P) and calcium (Ca), are potentially affecting remote aquatic ecosystems. In this study, we examine changes in cladoceran assemblage composition and chlorophyll-a concentrations over the past ~150 years from high-resolution, well-dated sediment cores retrieved from six remote high mountain lakes in the Sierra Nevada Mountains of Southern Spain, a region affected by Saharan dust deposition. In each lake, marked shifts in cladoceran assemblages and chlorophyll-a concentrations in recent decades indicate a regional-scale response to climate and Saharan dust deposition. Chlorophyll-a concentrations have increased since the 1970s, consistent with a response to rising air temperatures and the intensification of atmospheric deposition of Saharan P. Similar shifts in cladoceran taxa across lakes began over a century ago, but have intensified over the past ~50 years, concurrent with trends in regional air temperature, precipitation, and increased Saharan dust deposition. An abrupt increase in the relative abundance of the benthic cladoceran Alona quadrangularis at the expense of Chydorus sphaericus, and a significant increase in Daphnia pulex gr. was a common trend in these softwater lakes. Differences in the magnitude and timing of these changes are likely due to catchment and lake-specific differences. In contrast with other alpine lakes that are often affected by acid deposition, atmospheric Ca deposition appears to be a significant explanatory factor, amongst others, for the changes in the lake biota of Sierra Nevada that has not been previously considered. The effects observed in Sierra Nevada are likely occurring in other Mediterranean lake districts, especially in soft water, oligotrophic lakes. The predicted increases in global temperature and Saharan dust deposition in the future will further impact the ecological condition of these ecosystems.This article is protected by copyright. All rights reserved.
  • Toxic Toad Invasion of Wallacea: a Biodiversity Hotspot Characterized by
           Extraordinary Endemism
    • Abstract: Invasions of poisonous species can cause rapid population declines among native fauna because predators are naïve and often vulnerable to these toxins. The recent invasion of Madagascar by the poisonous Asian common toad, Duttaphrynus melanostictus, has sparked international attention (Kolby, 2015), as well as research and conservation efforts to predict the climate suitability of Madagascar for the invasive toads (Pearson 2015; Vences et al., 2017), pinpoint the origin of the invasive lineage (Wogan et al., 2016; Vences et al., 2017), determining the toads’ distribution, and educating local communities (Andreone, 2014). While the invasion in Madagascar has received much attention, an invasion of this same toad species on the islands of Wallacea in eastern Indonesia is ongoing but virtually unrecognized.This article is protected by copyright. All rights reserved.
  • Considering Land-Sea Interactions and Trade-offs for Food and Biodiversity
    • Abstract: With the human population expected to near 10 billion by 2050, and diets shifting towards greater per-capita consumption of animal protein, meeting future food demands will place ever-growing burdens on natural resources and those dependent on them. Solutions proposed to increase the sustainability of agriculture, aquaculture, and capture fisheries have typically approached development from single sector perspectives. Recent work highlights the importance of recognising links among food sectors, and the challenge cross-sector dependencies create for sustainable food production. Yet without understanding the full suite of interactions between food systems on land and sea, development in one sector may result in unanticipated trade-offs in another. We review the interactions between terrestrial and aquatic food systems. We show that most of the studied land-sea interactions fall into at least one of four categories: ecosystem connectivity, feed interdependencies, livelihood interactions, and climate feedback. Critically, these interactions modify nutrient flows, and the partitioning of natural resource use between land and sea, amid a backdrop of climate variability and change that reaches across all sectors. Addressing counter-productive trade-offs resulting from land-sea links will require simultaneous improvements in food production and consumption efficiency, while creating more sustainable feed products for fish and livestock. Food security research and policy also needs to better integrate aquatic and terrestrial production to anticipate how cross-sector interactions could transmit change across ecosystem and governance boundaries into the future.This article is protected by copyright. All rights reserved.
  • Tracing biogeochemical subsidies from glacier runoff into Alaska's coastal
           marine food webs
    • Abstract: Nearly half of the freshwater discharge into the Gulf of Alaska originates from landscapes draining glacier runoff, but the influence of the influx of riverine organic matter on the trophodynamics of coastal marine food webs is not well understood. We quantified the ecological impact of riverine organic matter subsidies to glacier-marine habitats by developing a multi-trophic level Bayesian three-isotope mixing model. We utilized large gradients in stable (δ13C, δ15N, δ2H) and radiogenic (Δ14C) isotopes that trace riverine and marine organic matter sources as they are passed from lower to higher trophic levels in glacial-marine habitats. We also compared isotope ratios between glacial-marine and more oceanic habitats. Based on isotopic measurements of potential baseline sources, ambient water and tissues of marine consumers, estimates of the riverine organic matter source contribution to upper trophic-level species including fish and seabirds ranged from 12-44%. Variability in resource use among similar taxa corresponded to variation in species distribution and life histories. For example, riverine organic matter assimilation by the glacier-nesting seabirds Kittlitz's murrelet (Brachyramphus brevirostris) was greater than that of the forest-nesting marbled murrelet (B. marmoratus). The particulate and dissolved organic carbon in glacial runoff and near surface coastal waters was aged (12100 to 1500 years BP 14C-age) but dissolved inorganic carbon and biota in coastal waters were young (530 years BP 14C-age to modern). Thus terrestrial-derived subsidies in marine food webs were primarily composed of young organic matter sources released from glacier ecosystems and their surrounding watersheds. Stable isotope compositions also revealed a divergence in food web structure between glacial-marine and oceanic sites. This work demonstrates linkages between terrestrial and marine ecosystems, and facilitates a greater understanding of how climate-driven changes in freshwater runoff have the potential to alter food web dynamics within coastal marine ecosystems in Alaska.This article is protected by copyright. All rights reserved.
