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Journal Cover Global Change Biology
  [SJR: 5.379]   [H-I: 167]   [128 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  [1589 journals]
  • Cocoa Production: Monocultures are Not the Solution to Climate Adaptation
           - - Response to Abdulai et al. 2017
    • Authors: Thomas Cherico Wanger; Dirk Hölscher, Edzo Veldkamp, Teja Tscharntke
      Abstract: Cocoa is a major trade commodity that is seeing increasing demand, but also climate-related yield declines1. There has been an ongoing discussion whether both, the effective adaptation of plantations to climate change and a long term increase of cocoa yields, can only be achieved with shaded agroforestry or also with full-sun monocultures2. Abdulai et al. 3 investigated the climate adaptation potential of full-sun cocoa monocultures and shaded agroforestry in Ghana West Africa.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-05T11:45:19.195251-05:
      DOI: 10.1111/gcb.14005
       
  • Rock glaciers in crystalline catchments: hidden permafrost‐related
           threats to alpine headwater lakes
    • Authors: Boris P. Ilyashuk; Elena A. Ilyashuk, Roland Psenner, Richard Tessadri, Karin A. Koinig
      Abstract: A global warming‐induced transition from glacial to periglacial processes has been identified in mountainous regions around the world. Degrading permafrost in pristine periglacial environments can produce acid rock drainage (ARD) and cause severe ecological damage in areas underlain by sulfide‐bearing bedrock. Limnological and paleolimnological approaches were used to assess and compare ARDs generated by rock glaciers, a typical landform of the mountain permafrost domain, and their effects on alpine headwater lakes with similar morphometric features and underlying bedrock geology, but characterized by different intensities of frost action in their catchments during the year. We argue that ARD and its effects on lakes are more severe in the alpine periglacial belt with mean annual air temperatures (MAAT) between −2 °C and +3 °C, where groundwater persists in the liquid phase for most of the year, in contrast to ARD in the periglacial belt where frost action dominates (MAAT < −2 °C). The findings clearly suggest that the ambient air temperature is an important factor affecting the ARD production in alpine periglacial environments. Applying the paleoecological analysis of morphological abnormalities in chironomids through the past millennium, we tested and rejected the hypothesis that unfavorable conditions for aquatic life in the ARD‐stressed lakes are largely related to the temperature increase over recent decades, responsible for the enhanced release of ARD contaminants. Our results indicate that the ARDs generated in the catchments are of a long‐lasting nature and the frequency of chironomid morphological deformities was significantly higher during the Little Ice Age (LIA) than during pre‐ or post‐LIA periods, suggesting that lower water temperatures may increase the adverse impacts of ARD on aquatic invertebrates. This highlights that temperature‐mediated modulations of the metabolism and life cycle of aquatic organisms should be considered when reconstructing long‐term trends in the ecotoxicological state of lakes.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-04T00:45:56.729956-05:
      DOI: 10.1111/gcb.13985
       
  • Forest biomass, productivity and carbon cycling along a rainfall gradient
           in West Africa
    • Authors: Sam Moore; Stephen Adu-Bredu, Akwasi Duah-Gyamfi, Shalom D. Addo-Danso, Forzia Ibrahim, Armel T. Mbou, Agnès Grandcourt, Riccardo Valentini, Giacomo Nicolini, Gloria Djagbletey, Kennedy Owusu-Afriyie, Agne Gvozdevaite, Imma Oliveras, Maria C. Ruiz-Jaen, Yadvinder Malhi
      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.
      PubDate: 2017-12-04T00:45:37.336461-05:
      DOI: 10.1111/gcb.13907
       
  • New insights on plant phenological response to temperature revealed from
           long-term widespread observations in China
    • Authors: Haicheng Zhang; Shuguang Liu, Pierre Regnier, Wenping Yuan
      Abstract: Constraints of temperature on spring plant phenology are closely related to plant growth, vegetation dynamics and ecosystem carbon cycle. However, the effects of temperature on leaf onset, especially for winter chilling, are still not well understood. Using long-term, widespread in situ phenology observations collected over China for multiple plant species, this study analyzes the quantitative response of leaf onset to temperature, and compares empirical findings with existing theories and modeling approaches, as implemented in eighteen phenology algorithms. Results show that the growing degree days (GDD) required for leaf onset vary distinctly among plant species and geographical locations as well as at organizational levels (species and community), pointing to diverse adaptation strategies. Chilling durations (CHD) needed for releasing bud dormancy decline monotonously from cold to warm areas with very limited inter-species variations. Results also reveal that winter chilling is a crucial component of phenology models, and its effect is better captured with an index that accounts for the inhomogeneous effectiveness of low temperature to chilling rate than with the conventional CHD index. The impact of spring warming on leaf onset is non-linear, better represented by a logistical function of temperature than by the linear function currently implemented in biosphere models. The optimized base temperatures for thermal accumulation and the optimal chilling temperatures are species-dependent and average at 6.9 and 0.2 °C, respectively. Overall, plants’ chilling requirements is not a constant and more chilling generally results in less requirement of thermal accumulation for leaf onset. Our results clearly demonstrate multiple deficiencies of the parameters (e.g., base temperature) and algorithms (e.g., method for calculating GDD) in conventional phenology models to represent leaf onset. Therefore, this study not only advances our mechanistic and quantitative understanding of temperature controls on leaf onset but also provides critical information for improving existing phenology models.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-02T03:50:25.89263-05:0
      DOI: 10.1111/gcb.14002
       
  • Peak season plant activity shift towards spring is reflected by increasing
           carbon uptake by extra-tropical ecosystems
    • Authors: Alemu Gonsamo; Jing M. Chen, Ying Woei Ooi
      Abstract: Climate change is lengthening the growing season of the Northern Hemisphere extra-tropical terrestrial ecosystems, but little is known regarding the timing and dynamics of the peak season of plant activity. Here we use 34-year satellite normalized difference vegetation index (NDVI) observations, and atmospheric CO2 concentration and δ13C isotope measurements at Point Barrow (Alaska, USA, 71° N) to study the dynamics of the peak of season (POS) of plant activity. Averaged across extra-tropical (>23oN) non-evergreen-dominated pixels, NDVI data show that the POS has advanced by 1.2±0.6 days decade−1 in response to the spring-ward shifts of the start (1.0±0.8 days decade−1) and end (1.5±1.0 days decade−1) of peak activity, and the earlier onset of the start of growing season (1.4±0.8 days decade−1), while POS maximum NDVI value increased by 7.8±1.8% for 1982−2015. Similarly, the peak day of carbon uptake, based on calculations from atmospheric CO2 concentration and δ13C data, is advancing by 2.5±2.6 and 4.3±2.9 days decade−1, respectively. POS maximum NDVI value shows strong negative relationships (p < 0.01) with the earlier onset of the start of growing season and POS days. Given that the maximum solar irradiance and day length occur before the average POS day, the earlier occurrence of peak plant activity results in increased plant productivity. Both the advancing POS day and increasing POS vegetation greenness are consistent with the shifting peak productivity towards spring and the increasing annual maximum values of gross and net ecosystem productivity simulated by coupled Earth system models. Our results further indicate that the decline in autumn NDVI is contributing the most to the overall browning of the northern high latitudes (>50oN) since 2011. The spring-ward shift of peak season plant activity is expected to disrupt synchrony of biotic interaction and exert strong biophysical feedbacks on climate by modifying the surface albedo and energy budget.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-01T08:55:22.77946-05:0
      DOI: 10.1111/gcb.14001
       
  • Elevated carbon dioxide and warming impact silicon and phenolic‐based
           defences differently in native and exotic grasses
    • Authors: Scott N. Johnson; Susan E. Hartley
      Abstract: Global climate change may increase invasions of exotic plant species by directly promoting the success of invasive/exotic species or by reducing the competitive abilities of native species. Changes in plant chemistry, leading to altered susceptibility to stress, could mediate these effects. Grasses are hyper‐accumulators of silicon, which plays a crucial function in the alleviation of diverse biotic and abiotic stresses. It is unknown how predicted increases in atmospheric carbon dioxide (CO2) and air temperature affect silicon accumulation in grasses, especially in relation to primary and secondary metabolites. We tested how elevated CO2 (eCO2) (+240ppm) and temperature (eT) (+4⁰C) affected chemical composition (silicon, phenolics, carbon and nitrogen) and plant growth in eight grass species, either native or exotic to Australia. eCO2 increased phenolic concentrations by 11%, but caused silicon accumulation to decline by 12%. Moreover, declines in silicon occurred mainly in native species (‐19%), but remained largely unchanged in exotic species. Conversely, eT increased silicon accumulation in native species (+19%) but decreased silicon accumulation in exotic species (‐10%). Silicon and phenolic concentrations were negatively correlated with each other, potentially reflecting a defensive trade‐off. Moreover, both defences were negatively correlated with plant mass, compatible with a growth‐defence trade‐off. Grasses responded in a species‐specific manner, suggesting that the relative susceptibility of different species may differ under future climates compared to current species rankings of resource quality. For example, the native Microlaena stipoides was less well defended under eCO2 in terms of both phenolics and silicon, so could suffer greater vulnerability to herbivores. To our knowledge, this is the first demonstration of the impacts of eCO2 and eT on silicon accumulation in grasses. We speculate that the greater plasticity in silicon uptake shown by Australian native grasses may be partly a consequence of evolving in a low nutrient and seasonally arid environment.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-01T02:03:23.360829-05:
      DOI: 10.1111/gcb.13971
       
  • Ecosystem state shifts during long‐term development of an Amazonian
           peatland
    • Authors: Graeme T. Swindles; Paul J. Morris, Bronwen Whitney, Jennifer M. Galloway, Mariusz Gałka, Angela Gallego-Sala, Andrew L. Macumber, Donal Mullan, Mark W. Smith, Matthew J. Amesbury, Thomas P. Roland, Hamed Sanei, R. Timothy Patterson, Nicole Sanderson, Lauren Parry, Dan J. Charman, Omar Lopez, Elvis Valderamma, Elizabeth J. Watson, Ruza F. Ivanovic, Paul J. Valdes, T. Edward Turner, Outi Lähteenoja
      Abstract: The most carbon (C) dense ecosystems of Amazonia are areas characterised by the presence of peatlands. However, Amazonian peatland ecosystems are poorly understood and are threatened by human activities. Here we present an investigation into long‐term ecohydrological controls on C accumulation in an Amazonian peat dome. This site is the oldest peatland yet discovered in Amazonia (peat initiation c. 8.9 ka BP), and developed in three stages; (i) peat initiated in an abandoned river channel with open water and aquatic plants; (ii) inundated forest swamp; and (iii) raised peat dome (since c. 3.9 ka BP). Local burning occurred at least three times in the past 4,500 years. Two phases of particularly rapid C accumulation (c. 6.6‐6.1 and c. 4.9‐3.9 ka BP), potentially resulting from increased net primary productivity, were seemingly driven by drier conditions associated with widespread drought events. The association of drought phases with major ecosystem state shifts (open water wetland – forest swamp – peat dome) suggests a potential climatic control on the developmental trajectory of this tropical peatland. A third drought phase centred on c. 1.8‐1.1 ka BP led to markedly reduced C accumulation and potentially a hiatus during the peat dome stage. Our results suggest that future droughts may lead to phases of rapid C accumulation in some inundated tropical peat swamps, although this can lead ultimately to a shift to ombrotrophy and a subsequent return to slower C accumulation. Conversely, in ombrotrophic peat domes, droughts may lead to reduced C accumulation or even net loss of peat. Increased surface wetness at our site in recent decades may reflect a shift towards a wetter climate in western Amazonia. Amazonian peatlands represent important carbon stores and habitats, and are important archives of past climatic and ecological information. They should form key foci for conservation efforts.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-01T01:57:59.939327-05:
      DOI: 10.1111/gcb.13950
       
  • Bleaching events regulate shifts from corals to excavating sponges in
           algae dominated reefs
    • Authors: Andia Chaves-Fonnegra; Bernhard Riegl, Sven Zea, Jose V. Lopez, Tyler Smith, Marilyn Brandt, David S. Gilliam
      Abstract: Changes in coral‐sponge interactions can alter reef accretion/erosion balance and are important to predict trends on current algal‐dominated Caribbean reefs. Although sponge abundance is increasing on some coral reefs, we lack information on how shifts from corals to bioeroding sponges occur, and how environmental factors such as anomalous seawater temperatures and consequent coral bleaching and mortality influence these shifts. A state transition model (Markov chain) was developed to evaluate the response of coral excavating sponges (Cliona delitrix Pang 1973) after coral bleaching events. To understand possible outcomes of the sponge‐coral interaction and build the descriptive model, sponge‐corals were monitored in San Andres Island, Colombia (2004‐2011) and Fort Lauderdale, Florida (2012‐2013). To run the model and determine possible shifts from corals to excavating sponges, 217 coral colonies were monitored over 10 years (2000‐2010) in Fort Lauderdale, Florida, and validated with data from 2011 to 2015. To compare and test its scalability, the model was also run with 271 coral colonies monitored in St. Croix, U.S. Virgin Islands over 11 years (2004‐2011), and validated with data from 2012‐2015. Projections and sensitivity analyses confirmed coral recruitment to be key for coral persistence. Excavating sponge abundance increased in both Fort Lauderdale and St. Croix reefs after a regional mass bleaching event in 2005. The increase was more drastic in St. Croix than in Fort Lauderdale, where 25% of the healthy corals that deteriorated were overtaken by excavating sponges. Projections over 100 years suggested successive events of moderate coral mortality could shift algae‐coral dominated reefs into algae‐sponge dominated. The success of excavating sponges depended of the intensity of coral bleaching and consequent coral mortality. Thus, the proportion of Cliona delitrix excavating sponges is a sensitive indicator for the intensity and frequency of recent disturbance on Caribbean coral reefs.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-01T01:41:44.667346-05:
      DOI: 10.1111/gcb.13962
       
  • Nitrogen limitation of decomposition and decay: how can it occur'
    • Authors: Colin Averill; Bonnie Waring
      Abstract: The availability of nitrogen (N) is a critical control on the cycling and storage of soil carbon (C). Yet there are conflicting conceptual models to explain how N availability influences decomposition of organic matter by soil microbial communities. Several lines of evidence suggest that N availability limits decomposition: the earliest stages of leaf litter decay are associated with a net import of N from the soil environment, and both observations and models show that high‐N organic matter decomposes more rapidly. In direct contrast to these findings, experimental additions of inorganic N to soils broadly show a suppression of microbial activity, which is inconsistent with N limitation of decomposition. Resolving this apparent contradiction is critical to representing nutrient dynamics in predictive ecosystem models under a multitude of global change factors that alter soil N availability.Here, we propose a new conceptual framework, the Carbon, Acidity and Mineral Protection (CAMP) hypothesis, to understand the effects of N availability on soil C cycling and storage, and explore the predictions of this framework with a mathematical model. Our model simulations demonstrate that N addition can have opposing effects on separate soil C pools (particulate and mineral‐protected carbon), because they are differentially affected by microbial biomass growth. Moreover, changes in N availability are frequently linked to shifts in soil pH or osmotic stress, which can independently affect microbial biomass dynamics and mask N stimulation of microbial activity. Thus, the net effect of N addition on soil C is dependent upon interactions among microbial physiology, soil mineralogy, and soil acidity. We believe our synthesis provides a broadly applicable conceptual framework to understand and predict the effect of changes in soil N availability on ecosystem C cycling under global change.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-01T01:40:47.581866-05:
      DOI: 10.1111/gcb.13980
       
  • Environmental heterogeneity and biotic interactions mediate climate
           impacts on tropical forest regeneration
    • Authors: María Uriarte; R. Muscarella, Jess K. Zimmerman
      Abstract: Predicting the fate of tropical forests under a changing climate requires understanding species responses to climatic variability and extremes. Seedlings may be particularly vulnerable to climatic stress given low stored resources and undeveloped roots; they also portend the potential effects of climate change on future forest composition. Here we use data for ca. 50,000 tropical seedlings representing 25 woody species to assess (a) the effects of interannual variation in rainfall and solar radiation between 2007 and 2016 on seedling survival over 9 years in a subtropical forest; and (b) how spatial heterogeneity in three environmental factors–soil moisture, understory light, and conspecific neighborhood density– modulate these responses.Community-wide seedling survival was not sensitive to interannual rainfall variability but interspecific variation in these responses was large, overwhelming the average community response. In contrast, community-wide responses to solar radiation were predominantly positive. Spatial heterogeneity in soil moisture and conspecific density were the predominant and most consistent drivers of seedling survival, with the majority of species exhibiting greater survival at low conspecific densities and positive or non-linear responses to soil moisture. This environmental heterogeneity modulated impacts of rainfall and solar radiation. Negative conspecific effects were amplified during rainy years and at dry sites while the positive effects of radiation on survival were more pronounced for seedlings existing at high understory light levels. These results demonstrate that environmental heterogeneity is not only the main driver of seedling survival in this forest but also plays a central role in buffering or exacerbating impacts of climate fluctuations on forest regeneration. Since seedlings represent a key bottleneck in the demographic cycle of trees, efforts to predict the long-term effects of a changing climate on tropical forests must take into account this environmental heterogeneity and how its effects on regeneration dynamics play out in long-term stand dynamics.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-30T11:25:23.427799-05:
      DOI: 10.1111/gcb.14000
       
  • Vessel noise cuts down communication space for vocalising fish and marine
           mammals
    • Authors: R L Putland; N D Merchant, A Farcas, C A Radford
      Abstract: Anthropogenic noise across the world's oceans threatens the ability of vocalising marine species to communicate. Some species vocalise at key life stages or whilst foraging, and disruption to the acoustic habitat at these times could lead to adverse consequences at the population level. To investigate the risk of these impacts, we investigated the effect of vessel noise on the communication space of the Bryde's whale Balaenoptera edeni, an endangered species which vocalises at low frequencies, and bigeye Pempheris adspersa, a nocturnal fish species which uses contact calls to maintain group cohesion while foraging. By combining long-term acoustic monitoring data with AIS vessel-tracking data and acoustic propagation modelling, the impact of vessel noise on their communication space was determined. Routine vessel passages cut down communication space by up to 61.5% for bigeyes and 87.4% for Bryde's whales. This influence of vessel noise on communication space exceeded natural variability for between 3.9 - 18.9% of the monitoring period. Additionally, during the closest point of approach of a large commercial vessel, less than 10 km from the listening station, the communication space of both species was reduced by a maximum of 99% compared to the ambient soundscape. These results suggest that vessel noise reduces communication space beyond the evolutionary context of these species and may have chronic effects on these populations. To combat this risk, we propose the application or extension of ship speed restrictions in ecologically significant areas, since our results indicate a reduction in sound source levels for vessels transiting at lower speeds.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-30T08:30:31.277245-05:
      DOI: 10.1111/gcb.13996
       
  • Deforestation may increase soil carbon but it is unlikely to be continuous
           or unlimited
    • Authors: Louis Schipper; Pete Smith
      Abstract: Identifying land uses and management practices that maintain or enhance soil carbon storage are important for sequestering carbon from the atmosphere and improving soil ecosystem services (Herrero et al., 2016). There is debate about how much additional carbon can be stored annually in soil, and for how long, following change in land use or management (Smith, 2014) and resolving this question is important. This is particularly relevant now following the aspirational goal established in the 4 per mille initiative (4p1000, 2017).This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-29T09:35:32.902595-05:
      DOI: 10.1111/gcb.13999
       