  • Negative Emissions from Stopping Deforestation and Forest Degradation,
    • Abstract: Forest growth provides negative emissions of carbon that could help keep the earth's surface temperature from exceeding 2°C, but the global potential is uncertain. Here we use land-use information from the FAO and a bookkeeping model to calculate the potential negative emissions that would result from allowing secondary forests to recover. We find the current gross carbon sink in forests recovering from harvests and abandoned agriculture to be -4.4 PgC yr−1, globally. The sink represents the potential for negative emissions if positive emissions from deforestation and wood harvest were eliminated. However, the sink is largely offset by emissions from wood products built up over the last century. Accounting for these committed emissions, we estimate that stopping deforestation and allowing secondary forests to grow would yield cumulative negative emissions between 2016 and 2100 of about 120 PgC, globally. Extending the lifetimes of wood products could potentially remove another 10 PgC from the atmosphere, for a total of approximately 130 PgC, or about 13 years of fossil fuel use at today's rate. As an upper limit, the estimate is conservative. It is based largely on past and current practices. But if greater negative emissions are to be realized, they will require an expansion of forest area, greater efficiencies in converting harvested wood to long-lasting products and sources of energy, and novel approaches for sequestering carbon in soils. That is, they will require current management practices to change.This article is protected by copyright. All rights reserved.
  • Contrasting physiological responses to future ocean acidification among
           Arctic copepod populations
    • Abstract: Widespread ocean acidification (OA) is modifying the chemistry of the global ocean, and the Arctic is recognised as the region where the changes will progress at the fastest rate. Moreover, Arctic species show lower capacity for cellular homeostasis and acid-base regulation rendering them particularly vulnerable to OA. In the present study, we found physiological differences in OA response across geographically separated populations of the keystone Arctic copepod Calanus glacialis. In copepodite stage CIV, measured reaction norms of ingestion rate and metabolic rate showed severe reductions in ingestion and increased metabolic expenses in two populations from Svalbard (Kongsfjord and Billefjord) whereas no effects were observed in a population from the Disko Bay, West Greenland. At pHT 7.87, which has been predicted for the Svalbard west coast by year 2100, these changes resulted in reductions in scope for growth of 19% in the Kongsfjord and a staggering 50% in the Billefjord. Interestingly, these effects were not observed in stage CV copepodites from any of the three locations. It seems that CVs may be more tolerant to OA perhaps due to a general physiological reorganisation to meet low intracellular pH during hibernation. Needless to say, the observed changes in the CIV stage will have serious implications for the C. glacialis population health status and growth around Svalbard. However, OA tolerant populations such as the one in the Disko Bay could help to alleviate severe effects in C. glacialis as a species.This article is protected by copyright. All rights reserved.
  • Offsetting global warming-induced elevated greenhouse gas emissions from
           an arable soil by biochar application
    • Abstract: Global warming will likely enhance greenhouse gas (GHG) emissions from soils. Due to its slow decomposability, biochar is widely recognized as effective in long-term soil carbon (C) sequestration and in mitigation of soil GHG emissions. In a long-term soil warming experiment (+2.5 °C, since July 2008) we studied the effect of applying high-temperature Miscanthus biochar (0, 30 t ha−1, since August 2013) on GHG emissions and their global warming potential (GWP) during two years in a temperate agroecosystem. Crop growth, physical and chemical soil properties, temperature sensitivity of soil respiration (Rs) and metabolic quotient (qCO2) were investigated to yield further information about single effects of soil warming and biochar as well as on their interactions. Soil warming increased total CO2 emissions by 28% over two years. The effect of warming on soil respiration did not level off as has often been observed in less intensively managed ecosystems. However, the temperature sensitivity of soil respiration was not affected by warming. Overall, biochar had no effect on most of the measured parameters, suggesting its high degradation stability and its low influence on microbial C cycling even under elevated soil temperatures. In contrast, biochar × warming interactions led to higher total N2O emissions, possibly due to accelerated N-cycling at elevated soil temperature and to biochar-induced changes in soil properties and environmental conditions. Methane uptake was not affected by soil warming or biochar. The incorporation of biochar-C into soil was estimated to offset warming-induced elevated GHG emissions for 25 years. Our results highlight the suitability of biochar for C sequestration in cultivated temperate agricultural soil under a future elevated temperature. However, the increased N2O emissions under warming limit the GHG mitigation potential of biochar.This article is protected by copyright. All rights reserved.
  • The interplay of climate and land use change affects the distribution of
           EU bumblebees
    • Abstract: Bumblebees in Europe have been in steady decline since the 1900s. This decline is expected to continue with climate change as the main driver. However, at the local scale, land use and land cover (LULC) change strongly affects the occurrence of bumblebees. At present, LULC change is rarely included in models of future distributions of species. This study's objective is to compare the roles of dynamic LULC change and climate change on the projected distribution patterns of 48 European bumblebee species for three change scenarios until 2100 at the scales of Europe, and Belgium, Netherlands and Luxembourg (BENELUX). We compared three types of models: (1) only climate covariates, (2) climate and static LULC covariates and (3) climate and dynamic LULC covariates. The climate and LULC change scenarios used in the models include, extreme growth applied strategy (GRAS), business as might be usual (BAMBU) and sustainable European development goals (SEDG). We analysed model performance, range gain/loss and the shift in range limits for all bumblebees. Overall, model performance improved with the introduction of LULC covariates. Dynamic models projected less range loss and gain than climate-only projections, and greater range loss and gain than static models. Overall, there is considerable variation in species responses and effects were most pronounced at the BENELUX scale. The majority of species were predicted to lose considerable range, particularly under the extreme growth scenario (GRAS; overall mean: 64% ± 34). Model simulations project a number of local extinctions and considerable range loss at the BENELUX scale (overall mean: 56% ± 39). Therefore, we recommend species-specific modelling to understand how LULC and climate interact in future modelling. The efficacy of dynamic LULC change should improve with higher thematic and spatial resolution. Nevertheless, current broad scale representations of change in major land use classes impact modelled future distribution patterns.This article is protected by copyright. All rights reserved.