  • Can Antarctic lichens acclimatise to changes in temperature'
    • Authors: Claudia Colesie; Burkhard Büdel, Vaughan Hurry, Thomas George Allan Green
      Abstract: The Antarctic Peninsula, a tundra biome dominated by lichens and bryophytes, is an ecozone undergoing rapid temperature shifts. Such changes may demand a high physiological plasticity of the local lichen species in order for them to maintain their role as key drivers in this pristine habitat. This study examines the response of net photosynthesis and respiration to increasing temperatures for three Antarctic lichen species with different ecological response amplitudes. We hypothesise that negative effects caused by increased temperatures can be mitigated by thermal acclimation of respiration and/or photosynthesis. The fully controlled growth chamber experiment simulated intermediate and extreme temperature increases over the time course of six weeks. Results showed that, in contrast to our hypothesis, none of the species was able to downregulate temperature‐driven respiratory losses through thermal acclimation of respiration. Instead, severe effects on photobiont vitality demonstrated that temperatures around 15°C mark the upper limit for the two species restricted to the Antarctic, and when mycobiont demands exceeded the photobiont capacity they could not survive within the lichen thallus. In contrast, the widespread lichen species was able to recover its homoeostasis by rapidly increasing net photosynthesis. We conclude that in order to understand the complete lichen response, acclimation processes of both symbionts, the photo‐ and the mycobiont, have to be evaluated separately. As a result, we postulate that any acclimation processes in lichen are species specific. This, together with the high degree of response variability and sensitivity to temperature in different species that co‐occur spatially close, complicates any predictions regarding future community composition in the Antarctic. Nevertheless, our results suggest that species with a broad ecological amplitude may be favoured with ongoing changes in temperature.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-29T05:41:39.485134-05:
      DOI: 10.1111/gcb.13984
       
  • Impacts of climate and land use on N2O and CH4 fluxes from tropical
           ecosystems in the Mt. Kilimanjaro region, Tanzania
    • Authors: Adrian Gütlein; Friederike Gerschlauer, Imani Kikoti, Ralf Kiese
      Abstract: In this study, we quantify the impacts of climate and land use on soil N2O and CH4 fluxes from tropical forest, agroforest, arable and savanna ecosystems in Africa. To do so, we measured GHG fluxes from twelve different ecosystems along climate and land‐use gradients at Mt. Kilimanjaro, combining long‐term in situ chamber and laboratory soil‐core incubation techniques. Both methods showed similar patterns of GHG exchange. Although there were distinct differences from ecosystem to ecosystem, soils generally functioned as net sources and sinks for N2O and CH4, respectively. N2O emissions correlated positively with soil moisture and total soil nitrogen content. CH4 uptake rates correlated negatively with soil moisture and clay content and positively with SOC. Due to moderate soil moisture contents and the dominance of nitrification in soil N turnover, N2O emissions of tropical montane forests were generally low (< 1.2 kg N ha−1 yr−1), and it is likely that ecosystem N losses are driven instead by nitrate leaching (~10 kg N ha−1 yr−1). Forest soils with well‐aerated litter layers were a significant sink for atmospheric CH4 (up to 4 kg C ha−1 yr−1) regardless of low mean annual temperatures at higher elevations. Land‐use intensification significantly increased the soil N2O source strength and significantly decreased the soil CH4 sink. Compared to decreases in aboveground and belowground carbon stocks enhanced soil non‐CO2 GHG emissions following land‐use conversion from tropical forests to homegardens and coffee plantations were only a small factor in the total GHG budget. However, due to lower ecosystem carbon stock changes, enhanced N2O emissions significantly contributed to total GHG emissions following conversion of savanna into grassland and particularly maize. Overall, we found that the protection and sustainable management of aboveground and belowground carbon and nitrogen stocks of agroforestry and arable systems is most crucial for mitigating GHG emissions from land‐use change.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-28T02:00:41.493356-05:
      DOI: 10.1111/gcb.13944
       
  • Extremely low genetic diversity across mangrove taxa reflects past sea
           level changes and hints at poor future responses
    • Authors: Zixiao Guo; Xinnian Li, Ziwen He, Yuchen Yang, Wenqing Wang, Cairong Zhong, Anthony J. Greenberg, Chung-I Wu, Norman C. Duke, Suhua Shi
      Abstract: The projected increases in sea levels are expected to affect coastal ecosystems. Tropical communities, anchored by mangrove trees and having experienced frequent past sea level changes, appear to be vibrant at present. However, any optimism about the resilience of these ecosystems is premature because the impact of past climate events may not be reflected in the current abundance. To assess the impact of historical sea level changes, we conducted an extensive genetic diversity survey on the Indo‐Malayan coast, a hotspot with a large global mangrove distribution. A survey of 26 populations in six species reveals extremely low genome‐wide nucleotide diversity and hence very small effective population sizes (Ne) in all populations. Whole‐genome sequencing of three mangrove species further shows the decline in Ne to be strongly associated with the speed of past changes in sea level. We also used a recent series of flooding events in Yalong Bay, southern China, to test the robustness of mangroves to sea level changes in relation to their genetic diversity. The events resulted in the death of half of the mangrove trees in this area. Significantly, less genetically diverse mangrove species suffered much greater destruction. The dieback was accompanied by a drastic reduction in local invertebrate biodiversity. We thus predict that tropical coastal communities will be seriously endangered as the global sea level rises. Well‐planned coastal development near mangrove forests will be essential to avert this crisis.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-28T01:57:44.743575-05:
      DOI: 10.1111/gcb.13968
       
  • Matrix approach to land carbon cycle modeling: A case study with Community
           Land Model
    • Authors: Yuanyuan Huang; Xingjie Lu, Zheng Shi, David Lawrence, Charles D. Koven, Jianyang Xia, Zhenggang Du, Erik Kluzek, Yiqi Luo
      Abstract: The terrestrial carbon (C) cycle has been commonly represented by a series of C balance equations to track C influxes into and effluxes out of individual pools in earth system models (ESMs). This representation matches our understanding of C cycle processes well but makes it difficult to track model behaviors. It is also computationally expensive, limiting the ability to conduct comprehensive parametric sensitivity analyses. To overcome these challenges, we have developed a matrix approach, which reorganizes the C balance equations in the original ESM into one matrix equation without changing any modeled C cycle processes and mechanisms. We applied the matrix approach to the Community Land Model (CLM4.5) with vertically resolved biogeochemistry. The matrix equation exactly reproduces litter and soil organic carbon (SOC) dynamics of the standard CLM4.5 across different spatial‐temporal scales. The matrix approach enables effective diagnosis of system properties such as C residence time and attribution of global change impacts to relevant processes. We illustrated, for example, the impacts of CO2 fertilization on litter and SOC dynamics can be easily decomposed into the relative contributions from C input, allocation of external C into different C pools, nitrogen regulation, altered soil environmental conditions, and vertical mixing along the soil profile. In addition, the matrix tool can accelerate model spin‐up, permit thorough parametric sensitivity tests, enable pool‐based data assimilation, and facilitate tracking and benchmarking of model behaviors. Overall, the matrix approach can make a broad range of future modeling activities more efficient and effective.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-28T01:56:00.023067-05:
      DOI: 10.1111/gcb.13948
       
  • Differential adult survival at close seabird colonies: the importance of
           spatial foraging segregation and bycatch risk during the breeding season
    • Authors: M Genovart; J Bécares, J.M Igual, A Martínez-Abraín, R Escandell, A Sánchez, B Rodríguez, J. M Arcos, D Oro
      Abstract: Marine megafauna, including seabirds, are critically affected by fisheries bycatch. However, bycatch risk may differ on temporal and spatial scales due to the uneven distribution and effort of fleets operating different fishing gear, and to focal species distribution and foraging behaviour. Scopoli's shearwater Calonectris diomedea is a long‐lived seabird that experiences high bycatch rates in longline fisheries and strong population‐level impacts due to this type of anthropogenic mortality. Analyzing a long‐term data set on individual monitoring, we compared adult survival (by means of multi‐event capture‐recapture models) among three close predator‐free Mediterranean colonies of the species. Unexpectedly for a long‐lived organism, adult survival varied among colonies. We explored potential causes of this differential survival, by: (1) measuring egg volume as a proxy of food availability and parental condition; (2) building a specific longline bycatch risk map for the species; and (3) assessing the distribution patterns of breeding birds from the three study colonies via GPS tracking. Egg volume was very similar between colonies over time, suggesting that environmental variability related to habitat foraging suitability was not the main cause of differential survival. On the other hand, differences in foraging movements among individuals from the three colonies expose them to differential mortality risk, which likely influenced the observed differences in adult survival. The overlap of information obtained by the generation of specific bycatch risk maps, the quantification of population demographic parameters and the foraging spatial analysis should inform managers about differential sensitivity to the anthropogenic impact at mesoscale level and guide decisions depending on the spatial configuration of local populations. The approach would apply and should be considered in any species where foraging distribution is colony‐specific and mortality risk varies spatially.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T09:30:32.503615-05:
      DOI: 10.1111/gcb.13997
       
  • Lags in the response of mountain plant communities to climate change
    • Authors: Jake M. Alexander; Loïc Chalmandrier, Jonathan Lenoir, Treena I. Burgess, Franz Essl, Sylvia Haider, Christoph Kueffer, Keith McDougall, Ann Milbau, Martin A. Nuñez, Aníbal Pauchard, Wolfgang Rabitsch, Lisa J. Rew, Nathan J. Sanders, Loïc Pellissier
      Abstract: Rapid climatic changes and increasing human influence at high elevations around the world will have profound impacts on mountain biodiversity. However, forecasts from statistical models (e.g. species distribution models) rarely consider that plant community changes could substantially lag behind climatic changes, hindering our ability to make temporally realistic projections for the coming century. Indeed, the magnitudes of lags, and the relative importance of the different factors giving rise to them, remain poorly understood. We review evidence for three types of lag: “dispersal lags” affecting plant species’ spread along elevational gradients, “establishment lags” following their arrival in recipient communities, and “extinction lags” of resident species. Variation in lags is explained by variation among species in physiological and demographic responses, by effects of altered biotic interactions, and by aspects of the physical environment. Of these, altered biotic interactions could contribute substantially to establishment and extinction lags, yet impacts of biotic interactions on range dynamics are poorly understood. We develop a mechanistic community model to illustrate how species turnover in future communities might lag behind simple expectations based on species’ range shifts with unlimited dispersal. The model shows a combined contribution of altered biotic interactions and dispersal lags to plant community turnover along an elevational gradient following climate warming. Our review and simulation support the view that accounting for disequilibrium range dynamics will be essential for realistic forecasts of patterns of biodiversity under climate change, with implications for the conservation of mountain species and the ecosystem functions they provide.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T05:56:35.147695-05:
      DOI: 10.1111/gcb.13976
       
  • In modelling effects of global warming, invalid assumptions lead to
           unrealistic projections
    • Authors: Sjannie Lefevre; David J. McKenzie, Göran E. Nilsson
      Abstract: In a recent Opinion paper, Pauly and Cheung (2017) argue against the criticisms we raised (Lefevre et al., 2017) about the Gill‐Oxygen Limitation Theory (GOLT) and its application in modelling. Rather than providing point‐by‐point responses to their arguments we highlight some key issues that, in our opinion, disqualify GOLT as a mechanistic basis for model projections about the future size of fishes.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T05:41:41.695469-05:
      DOI: 10.1111/gcb.13978
       
  • Outcomes from 10 years of biodiversity offsetting
    • Authors: Philip Gibbons; Andrew Macintosh, Amy Louise Constable, Kiichiro Hayashi
      Abstract: We quantified net changes to the area and quality of native vegetation after the introduction of biodiversity offsetting in New South Wales, Australia—a policy intended to “prevent broad‐scale clearing of native vegetation unless it improves or maintains environmental values.” Over 10 years, a total of 21,928ha of native vegetation was approved for clearing under this policy and 83,459ha was established as biodiversity offsets. We estimated that no net loss in the area of native vegetation under this policy will not occur for 146 years. This is because 82% of the total area offset was obtained by averting losses to existing native vegetation and the rate that these averted losses accrue was not explicit in the policy. There were predicted net gains in 10 of the 14 attributes used to assess the quality of habitat. An overall net gain in the quality of habitat was assessed under this policy by substituting habitat attributes that are difficult to restore (e.g., mature trees) with habitat attributes for which restoration is relatively easy (e.g., tree seedlings). Long‐term rates of annual deforestation did not significantly change across the study area after biodiversity offsetting was introduced. Overall, the policy examined here provides no net loss of biodiversity: (a) many generations into the future, which is not consistent with inter‐generational equity; and (b) by substituting different habitat attributes, so gains are not equivalent to losses. We recommend a number of changes to biodiversity offsetting policy to overcome these issues.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T05:30:39.375755-05:
      DOI: 10.1111/gcb.13977
       
  • Do all leaf photosynthesis parameters of rice acclimate to elevated CO2,
           elevated temperature, and their combination, in FACE environments'
    • Authors: Chuang Cai; Gang Li, Hailong Yang, Jiaheng Yang, Hong Liu, Paul C. Struik, Weihong Luo, Xinyou Yin, Lijun Di, Xuanhe Guo, Wenyu Jiang, Chuanfei Si, Genxing Pan, Jianguo Zhu
      Abstract: Leaf photosynthesis of crops acclimates to elevated CO2 and temperature, but studies quantifying responses of leaf photosynthetic parameters to combined CO2 and temperature increases under field conditions are scarce. We measured leaf photosynthesis of rice cultivars Changyou 5 and Nanjing 9108 grown in two free‐air CO2 enrichment (FACE) systems, respectively, installed in paddy fields. Each FACE system had four combinations of two levels of CO2 (ambient and enriched) and two levels of canopy temperature (no warming and warmed by 1.0‐2.0 °C). Parameters of the C3 photosynthesis model of Farquhar, von Caemmerer and Berry (the FvCB model), and of a stomatal conductance (gs) model were estimated for the four conditions. Most photosynthetic parameters acclimated to elevated CO2, elevated temperature, and their combination. The combination of elevated CO2 and temperature changed the functional relationships between biochemical parameters and leaf nitrogen content for Changyou 5. The gs model significantly underestimated gs under the combination of elevated CO2 and temperature by 19% for Changyou 5 and by 10% for Nanjing 9108 if no acclimation was assumed. However, our further analysis applying the coupled gs–FvCB model to an independent, previously published FACE experiment showed that including such an acclimation response of gs hardly improved prediction of leaf photosynthesis under the four combinations of CO2 and temperature. Therefore, the typical procedure that crop models using the FvCB and gs models are parameterized from plants grown under current ambient conditions may not result in critical errors in projecting productivity of paddy rice under future global change.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T05:26:01.724751-05:
      DOI: 10.1111/gcb.13961
       
  • Carbon cycle confidence and uncertainty: exploring variation among soil
           biogeochemical models
    • Authors: William R. Wieder; Melannie D. Hartman, Benjamin N. Sulman, Ying-Ping Wang, Charles D. Koven, Gordon B. Bonan
      Abstract: Emerging insights into factors responsible for soil organic matter stabilization and decomposition are being applied in a variety of contexts, but new tools are needed to facilitate the understanding, evaluation and improvement of soil biogeochemical theory and models at regional to global scales. To isolate the effects of model structural uncertainty on the global distribution of soil carbon stocks and turnover times we developed a soil biogeochemical testbed that forces three different soil models with consistent climate and plant productivity inputs. The models tested here include a first‐order, microbial implicit approach (CASA‐CNP), and two recently developed microbially explicit models that can be run at global scales (MIMICS and CORPSE). When forced with common environmental drivers, the soil models generated similar estimates of initial soil carbon stocks (roughly 1400 Pg C globally, 0‐100 cm), but each model shows a different functional relationship between mean annual temperature and inferred turnover times. Subsequently, the models made divergent projections about the fate of these soil carbon stocks over the 20th century, with models either gaining or losing over 20 Pg C globally between 1901 and 2010. Single‐forcing experiments with changed inputs, temperature, and moisture suggest that uncertainty associated with freeze‐thaw processes as well as soil textural effects on soil carbon stabilization were larger than direct temperature uncertainties among models. Finally, the models generated distinct projections about the timing and magnitude of seasonal heterotrophic respiration rates, again reflecting structural uncertainties that were related to environmental sensitivities and assumptions about physicochemical stabilization of soil organic matter. By providing a computationally tractable and numerically consistent framework to evaluate models we aim to better understand uncertainties among models and generate insights about factors regulating turnover of soil organic matter.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T05:01:34.68528-05:0
      DOI: 10.1111/gcb.13979
       
  • Shifts of growing‐season precipitation peaks decrease soil
           respiration in a semiarid grassland
    • Authors: Jingyi Ru; Yaqiong Zhou, Dafeng Hui, Mengmei Zheng, Shiqiang Wan
      Abstract: Changing precipitation regimes could have profound influences on carbon (C) cycle in the biosphere. However, how soil C release from terrestrial ecosystems responds to changing seasonal distribution of precipitation remains unclear. A field experiment was conducted for 4 years (2013‐2016) to examine effects of altered precipitation distributions in the growing season on soil respiration in a temperate steppe in the Mongolian Plateau. Over the 4 years, both advanced and delayed precipitation peaks suppressed soil respiration, and the reductions mainly occurred in August. The decreased soil respiration could be primarily attributable to water stress and subsequently limited plant growth (community cover and belowground net primary productivity) and soil microbial activities in the middle growing season, suggesting that precipitation amount in the middle growing season is more important than that in the early, late or whole growing seasons in regulating soil C release in grasslands. The observations of the additive effects of advanced and delayed precipitation peaks indicate semiarid grasslands will release less C through soil respiratory processes under the projected seasonal redistribution of precipitation in the future. Our findings highlight the potential role of intra‐annual redistribution of precipitation in regulating ecosystem C cycling in arid and semiarid regions.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T04:56:26.20382-05:0
      DOI: 10.1111/gcb.13941
       
  • Landscape‐level Effects on Aboveground Biomass of Tropical Forests:
           a Conceptual Framework
    • Authors: Melina Melito; Jean Paul Metzger, Alexandre A. de Oliveira
      Abstract: Despite the general recognition that fragmentation can reduce forest biomass through edge effects, a systematic review of the literature does not reveal a clear role of edges in modulating biomass loss. Additionally, the edge effects appear to be constrained by matrix type, suggesting that landscape composition has an influence on biomass stocks. The lack of empirical evidence of pervasive edge‐related biomass losses across tropical forests highlights the necessity for a general framework linking landscape structure with aboveground biomass. Here, we propose a conceptual model in which landscape composition and configuration mediate the magnitude of edge effects and seed‐flux among forest patches, which ultimately has an influence on biomass. Our model hypothesizes that a rapid reduction of biomass can occur below a threshold of forest cover loss. Just below this threshold, we predict that changes in landscape configuration can strongly influence the patch's isolation thus enhancing biomass loss. Moreover, we expect a synergism between landscape composition and patch attributes, where matrix type mediates the effects of edges on species decline, particularly for shade‐tolerant species. To test our conceptual framework, we propose a sampling protocol where the effects of edges, forest amount, forest isolation, fragment size, and matrix type on biomass stocks can be assessed both collectively and individually. The proposed model unifies the combined effects of landscape and patch structure on biomass into a single framework, providing a new set of main drivers of biomass loss in human‐modified landscapes. We argue that carbon trading agendas (e.g. REDD+) and carbon‐conservation initiatives must go beyond the effects of forest loss and edges on biomass, considering the whole set of effects on biomass related to changes in landscape composition and configuration.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T04:51:10.124099-05:
      DOI: 10.1111/gcb.13970
       