  • Direct and indirect effects of episodic frost on plant growth and
           reproduction in subalpine wildflowers
    • Abstract: Frost is an important episodic event that damages plant tissues through the formation of ice crystals at or below freezing temperatures. In montane regions, where climate change is expected to cause earlier snowmelt but may not change the last frost-free day of the year, plants that bud earlier might be directly impacted by frost through damage to flower buds and reproductive structures. However, the indirect effects of frost mediated through changes in plant-pollinator interactions have rarely been explored. We examined the direct and pollinator-mediated indirect effects of frost on three wildflower species in southwestern Colorado, USA, Delphinium barbeyi (Ranunculaceae), Erigeron speciosus (Asteraceae), and Polemonium foliosissimum (Polemoniaceae), by simulating moderate (-1 to -5°C) frost events in early spring in plants in situ. Subsequently, we measured plant growth, and upon flowering measured flower morphology and phenology. Throughout the flowering season, we monitored pollinator visitation and collected seeds to measure plant reproduction. We found that frost had species-specific direct and indirect effects. Frost had direct effects on two of the three species. Frost significantly reduced flower size, total flowers produced, and seed production of Erigeron. Further, frost reduced above-ground plant survival and seed production for Polemonium. However, we found no direct effects of frost on Delphinium. When we considered the indirect impacts of frost mediated through changes in pollinator visitation, one species, Erigeron, incurred indirect, negative effects of frost on plant reproduction through changes in floral traits and pollinator visitation, along with direct effects. Overall, we found that flowering plants exhibited species-specific direct and pollinator-mediated indirect responses to frost, thus suggesting that frost may play an important role in affecting plant communities under climate change.This article is protected by copyright. All rights reserved.
  • Extreme weather-year sequences have non-additive effects on environmental
           nitrogen losses
    • Abstract: The frequency and intensity of extreme weather years, characterized by abnormal precipitation and temperature, are increasing. In isolation, these years have disproportionately large effects on environmental N losses. However, the sequence of extreme weather years (e.g., wet-dry vs. dry-wet) may affect cumulative N losses. We calibrated and validated the DAYCENT ecosystem process model with a comprehensive set of biogeophysical measurements from a corn-soybean rotation managed at three N fertilizer inputs with and without a winter cover crop in Iowa, USA. Our objectives were to determine: i) how two-year sequences of extreme weather affect two-year cumulative N losses across the crop rotation, and ii) if N fertilizer management and the inclusion of a winter cover crop between corn and soybean mitigate the effect of extreme weather on N losses. Using historical weather (1951-2013), we created nine two-year scenarios with all possible combinations of the driest (‘dry’), wettest (‘wet’), and average (‘normal’) weather years. We analyzed the effects of these scenarios following several consecutive years of relatively normal weather. Compared to the normal-normal two-year weather scenario, two-year extreme weather scenarios affected two-year cumulative NO3- leaching (range: -93 to +290%) more than N2O emissions (range: -49 to +18%). The two-year weather scenarios had non-additive effects on N losses: compared to the normal-normal scenario, the dry-wet sequence decreased two-year cumulative N2O emissions while the wet-dry sequence increased two-year cumulative N2O emissions. Although dry weather decreased NO3- leaching and N2O emissions in isolation, two-year cumulative N losses from the wet-dry scenario were greater than the dry-wet scenario. Cover crops reduced the effects of extreme weather on NO3- leaching but had a lesser effect on N2O emissions. As the frequency of extreme weather is expected to increase, these data suggest that the sequence of inter-annual weather patterns can be used to develop short-term mitigation strategies that manipulate N fertilizer and crop rotation to maximize crop N uptake while reducing environmental N losses.This article is protected by copyright. All rights reserved.
  • Improving predictions of tropical forest response to climate change
           through integration of field studies and ecosystem modeling
    • Abstract: Tropical forests play a critical role in carbon and water cycles at a global scale. Rapid climate change is anticipated in tropical regions over the coming decades and, under a warmer and drier climate, tropical forests are likely to be net sources of carbon rather than sinks. However, our understanding of tropical forest response and feedback to climate change is very limited. Efforts to model climate change impacts on carbon fluxes in tropical forests have not reached a consensus. Here we use the Ecosystem Demography model (ED2) to predict carbon fluxes of a Puerto Rican tropical forest under realistic climate change scenarios. We parameterized ED2 with species-specific tree physiological data using the Predictive Ecosystem Analyzer workflow and projected the fate of this ecosystem under five future climate scenarios. The model successfully captured inter-annual variability in the dynamics of this tropical forest. Model predictions closely followed observed values across a wide range of metrics including above-ground biomass, tree diameter growth, tree size class distributions, and leaf area index. Under a future warming and drying climate scenario, the model predicted reductions in carbon storage and tree growth, together with large shifts in forest community composition and structure. Such rapid changes in climate led the forest to transition from a sink to a source of carbon. Growth respiration and root allocation parameters were responsible for the highest fraction of predictive uncertainty in modeled biomass, highlighting the need to target these processes in future data collection. Our study is the first effort to rely on Bayesian model calibration and synthesis to elucidate the key physiological parameters that drive uncertainty in tropical forests responses to climatic change. We propose a new path forward for model-data synthesis that can substantially reduce uncertainty in our ability to model tropical forest responses to future climate.This article is protected by copyright. All rights reserved.