  • How much do direct livestock emissions actually contribute to global
           warming'
    • Authors: Andy Reisinger; Harry Clark
      Abstract: Agriculture directly contributes about 10‐12% of current global anthropogenic greenhouse gas (GHG) emissions, mostly from livestock. However, such percentage estimates are based on Global Warming Potentials (GWPs), which do not measure the actual warming caused by emissions and ignore the fact that methane does not accumulate in the atmosphere in the same way as CO2. Here we employ a simple carbon cycle‐climate model, historical estimates and future projections of livestock emissions to infer the fraction of actual warming that is attributable to direct livestock non‐CO2 emissions now and in future, and to CO2 from pasture conversions, without relying on GWPs. We find that direct livestock non‐CO2 emissions caused about 19% of the total modelled warming of 0.81°C from all anthropogenic sources in 2010. CO2 from pasture conversions contributed at least another 0.03°C, bringing the warming directly attributable to livestock to 23% of the total warming in 2010. The significance of direct livestock emissions to future warming depends strongly on global actions to reduce emissions from other sectors. Direct non‐CO2 livestock emissions would contribute only about 5% of the warming in 2100 if emissions from other sectors increase unabated, but could constitute as much as 18% (0.27°C) of the warming in 2100 if global CO2 emissions from other sectors are reduced to near or below zero by 2100, consistent with the goal of limiting warming to well below 2°C. These estimates constitute a lower bound since indirect emissions linked to livestock feed production and supply chains were not included. Our estimates demonstrate that expanding the mitigation potential and realizing substantial reductions of direct livestock non‐CO2 emissions through demand and supply side measures can make an important contribution to achieve the stringent mitigation goals set out in the Paris Agreement, including by increasing the carbon budget consistent with the 1.5°C goal.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T04:41:13.413683-05:
      DOI: 10.1111/gcb.13975
       
  • Warming‐induced upward migration of the alpine treeline in the Changbai
           Mountains, northeast China
    • Authors: Haibo Du; Jie Liu, Mai-He Li, Ulf Büntgen, Yue Yang, Lei Wang, Zhengfang Wu, Hong S. He
      Abstract: Treeline responses to environmental changes describe an important phenomenon in global change research. Often conflicting results and generally too short observations are, however, still challenging our understanding of climate‐induced treeline dynamics. Here, we use a state‐of‐the‐art dendroecological approach to reconstruct long‐term changes in the position of the alpine treeline in relation to air temperature at two sides in the Changbai Mountains in northeast China. Over the past 160 years, the treeline increased by around 80 m, a process that can be divided into three phases of different rates and drives. The first phase was mainly influenced by vegetation recovery after an eruption of the Tianchi volcano in 1702. The slowly upward shift in the second phase was consistent with the slowly increasing temperature. The last phase coincided with rapid warming since 1985, and shows with 33 m per 1°C, the most intense upward shift. The spatial distribution and age structure of trees beyond the current treeline confirm the latest, warming‐induced upward shift. Our results suggest that the alpine treeline will continue to rise, and that the alpine tundra may disappear if temperatures will increase further. This study not only enhances mechanistic understanding of long‐term treeline dynamics, but also highlights the effects of rising temperatures on high‐elevation vegetation dynamics.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-27T04:41:01.551424-05:
      DOI: 10.1111/gcb.13963
       
  • Assessing uncertainties in crop and pasture ensemble model simulations of
           productivity and N2O emissions
    • Authors: Fiona Ehrhardt; Jean-François Soussana, Gianni Bellocchi, Peter Grace, Russel McAuliffe, Sylvie Recous, Renáta Sándor, Pete Smith, Val Snow, Massimiliano de Antoni Migliorati, Bruno Basso, Arti Bhatia, Lorenzo Brilli, Jordi Doltra, Christopher D. Dorich, Luca Doro, Nuala Fitton, Sandro J. Giacomini, Brian Grant, Matthew T. Harrison, Stephanie K. Jones, Miko U. F. Kirschbaum, Katja Klumpp, Patricia Laville, Joël Léonard, Mark Liebig, Mark Lieffering, Raphaël Martin, Raia S. Massad, Elizabeth Meier, Lutz Merbold, Andrew D. Moore, Vasileios Myrgiotis, Paul Newton, Elizabeth Pattey, Susanne Rolinski, Joanna Sharp, Ward N. Smith, Lianhai Wu, Qing Zhang
      Abstract: Simulation models are extensively used to predict agricultural productivity and greenhouse gas (GHG) emissions. However, the uncertainties of (reduced) model ensemble simulations have not been assessed systematically for variables affecting food security and climate change mitigation, within multispecies agricultural contexts. We report an international model comparison and benchmarking exercise, showing the potential of multimodel ensembles to predict productivity and nitrous oxide (N2O) emissions for wheat, maize, rice and temperate grasslands. Using a multistage modelling protocol, from blind simulations (stage 1) to partial (stages 2‐4) and full calibration (stage 5), 24 process‐based biogeochemical models were assessed individually or as an ensemble against long‐term experimental data from four temperate grassland and five arable crop rotation sites spanning four continents. Comparisons were performed by reference to the experimental uncertainties of observed yields and N2O emissions. Results showed that across sites and crop/grassland types, 23 to 40% of the uncalibrated individual models were within two standard deviations (s.d.) of observed yields, while 42 (rice) to 96% (grasslands) of the models were within one s.d. of observed N2O emissions. At stage 1, ensembles formed by the three lowest prediction model errors (RRMSE) predicted both yields and N2O emissions within experimental uncertainties for 44 and 33% of the crop and grassland growth cycles, respectively. Partial model calibration (stages 2 to 4) markedly reduced prediction errors of the full model ensemble E‐median for crop grain yields (from 36% at stage 1 down to 4% on average) and grassland productivity (from 44 to 27%) and to a lesser and more variable extent for N2O emissions. Yield‐scaled N2O emissions (N2O emissions divided by crop yields) were ranked accurately by 3‐model ensembles across crop species and field sites. The potential of using process‐based model ensembles to predict jointly productivity and N2O emissions at field scale is discussed.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-24T00:51:23.612828-05:
      DOI: 10.1111/gcb.13965
       
  • Vapor‐pressure deficit and extreme climatic variables limit tree
           growth
    • Authors: Paula Sanginés de Cárcer; Yann Vitasse, Josep Peñuelas, Vincent E. J. Jassey, Alexandre Buttler, Constant Signarbieux
      Abstract: Assessing the effect of global warming on forest growth requires a better understanding of species‐specific responses to climate change conditions. Norway spruce and European beech are among the dominant tree species in Europe and are largely used by the timber industry. Their sensitivity to changes in climate and extreme climatic events, however, endangers their future sustainability. Identifying the key climatic factors limiting their growth and survival is therefore crucial for assessing the responses of these two species to ongoing climate change. We studied the vulnerability of beech and spruce to warmer and drier conditions by transplanting saplings from the top to the bottom of an elevational gradient in the Jura Mountains in Switzerland. We (1) demonstrated that a longer growing season due to warming could not fully account for the positive growth responses, and the positive effect on sapling productivity was species‐dependent, (2) demonstrated that the contrasting growth responses of beech and spruce were mainly due to different sensitivities to elevated vapor‐pressure deficits, (3) determined the species specific limits to vapor‐pressure deficit above which growth rate began to decline and (4) demonstrated that models incorporating extreme climatic events could account for the response of growth to warming better than models using only average values. These results support that the sustainability of forest trees in the coming decades will depend on how extreme climatic events will change, irrespective of the overall warming trend.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-24T00:50:30.925633-05:
      DOI: 10.1111/gcb.13973
       
  • Soil pH as the chief modifier for regional nitrous oxide emissions: New
           evidence and implications for global estimates and mitigation
    • Authors: Yajing Wang; Jingheng Guo, Rolf David Vogt, Jan Mulder, Jingguo Wang, Xiaoshan Zhang
      Abstract: Nitrous oxide (N2O) is a greenhouse gas that also plays the primary role in stratospheric ozone depletion. The use of nitrogen fertilizers is known as the major reason for atmospheric N2O increase. Empirical bottom‐up models therefore estimate agricultural N2O inventories using N loading as the sole predictor, disregarding the regional heterogeneities in soil inherent response to external N loading. Several environmental factors have been found to influence the response in soil N2O emission to N fertilization, but their interdependence and relative importance have not been addressed properly. Here, we show that soil pH is the chief factor explaining regional disparities in N2O emission, using a global meta‐analysis of 1,104 field measurements. The emission factor (EF) of N2O increases significantly (p 
      PubDate: 2017-11-24T00:46:00.68563-05:0
      DOI: 10.1111/gcb.13966
       
  • Fire effects and ecological recovery pathways of Tropical Montane Cloud
           Forests along a time chronosequence
    • Authors: Imma Oliveras; Rosa M. Román-Cuesta, Erickson Urquiaga-Flores, Jose A. Quintano Loayza, Jose Kala, Vicky Huamán, Nohemi Lizárraga, Guissela Sans, Katia Quispe, Efrain Lopez, David Lopez, Israel Cuba Torres, Brian J. Enquist, Yadvinder Malhi
      Abstract: Tropical montane cloud forests (TMCFs) harbour high levels of biodiversity and large carbon stocks. Their location at high elevations make them especially sensitive to climate change, because a warming climate is enhancing upslope species migration, but human disturbance (especially fire) may in many cases be pushing the treeline downslope. TMCFs are increasingly being affected by fire, and the long‐term effects of fire are still unknown. Here we present a 28‐years chronosequence to assess the effects of fire and recovery pathways of burned TMCFs, with a detailed analysis of carbon stocks, forest structure and diversity. We assessed rates of change of carbon (C) stock pools, forest structure, and tree size distribution pathways and tested several hypotheses regarding metabolic scaling theory (MST), C recovery and biodiversity. We found four different C stock recovery pathways depending on the selected C pool and time since last fire, with a recovery of total C stocks but not of aboveground C stocks. In terms of forest structure, there was an increase in the number of small stems in the burned forests up to 5‐9 years after fire because of regeneration patterns, but no differences on larger trees between burned and unburned plots in the long term. In support of MST, after fire, forest structure appears to approximate steady state size distribution in less than 30 years. However, our results also provide new evidence that the species recovery of TMCF after fire is idiosyncratic and follows multiple pathways. While fire increased species richness it also enhanced species dissimilarity with geographical distance. This is the first study to report a long‐term chronosequence of recovery pathways to fire suggesting faster recovery rates than previously reported, but at the expense of biodiversity and aboveground C stocks.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-24T00:40:38.830964-05:
      DOI: 10.1111/gcb.13951
       
  • Diversification in tropics and subtropics following the mid‐Miocene
           climate change: a case study of the spider genus Nesticella
    • Authors: Francesco Ballarin; Shuqiang Li
      Abstract: Caves may offer suitable refugia for troglophilic invertebrates during periods of unfavourable climatic conditions because of their stable microclimates. As a consequence, allopatric divergence from their epigean counterparts may occur, leading to formation of truly hypogean communities (the Climatic Relict Hypothesis). Unlike the well‐studied effects of Pleistocene glaciations, we know little about how ancient climate changes drove the development of cave‐dwelling organisms living at both middle and lower latitudes. We investigate the evolutionary history of the troglophilic spider genus Nesticella (Araneae, Nesticidae) in relation to Asian Neogene (23–2.6 Ma) climatic changes. Our analyses discern clear differences in the evolution of the two main clades of Nesticella, which occur in temperate/subtropical and tropical latitudes. Eastern Asian Nesticella gradually evolved greater sedentariness and a strict subterranean lifestyle starting from the middle Miocene Epoch (~15–14 Ma) in conjunction with the progressive deterioration of the climate and vegetational shifts. Caves appear to have acted as refugia because of their internally uniform temperature and humidity, which allowed these spiders to survive increasing external seasonality and habitat loss. In contrast, a uniform accumulation of lineages, long‐lasting times for dispersals and the lack of a comparable habitat shifting characterised the tropical lineage. This difference in pattern likely owes to the mild effects of climate change at low latitudes and the consequent lack of strong climatic drivers in tropical environments. Thus, the mid‐Miocene climatic shift appears to be the major evolutionary force shaping the ecological differences between Asian troglophilic invertebrates and the driver of the permanent hypogean communities in middle latitudes.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-24T00:36:05.277313-05:
      DOI: 10.1111/gcb.13958
       
  • Will Fluctuations in Salt Marsh ‐ Mangrove Dominance Alter Vulnerability
           of a Subtropical Wetland to Sea‐Level Rise'
    • Authors: Karen L. McKee; William C. Vervaeke
      Abstract: To avoid submergence during sea‐level rise, coastal wetlands build soil surfaces vertically through accumulation of inorganic sediment and organic matter. At climatic boundaries where mangroves are expanding and replacing salt marsh, wetland capacity to respond to sea‐level rise may change. To compare how well mangroves and salt marshes accommodate sea‐level rise, we conducted a manipulative field experiment in a subtropical plant community in the subsiding Mississippi River Delta. Experimental plots were established in spatially equivalent positions along creek banks in monospecific stands of Spartina alterniflora (smooth cordgrass) or Avicennia germinans (black mangrove) and in mixed stands containing both species. To examine the effect of disturbance on elevation dynamics, vegetation in half of the plots was subjected to freezing (mangrove) or wrack burial (salt marsh), which caused shoot mortality. Vertical soil development was monitored for six years with the surface elevation table‐marker horizon system. Comparison of land movement with relative sea‐level rise showed that this plant community was experiencing an elevation deficit (i.e., sea level was rising faster than the wetland was building vertically) and was relying on elevation capital (i.e., relative position in the tidal frame) to survive. Although Avicennia plots had more elevation capital, suggesting longer survival, than Spartina or mixed plots, vegetation type had no effect on rates of accretion, vertical movement in root and sub‐root zones, or net elevation change. Thus, these salt marsh and mangrove assemblages were accreting sediment and building vertically at equivalent rates. Small‐scale disturbance of the plant canopy also had no effect on elevation trajectories— contrary to work in peat‐forming wetlands showing elevation responses to changes in plant productivity. The findings indicate that in this deltaic setting with strong physical influences controlling elevation (sediment accretion, subsidence), mangrove replacement of salt marsh, with or without disturbance, will not necessarily alter vulnerability to sea‐level rise.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-23T01:49:22.413066-05:
      DOI: 10.1111/gcb.13945
       
  • Temperature and soil fertility as regulators of tree line Scots pine
           growth and survival – implications for the acclimation capacity of
           northern populations
    • Authors: Matti Rousi; Boy J. M. H. Possen, Seppo Ruotsalainen, Tarja Silfver, Juha Mikola
      Abstract: The acclimation capacity of leading‐edge tree populations is crucially important in a warming climate. Theoretical considerations suggest that adaptation through genetic change is needed, but this may be a slow process. Both positive and catastrophic outcomes have been predicted, while empirical studies have lagged behind theory development. Here we present results of a 30‐year study of 55 000 Scots pine (Pinus sylvestris) trees, planted in 15 common gardens in three consecutive years near and beyond the present Scots pine tree line. Our results show that, contrary to earlier predictions, even long‐distance transfers to the North can be successful when soil fertility is high. This suggests that present northern populations have a very high acclimation capacity. We also found that while temperature largely controls Scots pine growth, soil nutrient availability plays an important role ‐in concert with interpopulation genetic variation‐ in Scots pine survival and fitness in tree line conditions. These results suggest that rapid range expansions and substantial growth enhancements of Scots pine are possible in fertile sites as seed production and soil nutrient mineralization are both known to increase under a warming climate. Finally, as the ontogenetic pattern of tree mortality was highly site‐specific and unpredictable, our results emphasize the need for long‐term field trials when searching for the factors that control fitness of trees in the variable edaphic and climatic conditions of the far North.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-23T01:45:34.264664-05:
      DOI: 10.1111/gcb.13956
       
  • A review of urban impacts on avian life‐history evolution: Does city
           living lead to slower pace of life'
    • Authors: Tuul Sepp; Kevin J. McGraw, Ants Kaasik, Mathieu Giraudeau
      Abstract: The concept of a pace‐of‐life syndrome describes inter‐ and intraspecific variation in several life‐history traits along a slow‐to‐fast pace‐of‐life continuum, with long lifespans, low reproductive and metabolic rates, and elevated somatic defences at the slow end of the continuum and the opposite traits at the fast end. Pace‐of‐life can vary in relation to local environmental conditions (e.g. latitude, altitude), and here we propose that this variation may also occur along an anthropogenically modified environmental gradient. Based on a body of literature supporting the idea that city birds have longer lifespans, we predict that urban birds have a slower pace‐of‐life compared to rural birds and thus invest more in self maintenance and less in annual reproduction. Our statistical meta‐analysis of two key traits related to pace‐of‐life, survival and breeding investment (clutch size), indicated that urban birds generally have higher survival, but smaller clutch sizes. The latter finding (smaller clutches in urban habitats) seemed to be mainly a characteristic of smaller passerines. We also reviewed urbanization studies on other traits that can be associated with pace‐of‐life and are related to either reproductive investment or self‐maintenance. Though sample sizes were generally too small to conduct formal meta‐analyses, published literature suggests that urban birds tend to produce lower‐quality sexual signals and invest more in offspring care. The latter finding is in agreement with the adult survival hypothesis, proposing that higher adult survival prospects favour investment in fewer offspring per year. According to our hypothesis, differences in age structure should arise between urban and rural populations, providing a novel alternative explanation for physiological differences and earlier breeding. We encourage more research investigating how telomere dynamics, immune defences, antioxidants and oxidative damage in different tissues vary along the urbanization gradient, and suggest that applying pace‐of‐life framework to studies of variation in physiological traits along the urbanization gradient might be the next direction to improve our understanding of urbanization as an evolutionary process.The concept of a pace‐of‐life syndrome describes inter‐ and intraspecific variation in several life‐history traits along a slow‐to‐fast pace‐of‐life continuum. Based on a body of literature supporting the idea that city birds have longer lifespans, we predicted that urban birds have a slower pace‐of‐life compared to rural birds of the same species, and thus invest more in self maintenance and less in annual reproduction. This hypothesis was supported by a meta‐analysis on survival and clutch size. We also reviewed urbanization studies on other traits that can be associated with pace‐of‐life and are related to either reproductive investment or self‐maintenance. Published literature suggests that urban birds tend to produce lower‐quality sexual signals and invest more in offspring care, findings that can also be understood in the framework of slower pace‐of‐life.
      PubDate: 2017-11-23T01:40:46.221395-05:
      DOI: 10.1111/gcb.13969
       
  • Non‐linearities in bird responses across urbanisation gradients: a
           meta‐analysis
    • Authors: Péter Batáry; Kornélia Kurucz, Marcela Suarez-Rubio, Dan E. Chamberlain
      Abstract: Urbanisation is one of the most extreme forms of environmental alteration, posing a major threat to biodiversity. We studied the effects of urbanisation on avian communities via a systematic review using hierarchical and categorical meta‐analyses. Altogether, we found 42 observations from 37 case studies for species richness and 23 observations from 20 case studies for abundance. Urbanisation had an overall strong negative effect on bird species richness, whereas abundance increased marginally with urbanisation. There was no evidence that city size played a role in influencing the relationship between urbanisation and either species richness or abundance. Studies that examined long gradients (i.e. from urban to rural) were more likely to detect negative urbanisation effects on species richness than studies that considered short gradients (i.e. urban vs. suburban or urban vs. rural areas). In contrast, we found little evidence that the effect of urbanisation on abundance was influenced by gradient length. Effects of urbanization on species richness were more negative for studies including public green spaces (parks and other amenity areas) in the sampled landscapes. In contrast, studies performed solely in the urban matrix (i.e., no green spaces) revealed a strong positive effect on bird abundance. When performing subset analyses on urban‐suburban, suburban‐rural and suburban‐natural comparisons, species richness decreased from natural to urban areas, but with a stronger decrease at the urban–suburban interface, whereas bird abundance showed a clear intermediate peak along the urban‐rural gradient, although abundance in natural areas was comparable to that in suburban areas. This suggests that species loss happens especially at the urban‐suburban interface, and that the highest abundances occur in suburban areas compared to urban or rural areas. Thus, our study shows the importance of suburban areas, where the majority of birds occur with fairly high species richness.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-23T01:40:39.324564-05:
      DOI: 10.1111/gcb.13964
       