  • Warming of Subarctic waters accelerates development of a key marine
           zooplankton Calanus finmarchicus
    • Abstract: Recent observations confirm the rising temperatures of Atlantic waters transported into the Arctic Ocean via the West Spitsbergen Current (WSC). We studied the overall abundance and population structure of the North Atlantic keystone zooplankton copepod Calanus finmarchicus, which is the main prey for pelagic fish and some seabirds, in relation to selected environmental variables in this area between 2001 and 2011, when warming in the Arctic and Subarctic was particularly pronounced. Sampling within a three-week time window each summer demonstrated that trends in the overall abundance of C. finmarchicus varied between years, with the highest values in “extreme” years, due to high numbers of nauplii and early copepodite stages in colder years (2001, 2004, 2010), and contrary to that, the fifth copepodite stage (C5) peaking in warm years (2006, 2007, 2009). The most influential environmental variable, driving C. finmarchicus life cycle was temperature, which promoted an increased C5 abundance when the temperature was above 6°C, indicating earlier spawning and/or accelerated development, and possibly leading to their development to adults later in the summer and spawning for the second time, given adequate food supply. Based on the presented high interannual and spatial variability, we hypothesize that under a warmer climate, C. finmarchicus may annually produce two generations in the southern part of the WSC, what in turn could lead to food web reorganization of important top predators, such as little auks, and induce northward migrations of fish, especially the Norwegian herring.This article is protected by copyright. All rights reserved.
  • When and where to move: Dynamic occupancy models explain the range
           dynamics of a food nomadic bird under climate and land cover change
    • Abstract: Globally, long-term research is critical to monitor the responses of tropical species to climate and land cover change at the range scale. Citizen science surveys can reveal the long-term persistence of poorly known nomadic tropical birds occupying fragmented forest patches. We applied dynamic occupancy models to 13 years (2002-2014) of citizen science driven presence/absence data on Cape parrot (Poicephalus robustus), a food nomadic bird endemic to South Africa. We modelled its underlying range dynamics as a function of resource distribution, and change in climate and land cover through the estimation of colonization and extinction patterns. The range occupancy of Cape parrot changed little over time (ψ = 0.75-0.83) because extinction was balanced by recolonization. Yet, there was considerable regional variability in occupancy and detection probability increased over the years. Colonizations increased with warmer temperature and area of orchards, thus explaining their range shifts southeastwards in recent years. Although colonizations were higher in the presence of nests and yellowwood trees (Afrocarpus and Podocarpus spp.), the extinctions in small forest patches (≤ 227 ha) and during low precipitation (≤ 41 mm) are attributed to resource constraints and unsuitable climatic conditions. Loss of indigenous forest cover, and artificial lake/water bodies increased extinction probabilities of Cape parrot. The land use matrix (fruit farms, gardens and cultivations) surrounding forest patches provides alternative food sources thereby facilitating spatiotemporal colonization and extinction in the human-modified matrix. Our models show that Cape parrots are vulnerable to extreme climatic conditions such as drought which is predicted to increase under climate change. Therefore, management of optimum sized high quality forest patches is essential for long-term survival of Cape parrot populations. Our novel application of dynamic occupancy models to long-term citizen science monitoring data unfolds the complex relationships between the environmental dynamics and range fluctuations of this food nomadic species.This article is protected by copyright. All rights reserved.
  • Global-scale patterns of nutrient density and partitioning in forests in
           relation to climate
    • Abstract: Knowledge of nutrient storage and partitioning in forests is imperative for ecosystem models and ecological theory. Whether the nutrients (N, P, K, Ca, Mg) stored in forest biomass and their partitioning patterns vary systematically across climatic gradients remains unknown. Here, we explored the global-scale patterns of nutrient density and partitioning using a newly compiled dataset including 372 forest stands. We found that temperature and precipitation were key factors driving the nutrients stored in living biomass of forests at global-scale. The N, K, and Mg stored in living biomass tended to be greater in increasingly warm climates. The mean biomass N density was 577.0, 530.4, 513.2, and 336.7 kg/ha for tropical, subtropical, temperate, and boreal forests, respectively. Around 76% of the variation in biomass N density could be accounted by the empirical model combining biomass density, phylogeny (i.e., angiosperm, gymnosperm), and the interaction of mean annual temperature and precipitation. Climate, stand age, and biomass density significantly affected nutrients partitioning at forest community level. The fractional distribution of nutrients to roots decreased significantly with temperature, suggesting that forests in cold climates allocate greater nutrients to roots. Gymnosperm forests tended to allocate more nutrients to leaves as compared with angiosperm forests, whereas the angiosperm forests distributed more nutrients in stems. The nutrient-based Root:Shoot ratios (R:S), averaged 0.30 for R:SN, 0.36 for R:SP, 0.32 for R:SK, 0.27 for R:SCa, and 0.35 for R:SMg, respectively. The scaling exponents of the relationships describing root nutrients as a function of shoot nutrients were more than 1.0, suggesting that as nutrient allocated to shoot increases, nutrient allocated to roots increases faster than linearly with nutrient in shoot. Soil type significantly affected the total N, P, K, Ca, and Mg stored in living biomass of forests, and the Acrisols group displayed the lowest P, K, Ca, and Mg.This article is protected by copyright. All rights reserved.
  • Student's tutorial on bloom hypotheses in the context of phytoplankton
           annual cycles
    • Abstract: Phytoplankton blooms are elements in repeating annual cycles of phytoplankton biomass and they have significant ecological and biogeochemical consequences. Temporal changes in phytoplankton biomass are governed by complex predator-prey interactions and physically-driven variations in upper water-column the growth conditions (light, nutrient, temperature). Understanding these dependencies is fundamental to assessing future change in bloom frequency, duration, and magnitude and thus represents a quintessential challenge in global change biology. A variety of contrasting hypotheses have emerged in the literature to explain phytoplankton blooms, but over time the basic tenets of these hypotheses have become unclear. Here, we provide a ‘tutorial’ on the development of these concepts and the fundamental elements distinguishing each hypothesis. The intent of this tutorial is to provide a useful background and set of tools for reading the bloom literature and to give some suggestions for future studies. Our tutorial is written for ‘students’ at all stages of their career. We hope it is equally useful and interesting to those with only a cursory interest in blooms as those deeply immersed in the challenge of understanding the temporal dynamics of phytoplankton biomass and predicting its future change.This article is protected by copyright. All rights reserved.