  • Climate Change Impacts on Selected Global Rangeland Ecosystem Services
    • Authors: Randall B. Boone; Richard T. Conant, Jason Sircely, Philip K. Thornton, Mario Herrero
      Abstract: Rangelands are Earth's dominant land cover and are important providers of ecosystem services. Reliance on rangelands is projected to grow, thus understanding the sensitivity of rangelands to future climates is essential. We used a new ecosystem model of moderate complexity that allows, for the first time, to quantify global changes expected in rangelands under future climates. The mean global annual net primary production (NPP) may decline by 10 g C m−2 yr−1 in 2050 under Representative Concentration Pathway (RCP) 8.5, but herbaceous NPP is projected to increase slightly (i.e., average of 3 g C m−2 yr−1). Responses vary substantially from place‐to‐place, with large increases in annual productivity projected in northern regions (e.g., a 21% increase in productivity in the US and Canada) and large declines in western Africa (‐46% in sub‐Saharan western Africa) and Australia (‐17%). Soil organic carbon is projected to increase in Australia (9%), the Middle East (14%) and central Asia (16%), and decline in many African savannas (e.g., ‐18% in sub‐Saharan western Africa). Livestock are projected to decline 7.5 to 9.6%, an economic loss of from $9.7 to $12.6 billion. Our results suggest that forage production in Africa is sensitive to changes in climate, which will have substantial impacts on the livelihoods of the more than 180 million people who raise livestock on those rangelands. Our approach and the simulation tool presented here offer considerable potential for forecasting future conditions, highlight regions of concern, and support analyses where costs and benefits of adaptations and policies may be quantified. Otherwise, the technical options and policy and enabling environment that are needed to facilitate widespread adaptation may be very difficult to elucidate.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-21T11:25:20.243385-05:
      DOI: 10.1111/gcb.13995
       
  • Toward ecologically realistic predictions of species distributions: a
           cross‐time example from tropical montane cloud forests
    • Authors: Lázaro Guevara; Beth E. Gerstner, Jamie M. Kass, Robert P. Anderson
      Abstract: There is an urgent need for more ecologically realistic models for better predicting the effects of climate change on species’ potential geographic distributions. Here we build ecological niche models using MAXENT and test whether selecting predictor variables based on biological knowledge and selecting ecologically realistic response curves can improve cross‐time distributional predictions. We also evaluate how the method chosen for extrapolation into nonanalog conditions affects the prediction. We do so by estimating the potential distribution of a montane shrew (Mammalia, Soricidae, Cryptotis mexicanus) at present and the Last Glacial Maximum (LGM). Because it is tightly associated with cloud forests (with climatically determined upper and lower limits) whose distributional shifts are well characterized, this species provides clear expectations of plausible vs. implausible results. Response curves for the MAXENT model made using variables selected via biological justification were ecologically more realistic compared with those of the model made using many potential predictors. This strategy also led to a much more plausible geographic predictions for upper and lower elevational limits of the species both for the present and during the LGM. By inspecting the modeled response curves, we also determined the most appropriate way to extrapolate into nonanalog environments, a previously overlooked factor in studies involving model transfer. This study provides intuitive context for recommendations that should promote more realistic ecological niche models for transfer across space and time.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-20T12:40:21.563615-05:
      DOI: 10.1111/gcb.13992
       
  • Climate‐mediated changes in marine ecosystem regulation during El
           Niño
    • Authors: Martin Lindegren; David M. Checkley, J. Anthony Koslow, Ralf Goericke, Mark D. Ohman
      Abstract: The degree to which ecosystems are regulated through bottom‐up, top‐down or direct physical processes represents a long‐standing issue in ecology, with important consequences for resource management and conservation. In marine ecosystems, the role of bottom‐up and top‐down forcing has been shown to vary over spatio‐temporal scales, often linked to highly variable and heterogeneously distributed environmental conditions. Ecosystem dynamics in the Northeast Pacific have been suggested to be predominately bottom‐up regulated. However, it remains unknown to what extent top‐down regulation occurs, or whether the relative importance of bottom‐up and top‐down forcing may shift in response to climate change. In this study, we investigate the effects and relative importance of bottom‐up, top‐down and physical forcing during changing climate conditions on ecosystem regulation in the Southern California Current System (SCCS) using a generalized food web model. This statistical approach is based on non‐linear threshold models and a long‐term data set (~60 year) covering multiple trophic levels from phytoplankton to predatory fish. We found bottom‐up control to be the primary mode of ecosystem regulation. However, our results also demonstrate an alternative mode of regulation represented by interacting bottom‐up and top‐down forcing, analogous to wasp‐waist dynamics, but occurring across multiple trophic levels and only during periods of reduced bottom‐up forcing (i.e., weak upwelling, low nutrient concentrations and primary production). The shifts in ecosystem regulation are caused by changes in ocean‐atmosphere forcing and triggered by highly variable climate conditions associated with El Niño. Furthermore, we show that biota respond differently to major El Niño events during positive or negative phases of the Pacific Decadal Oscillation (PDO), as well as highlight potential concerns for marine and fisheries management by demonstrating increased sensitivity of pelagic fish to exploitation during El Niño.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-20T12:40:19.659154-05:
      DOI: 10.1111/gcb.13993
       
  • Multifarious anchovy and sardine regimes in the Humboldt Current System
           during the last 150 years
    • Authors: Renato Salvatteci; David Field, Dimitri Gutierrez, Tim Baumgartner, Vicente Ferreira, Luc Ortlieb, Abdel Sifeddine, Daniel Grados, Arnaud Bertrand
      Abstract: The Humboldt Current System (HCS) has the highest production of forage fish in the world, though it is highly variable and the future of the primary component, anchovy, is uncertain in the context of global warming. Paradigms based on late 20th century observations suggest that large‐scale forcing controls decadal‐scale fluctuations of anchovy and sardine across different boundary currents of the Pacific. We develop records of anchovy and sardine fluctuations since 1860 AD using fish scales from multiple sites containing laminated sediments and compare them with Pacific basin‐scale and regional indices of ocean‐climate variability. Our records reveal two main anchovy and sardine phases with a timescale that is not consistent with previously proposed periodicities. Rather, the regime shifts in the HCS are related to 3D habitat changes driven by changes in upwelling intensity from both regional and large‐scale forcing. Moreover, we show that a long‐term increase in coastal upwelling translates via a bottom‐up mechanism to top predators suggesting that the warming climate, at least up to the start of the 21st century, was favourable for fishery productivity in the HCS.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-20T12:35:20.719825-05:
      DOI: 10.1111/gcb.13991
       
  • Both life history plasticity and local adaptation will shape range‐wide
           responses to climate warming in the tundra plant Silene acaulis
    • Authors: Megan L. Peterson; Daniel F. Doak, William F. Morris
      Abstract: Many predictions of how climate change will impact biodiversity have focused on range shifts using species‐wide climate tolerances, an approach that ignores the demographic mechanisms that enable species to attain broad geographic distributions. But these mechanisms matter, as responses to climate change could fundamentally differ depending on the contributions of life history plasticity vs local adaptation to species‐wide climate tolerances. In particular, if local adaptation to climate is strong, populations across a species’ range – not only those at the trailing range edge ‐ could decline sharply with global climate change. Indeed, faster rates of climate change in many high latitude regions could combine with local adaptation to generate sharper declines well away from trailing edges. Combining 15 years of demographic data from field populations across North America with growth chamber warming experiments, we show that growth and survival in a widespread tundra plant show compensatory responses to warming throughout the species’ latitudinal range, buffering overall performance across a range of temperatures. However, populations also differ in their temperature responses, consistent with adaptation to local climate, especially growing season temperature. In particular, warming begins to negatively impact plant growth at cooler temperatures for plants from colder, northern populations than for those from warmer, southern populations, both in the field and in growth chambers. Further, the individuals and maternal families with the fastest growth also have the lowest water use efficiency at all temperatures, suggesting that a trade‐off between growth and water use efficiency could further constrain responses to forecasted warming and drying. Taken together, these results suggest that populations throughout species’ ranges could be at risk of decline with continued climate change, and that the focus on trailing edge populations risks overlooking the largest potential impacts of climate change on species’ abundance and distribution.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-20T11:00:56.370276-05:
      DOI: 10.1111/gcb.13990
       
  • Antarctic emerald rockcod have the capacity to compensate for warming when
           uncoupled from CO2‐acidification
    • Authors: Brittany E. Davis; Erin E. Flynn, Nathan A. Miller, Frederick A. Nelson, Nann A. Fangue, Anne E. Todgham
      Abstract: Increases in atmospheric CO2 levels and associated ocean changes are expected to have dramatic impacts on marine ecosystems. Although the Southern Ocean is experiencing some of the fastest rates of change, few studies have explored how Antarctic fishes may be affected by co‐occurring ocean changes, and even fewer have examined early life stages. To date, no studies have characterized potential trade‐offs in physiology and behavior in response to projected multiple climate change stressors (ocean acidification and warming) on Antarctic fishes. We exposed juvenile emerald rockcod Trematomus bernacchii to three PCO2 treatments (~450, ~850 and ~1200 μatm PCO2) at two temperatures (‐1º or 2°C). After 2, 7, 14, and 28 days, metrics of physiological performance including cardiorespiratory function (heart rate [fH] and ventilation rate [fV]), metabolic rate (ṀO2), and cellular enzyme activity were measured. Behavioral responses, including scototaxis, activity, exploration and escape response were assessed after 7 and 14 days. Elevated PCO2 independently had little impact on either physiology or behavior in juvenile rockcod, whereas warming resulted in significant changes across acclimation time. After 14 days, fH, fV and ṀO2 significantly increased with warming, but not with elevated PCO2. Increased physiological costs were accompanied by behavioral alterations including increased dark zone preference up to 14%, reduced activity by 12%, as well as reduced escape time suggesting potential trade‐offs in energetics. After 28 days, juvenile rockcod demonstrated a degree of temperature compensation as fV, ṀO2, and cellular metabolism significantly decreased following the peak at 14 days; however, temperature compensation was only evident in the absence of elevated PCO2. Sustained increases in fV and ṀO2 after 28 days exposure to elevated PCO2 indicate additive (fV) and synergistic (ṀO2) interactions occurred in combination with warming. Stressor‐induced energetic trade‐offs in physiology and behavior may be an important mechanism leading to vulnerability of Antarctic fishes to future ocean change.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-20T10:55:28.253471-05:
      DOI: 10.1111/gcb.13987
       
  • The sensitivity of breeding songbirds to changes in seasonal timing is
           linked to population change but cannot be directly attributed to the
           effects of trophic asynchrony on productivity
    • Authors: Samantha E. Franks; James W. Pearce-Higgins, Sian Atkinson, James R. Bell, Marc S. Botham, Tom M. Brereton, Richard Harrington, David I. Leech
      Abstract: A consequence of climate change has been an advance in the timing of seasonal events. Differences in the rate of advance between trophic levels may result in predators becoming mismatched with prey availability, reducing fitness and potentially driving population declines. Such “trophic asynchrony” is hypothesized to have contributed to recent population declines of long‐distance migratory birds in particular. Using spatially extensive survey data from 1983 to 2010 to estimate variation in spring phenology from 280 plant and insect species and the egg‐laying phenology of 21 British songbird species, we explored the effects of trophic asynchrony on avian population trends and potential underlying demographic mechanisms. Species which advanced their laying dates least over the last three decades, and were therefore at greatest risk of asynchrony, exhibited the most negative population trends. We expressed asynchrony as the annual variation in bird phenology relative to spring phenology, and related asynchrony to annual avian productivity. In warmer springs, birds were more asynchronous, but productivity was only marginally reduced; long‐distance migrants, short‐distance migrants and resident bird species all exhibited effects of similar magnitude. Long‐term population, but not productivity, declines were greatest among those species whose annual productivity was most greatly reduced by asynchrony. This suggests that population change is not mechanistically driven by the negative effects of asynchrony on productivity. The apparent effects of asynchrony on population trends are therefore either more likely to be strongly expressed via other demographic pathways, or alternatively, are a surrogate for species' sensitivity to other environmental pressures which are the ultimate cause of decline.We use spatially extensive survey data of plants, invertebrates and birds to investigate whether asynchronous changes in egg‐laying dates relative to spring onset are associated with reduced avian productivity and consequently population change. Bird species which have advanced egg‐laying dates the least are declining fastest. In warmer springs, birds breed late relative to spring onset and productivity is reduced. Although species whose productivity is reduced the most are declining fastest, the mechanism cannot be directly attributed to the effects of asynchrony on productivity.
      PubDate: 2017-11-20T04:00:01.343911-05:
      DOI: 10.1111/gcb.13960
       
  • How complex should models be' Comparing correlative and mechanistic
           range dynamics models
    • Authors: Damien A. Fordham; Cleo Bertelsmeier, Barry W. Brook, Regan Early, Dora Neto, Stuart C. Brown, Sébastien Ollier, Miguel B. Araújo
      Abstract: Criticism has been levelled at climate‐change‐induced forecasts of species range shifts that do not account explicitly for complex population dynamics. The relative importance of such dynamics under climate change is, however, undetermined because direct tests comparing the performance of demographic models vs. simpler ecological niche models are still lacking owing to difficulties in evaluating forecasts using real‐world data. We provide the first comparison of the skill of coupled ecological‐niche‐population models and ecological niche models in predicting documented shifts in the ranges of 20 British breeding bird species across a 40‐year period. Forecasts from models calibrated with data centred on 1970 were evaluated using data centred on 2010. We found that more complex coupled ecological‐niche‐population models (that account for dispersal and metapopulation dynamics) tend to have higher predictive accuracy in forecasting species range shifts than structurally simpler models that only account for variation in climate. However, these better forecasts are achieved only if ecological responses to climate change are simulated without static snapshots of historic land use, taken at a single point in time. In contrast, including both static land use and dynamic climate variables in simpler ecological niche models improve forecasts of observed range shifts. Despite being less skilful at predicting range changes at the grid‐cell level, ecological niche models do as well, or better, than more complex models at predicting the magnitude of relative change in range size. Therefore, ecological niche models can provide a reasonable first approximation of the magnitude of species' potential range shifts, especially when more detailed data are lacking on dispersal dynamics, demographic processes underpinning population performance, and change in land cover.We compare for the first time the skill of demographic models vs. simpler ecological niche models in predicting documented shifts in the ranges of 20 British breeding bird species across a 40‐year period of observed climate change. We show that more complex demographic models, which account for dispersal and metapopulation dynamics, tend to have higher predictive accuracy in forecasting observed species range shifts than structurally simpler models that only account for variation in climate. However, simpler ecological niche models do as well, or better, than more complex models at predicting the magnitude of relative change in range size.
      PubDate: 2017-11-20T00:30:02.483536-05:
      DOI: 10.1111/gcb.13935
       
  • Vegetation cover ‐ another dominant factor in determining global water
           resources in forested regions
    • Authors: Xiaohua Wei; Qiang Li, Mingfang Zhang, Krysta Giles-Hansen, Wenfei Liu, Houbao Fan, Yi Wang, Guoyi Zhou, Shilong Piao, Shirong Liu
      Abstract: Forested catchments provide critically important water resources. Due to dramatic global forest change over the past decades, the importance of including forest or vegetation change in the assessment of water resources under climate change has been highly recognized by Intergovernmental Panel on Climate Change (IPCC); however, this importance has not yet been examined quantitatively across the globe. Here, we used four remote sensing‐based indices to represent changes in vegetation cover in forest dominated regions, and then applied them to widely‐used models: the Fuh model and the Choudhury‐Yang model to assess relative contributions of vegetation and climate changes to annual runoff variations from 2000 to 2011 in forested landscape (forest coverage > 30%) across the globe. Our simulations show that the global average variation in annual runoff due to change in vegetation cover is 30.7 ± 22.5% with the rest attributed to climate change. Large annual runoff variation in response to vegetation change are found in tropical and boreal forests due to greater forest losses. Our simulations also demonstrate both offsetting and additive effects of vegetation cover and climate in determining water resource change. We conclude that vegetation cover change must be included in any global models for assessing global water resource change under climate change in forest‐dominant areas.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-15T09:45:25.513302-05:
      DOI: 10.1111/gcb.13983
       
  • Annual Global Mean Temperature explains reproductive success in a marine
           vertebrate from 1955‐2010
    • Authors: Robert A. Mauck; Donald C. Dearborn, Charles E. Huntington
      Abstract: The salient feature of anthropogenic climate change over the last century has been the rise in global mean temperature. However, global mean temperature is not used as an explanatory variable in studies of population‐level response to climate change, perhaps because the signal to noise ratio of this gross measure makes its effect difficult to detect in any but the longest of datasets. Using a population of Leach's storm‐petrels breeding in the Bay of Fundy, we tested whether local, regional, or global temperature measures are the best index of reproductive success in the face of climate change in species that travel widely between and within seasons. With a 56‐year dataset, we found that Annual Global Mean Temperature (AGMT) was the single most important predictor of hatching success, more so than regional sea surface temperatures (breeding season or winter) and local air temperatures at the nesting colony. Storm‐petrel reproductive success showed a quadratic response to rising temperatures, in that hatching success increased up to some critical temperature, then declined when AGMT exceeded that temperature. The year at which AGMT began to consistently exceed that critical temperature was 1988. Importantly, in this population of known‐age individuals, the impact of changing climate was greatest on inexperienced breeders: reproductive success of inexperienced birds increased more rapidly as temperatures rose and declined more rapidly after the tipping point than did reproductive success of experienced individuals. The generality of our finding that AGMT is the best predictor of reproductive success in this system may hinge on two things. First, an integrative global measure may be best for species in which individuals move across an enormous spatial range, especially within seasons. Second, the length of our dataset and our capacity to account for individual‐ and age‐based variation in reproductive success increase our ability to detect a noisy signal.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-15T09:40:29.205204-05:
      DOI: 10.1111/gcb.13982
       