  • Pelagic marine refugia and climatically sensitive areas in an eastern
           boundary current upwelling system
    • Abstract: Refugia are areas relatively buffered from contemporary climate change that enable the persistence of valued physical, ecological or socio-cultural resources. Spatially identifying refugia is important for conservation and applied management. Yet the concept of refugia has not been broadly extended to marine ecosystems. Here, we analyze data from a unique and long-term (1999-2015) standardized survey of pelagic marine and anadromous species off Oregon and Washington in the northern California Current to identify such refugia. We use quantitative approaches to assess locations with high species richness and assemblage persistence relative to local and basin-scale environmental fluctuations. We have identified a potential climate change refugial zone along the continental shelf of Washington State in the Northeastern Pacific Ocean, characterized by a species-rich assemblage with low interannual temporal community change. This region contrasts with adjacent areas to the south and offshore that have lower species richness, and higher temporal species assemblage change. Also, using spatially variant generalized additive mixed models, we identify areas with species assemblages that are be more influenced by basin-scale climatic fluctuations than others. We propose that upwelling regions with retentive topographic features, such as wide continental shelves, can function as marine refugia for pelagic fauna, whereas offshore locations are potentially more climatically sensitive and experience high temporal change in species composition. Further identification of these marine refugia using in-situ data for pelagic biodiversity and climatically sensitive areas can help guide management in the face of inevitable climatically driven change.This article is protected by copyright. All rights reserved.
  • History matters: heterotrophic microbial community structure and function
           adapt to multiple stressors
    • Abstract: Ecosystem functions in streams (e.g., microbially mediated leaf litter breakdown) are threatened globally by the predicted agricultural intensification and its expansion into pristine areas, which is associated with increasing use of fertilizers and pesticides. However, the ecological consequences may depend on the disturbance history of microbial communities. To test this, we assessed the effects of fungicides and nutrients (four levels each) on the structural and functional resilience of leaf-associated microbial communities with differing disturbance histories (pristine vs. previously disturbed) in a 2×4×4-factorial design (n=6) over 21 d. Microbial leaf breakdown was assessed as a functional variable, whereas structural changes were characterized by the fungal community composition, species richness, biomass, and other factors. Leaf breakdown by the pristine microbial community was reduced by up to 30% upon fungicide exposure compared to controls, whereas the previously disturbed microbial community increased leaf breakdown by up to 85%. This significant difference in the functional response increased in magnitude with increasing nutrient concentrations. A pollution-induced community tolerance in the previously disturbed microbial community, which was dominated by a few species with high breakdown efficacies, may explain the maintained function under stress. Hence, the global pressure on pristine ecosystems by agricultural expansion is expected to cause a modification in the structure and function of heterotrophic microbial communities, with microbially mediated leaf litter breakdown likely becoming more stable over time as a consequence of fungal community adaptions.This article is protected by copyright. All rights reserved.
  • Natural acidification changes the timing and rate of succession, alters
           community structure, and increases homogeneity in marine biofouling
    • Abstract: Ocean acidification may have far-reaching consequences for marine community and ecosystem dynamics, but its full impacts remain poorly understood due to the difficulty of manipulating pCO2 at the ecosystem level to mimic realistic fluctuations that occur on a number of different timescales. It is especially unclear how quickly communities at various stages of development respond to intermediate-scale pCO2 change and, if high pCO2 is relieved mid-succession, whether past acidification effects persist, are reversed by alleviation of pCO2 stress, or are worsened by departures from prior high pCO2 conditions to which organisms had acclimatized. Here, we used reciprocal transplant experiments along a shallow water volcanic pCO2 gradient to assess the importance of the timing and duration of high pCO2 exposure (i.e. discrete events at different stages of successional development vs. continuous exposure) on patterns of colonization and succession in a benthic fouling community. We show that succession at the acidified site was initially delayed (less community change by eight weeks) but then caught up over the next four weeks. These changes in succession led to homogenization of communities maintained in or transplanted to acidified conditions, and altered community structure in ways that reflected both short- and longer-term acidification history. These community shifts are likely a result of interspecific variability in response to increased pCO2 and changes in species interactions. High pCO2 altered biofilm development, allowing serpulids to do best at the acidified site by the end of the experiment, although early (pre-transplant), negative effects of pCO2 on recruitment of these worms was still detectable. The ascidians Diplosoma sp. and Botryllus sp. settled later and were more tolerant to acidification. Overall, transient and persistent acidification-driven changes in the biofouling community, via both past and more recent exposure, could have important implications for ecosystem function and food web dynamics.This article is protected by copyright. All rights reserved.
  • Contributions of insects and droughts to growth decline of trembling aspen
           mixed boreal forest of western Canada
    • Abstract: Insects, diseases, fire and drought and other disturbances associated with global climate change contribute to forest decline and mortality in many parts of the world. Forest decline and mortality related to drought or insect outbreaks have been observed in North American aspen forests. However, little research has been done to partition and estimate their relative contributions to growth declines. In this study, we combined tree-ring width and basal area increment series from 40 trembling aspen (Populus tremuloides Michx.) sites along a latitudinal gradient (from 52° to 58° N) in western Canada and attempted to investigate the effect of drought and insect outbreaks on growth decline, and simultaneously partition and quantify their relative contributions. Results indicated that the influence of drought on forest decline was stronger than insect outbreaks although both had significant effects. Furthermore, the influence of drought and insect outbreaks showed spatiotemporal variability. In addition, our data suggest that insect outbreaks could be triggered by warmer early spring temperature instead of drought, implicating that potentially increased insect outbreaks are expected with continued warming springs, which may further exacerbate growth decline and death in North America aspen mixed forests.This article is protected by copyright. All rights reserved.