  • Rapid evolution of phenology during range expansion with recent climate
           change
    • Authors: Nicky Lustenhouwer; Rutger A. Wilschut, Jennifer L. Williams, Wim H. Putten, Jonathan M. Levine
      Abstract: Although climate warming is expected to make habitat beyond species’ current cold range edge suitable for future colonization, this new habitat may present an array of biotic or abiotic conditions not experienced within the current range. Species’ ability to shift their range with climate change may therefore depend on how populations evolve in response to such novel environmental conditions. However, due to the recent nature of thus far observed range expansions, the role of rapid adaptation during climate change migration is only beginning to be understood. Here, we evaluated evolution during the recent native range expansion of the annual plant Dittrichia graveolens, which is spreading northward in Europe from the Mediterranean region. We examined genetically based differentiation between core and edge populations in their phenology, a trait that is likely under selection with shorter growing seasons and greater seasonality at northern latitudes. In parallel common garden experiments at range edges in Switzerland and the Netherlands, we grew plants from Dutch, Swiss, and central and southern French populations. Population genetic analysis following RAD‐sequencing of these populations supported the hypothesized central France origins of the Swiss and Dutch range edge populations. We found that in both common gardens, northern plants flowered up to four weeks earlier than southern plants. This differentiation in phenology extended from the core of the range to the Netherlands, a region only reached from central France over approximately the last 50 years. Fitness decreased as plants flowered later, supporting the hypothesized benefits of earlier flowering at the range edge. Our results suggest that native range expanding populations can rapidly adapt to novel environmental conditions in the expanded range, potentially promoting their ability to spread.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-15T07:16:33.489673-05:
      DOI: 10.1111/gcb.13947
       
  • Differential declines in Alaskan boreal forest vitality related to climate
           and competition
    • Authors: Anna T. Trugman; David Medvigy, William R. L. Anderegg, Stephen W. Pacala
      Abstract: Rapid warming and changes in water availability at high latitudes alter resource abundance, tree competition, and disturbance regimes. While these changes are expected to disrupt the functioning of boreal forests, their ultimate implications for forest composition are uncertain. In particular, recent site‐level studies of the Alaskan boreal forest have reported both increases and decreases in productivity over the past few decades. Here, we test the idea that variations in Alaskan forest growth and mortality rates are contingent on species composition. Using forest inventory measurements and climate data from plots located throughout interior and south‐central Alaska, we show significant growth and mortality responses associated with competition, midsummer vapor pressure deficit, and increased growing season length. The governing climate and competition processes differed substantially across species. Surprisingly, the most dramatic climate response occurred in the drought tolerant angiosperm species, trembling aspen, and linked high midsummer vapor pressure deficits to decreased growth and increased insect‐related mortality. Given that species composition in the Alaskan and western Canadian boreal forests is projected to shift towards early‐successional angiosperm species due to fire regime, these results underscore the potential for a reduction in boreal productivity stemming from increases in midsummer evaporative demand.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-15T07:16:07.614115-05:
      DOI: 10.1111/gcb.13952
       
  • Increased water‐use efficiency translates into contrasting growth
           patterns of Scots pine and sessile oak at their southern distribution
           limits
    • Authors: Elisabet Martínez-Sancho; Isabel Dorado-Liñán, Emilia Gutiérrez Merino, Michael Matiu, Gerhard Helle, Ingo Heinrich, Annette Menzel
      Abstract: In forests, the increase of atmospheric CO2 concentrations (Ca) has been related to enhanced tree growth and intrinsic water‐use efficiency (iWUE). However, in drought‐prone areas such as the Mediterranean Basin it is not yet clear to what extent this ‘fertilizing’ effect may compensate for drought‐induced growth reduction. We investigated tree growth and physiological responses at five Scots pine (Pinus sylvestris L.) and five sessile oak (Quercus petraea (Matt.) Liebl.) sites located at their southernmost distribution limits in Europe for the period 1960‐2012 using annually resolved tree‐ring width and δ13C data to track ecophysiological processes. Results indicated that all ten natural stands significantly increased their leaf intercellular CO2 concentration (Ci), and consequently iWUE. Different trends in the theoretical gas exchange scenarios as a response to increasing Ca were found: generally, Ci tended to increase proportionally to Ca, except for trees at the driest sites in which Ci remained constant. Ci from the oak sites displaying higher water availability tended to increase at a comparable rate to Ca. Multiple linear models fitted at site level to predict basal area increment (BAI) using iWUE and climatic variables better explained tree growth in pines (31.9 ‐ 71.4%) than in oak stands (15.8 ‐ 46.8%). iWUE was negatively linked to pine growth whereas its effect on growth of oak differed across sites. Tree growth in the western and central oak stands was negatively related to iWUE, whereas BAI from the easternmost stand was positively associated with iWUE. Thus, some Q. petraea stands might have partially benefited from the ‘fertilizing’ effect of rising Ca, whereas P. sylvestris stands due to their strict closure of stomata did not profit from increased iWUE and consequently showed in general growth reductions across sites. Additionally, the inter‐annual variability of BAI and iWUE displayed a geographical polarity in the Mediterranean.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-15T07:15:45.164341-05:
      DOI: 10.1111/gcb.13937
       
  • Simulating the onset of spring vegetation growth across the Northern
           Hemisphere
    • Authors: Qiang Liu; Yongshuo H. Fu, Yongwen Liu, Ivan A. Janssens, Shilong Piao
      Abstract: Changes in the spring onset of vegetation growth in response to climate change can profoundly impact climate–biosphere interactions. Thus, robust simulation of spring onset is essential to accurately predict ecosystem responses and feedback to ongoing climate change. To date, the ability of vegetation phenology models to reproduce spatiotemporal patterns of spring onset at larger scales has not been thoroughly investigated. In this study, we took advantage of phenology observations via remote sensing to calibrate and evaluated six models, including both one‐phase (considering only forcing temperatures) and two‐phase (involving forcing, chilling, and photoperiod) models across the Northern Hemisphere between 1982 and 2012. Overall, we found that the model that integrated the photoperiod effect performed best at capturing spatiotemporal patterns of spring phenology in boreal and temperate forests. By contrast, all of the models performed poorly in simulating the onset of growth in grasslands. These results suggest that the photoperiod plays a role in controlling the onset of growth in most Northern Hemisphere forests, whereas other environmental factors (e.g., precipitation) should be considered when simulating the onset of growth in grasslands. We also found that the one‐phase model performed as well as the two‐phase models in boreal forests, which implies that the chilling requirement is probably fulfilled across most of the boreal zone. Conversely, two‐phase models performed better in temperate forests than the one‐phase model, suggesting that photoperiod and chilling play important roles in these temperate forests. Our results highlight the significance of including chilling and photoperiod effects in models of the spring onset of forest growth at large scales, and indicate that the consideration of additional drivers may be required for grasslands.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-15T07:06:06.660624-05:
      DOI: 10.1111/gcb.13954
       
  • Quantitative losses vs. qualitative stability of ectomycorrhizal community
           responses to 3 years of experimental summer drought in a beech‐spruce
           forest
    • Authors: Uwe T. Nickel; Fabian Weikl, René Kerner, Cynthia Schäfer, Christian Kallenbach, Jean C. Munch, Karin Pritsch
      Abstract: Forest ecosystems in central Europe are predicted to face an increasing frequency and severity of summer droughts because of global climate change. European beech and Norway spruce often coexist in these forests with mostly positive effects on their growth. However, their different below‐ground responses to drought may lead to differences in ectomycorrhizal (ECM) fungal community composition and functions which we examined at the individual root and ecosystem levels. We installed retractable roofs over plots in Kranzberg Forest (11°39′42″E, 48°25′12″N; 490 m a.s.l.) to impose repeated summer drought conditions and assigned zones within each plot where trees neighboured the same or different species to study mixed species effects. We found that ECM fungal community composition changed and the numbers of vital mycorrhizae decreased for both tree species over 3 drought years (2014–2016), with the ECM fungal community diversity of beech exhibiting a faster and of spruce a stronger decline. Mixed stands had a positive effect on the ECM fungal community diversity of both tree species after the third drought year. Ectomycorrhizae with long rhizomorphs increased in both species under drought, indicating long‐distance water transport. However, there was a progressive decline in the number of vital fine roots during the experiment, resulting in a strong reduction in enzyme activity per unit volume of soil. Hydrolytic enzyme activities of the surviving ectomycorrhizae were stable or stimulated upon drought, but there was a large decline in ECM fungal species with laccase activity, indicating a decreased potential to exploit nutrients bound to phenolic compounds. Thus, the ectomycorrhizae responded to repeated drought by maintaining or increasing their functionality at the individual root level, but were unable to compensate for quantitative losses at the ecosystem level. These findings demonstrate a strong below‐ground impact of recurrent drought events in forests.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-15T07:05:41.655585-05:
      DOI: 10.1111/gcb.13957
       
  • Global Climate Change Increases Risk of Crop Yield Losses and Food
           Insecurity in the Tropical Andes
    • Authors: Richard Tito; Heraldo L. Vasconcelos, Kenneth J. Feeley
      Abstract: One of the greatest current challenges to human society is ensuring adequate food production and security for a rapidly growing population under changing climatic conditions. Climate change, and specifically rising temperatures, will alter the suitability of areas for specific crops and cultivation systems. In order to maintain yields, farmers may be forced to change cultivation practices, the timing of cultivation, or even the type of crops grown. Alternatively, farmers can change the location where crops are cultivated (e.g., to higher elevations) to track suitable climates (in which case the plants will have to grow in different soils), as cultivated plants will otherwise have to tolerate warmer temperatures and possibly face novel enemies. We simulated these two last possible scenarios (for temperature increases of 1.3 and 2.6°C) in the Peruvian Andes through a field experiment in which several traditionally‐grown varieties of potato and maize were planted at different elevations (and thus temperatures) using either the local soil or soil translocated from higher elevations. Maize production declined by 21‐29% in response to new soil conditions. The production of maize and potatoes declined by >87% when plants were grown under warmer temperatures, mainly as result of the greater incidence of novel pests. Crop quality and value also declined under simulated migration and warming scenarios. We estimated that local farmers may experience severe economic losses of up to 2300 US$ ha−1 yr−1. These findings reveal that climate change is a real and imminent threat to agriculture and that there is a pressing need to develop effective management strategies to reduce yield losses and prevent food insecurity. Importantly, such strategies should take into account the influences of non‐climatic and/or biotic factors (e.g., novel pests) on plant development.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-15T07:01:44.479436-05:
      DOI: 10.1111/gcb.13959
       
  • Patterns and drivers of fish extirpations in rivers of the American
           Southwest and Southeast
    • Authors: John S. Kominoski; Albert Ruhí, Megan M. Hagler, Kelly Petersen, John L. Sabo, Tushar Sinha, Arumugam Sankarasubramanian, Julian D. Olden
      Abstract: Effective conservation of freshwater biodiversity requires spatially explicit investigations of how dams and hydroclimatic alterations among climate regions may interact to drive species to extinction. We investigated how dams and hydroclimatic alterations interact with species ecological and life history traits to influence past extirpation probabilities of native freshwater fishes in the Upper and Lower Colorado River (CR), Alabama‐Coosa‐Tallapoosa (ACT), and Apalachicola‐Chattahoochee‐Flint (ACF) basins. Using long‐term discharge data for continuously gaged streams and rivers, we quantified streamflow anomalies (i.e., departure “expected” streamflow) at the sub‐basin scale over the past half‐century. Next, we related extirpation probabilities of native fishes in both regions to streamflow anomalies, river basin characteristics, species traits, and non‐native species richness using binomial logistic regression. Sub‐basin extirpations in the Southwest (n = 95 Upper CR, n = 130 Lower CR) were highest in lowland mainstem rivers impacted by large dams and in desert springs. Dampened flow seasonality, increased longevity (i.e., delayed reproduction), and decreased fish egg sizes (i.e., lower parental care) were related to elevated fish extirpation probability in the Southwest. Sub‐basin extirpations in the Southeast (ACT n = 46, ACF n = 22) were most prevalent in upland rivers, with flow dependency, greater age and length at maturity, isolation by dams, and greater distance upstream. Our results confirm that dams are an overriding driver of native fish species losses, irrespective of basin‐wide differences in native or non‐native species richness. Dams and hydrologic alterations interact with species traits to influence community disassembly, and very high extirpation risks in the Southeast are due to interactions between high dam density and species restricted ranges. Given global surges in dam building and retrofitting, increased extirpation risks should be expected unless management strategies that balance flow regulation with ecological outcomes are widely implemented.Effective conservation of freshwater biodiversity requires an understanding of how dams, climate, and hydrology differentially impact species. We studied long‐term changes in hydrology and fish species throughout rivers in the American Southwest and Southeast. Our results confirm that dams are an overriding driver of native fish species losses, irrespective of basin‐wide differences in native or non‐native species richness and climate‐driven changes in hydrology.
      PubDate: 2017-11-15T00:30:02.950513-05:
      DOI: 10.1111/gcb.13940
       
  • Increasing canopy photosynthesis in rice can be achieved without a large
           increase in water use–a model based on free‐air CO2 enrichment
    • Authors: Hiroki Ikawa; Charles P. Chen, Martin Sikma, Mayumi Yoshimoto, Hidemitsu Sakai, Takeshi Tokida, Yasuhiro Usui, Hirofumi Nakamura, Keisuke Ono, Atsushi Maruyama, Tsutomu Watanabe, Tsuneo Kuwagata, Toshihiro Hasegawa
      Abstract: Achieving higher canopy photosynthesis rates is one of the keys to increasing future crop production; however, this typically requires additional water inputs because of increased water loss through the stomata. Lowland rice canopies presently consume a large amount of water, and any further increase in water usage may significantly impact local water resources. This situation is further complicated by changing environmental conditions such as rising atmospheric CO2 concentration ([CO2]). Here we modeled and compared evapotranspiration of fully developed rice canopies of a high‐yielding rice cultivar (Oryza sativa L. cv. Takanari) with a common cultivar (cv. Koshihikari) under ambient and elevated [CO2] (A‐CO2 and E‐CO2, respectively) via leaf ecophysiological parameters derived from a free‐air CO2 enrichment (FACE) experiment. Takanari had 4–5% higher evapotranspiration than Koshihikari under both A‐CO2 and E‐CO2, and E‐CO2 decreased evapotranspiration of both varieties by 4–6%. Therefore, if Takanari was cultivated under future [CO2] conditions, the cost for water could be maintained at the same level as for cultivating Koshihikari at current [CO2] with an increase in canopy photosynthesis by 36%. Sensitivity analyses determined that stomatal conductance was a significant physiological factor responsible for the greater canopy photosynthesis in Takanari over Koshihikari. Takanari had 30–40% higher stomatal conductance than Koshihikari; however, the presence of high aerodynamic resistance in the natural field and lower canopy temperature of Takanari than Koshihikari resulted in the small difference in evapotranspiration. Despite the small difference in evapotranspiration between varieties, the model simulations showed that Takanari clearly decreased canopy and air temperatures within the planetary boundary layer compared to Koshihikari. Our results indicate that lowland rice varieties characterized by high stomatal conductance can play a key role in enhancing productivity and moderating heat‐induced damage to grain quality in the coming decades, without significantly increasing crop water use.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-14T12:10:40.667783-05:
      DOI: 10.1111/gcb.13981
       
  • Selection for life‐history traits to maximize population growth in
           an invasive marine species
    • Authors: Cornelia Jaspers; Lise Marty, Thomas Kiørboe
      Abstract: Species establishing outside their natural range, negatively impacting local ecosystems, are of increasing global concern. They often display life‐history features characteristic for r‐selected populations with fast growth and high reproduction rates to achieve positive population growth rates (r) in invaded habitats. Here, we demonstrate substantially earlier maturation at a 2 orders of magnitude lower body mass at first reproduction in invasive compared to native populations of the comb jelly Mnemiopsis leidyi. Empirical results are corroborated by a theoretical model for competing life‐history traits that predicts maturation at the smallest possible size to optimize r, while individual lifetime reproductive success (R0), optimized in native populations, is near constant over a large range of intermediate maturation sizes. We suggest that high variability in reproductive tactics in native populations is an underappreciated determinant of invasiveness, acting as substrate upon which selection can act during the invasion process.What characterizes potent source populations of invasive species and what is the role of evolutionary change for their subsequent proliferation' Life‐history modeling conducted for the marine invasive comb jelly Mnemiopsis leidyi predicts maturation at smallest possible size to optimize population growth. In accordance, we observe a two‐order of magnitude lower maturation size in invasive compared to native populations. We suggest that high variability in reproductive tactics in native populations is an underappreciated determinant of invasiveness, acting as a substrate upon which selection can act during the invasion process.
      PubDate: 2017-11-14T06:15:26.39167-05:0
      DOI: 10.1111/gcb.13955
       
  • Macromolecular Rate Theory (MMRT) Provides a Thermodynamics Rationale to
           Underpin the Convergent Temperature Response in Plant Leaf Respiration
    • Authors: Liyin L. Liang; Vickery L. Arcus, Mary A. Heskel, Odhran S. O'Sullivan, Lasantha K. Weerasinghe, Danielle Creek, John J. G. Egerton, Mark G. Tjoelker, Owen K. Atkin, Louis A. Schipper
      Abstract: Temperature is a crucial factor in determining the rates of ecosystem processes, e.g. leaf respiration (R) − the flux of plant respired CO2 from leaves to the atmosphere. Generally, R increases exponentially with temperature and formulations such as the Arrhenius equation are widely used in earth system models. However, experimental observations have shown a consequential and consistent departure from an exponential increase in R. What are the principles that underlie these observed patterns' Here, we demonstrate that macromolecular rate theory (MMRT), based on transition state theory for enzyme‐catalyzed kinetics, provides a thermodynamic explanation for the observed departure and the convergent temperature response of R using a global database. Three meaningful parameters emerge from MMRT analysis: the temperature at which the rate of respiration would theoretically reach a maximum (the optimum temperature, Topt), the temperature at which the respiration rate is most sensitive to changes in temperature (the inflection temperature, Tinf) and the overall curvature of the log(rate) versus temperature plot (the change in heat capacity for the system, ∆Cp‡). On average the highest potential enzyme‐catalyzed rates of respiratory enzymes for R is predicted to occur at 67.0±1.2 °C and the maximum temperature sensitivity at 41.4±0.7 °C from MMRT. The average curvature (average negative ∆Cp‡) was ‐1.2±0.1 kJ.mol‐1K‐1. Interestingly, Topt, Tinf and ∆Cp‡ appear insignificantly different across biomes and plant functional types (PFTs), suggesting that thermal response of respiratory enzymes in leaves could be conserved. The derived parameters from MMRT can serve as thermal traits for plant leaves that represents the collective temperature response of metabolic respiratory enzymes and could be useful to understand regulations of R under a warmer climate. MMRT extends the classic transition state theory to enzyme‐catalyzed reactions and provides an accurate and mechanistic model for the short‐term temperature response of R around the globe.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-14T01:05:36.194811-05:
      DOI: 10.1111/gcb.13936
       
  • The importance and requirement of belowground carbon inputs for robust
           estimation of soil organic carbon dynamics: Reply to Keel et al. (2017)
    • Authors: Zhongkui Luo; Enli Wang, Wenting Feng, Yiqi Luo, Jeff Baldock
      Abstract: In a recent paper, we assessed the legacy data reported by Skjemstad and Spouncer (2003) and found that the amount of aboveground carbon (C) input (i.e., crop residues) in Australian cropping systems was the most important factor affecting soil C change among all the assessed drivers including the quantity and quality of C inputs, climate and soil properties (Luo et al., 2017). Keel et al. (2017) argued that the C input data used in our study “may have led to important biases and critical omissions”, due to: 1) ignorance of belowground C inputs from roots/rhizodeposition, and 2) use of a constant harvest index (HI) for crops. They contended that “belowground C inputs can contribute as much as 90% to total carbon inputs in agroecosystems” by citing Kätterer et al. (2011) and Bolinder et al. (2007), and that C partitioning above‐ and below‐ground also responds to fertilization and management. For these reasons, Keel et al. (2017) concluded that our results on the driver importance may be biased.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-14T01:00:19.445629-05:
      DOI: 10.1111/gcb.13949
       
  • A decrease in the abundance and strategic sophistication of cleaner fish
           after environmental perturbations
    • Authors: Zegni Triki; Sharon Wismer, Elena Levorato, Redouan Bshary
      Abstract: Coral reef ecosystems are declining worldwide and under foreseeable threat due to climate change, resulting in significant changes in reef communities. It is unknown, however, how such community changes impact interspecific interactions. Recent extreme weather events affecting the Great Barrier Reef, that is, consecutive cyclones and the 2016 El Niño event, allowed us to explore potential consequences in the mutualistic interactions involving cleaner fish Labroides dimidiatus (hereafter “cleaner”). After the perturbations, cleaner densities were reduced by 80%, disproportionally compared to the variety of reef fish clients from which cleaners remove ectoparasites. Consequently, shifts in supply and demand yielded an increase in the clients’ demand for cleaning. Therefore, clients became less selective toward cleaners, whereas cleaners were able to choose from a multitude of partners. In parallel, we found a significant decline in the ability of cleaners to manage their reputation and to learn to prioritize ephemeral food sources to maximize food intake in laboratory experiments. In other words, cleaners failed to display the previously documented strategic sophistication that made this species a prime example for fish intelligence. In conclusion, low population densities may cause various effects on individual behavior, and as a consequence, interspecific interactions. At the same time, our data suggest that a recovery of population densities would cause a recovery of previously described interaction patterns and cleaner strategic sophistication within the lifetime of individuals.We explored potential consequences of environmental disturbances in the mutualistic interactions involving a cleaner wrasse. After the disturbances, cleaner wrasse densities were reduced by 80%, which correlated cleaners showing low strategic sophistication in laboratory experiments. Climate change causing more frequent environmental perturbations could thus severely disturb species communities by changing interspecific interaction patterns.
      PubDate: 2017-11-14T00:30:01.137226-05:
      DOI: 10.1111/gcb.13943
       
  • Soil carbon cycling proxies: Understanding their critical role in
           predicting climate change feedbacks
    • Authors: Vanessa L. Bailey; Ben Bond-Lamberty, Kristen DeAngelis, A. Stuart Grandy, Christine V. Hawkes, Kate Heckman, Kate Lajtha, Richard P. Phillips, Benjamin N. Sulman, Katherine E. O. Todd-Brown, Matthew D. Wallenstein
      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.
      PubDate: 2017-11-13T01:01:10.347159-05:
      DOI: 10.1111/gcb.13926
       
  • A framework for the identification of hotspots of climate change risk for
           mammals
    • Authors: Michela Pacifici; Piero Visconti, Carlo Rondinini
      Abstract: As rates of global warming increase rapidly, identifying species at risk of decline due to climate impacts and the factors affecting this risk have become key challenges in ecology and conservation biology. Here we present a framework for assessing three components of climate‐related risk for species: vulnerability, exposure and hazard. We used the relationship between the observed response of species to climate change and a set of intrinsic traits (e.g., weaning age) and extrinsic factors (e.g., precipitation seasonality within a species geographic range) to predict, respectively, the vulnerability and exposure of all data‐sufficient terrestrial non‐volant mammals (3953 species). Combining this information with hazard (the magnitude of projected climate change within a species geographic range) we identified global hotspots of species at risk from climate change that includes the western Amazon basin, south‐western Kenya, north‐eastern Tanzania, north‐eastern South Africa, Yunnan province in China, and mountain chains in Papua‐New Guinea. Our framework identifies priority areas for monitoring climate change effects on species and directing climate mitigation actions for biodiversity.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-13T01:00:53.746553-05:
      DOI: 10.1111/gcb.13942
       
  • Responses of phenology and biomass production of boreal fens to climate
           warming under different water‐table level regimes
    • Authors: Päivi Mäkiranta; Raija Laiho, Lauri Mehtätalo, Petra Straková, Janne Sormunen, Kari Minkkinen, Timo Penttilä, Hannu Fritze, Eeva-Stiina Tuittila
      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.
      PubDate: 2017-11-13T00:55:49.101416-05:
      DOI: 10.1111/gcb.13934
       
  • Why artificial light at night should be a focus for global change research
           in the 21st century
    • Authors: Thomas W. Davies; Tim Smyth
      Abstract: The environmental impacts of artificial light at night have been a rapidly growing field of global change science in recent years. Yet, light pollution has not achieved parity with other global change phenomena in the level of concern and interest it receives from the scientific community, government and nongovernmental organizations. This is despite the globally widespread, expanding and changing nature of night‐time lighting and the immediacy, severity and phylogenetic breath of its impacts. In this opinion piece, we evidence 10 reasons why artificial light at night should be a focus for global change research in the 21st century. Our reasons extend beyond those concerned principally with the environment, to also include impacts on human health, culture and biodiversity conservation more generally. We conclude that the growing use of night‐time lighting will continue to raise numerous ecological, human health and cultural issues, but that opportunities exist to mitigate its impacts by combining novel technologies with sound scientific evidence. The potential gains from appropriate management extend far beyond those for the environment, indeed it may play a key role in transitioning towards a more sustainable society.The trend in research outputs associated with light pollution and climate change since the year 2000. Bar heights represent the cumulative number of articles expressed as a percentage of the total number of articles published by the end of 2016; numbers are the cumulative number of articles published by the end of each year. Note that the total number of articles does not reflect the total number published in the research area, only the number returned from the search. The data were collected from a Web of Science search for phrases in article titles. The search phrases used for light pollution research outputs were “Light pollution” OR “Artificial Light at Night” OR “Nighttime lighting” OR “Night‐time lighting” OR “Night time lighting” OR “Street Lighting” OR “LED lighting” OR “Light‐emitting diode lighting.” The search phrase for climate change was “Climate change” and results were not refined by research area. The search for articles on light pollution was refined by research areas: (Plant Sciences or Ornithology or Psychology Multidisciplinary or Environmental Sciences or Evolutionary Biology or Physics Applied or Entomology or Engineering Environmental or Ecology or Urban Studies or Fisheries or Biodiversity Conservation or Biology or Physics Multidisciplinary or Zoology or Oceanography or Geography Physical or Geography or Remote Sensing or Physiology or Marine Freshwater Biology or Public Environmental Occupational Health).
      PubDate: 2017-11-10T00:00:51.618015-05:
      DOI: 10.1111/gcb.13927
       
  • Dynamics of soil biogeochemical gas emissions shaped by remolded aggregate
           sizes and carbon configurations under hydration cycles
    • Authors: Ali Ebrahimi; Dani Or
      Abstract: Changes in soil hydration status affect microbial community dynamics and shape key biogeochemical processes. Evidence suggests that local anoxic conditions may persist and support anaerobic microbial activity in soil aggregates (or in similar hot spots) long after the bulk soil becomes aerated. To facilitate systematic studies of interactions among environmental factors with biogeochemical emissions of CO2, N2O and CH4 from soil aggregates, we remolded silt soil aggregates to different sizes and incorporated carbon at different configurations (core, mixed, no addition). Assemblies of remolded soil aggregates of three sizes (18, 12, and 6 mm) and equal volumetric proportions were embedded in sand columns at four distinct layers. The water table level in each column varied periodically while obtaining measurements of soil GHG emissions for the different aggregate carbon configurations. Experimental results illustrate that methane production required prolonged inundation and highly anoxic conditions for inducing measurable fluxes. The onset of unsaturated conditions (lowering water table) resulted in a decrease in CH4 emissions while temporarily increasing N2O fluxes. Interestingly, N2O fluxes were about 80% higher form aggregates with carbon placement in center (anoxic) core compared to mixed carbon within aggregates. The fluxes of CO2 were comparable for both scenarios of carbon sources. These experimental results highlight the importance of hydration dynamics in activating different GHG production and affecting various transport mechanisms about 80% of total methane emissions during lowering water table level are attributed to physical storage (rather than production), whereas CO2 emissions (~80%) are attributed to biological activity. A biophysical model for microbial activity within soil aggregates and profiles provides a means for results interpretation and prediction of trends within natural soils under a wide range of conditions.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-09T01:45:53.91736-05:0
      DOI: 10.1111/gcb.13938
       
  • Increasing drought and diminishing benefits of elevated carbon dioxide for
           soybean yields across the US Midwest
    • Authors: Zhenong Jin; Elizabeth A. Ainsworth, Andrew D. B. Leakey, David B. Lobell
      Abstract: Elevated atmospheric CO2 concentrations ([CO2]) are expected to increase C3 crop yield through the CO2 fertilization effect (CFE) by stimulating photosynthesis and by reducing stomatal conductance and transpiration. The latter effect is widely believed to lead to greater benefits in dry rather than wet conditions, although some recent experimental evidence challenges this view. Here we used a process‐based crop model, the Agricultural Production Systems sIMulator (APSIM), to quantify the contemporary and future CFE on soybean in one of its primary production area of the US Midwest. APSIM accurately reproduced experimental data from the Soybean Free‐Air CO2 Enrichment site showing that the CFE declined with increasing drought stress. This resulted from greater radiation use efficiency (RUE) and above‐ground biomass production at elevated [CO2] that outpaced gains in transpiration efficiency (TE). Using an ensemble of eight climate model projections, we found that drought frequency in the US Midwest is projected to increase from once every 5 years currently to once every other year by 2050. In addition to directly driving yield loss, greater drought also significantly limited the benefit from rising [CO2]. This study provides a link between localized experiments and regional‐scale modeling to highlight that increased drought frequency and severity pose a formidable challenge to maintaining soybean yield progress that is not offset by rising [CO2] as previously anticipated. Evaluating the relative sensitivity of RUE and TE to elevated [CO2] will be an important target for future modeling and experimental studies of climate change impacts and adaptation in C3 crops.Left two panels (a, b) show changes in the model simulated CO2 fertilization effects (CFE) on biomass and yield and the marginal effect of additional unit increase in [CO2] on biomass and yield. Red lines goes under blue ones indicating the benefit of greater photosynthesis potential is not fully translated to the yield production, which is likely due to the interaction between drought and [CO2]. Right two panels (c, d) show percentage changes in the regional mean biomass and yield under future climate relative to the baseline period of 1991–2010.
      PubDate: 2017-11-07T00:11:00.735087-05:
      DOI: 10.1111/gcb.13946
       
  • Tipping point effect in plant‐fungal interactions under severe drought
           causes abrupt rise in peatland ecosystem respiration
    • Authors: Vincent E. J. Jassey; Monika K. Reczuga, Małgorzata Zielińska, Sandra Słowińska, Bjorn J. M. Robroek, Pierre Mariotte, Christophe V. W. Seppey, Enrique Lara, Jan Barabach, Michał Słowiński, Luca Bragazza, Bogdan H. Chojnicki, Mariusz Lamentowicz, Edward A. D. Mitchell, Alexandre Buttler
      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.
      PubDate: 2017-11-06T00:26:15.16157-05:0
      DOI: 10.1111/gcb.13928
       
  • Spring fasting behavior in a marine apex predator provides an index of
           ecosystem productivity
    • Authors: Karyn D. Rode; Ryan R. Wilson, David C. Douglas, Vanessa Muhlenbruch, Todd C. Atwood, Eric V. Regehr, Evan S. Richardson, Nicholas W. Pilfold, Andrew E. Derocher, George M. Durner, Ian Stirling, Steven C. Amstrup, Michelle St. Martin, Anthony M. Pagano, Kristin Simac
      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.
      PubDate: 2017-11-06T00:23:11.083228-05:
      DOI: 10.1111/gcb.13933
       
  • Land use of drained peatlands: greenhouse gas fluxes, plant production,
           and economics
    • Authors: Åsa Kasimir; Hongxing He, Jessica Coria, Anna Nordén
      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.
      PubDate: 2017-11-06T00:21:35.291289-05:
      DOI: 10.1111/gcb.13931
       
  • Simulating the recent impacts of multiple biotic disturbances on forest
           carbon cycling across the United States
    • Authors: M. Kautz; P. Anthoni, A. J. H. Meddens, T. A. M. Pugh, A. Arneth
      Abstract: Biotic disturbances (BDs, e.g., insects, pathogens and wildlife herbivory) substantially affect boreal and temperate forest ecosystems globally. However, accurate impact assessments comprising larger spatial scales are lacking to date, although these are critically needed given the expected disturbance intensification under a warming climate. Hence, our quantitative knowledge on current and future BD impacts, e.g., on forest carbon (C) cycling, is strongly limited. We extended a Dynamic Global Vegetation Model to simulate ecosystem response to prescribed tree mortality and defoliation due to multiple biotic agents across United States forests during the period 1997‐2015, and quantified the BD‐induced vegetation C loss, i.e., C fluxes from live vegetation to dead organic matter pools. Annual disturbance fractions separated by BD type (tree mortality and defoliation) and agent (bark beetles, defoliator insects, other insects, pathogens, and other biotic agents) were calculated at 0.5° resolution from aerial‐surveyed data and applied within the model. Simulated BD‐induced C fluxes totaled 251.6 Mt C (annual mean: 13.2 Mt C yr−1, SD ±7.3 Mt C yr−1 between years) across the study domain, to which tree mortality contributed 95% and defoliation 5%. Among BD agents, bark beetles caused most C fluxes (61%), and total insect‐induced C fluxes were about five times larger compared to non‐insect agents, e.g., pathogens and wildlife. Our findings further demonstrate that BD‐induced C cycle impacts (i) displayed high spatio‐temporal variability, (ii) were dominated by different agents across BD types and regions, and (iii) were comparable in magnitude to fire‐induced impacts. This study provides the first ecosystem model‐based assessment of BD‐induced impacts on forest C cycling at the continental scale and going beyond single agent‐host systems, thus allowing for comparisons across regions, BD types and agents. Ultimately, a perspective on the potential and limitations of a more process‐based incorporation of multiple BDs in ecosystem models is offered.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-03T07:20:26.410452-05:
      DOI: 10.1111/gcb.13974
       
  • Enhanced‐efficiency fertilizers are not a panacea for resolving the
           nitrogen problem
    • Authors: Tingyu Li; Weifeng Zhang, Jiao Yin, David Chadwick, David Norse, Yuelai Lu, Xuejun Liu, Xinping Chen, Fusuo Zhang, David Powlson, Zhengxia Dou
      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.
      PubDate: 2017-11-02T06:00:46.767636-05:
      DOI: 10.1111/gcb.13918
       
  • Disentangling the mechanisms behind winter snow impact on vegetation
           activity in northern ecosystems
    • Authors: Xiaoyi Wang; Tao Wang, Hui Guo, Dan Liu, Yutong Zhao, Taotao Zhang, Qiang Liu, Shilong Piao
      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.
      PubDate: 2017-11-01T05:11:05.472628-05:
      DOI: 10.1111/gcb.13930
       
  • Improving models of photosynthetic thermal acclimation: which parameters
           are most important and how many should be modified'
    • Authors: Joseph R. Stinziano; Danielle A. Way, William L. Bauerle
      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.
      PubDate: 2017-11-01T05:10:48.105283-05:
      DOI: 10.1111/gcb.13924
       
  • Climate change and Saharan dust drive recent cladoceran and primary
           production changes in remote alpine lakes of Sierra Nevada, Spain
    • Authors: Laura Jiménez; Kathleen M. Rühland, Adam Jeziorski, John P. Smol, Carmen Pérez-Martínez
      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.
      PubDate: 2017-11-01T05:00:40.614664-05:
      DOI: 10.1111/gcb.13878
       
  • Uncertain recovery of the North Atlantic right whale in a changing ocean
    • Authors: Erin L. Meyer-Gutbrod; Charles H. Greene
      Abstract: Human activities have placed populations of many endangered species at risk and mitigation efforts typically focus on reducing anthropogenic sources of mortality. However, failing to recognize the additional role of environmental factors in regulating birth and mortality rates can lead to erroneous demographic analyses and conclusions. The North Atlantic right whale population is currently the focus of conservation efforts aimed at reducing mortality rates associated with ship strikes and entanglement in fishing gear. Consistent monitoring of the population since 1980 has revealed evidence that climate‐associated changes in prey availability have played an important role in the population's recovery. The considerable interdecadal differences observed in population growth coincide with remote Arctic and North Atlantic oceanographic processes that link to the Gulf of Maine ecosystem. Here, we build capture‐recapture models to quantify the role of prey availability on right whale demographic transitional probabilities and use a corresponding demographic model to project population growth rates into the next century. Contrary to previous predictions, the right whale population is projected to recover in the future as long as prey availability and mortality rates remain within the ranges observed during 1980–2012. However, recent events indicate a northward range shift in right whale prey, potentially resulting in decreased prey availability and/or an expansion of right whale habitat into unprotected waters. An annual increase in the number of whale deaths comparable to that observed during the summer 2017 mass mortality event may cause a decline to extinction even under conditions of normal prey availability. This study highlights the importance of understanding the oceanographic context for observed population changes when evaluating the efficacy of conservation management plans for endangered marine species.Successful management of the North Atlantic right whale requires awareness of environmental influences on population growth and demography. Decadal‐scale regime shifts in prey availability have driven a significant amount of demographic change since population monitoring began in 1980. We build a prey‐dependent full demographic capture–recapture model to characterize this relationship and project right whale growth into the next century. An increase in prey in the first decade of the new millennium has contributed to an increase in the population size. However, more recent trends in calving and an unusual mortality event in 2017 may herald a shift into a regime of population decline.
      PubDate: 2017-10-30T13:30:01.938833-05:
      DOI: 10.1111/gcb.13929
       
  • Temporal changes in soil C‐N‐P stoichiometry over the past 60 years
           across subtropical China
    • Authors: Zaipeng Yu; Minhuang Wang, Zhiqun Huang, Teng-Chiu Lin, Matthew A. Vadeboncoeur, Eric B. Searle, Han Y. H. Chen
      Abstract: Controlled experiments have shown that global changes decouple the biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P), resulting in shifting stoichiometry that lies at the core of ecosystem functioning. However, the response of soil stoichiometry to global changes in natural ecosystems with different soil depths, vegetation types, and climate gradients remain poorly understood. Based on 2,736 observations along soil profiles of 0‐150 cm depth from 1955 to 2016, we evaluated the temporal changes in soil C‐N‐P stoichiometry across subtropical China, where soils are P‐impoverished, with diverse vegetation, soil, and parent material types and a wide range of climate gradients. We found a significant overall increase in soil total C concentration and a decrease in soil total P concentration, resulting in increasing soil C:P and N:P ratios during the past 60 years across all soil depths. Though average soil N concentration did not change, soil C:N increased in topsoil while decreasing in deeper soil. The temporal trends in soil C‐N‐P stoichiometry differed among vegetation, soil, parent material types and spatial climate variations, with significantly increased C:P and N:P ratios for evergreen broadleaf forest and highly weathered Ultisols, and more pronounced temporal changes in soil C:N, N:P, and C:P ratios at low elevations. Our sensitivity analysis suggests that the temporal changes in soil stoichiometry resulted from elevated N deposition, rising atmospheric CO2 concentration and regional warming. Our findings revealed that the responses of soil C‐N‐P and stoichiometry to long‐term global changes have occurred across the whole soil depth in subtropical China and the magnitudes of the changes in soil stoichiometry are dependent on vegetation types, soil types, and spatial climate variations.This article is protected by copyright. All rights reserved.
      PubDate: 2017-10-30T02:00:42.57187-05:0
      DOI: 10.1111/gcb.13939
       
  • How much does climate change threaten European forest tree species
           distributions'
    • Authors: Marcin K. Dyderski; Sonia Paź, Lee E. Frelich, Andrzej M. Jagodziński
      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.
      PubDate: 2017-10-30T01:56:36.182716-05:
      DOI: 10.1111/gcb.13925
       