  • How disturbance, competition and dispersal interact to prevent tree range
           boundaries from keeping pace with climate change
    • Abstract: Climate change is expected to cause geographic shifts in tree species’ ranges, but such shifts may not keep pace with climate changes because seed dispersal distances are often limited and competition-induced changes in community composition can be relatively slow. Disturbances may speed changes in community composition, but the interactions among climate change, disturbance and competitive interactions to produce range shifts are poorly understood. We used a physiologically-based mechanistic landscape model to study these interactions in the northeastern United States. We designed a series of disturbance scenarios to represent varied disturbance regimes in terms of both disturbance extent and intensity. We simulated forest succession by incorporating climate change under a high emissions future, disturbances, seed dispersal, and competition using the landscape model parameterized with forest inventory data. Tree species range boundary shifts in the next century were quantified as the change in the location of the 5th (the trailing edge) and 95th (the leading edge) percentiles of the spatial distribution of simulated species. Simulated tree species range boundary shifts in New England over the next century were far below (usually < 20 km) that required to track the velocity of temperature change (usually more than 110 km over 100 years) under a high emissions scenario. Simulated species' ranges shifted northward at both the leading edge (northern boundary) and trailing edge (southern boundary). Disturbances may expedite species' recruitment into new sites, but they had little effect on the velocity of simulated range boundary shifts. Range shifts at the trailing edge tended to be associated with photosynthetic capacity, competitive ability for light and seed dispersal ability, whereas shifts at the leading edge were associated only with photosynthetic capacity and competition for light. This study underscores the importance of understanding the role of interspecific competition and disturbance when studying tree range shifts.This article is protected by copyright. All rights reserved.
  • Identifying keystone habitats with a mosaic approach can improve
           biodiversity conservation in disturbed ecosystems
    • Abstract: Conserving native biodiversity in the face of human- and climate-related impacts is a challenging and globally important ecological problem that requires an understanding of spatially-connected, organismal-habitat relationships. Globally, a suite of disturbances (e.g., agriculture, urbanization, climate change) degrades habitats and threatens biodiversity. A mosaic approach (in which connected, interacting collections of juxtaposed habitat patches are examined) provides a scientific foundation for addressing many disturbance-related, ecologically-based conservation problems. For example, if specific habitat types disproportionately increase biodiversity, these keystones should be incorporated into research and management plans. Our sampling of fish biodiversity and aquatic habitat along ten 3-km sites within the Upper Neosho River sub-drainage, KS, from June-August 2013 yielded three generalizable ecological insights. First, specific types of mesohabitat patches (i.e., pool, riffle, run, and glide) were physically distinct and created unique mosaics of mesohabitats that varied across sites. Second, species richness was higher in riffle mesohabitats when mesohabitat size reflected field availability. Furthermore, habitat mosaics that included more riffles had greater habitat diversity and more fish species. Thus, riffles (
  • Variable silicon accumulation in plants affects terrestrial carbon cycling
           by controlling lignin synthesis
    • Abstract: Current climate and land-use changes affect regional and global cycles of silicon (Si), with yet uncertain consequences for ecosystems. The key role of Si in marine ecology by controlling algae growth is well recognized but research on terrestrial ecosystems neglected Si since not considered an essential plant nutrient. However, grasses and various other plants accumulate large amounts of Si, and recently it has been hypothesized that incorporation of Si as a structural plant component may substitute for the energetically more expensive biosynthesis of lignin. Herein we provide evidence supporting this hypothesis. We demonstrate that in straw of rice (Oryza sativa) deriving from a large geographic gradient across South-East Asia, the Si concentrations (ranging from 1.6 to 10.7%) are negatively related to the concentrations of carbon (31.3 to 42.5%) and lignin-derived phenols (32 to 102 mg g−1 carbon). Less lignin may explain results of previous studies that Si-rich straw decomposes faster Hence, Si seems a significant but hardly recognized factor in organic carbon cycling through grasslands and other ecosystems dominated by Si-accumulating plants.This article is protected by copyright. All rights reserved.
  • Impact of winter roads on boreal peatland carbon exchange
    • Abstract: Across Canada's boreal forest, linear disturbances, including cutlines such as seismic lines and roads, crisscross the landscape to facilitate resource exploration and extraction; many of these linear disturbances cross peatland ecosystems. Changes in tree canopy cover and the compression of the peat by heavy equipment alters local thermal, hydrological and ecological conditions, likely changing carbon exchange on the disturbance, and possibly in the adjacent peatland. We measured bulk density, water table, soil temperature, plant cover, and CO2 and CH4 flux along triplicate transects crossing a winter road through a wooded fen near Peace River, Alberta, Canada. Sample plots were located 1, 5 and 10 m from the road on both sides with an additional three plots on the road. Productivity of the overstory trees, when present, was also determined. The winter road had higher bulk density, shallower water table, higher graminoid cover, and thawed earlier than the adjacent peatland. Tree productivity and CO2 flux varied between the plots, and there was no clear pattern in relation to distance from the road. The plots on the winter road acted as a greater CO2 sink and greater CH4 source compared to the adjacent peatland. with plots on the winter road emitting on average (standard error) 479 (138) compared to 41 (10) mg CH4 m−2 d−1 in the adjacent peatland. Considering both gases, global warming potential increased from 70 to 250 g CO2e m−2 yr−1 in the undisturbed area to 2100 g CO2e m−2 yr−1 on the winter road. Although carbon fluxes on any given cutline through peatland will vary depending on level of compaction, line width and vegetation community shifts, the large number of linear disturbances in Canada's boreal forest and slow recovery on peatland ecosites suggest they could represent an important source anthropogenic greenhouse gas source.This article is protected by copyright. All rights reserved.