  • Why decadal to century timescale paleoclimate data is needed to explain
           present‐day patterns of biological diversity and change
    • Authors: Damien A. Fordham; Frédérik Saltré, Stuart C. Brown, Camille Mellin, Tom M. L. Wigley
      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.
      PubDate: 2017-10-30T01:55:49.330713-05:
      DOI: 10.1111/gcb.13932
       
  • Projecting the future of an alpine ungulate under climate change scenarios
    • Authors: Kevin S. White; David P. Gregovich, Taal Levi
      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.
      PubDate: 2017-10-27T01:35:44.449972-05:
      DOI: 10.1111/gcb.13919
       
  • 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)
    • Authors: Tara Stephens; Sian C. Wilson, Ffion Cassidy, Darren Bender, David Gummer, Des H. V. Smith, Natasha Lloyd, Jana M. McPherson, Axel Moehrenschlager
      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.
      PubDate: 2017-10-27T01:30:32.019837-05:
      DOI: 10.1111/gcb.13922
       
  • Clarifying the landscape approach: A response to the Editor
    • Authors: James Reed; Josh Vianen, Jos Barlow, Terry Sunderland
      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.
      PubDate: 2017-10-19T00:10:29.709257-05:
      DOI: 10.1111/gcb.13917
       
  • Decoupling the direct and indirect effects of climate on plant litter
           decomposition and terrestrial nutrient cycling
    • Authors: Vidya Suseela; Nishanth Tharayil
      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.
      PubDate: 2017-10-07T01:50:48.579245-05:
      DOI: 10.1111/gcb.13923
       
  • What type of rigorous experiments are needed to investigate the impact of
           artificial light at night on individuals and populations'
    • Authors: Jenny Qianni Ouyang; Maaike Jong, Roy H. A. Grunsven, Kevin D. Matson, Mark F. Haussmann, Peter Meerlo, Marcel Visser, Kamiel Spoelstra
      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.
      PubDate: 2017-10-06T05:05:23.160314-05:
      DOI: 10.1111/gcb.13894
       
  • No evidence for ecological segregation protecting native trout from
           invasive hybridization
    • Authors: Ryan P. Kovach; Clint C. Muhlfeld, Robert Al-Chokhachy, Stephen J. Amish, Jeffrey L. Kershner, Robb F. Leary, Winsor H. Lowe, Gordon Luikart, Phil Matson, David A. Schmetterling, Bradley B. Shepard, Peter A. H. Westley, Diane Whited, Andrew Whiteley, Fred W. Allendorf
      PubDate: 2017-08-17T04:15:23.803504-05:
      DOI: 10.1111/gcb.13825
       
  • Ecological segregation moderates a climactic conclusion to trout
           hybridization
    • Authors: Michael K. Young; Daniel J. Isaak, Kevin S. McKelvey, Taylor M. Wilcox, Matthew R. Campbell, Matthew P. Corsi, Dona Horan, Michael K. Schwartz
      First page: 5021
      Abstract: For decades, it has been assumed that introgressive hybridization between introduced rainbow trout and native cutthroat trout in western North America will lead to genomic extinction of the latter. A broad‐scale re‐examination of their interaction indicates that ecological differences between these species and demographic processes are dictating the location and extent of their hybrid zones, and that runaway introgression between these taxa is unlikely.
      PubDate: 2017-08-17T04:11:21.85609-05:0
      DOI: 10.1111/gcb.13828
       
  • Rigorous field experiments are essential to understand the genuine
           severity of light pollution and to identify possible solutions
    • Authors: Thomas Raap; Rianne Pinxten, Marcel Eens
      First page: 5024
      PubDate: 2017-08-21T00:06:20.589548-05:
      DOI: 10.1111/gcb.13843
       
  • Quality‐assured long‐term satellite‐based leaf area
           index product
    • Authors: Jian Peng; Simon Blessing, Ralf Giering, Benjamin Müller, Nadine Gobron, Joanne Nightingale, Folkert Boersma, Jan-Peter Muller
      First page: 5027
      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.
      PubDate: 2017-09-23T00:40:21.295388-05:
      DOI: 10.1111/gcb.13888
       
  • Toxic Toad Invasion of Wallacea: a Biodiversity Hotspot Characterized by
           Extraordinary Endemism
    • Authors: Sean B. Reilly; Guinevere O. U. Wogan, Alexander L. Stubbs, Evy Arida, Djoko T. Iskandar, Jimmy A. McGuire
      First page: 5029
      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.
      PubDate: 2017-10-06T05:15:38.702283-05:
      DOI: 10.1111/gcb.13877
       
  • Exploring uncertainty of Amazon dieback in a perturbed parameter Earth
           system ensemble
    • Authors: Chris A. Boulton; Ben B. B. Booth, Peter Good
      First page: 5032
      Abstract: The future of the Amazon rainforest is unknown due to uncertainties in projected climate change and the response of the forest to this change (forest resiliency). Here, we explore the effect of some uncertainties in climate and land surface processes on the future of the forest, using a perturbed physics ensemble of HadCM3C. This is the first time Amazon forest changes are presented using an ensemble exploring both land vegetation processes and physical climate feedbacks in a fully coupled modelling framework. Under three different emissions scenarios, we measure the change in the forest coverage by the end of the 21st century (the transient response) and make a novel adaptation to a previously used method known as “dry‐season resilience” to predict the long‐term committed response of the forest, should the state of the climate remain constant past 2100. Our analysis of this ensemble suggests that there will be a high chance of greater forest loss on longer timescales than is realized by 2100, especially for mid‐range and low emissions scenarios. In both the transient and predicted committed responses, there is an increasing uncertainty in the outcome of the forest as the strength of the emissions scenarios increases. It is important to note however, that very few of the simulations produce future forest loss of the magnitude previously shown under the standard model configuration. We find that low optimum temperatures for photosynthesis and a high minimum leaf area index needed for the forest to compete for space appear to be precursors for dieback. We then decompose the uncertainty into that associated with future climate change and that associated with forest resiliency, finding that it is important to reduce the uncertainty in both of these if we are to better determine the Amazon's outcome.We explore the effect of uncertainties in climate and land surface processes on the future of the Amazon forest, using a perturbed physics ensemble. We measure the change in the forest coverage by 2100 and predict the long‐term response of the forest, should the climate remain constant past 2100. We find that there is an increasing uncertainty in future forest coverage under stronger emissions and that reducing uncertainty in both climate and forest resiliency is important.
      PubDate: 2017-06-01T03:50:51.327632-05:
      DOI: 10.1111/gcb.13733
       
  • Simulated climate change, epidemic size, and host evolution across
           host–parasite populations
    • Authors: Stuart K.J.R. Auld; June Brand
      First page: 5045
      Abstract: Climate change is causing warmer and more variable temperatures as well as physical flux in natural populations, which will affect the ecology and evolution of infectious disease epidemics. Using replicate seminatural populations of a coevolving freshwater invertebrate‐parasite system (host: Daphnia magna, parasite: Pasteuria ramosa), we quantified the effects of ambient temperature and population mixing (physical flux within populations) on epidemic size and population health. Each population was seeded with an identical suite of host genotypes and dose of parasite transmission spores. Biologically reasonable increases in environmental temperature caused larger epidemics, and population mixing reduced overall epidemic size. Mixing also had a detrimental effect on host populations independent of disease. Epidemics drove parasite‐mediated selection, leading to a loss of host genetic diversity, and mixed populations experienced greater evolution due to genetic drift over the season. These findings further our understanding of how diversity loss will reduce the host populations’ capacity to respond to changes in selection, therefore stymying adaptation to further environmental change.Using replicate semi‐natural populations of a coevolving invertebrate‐parasite system, we demonstrated that biologically reasonable increases in environmental temperature led to larger epidemics, and population mixing reduced overall epidemic size. Mixing also had a detrimental effect on host populations independent of disease. Epidemics drove parasite‐mediated selection, leading to a loss of host genetic diversity, and mixed populations experienced greater evolution due to genetic drift over the season.
      PubDate: 2017-07-08T02:25:24.233298-05:
      DOI: 10.1111/gcb.13769
       
  • Increasing carbon discrimination rates and depth of water uptake favor the
           growth of Mediterranean evergreen trees in the ecotone with temperate
           deciduous forests
    • Authors: Adrià Barbeta; Josep Peñuelas
      First page: 5054
      Abstract: Tree populations at the low‐altitudinal or ‐latitudinal limits of species' distributional ranges are predicted to retreat toward higher altitudes and latitudes to track the ongoing changes in climate. Studies have focused on the climatic sensitivity of the retreating species, whereas little is known about the potential replacements. Competition between tree species in forest ecotones will likely be strongly influenced by the ecophysiological responses to heat and drought. We used tree‐ring widths and δ13C and δ18O chronologies to compare the growth rates and long‐term ecophysiological responses to climate in the temperate‐Mediterranean ecotone formed by the deciduous Fagus sylvatica and the evergreen Quercus ilex at the low altitudinal and southern latitudinal limit of F. sylvatica (NE Iberian Peninsula). F. sylvatica growth rates were similar to those of other southern populations and were surprisingly not higher than those of Q. ilex, which were an order of magnitude higher than those in nearby drier sites. Higher Q. ilex growth rates were associated with high temperatures, which have increased carbon discrimination rates in the last 25 years. In contrast, stomatal regulation in F. sylvatica was proportional to the increase in atmospheric CO2. Tree‐ring δ18O for both species were mostly correlated with δ18O in the source water. In contrast to many previous studies, relative humidity was not negatively correlated with tree‐ring δ18O but had a positive effect on Q. ilex tree‐ring δ18O. Furthermore, tree‐ring δ18O decreased in Q. ilex over time. The sensitivity of Q. ilex to climate likely reflects the uptake of deep water that allowed it to benefit from the effect of CO2 fertilization, in contrast to the water‐limited F. sylvatica. Consequently, Q. ilex is a strong competitor at sites currently dominated by F. sylvatica and could be favored by increasingly warmer conditions.In this forest ecotone, growth rates of the Mediterranean tree were surprisingly similar to the temperate deciduous tree species and higher than in sites with typical Mediterranean conditions. The Mediterranean species' carbon discrimination rates were enhanced in the last years in response to warmer temperatures and thanks to a deeper water uptake, as shown by the more depleted and less variable tree‐ring δ18O. In contrast, the physiology of the temperate species was limited by a tighter stomatal regulation. Source water appeared as the paramount factor determining tree‐ring δ18O.
      PubDate: 2017-06-12T04:10:24.732495-05:
      DOI: 10.1111/gcb.13770
       
  • A common thermal niche among geographically diverse populations of the
           widely distributed tree species Eucalyptus tereticornis: No evidence for
           adaptation to climate‐of‐origin
    • Authors: John E. Drake; Angelica Vårhammar, Dushan Kumarathunge, Belinda E. Medlyn, Sebastian Pfautsch, Peter B. Reich, David T. Tissue, Oula Ghannoum, Mark G. Tjoelker
      First page: 5069
      Abstract: Impacts of climate warming depend on the degree to which plants are constrained by adaptation to their climate‐of‐origin or exhibit broad climatic suitability. We grew cool‐origin, central and warm‐origin provenances of Eucalyptus tereticornis in an array of common temperature environments from 18 to 35.5°C to determine if this widely distributed tree species consists of geographically contrasting provenances with differentiated and narrow thermal niches, or if provenances share a common thermal niche. The temperature responses of photosynthesis, respiration, and growth were equivalent across the three provenances, reflecting a common thermal niche despite a 2,200 km geographic distance and 13°C difference in mean annual temperature at seed origin. The temperature dependence of growth was primarily mediated by changes in leaf area per unit plant mass, photosynthesis, and whole‐plant respiration. Thermal acclimation of leaf, stem, and root respiration moderated the increase in respiration with temperature, but acclimation was constrained at high temperatures. We conclude that this species consists of provenances that are not differentiated in their thermal responses, thus rejecting our hypothesis of adaptation to climate‐of‐origin and suggesting a shared thermal niche. In addition, growth declines with warming above the temperature optima were driven by reductions in whole‐plant leaf area and increased respiratory carbon losses. The impacts of climate warming will nonetheless vary across the geographic range of this and other such species, depending primarily on each provenance's climate position on the temperature response curves for photosynthesis, respiration, and growth.
      PubDate: 2017-07-08T02:00:33.853706-05:
      DOI: 10.1111/gcb.13771
       
  • Polar zoobenthos blue carbon storage increases with sea ice losses,
           because across‐shelf growth gains from longer algal blooms outweigh ice
           scour mortality in the shallows
    • Authors: David K. A. Barnes
      First page: 5083
      Abstract: One of the major climate‐forced global changes has been white to blue to green; losses of sea ice extent in time and space around Arctic and West Antarctic seas has increased open water and the duration (though not magnitude) of phytoplankton blooms. Blueing of the poles has increases potential for heat absorption for positive feedback but conversely the longer phytoplankton blooms have increased carbon export to storage and sequestration by shelf benthos. However, ice shelf collapses and glacier retreat can calve more icebergs, and the increased open water allows icebergs more opportunities to scour the seabed, reducing zoobenthic blue carbon capture and storage. Here the size and variability in benthic blue carbon in mega and macrobenthos was assessed in time and space at Ryder and Marguerite bays of the West Antarctic Peninsula (WAP). In particular the influence of the duration of primary productivity and ice scour are investigated from the shallows to typical shelf depths of 500 m. Ice scour frequency dominated influence on benthic blue carbon at 5 m, to comparable with phytoplankton duration by 25 m depth. At 500 m only phytoplankton duration was significant and influential. WAP zoobenthos was calculated to generate ~107, 4.5 × 106 and 1.6 × 106 tonnes per year (between 2002 and 2015) in terms of production, immobilization and sequestration of carbon respectively. Thus about 1% of annual primary productivity has sequestration potential at the end of the trophic cascade. Polar zoobenthic blue carbon capture and storage responses to sea ice losses, the largest negative feedback on climate change, has been underestimated despite some offsetting of gain by increased ice scouring with more open water. Equivalent survey of Arctic and sub‐Antarctic shelves, for which new projects have started, should reveal the true extent of this feedback and how much its variability contributes to uncertainty in climate models.Blue carbon comes into the cold. Losses of sea ice over continental shelf around Arctic and West Antarctic seas has increased the duration of open water and phytoplankton blooms. About 1% of this carbon becomes immobilized by shelf benthos ‐ worth millions of tonnes per year along the Antarctic Peninsula. Iceberg scouring may increase, reducing blue carbon in the productive shallows, but this is more than compensated for by greater productivity in deeper shelf waters.
      PubDate: 2017-06-23T00:52:38.912727-05:
      DOI: 10.1111/gcb.13772
       
  • Coupled effects of wind‐storms and drought on tree mortality across 115
           forest stands from the Western Alps and the Jura mountains
    • Authors: Katalin Csilléry; Georges Kunstler, Benoît Courbaud, Denis Allard, Pierre Lassègues, Klaus Haslinger, Barry Gardiner
      First page: 5092
      Abstract: Damage due to wind‐storms and droughts is increasing in many temperate forests, yet little is known about the long‐term roles of these key climatic factors in forest dynamics and in the carbon budget. The objective of this study was to estimate individual and coupled effects of droughts and wind‐storms on adult tree mortality across a 31‐year period in 115 managed, mixed coniferous forest stands from the Western Alps and the Jura mountains. For each stand, yearly mortality was inferred from management records, yearly drought from interpolated fields of monthly temperature, precipitation and soil water holding capacity, and wind‐storms from interpolated fields of daily maximum wind speed. We performed a thorough model selection based on a leave‐one‐out cross‐validation of the time series. We compared different critical wind speeds (CWSs) for damage, wind‐storm, and stand variables and statistical models. We found that a model including stand characteristics, drought, and storm strength using a CWS of 25 ms−1 performed the best across most stands. Using this best model, we found that drought increased damage risk only in the most southerly forests, and its effect is generally maintained for up to 2 years. Storm strength increased damage risk in all forests in a relatively uniform way. In some stands, we found positive interaction between drought and storm strength most likely because drought weakens trees, and they became more prone to stem breakage under wind‐loading. In other stands, we found negative interaction between drought and storm strength, where excessive rain likely leads to soil water saturation making trees more susceptible to overturning in a wind‐storm. Our results stress that temporal data are essential to make valid inferences about ecological impacts of disturbance events, and that making inferences about disturbance agents separately can be of limited validity. Under projected future climatic conditions, the direction and strength of these ecological interactions could also change.We investigated the role of droughts and wind‐storms on adult tree mortality using 31‐year long time series from 115 stands in managed coniferous mountain forests from the Western Alps and the Jura mountains. We found that drought increased damage in the most southerly forests, and storms increased damage in all forests when the wind speed was higher than 25 ms−1. Our data also suggest that drought may weakens trees, so that they became more prone to breakage under wind‐loading, but excessive rain may also lead to soil water saturation, which make trees more susceptible to overturning in a wind‐storm.
      PubDate: 2017-07-06T01:20:54.204511-05:
      DOI: 10.1111/gcb.13773
       
  • Silver fir and Douglas fir are more tolerant to extreme droughts than
           Norway spruce in south‐western Germany
    • Authors: Valentina Vitali; Ulf Büntgen, Jürgen Bauhus
      First page: 5108
      Abstract: Improving our understanding of the potential of forest adaptation is an urgent task in the light of predicted climate change. Long‐term alternatives for susceptible yet economically important tree species such as Norway spruce (Picea abies) are required, if the frequency and intensity of summer droughts will continue to increase. Although Silver fir (Abies alba) and Douglas fir (Pseudotsuga menziesii) have both been described as drought‐tolerant species, our understanding of their growth responses to drought extremes is still limited. Here, we use a dendroecological approach to assess the resistance, resilience, and recovery of these important central Europe to conifer species the exceptional droughts in 1976 and 2003. A total of 270 trees per species were sampled in 18 managed mixed‐species stands along an altitudinal gradient (400–1200 m a.s.l.) at the western slopes of the southern and central Black Forest in southwest Germany. While radial growth in all species responded similarly to the 1976 drought, Norway spruce was least resistant and resilient to the 2003 summer drought. Silver fir showed the overall highest resistance to drought, similarly to Douglas fir, which exhibited the widest growth rings. Silver fir trees from lower elevations were more drought prone than trees at higher elevations. Douglas fir and Norway spruce, however, revealed lower drought resilience at higher altitudes. Although the 1976 and 2003 drought extremes were quite different, Douglas fir maintained consistently the highest radial growth. Although our study did not examine population‐level responses, it clearly indicates that Silver fir and Douglas fir are generally more resistant and resilient to previous drought extremes and are therefore suitable alternatives to Norway spruce; Silver fir more so at higher altitudes. Cultivating these species instead of Norway spruce will contribute to maintaining a high level of productivity across many Central European mountain forests under future climate change.The two extreme droughts in 1976 and 2003 affected negatively the radial growth response of Norway spruce, Silver and Douglas fir in the Black forest at all elevations. The 1976 drought had a less pronounced effect than the 2003 summer drought; however, firs were noticeably more resistant and resilient to extreme drought than spruce. Spruce was the most affected species when comparing performances of drought indices, and Silver fir the least affected. Douglas fir showed consistently the highest growth rates.
      PubDate: 2017-06-26T05:58:08.180343-05:
      DOI: 10.1111/gcb.13774
       