  • Unexpected resilience of a seagrass system exposed to global stressors
    • Abstract: Despite a growing interest in identifying tipping points in response to environmental change, our understanding of the ecological mechanisms underlying non-linear ecosystem dynamics is limited. Ecosystems governed by strong species interactions can provide important insight into how non-linear relationships between organisms and their environment propagate through ecosystems, and the potential for environmentally mediated species interactions to drive or protect against sudden ecosystem shifts. Here, we experimentally determine the functional relationships (i.e., the shapes of the relationships between predictor and response variables) of a seagrass assemblage with well-defined species interactions to ocean acidification (enrichment of CO2) in isolation and in combination with nutrient loading. We demonstrate that the effect of ocean acidification on grazer biomass (Phyllaplysia taylori and Idotea resecata) was quadratic, with the peak of grazer biomass at mid-pH levels. Algal grazing was negatively affected by nutrients, potentially due to low grazer affinity for macroalgae (Ulva intestinalis), as recruitment of both macroalgae and diatoms were favored in elevated nutrient conditions. This led to an exponential increase in macroalgal and epiphyte biomass with ocean acidification, regardless of nutrient concentration. When left unchecked algae can cause declines in seagrass productivity and persistence through shading and competition. Despite quadratic and exponential functional relationships to stressors that could cause a non-linear decrease in seagrass biomass, productivity of our model seagrass – the eelgrass (Zostera marina)- remained highly resilient to increasing acidification. These results suggest that important species interactions governing ecosystem dynamics may shift with environmental change, and ecosystem state may be decoupled from ecological responses at lower levels of organization.This article is protected by copyright. All rights reserved.
  • Peaks of in situ N2O emissions are influenced by N2O producing and
           reducing microbial communities across arable soils
    • Abstract: Agriculture is the main source of terrestrial N2O emissions, a potent greenhouse gas and the main cause of ozone depletion. The reduction of N2O into N2 by microorganisms carrying the nitrous oxide reductase gene (nosZ) is the only known biological process eliminating this greenhouse gas. Recent studies showed that a previously unknown clade of N2O-reducers (nosZII) was related to the potential capacity of the soil to act as a N2O sink. However little is known about how this group responds to different agricultural practices. Here, we investigated how N2O-producers and N2O-reducers were affected by agricultural practices across a range of cropping systems in order to evaluate the consequences for N2O emissions. The abundance of both ammonia oxidizers and denitrifiers was quantified by real-time qPCR, and the diversity of nosZ clades was determined by 454 pyrosequencing. Denitrification and nitrification potential activities as well as in situ N2O emissions were also assessed. Overall, greatest differences in microbial activity, diversity and abundance were observed between sites rather than between agricultural practices at each site. To better understand the contribution of abiotic and biotic factors to the in situ N2O emissions, we subdivided more than 59.000 field measurements into fractions from low to high rates. We found that the low N2O emission rates were mainly explained by variation in soil properties (up to 59%), while the high rates were explained by variation in abundance and diversity of microbial communities (up to 68%). Notably, the diversity of the nosZII clade but not of the nosZI clade was important to explain the variation of in situ N2O emissions. Altogether, these results lay the foundation for a better understanding of the response of N2O reducing bacteria to agricultural practices and how it may ultimately affect N2O emissions.This article is protected by copyright. All rights reserved.
  • Stand dynamics modulate water cycling and mortality risk in droughted
           tropical forest
    • Abstract: Transpiration from the Amazon rainforest generates an essential water source at a global and local scale. However, changes in rainforest function with climate change can disrupt this process, causing significant reductions in precipitation across Amazonia, and potentially at a global scale. We report the only study of forest transpiration following a long-term (>10 year) experimental drought treatment in Amazonian forest. After 15 years of receiving half the normal rainfall, drought-related tree mortality caused total forest transpiration to decrease by 30%. However, the surviving droughted trees maintained or increased transpiration because of reduced competition for water and increased light availability, which is consistent with increased growth rates. Consequently, the amount of water supplied as rainfall reaching the soil and directly recycled as transpiration increased to 100%. This value was 25% greater than for adjacent non-droughted forest. If these drought conditions were accompanied by a modest increase in temperature (e.g. 1.5°C), water demand would exceed supply, making the forest more prone to increased tree mortality.This article is protected by copyright. All rights reserved.
  • Carbon input by roots into the soil: Quantification of rhizodeposition
           from root to ecosystem scale
    • Abstract: Despite its fundamental role for carbon (C) and nutrient cycling, rhizodeposition remains ‘the hidden half of the hidden half’: it is highly dynamic and rhizodeposits are rapidly incorporated into microorganisms, soil organic matter, and decomposed to CO2. Therefore, rhizodeposition is rarely quantified and remains the most uncertain part of the soil C cycle and of C fluxes in terrestrial ecosystems.This review synthesizes and generalizes the literature on C inputs by rhizodeposition under crops and grasslands (281 data sets). The allocation dynamics of assimilated C (after 13C-CO2 or 14C-CO2 labeling of plants) were quantified within shoots, shoot respiration, roots, net rhizodeposition (i.e., C remaining in soil for longer periods), root-derived CO2, and microorganisms. Partitioning of C pools and fluxes were used to extrapolate belowground C inputs via rhizodeposition to ecosystem level.Allocation from shoots to roots reaches a maximum within the first day after C assimilation. Annual crops retained more C (45% of assimilated 13C or 14C) in shoots than grasses (34%), mainly perennials, and allocated 1.5 times less C belowground. For crops, belowground C allocation was maximal during the first 1-2 months of growth and decreased very fast thereafter. For grasses, it peaked after 2-4 months and remained very high within the second year causing much longer allocation periods.Despite higher belowground C allocation by grasses (33%) than crops (21%), its distribution between various belowground pools remain very similar. Hence, the total C allocated belowground depends on the plant species, but its further fate is species independent.This review demonstrates that C partitioning can be used in various approaches, e.g. root sampling, CO2 flux measurements, to assess rhizodeposits’ pools and fluxes at pot, plot, field and ecosystem scale and so, to close the most uncertain gap of the terrestrial C cycle.This article is protected by copyright. All rights reserved.
  • Seed origin and warming constrain lodgepole pine recruitment, slowing the
           pace of population range shifts
    • Abstract: Understanding how climate warming will affect the demographic rates of different ecotypes is critical to predicting shifts in species distributions. Here we present results from a common garden, climate change experiment in which we measured seedling recruitment of lodgepole pine, a widespread North American conifer that is also planted globally. Seeds from a low-elevation provenance had greater recruitment to their third year (by 323%) than seeds from a high-elevation provenance across sites within and above its native elevation range and across climate manipulations. Heating reduced (by 49%) recruitment to the third year of both low- and high-elevation seed sources across the elevation gradient, while watering alleviated some of the negative effects of heating (108% increase in watered plots). Demographic models based on recruitment data from the climate manipulations and long-term observations of adult populations revealed that heating could effectively halt modeled upslope range expansion except when combined with watering. Simulating fire and rapid post-fire forest recovery at lower elevations accelerated lodgepole pine expansion into the alpine, but did not alter final abundance rankings among climate scenarios. Regardless of climate scenario, greater recruitment of low-elevation seeds compensated for longer dispersal distances to treeline, assuming colonization was allowed to proceed over multiple centuries. Our results show that ecotypes from lower elevations within a species’ range could enhance recruitment and facilitate upslope range shifts with climate change.This article is protected by copyright. All rights reserved.
  • Spatial evaluation of Indonesia's 2015 fire affected area and estimated
           carbon emissions using Sentinel-1
    • Abstract: Fires raged once again across Indonesia in the latter half of 2015, creating a state of emergency due to poisonous smoke and haze across Southeast Asia as well as incurring great financial costs to the government. A strong El Niño-Southern Oscillation (ENSO) led to drought in many parts of Indonesia, resulting in elevated fire occurrence comparable with the previous catastrophic event in 1997/98. Synthetic Aperture Radar (SAR) data promise to provide improved detection of land use and land cover changes in the tropics as compared to methodologies dependent upon cloud and haze free images. This study presents the first spatially explicit estimates of burned area across Sumatra, Kalimantan and West Papua based on high resolution Sentinel-1A SAR imagery. Here we show that 4,604,569 hectares (ha) were burned during the 2015 fire season (overall accuracy 84 %), and compare this with other existing operational burned area products (MCD64, GFED4.0, GFED4.1s). Intersection of burned area with fine-scale land cover and peat layer maps indicates that 0.89 gigatons carbon dioxide equivalents (Gt CO2e) were released through the fire event. This result is compared to other estimates based on non-spatially explicit thermal anomaly measurements or atmospheric monitoring. Using freely available SAR C-band data from the Sentinel mission, we argue that the presented methodology is able to quickly and precisely detect burned areas, supporting improvement in fire control management as well as enhancing accuracy of emissions estimation.This article is protected by copyright. All rights reserved.
  • Wildlife species benefitting from a greener Arctic are most sensitive to
           shrub cover at leading range edges
    • Abstract: Widespread expansion of shrubs is occurring across the Arctic. Shrub expansion will substantially alter arctic wildlife habitats. Identifying which wildlife species are most affected by shrubification is central to predicting future arctic community composition. Through meta-analysis, we synthesized the published evidence for effects of canopy-forming shrubs on birds and mammals in the Arctic and Subarctic. We examined variation in species behaviour, distribution and population dynamics in birds and mammals in response to shrub cover (including shrub cover indicators such as shrub occurrence, extent, density and height). We also assessed the degree of heterogeneity in wildlife responses to shrub cover and synthesized the remaining literature that did not fit the criteria for our quantitative meta-analyses. Species from higher green vegetation biomass habitats (high Normalized Difference Vegetation Index, NDVI, across their distribution) were more likely to respond positively to shrub cover, demonstrating the potential for species to expand from boreal to arctic habitats under shrubification. Wildlife populations located in the lowest vegetation biomass (low NDVI) areas of their species’ range had the greatest proportion of positive responses to shrub cover, highlighting how increases in performance at leading edges of invaders distributions may be particularly rapid. This demonstrates the need to study species at these leading edges to accurately predict expansion potential. Arctic specialists were poorly represented across studies (limited to 5 bird and 0 mammal species), this knowledge gap potentially explains the few reported negative effects of shrub cover (3 of 29 species). Species responses to shrub cover showed substantial heterogeneity and varied among sites and years in all studies with sufficient replication to detect such variation. Our study highlights the importance of responses at species range edges in determining outcomes of shrubification for arctic birds and mammals and the need for greater examination of potential wildlife losers under shrubification.This article is protected by copyright. All rights reserved.
  • Functional genomic analysis of corals from natural CO2-seeps reveals core
           molecular responses involved in acclimatization to ocean acidification
    • Abstract: Little is known about the potential for acclimatization or adaptation of corals to ocean acidification and even less about the molecular mechanisms underpinning these processes. Here we examine global gene expression patterns in corals and their intracellular algal symbionts from two replicate population pairs in Papua New Guinea that have undergone long-term acclimatization to natural variation in pCO2. In the coral host, only 61 genes were differentially expressed in response to pCO2 environment, but the pattern of change was highly consistent between replicate populations, likely reflecting the core expression homeostasis response to ocean acidification. Functional annotations highlight lipid metabolism and a change in the stress response capacity of corals as key parts of this process. Specifically, constitutive downregulation of molecular chaperones was observed, which may impact response to combined climate-change related stressors. Elevated CO2 has been hypothesized to benefit photosynthetic organisms but expression changes of in hospite Symbiodinium in response to acidification were greater and less consistent among reef populations. This population-specific response suggests hosts may need to adapt not only to an acidified environment, but also to changes in their Symbiodinium populations that may not be consistent among environments, adding another challenging dimension to the physiological process of coping with climate change.This article is protected by copyright. All rights reserved.
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