  • Measuring canopy loss and climatic thresholds from an extreme drought
           along a fivefold precipitation gradient across Texas
    • Authors: Amanda M. Schwantes; Jennifer J. Swenson, Mariano González-Roglich, Daniel M. Johnson, Jean-Christophe Domec, Robert B. Jackson
      First page: 5120
      Abstract: Globally, trees are increasingly dying from extreme drought, a trend that is expected to increase with climate change. Loss of trees has significant ecological, biophysical, and biogeochemical consequences. In 2011, a record drought caused widespread tree mortality in Texas. Using remotely sensed imagery, we quantified canopy loss during and after the drought across the state at 30‐m spatial resolution, from the eastern pine/hardwood forests to the western shrublands, a region that includes the boundaries of many species ranges. Canopy loss observations in ~200 multitemporal fine‐scale orthophotos (1‐m) were used to train coarser Landsat imagery (30‐m) to create 30‐m binary statewide canopy loss maps. We found that canopy loss occurred across all major ecoregions of Texas, with an average loss of 9.5%. The drought had the highest impact in post oak woodlands, pinyon‐juniper shrublands and Ashe juniper woodlands. Focusing on a 100‐km by ~1,000‐km transect spanning the State's fivefold east–west precipitation gradient (~1,500 to ~300 mm), we compared spatially explicit 2011 climatic anomalies to our canopy loss maps. Much of the canopy loss occurred in areas that passed specific climatic thresholds: warm season anomalies in mean temperature (+1.6°C) and vapor pressure deficit (VPD, +0.66 kPa), annual percent deviation in precipitation (−38%), and 2011 difference between precipitation and potential evapotranspiration (−1,206 mm). Although similarly low precipitation occurred during the landmark 1950s drought, the VPD and temperature anomalies observed in 2011 were even greater. Furthermore, future climate data under the representative concentration pathway 8.5 trajectory project that average values will surpass the 2011 VPD anomaly during the 2070–2099 period and the temperature anomaly during the 2040–2099 period. Identifying vulnerable ecological systems to drought stress and climate thresholds associated with canopy loss will aid in predicting how forests will respond to a changing climate and how ecological landscapes will change in the near term.Using remotely sensed imagery, we quantified canopy loss across Texas due to the 2011 drought; we found a 9.5% loss in canopy and greater mortality of Juniperus ashei, an encroaching tree‐shrub, which suggests that woody‐shrub encroachment may be drought‐limited. Temperature (+1.6°C) and vapor pressure deficit (VPD, +0.66 kPa) anomaly thresholds effectively explained spatial patterns of tree mortality. Furthermore, future climate data (RCP 8.5) project that average values will surpass this VPD anomaly during the 2070–2099 period.
      PubDate: 2017-06-26T00:58:52.693732-05:
      DOI: 10.1111/gcb.13775
       
  • Decadal changes in habitat characteristics influence population
           trajectories of southern elephant seals
    • Authors: Mark A. Hindell; Michael Sumner, Sophie Bestley, Simon Wotherspoon, Robert G. Harcourt, Mary-Anne Lea, Rachael Alderman, Clive R. McMahon
      First page: 5136
      Abstract: Understanding divergent biological responses to climate change is important for predicting ecosystem level consequences. We use species habitat models to predict the winter foraging habitats of female southern elephant seals and investigate how changes in environmental variables within these habitats may be related to observed decreases in the Macquarie Island population. There were three main groups of seals that specialized in different ocean realms (the sub‐Antarctic, the Ross Sea and the Victoria Land Coast). The physical and climate attributes (e.g. wind strength, sea surface height, ocean current strength) varied amongst the realms and also displayed different temporal trends over the last two to four decades. Most notably, sea ice extent increased on average in the Victoria Land realm while it decreased overall in the Ross Sea realm. Using a species distribution model relating mean residence times (time spent in each 50 × 50 km grid cell) to 9 climate and physical co‐variates, we developed spatial predictions of residence time to identify the core regions used by the seals across the Southern Ocean from 120°E to 120°W. Population size at Macquarie Island was negatively correlated with ice concentration within the core habitat of seals using the Victoria Land Coast and the Ross Sea. Sea ice extent and concentration is predicted to continue to change in the Southern Ocean, having unknown consequences for the biota of the region. The proportion of Macquarie Island females (40%) utilizing the relatively stable sub‐Antarctic region, may buffer this population against longer‐term regional changes in habitat quality, but the Macquarie Island population has persistently decreased (−1.45% per annum) over seven decades indicating that environmental changes in the Antarctic are acting on the remaining 60% of the population to impose a long‐term population decline in a top Southern Ocean predator.This study explains the dramatic long‐term decrease in an elephant seal population (over 50% in seven decades). The decrease is related to long‐term increases in the regional sea ice extent in winter in two of the population's core habitats.
      PubDate: 2017-07-12T02:06:07.898439-05:
      DOI: 10.1111/gcb.13776
       
  • Multi‐scale responses to warming in an experimental insect
           metacommunity
    • Authors: Tess Nahanni Grainger; Benjamin Gilbert
      First page: 5151
      Abstract: In metacommunities, diversity is the product of species interactions at the local scale and dispersal between habitat patches at the regional scale. Although warming can alter both species interactions and dispersal, the combined effects of warming on these two processes remains uncertain. To determine the independent and interactive effects of warming‐induced changes to local species interactions and dispersal, we constructed experimental metacommunities consisting of enclosed milkweed patches seeded with five herbivorous milkweed specialist insect species. We treated metacommunities with two levels of warming (unwarmed and warmed) and three levels of connectivity (isolated, low connectivity, high connectivity). Based on metabolic theory, we predicted that if plant resources were limited, warming would accelerate resource drawdown, causing local insect declines and increasing both insect dispersal and the importance of connectivity to neighboring patches for insect persistence. Conversely, given abundant resources, warming could have positive local effects on insects, and the risk of traversing a corridor to reach a neighboring patch could outweigh the benefits of additional resources. We found support for the latter scenario. Neither resource drawdown nor the weak insect‐insect associations in our system were affected by warming, and most insect species did better locally in warmed conditions and had dispersal responses that were unchanged or indirectly affected by warming. Dispersal across the matrix posed a species‐specific risk that led to declines in two species in connected metacommunities. Combined, this scaled up to cause an interactive effect of warming and connectivity on diversity, with unwarmed metacommunities with low connectivity incurring the most rapid declines in diversity. Overall, this study demonstrates the importance of integrating the complex outcomes of species interactions and spatial structure in understanding community response to climate change.Despite the recognition that warming can alter both the local species interactions and dispersal dynamics that shape diversity in patchy systems, the impacts of warming on metacommunities remains uncertain. We warmed experimental two‐patch metacommunities of milkweed and their specialist herbivores, and found that warming had mostly positive effects on plants and insects locally, while dispersal between patches posed a species‐specific mortality risk. This created an interactive effect of warming and connectivity, with unwarmed low‐connectivity metacommunities experiencing the most rapid declines in diversity. This study demonstrates the importance of integrating spatial structure into our understanding of community response to climate change.
      PubDate: 2017-06-28T01:55:38.294865-05:
      DOI: 10.1111/gcb.13777
       
  • Water availability affects seasonal CO2‐induced photosynthetic
           enhancement in herbaceous species in a periodically dry woodland
    • Authors: Varsha S. Pathare; Kristine Y. Crous, Julia Cooke, Danielle Creek, Oula Ghannoum, David S. Ellsworth
      First page: 5164
      Abstract: Elevated atmospheric CO2 (eCO2) is expected to reduce the impacts of drought and increase photosynthetic rates via two key mechanisms: first, through decreased stomatal conductance (gs) and increased soil water content (VSWC) and second, through increased leaf internal CO2 (Ci) and decreased stomatal limitations (Slim). It is unclear if such findings from temperate grassland studies similarly pertain to warmer ecosystems with periodic water deficits. We tested these mechanisms in three important C3 herbaceous species in a periodically dry Eucalyptus woodland and investigated how eCO2‐induced photosynthetic enhancement varied with seasonal water availability, over a 3 year period. Leaf photosynthesis increased by 10%–50% with a 150 μmol mol−1 increase in atmospheric CO2 across seasons. This eCO2‐induced increase in photosynthesis was a function of seasonal water availability, given by recent precipitation and mean daily VSWC. The highest photosynthetic enhancement by eCO2 (>30%) was observed during the most water‐limited period, for example, with VSWC 30%) and decreased Ci under the ambient CO2 concentration (aCO2), with leaf photosynthesis strongly carboxylation‐limited. The alleviation of Slim by eCO2 was facilitated by increasing Ci, thus yielding a larger photosynthetic enhancement during dry periods. We demonstrated that water availability, but not eCO2, controls gs and hence the magnitude of photosynthetic enhancement in the understory herbaceous plants. Thus, eCO2 has the potential to alter vegetation functioning in a periodically dry woodland understory through changes in stomatal limitation to photosynthesis, not by the “water‐savings effect” usually invoked in grasslands.Elevated CO2 mitigated drought‐induced stomatal limitations, thus yielding a larger proportional photosynthetic enhancement during dry periods with higher stomatal limitations for three understory herbaceous species.
      PubDate: 2017-07-10T00:30:02.404148-05:
      DOI: 10.1111/gcb.13778
       
  • Tree‐ring analysis and modeling approaches yield contrary response of
           circumboreal forest productivity to climate change
    • Authors: Shunsuke Tei; Atsuko Sugimoto, Hitoshi Yonenobu, Yojiro Matsuura, Akira Osawa, Hisashi Sato, Junichi Fujinuma, Trofim Maximov
      First page: 5179
      Abstract: Circumboreal forest ecosystems are exposed to a larger magnitude of warming in comparison with the global average, as a result of warming‐induced environmental changes. However, it is not clear how tree growth in these ecosystems responds to these changes. In this study, we investigated the sensitivity of forest productivity to climate change using ring width indices (RWI) from a tree‐ring width dataset accessed from the International Tree‐Ring Data Bank and gridded climate datasets from the Climate Research Unit. A negative relationship of RWI with summer temperature and recent reductions in RWI were typically observed in continental dry regions, such as inner Alaska and Canada, southern Europe, and the southern part of eastern Siberia. We then developed a multiple regression model with regional meteorological parameters to predict RWI, and then applied to these models to predict how tree growth will respond to twenty‐first‐century climate change (RCP8.5 scenario). The projections showed a spatial variation and future continuous reduction in tree growth in those continental dry regions. The spatial variation, however, could not be reproduced by a dynamic global vegetation model (DGVM). The DGVM projected a generally positive trend in future tree growth all over the circumboreal region. These results indicate that DGVMs may overestimate future wood net primary productivity (NPP) in continental dry regions such as these; this seems to be common feature of current DGVMs. DGVMs should be able to express the negative effect of warming on tree growth, so that they simulate the observed recent reduction in tree growth in continental dry regions.The negative response of RWI to summer temperature is a widespread phenomenon over circumboreal forest, and the current CO2 fertilization effect for tree growth seems to be unable to overcome this negative effect. The negative response, however, could not be reproduced by a DGVM. DGVMs should be able to express the negative effect of warming on tree growth. Otherwise, future projections of tree NPP by DGVMs may be overestimated under the conditions of the expected future increase in global precipitation.
      PubDate: 2017-06-26T06:02:50.960149-05:
      DOI: 10.1111/gcb.13780
       
  • Changes in temperature sensitivity of spring phenology with recent climate
           warming in Switzerland are related to shifts of the preseason
    • Authors: Sabine Güsewell; Reinhard Furrer, Regula Gehrig, Barbara Pietragalla
      First page: 5189
      Abstract: The spring phenology of plants in temperate regions strongly responds to spring temperatures. Climate warming has caused substantial phenological advances in the past, but trends to be expected in the future are uncertain. A simple indicator is temperature sensitivity, the phenological advance statistically associated with a 1°C warmer mean temperature during the “preseason”, defined as the most temperature‐sensitive period preceding the phenological event. Recent analyses of phenological records have shown a decline in temperature sensitivity of leaf unfolding, but underlying mechanisms were not clear. Here, we propose that climate warming can reduce temperature sensitivity simply by reducing the length of the preseason due to faster bud development during this time period, unless the entire preseason shifts forward so that its temperature does not change. We derive these predictions theoretically from the widely used “thermal time model” for bud development and test them using data for 19 phenological events recorded in 1970–2012 at 108 stations spanning a 1600 m altitudinal range in Switzerland. We consider how temperature sensitivity, preseason start, preseason length and preseason temperature change (i) with altitude, (ii) between the periods 1970–1987 and 1995–2012, which differed mainly in spring temperatures, and (iii) between two non‐consecutive sets of 18 years that differed mainly in winter temperatures. On average, temperature sensitivity increased with altitude (colder climate) and was reduced in years with warmer springs, but not in years with warmer winters. These trends also varied among species. Decreasing temperature sensitivity in warmer springs was associated with a limited forward shift of preseason start, higher temperatures during the preseason and reduced preseason length, but not with reduced winter chilling. Our results imply that declining temperature sensitivity can result directly from spring warming and does not necessarily indicate altered physiological responses or stronger constraints such as reduced winter chilling.Model for possible changes in the temperature sensitivity of spring phenology with climate warming if the start date t0 of temperature‐driven bud ontogenesis (preseason) gets delayed. The later start date and higher daily temperatures lead to faster bud development, reducing preseason length. The end date of the preseason (average onset date t¯1) only slightly shifts forward due to the later start, causing the temperature at preseason end to be higher. These changes are predicted to result in reduced temperature sensitivity.
      PubDate: 2017-07-06T01:11:11.942374-05:
      DOI: 10.1111/gcb.13781
       
  • Thermal adaptation and phenotypic plasticity in a warming world: Insights
           from common garden experiments on Alaskan sockeye salmon
    • Authors: Morgan M. Sparks; Peter A. H. Westley, Jeffrey A. Falke, Thomas P. Quinn
      First page: 5203
      Abstract: An important unresolved question is how populations of coldwater‐dependent fishes will respond to rapidly warming water temperatures. For example, the culturally and economically important group, Pacific salmon (Oncorhynchus spp.), experience site‐specific thermal regimes during early development that could be disrupted by warming. To test for thermal local adaptation and heritable phenotypic plasticity in Pacific salmon embryos, we measured the developmental rate, survival, and body size at hatching in two populations of sockeye salmon (Oncorhynchus nerka) that overlap in timing of spawning but incubate in contrasting natural thermal regimes. Using a split half‐sibling design, we exposed embryos of 10 families from each of two populations to variable and constant thermal regimes. These represented both experienced temperatures by each population, and predicted temperatures under plausible future conditions based on a warming scenario from the downscaled global climate model (MIROC A1B scenario). We did not find evidence of thermal local adaptation during the embryonic stage for developmental rate or survival. Within treatments, populations hatched within 1 day of each other, on average, and among treatments, did not differ in survival in response to temperature. We did detect plasticity to temperature; embryos developed 2.5 times longer (189 days) in the coolest regime compared to the warmest regime (74 days). We also detected variation in developmental rates among families within and among temperature regimes, indicating heritable plasticity. Families exhibited a strong positive relationship between thermal variability and phenotypic variability in developmental rate but body length and mass at hatching were largely insensitive to temperature. Overall, our results indicated a lack of thermal local adaptation, but a presence of plasticity in populations experiencing contrasting conditions, as well as family‐specific heritable plasticity that could facilitate adaptive change.Using a common garden approach that uniquely accounts for natural thermal variability, we simultaneously tested for thermal local adaptation and heritable phenotypic plasticity and show that developmental rate is largely governed by plasticity that has a heritable family‐specific component. Taken as a whole, our study indicates that survival of this important ectothermic organism at this life history period may not be directly impacted by predicted thermal conditions and that heritable phenotypic plasticity may largely buffer these populations against the effects of warming.
      PubDate: 2017-07-06T01:15:37.607563-05:
      DOI: 10.1111/gcb.13782
       
  • The heat is on: Genetic adaptation to urbanization mediated by thermal
           tolerance and body size
    • Authors: Kristien I. Brans; Mieke Jansen, Joost Vanoverbeke, Nedim Tüzün, Robby Stoks, Luc De Meester
      First page: 5218
      Abstract: Worldwide, urbanization leads to tremendous anthropogenic environmental alterations, causing strong selection pressures on populations of animals and plants. Although a key feature of urban areas is their higher temperature (“urban heat islands”), adaptive thermal evolution in organisms inhabiting urban areas has rarely been studied. We tested for evolution of a higher heat tolerance (CTMAX) in urban populations of the water flea Daphnia magna, a keystone grazer in freshwater ecosystems, by carrying out a common garden experiment at two temperatures (20°C and 24°C) with genotypes of 13 natural populations ordered along a well‐defined urbanization gradient. We also assessed body size and haemoglobin concentration to identify underlying physiological drivers of responses in CTMAX. We found a higher CTMAX in animals isolated from urban compared to rural habitats and in animals reared at higher temperatures. We also observed substantial genetic variation in thermal tolerance within populations. Overall, smaller animals were more heat tolerant. While urban animals mature at smaller size, the effect of urbanization on thermal tolerance is only in part caused by reductions in body size. Although urban Daphnia contained higher concentrations of haemoglobin, this did not contribute to their higher CTMAX. Our results provide evidence of adaptive thermal evolution to urbanization in the water flea Daphnia. In addition, our results show both evolutionary potential and adaptive plasticity in rural as well as urban Daphnia populations, facilitating responses to warming. Given the important ecological role of Daphnia in ponds and lakes, these adaptive responses likely impact food web dynamics, top‐down control of algae, water quality, and the socio‐economic value of urban ponds.Urbanization causes habitat warming. The impact of “urban heat islands” on evolutionary processes in organisms is, however, rarely studied. A common garden experiment at two rearing temperatures (20°C and 24°C) revealed substantial evidence for thermal adaptation and adaptive plasticity in Daphnia in response to urbanization and rearing temperature. Urban Daphnia and animals reared at 24°C have a higher CTMAX and mature at a smaller size. While urban Daphnia are smaller, this only in part contributed to the evolutionary increase in CTMAX. The observed higher haemoglobin levels in urban animals did not induce a higher CTMAX. We additionally report substantial genetic variation for CTMAX within both rural and urban populations, facilitating responses to warming. Given that urban areas currently experience temperature increases expected to occur over the next 100 years due to climate change, these results, the first to be presented for aquatic organisms, provide the evidence that Daphnia are well equipped to cope with current and future anthropogenic warming.
      PubDate: 2017-07-20T00:20:50.783856-05:
      DOI: 10.1111/gcb.13784
       
  • Symbiotic soil fungi enhance ecosystem resilience to climate change
    • Authors: Laura B. Martínez-García; Gerlinde B. De Deyn, Francisco I. Pugnaire, David Kothamasi, Marcel G. A. Heijden
      First page: 5228
      Abstract: Substantial amounts of nutrients are lost from soils through leaching. These losses can be environmentally damaging, causing groundwater eutrophication and also comprise an economic burden in terms of lost agricultural production. More intense precipitation events caused by climate change will likely aggravate this problem. So far it is unresolved to which extent soil biota can make ecosystems more resilient to climate change and reduce nutrient leaching losses when rainfall intensity increases. In this study, we focused on arbuscular mycorrhizal (AM) fungi, common soil fungi that form symbiotic associations with most land plants and which increase plant nutrient uptake. We hypothesized that AM fungi mitigate nutrient losses following intensive precipitation events (higher amount of precipitation and rain events frequency). To test this, we manipulated the presence of AM fungi in model grassland communities subjected to two rainfall scenarios: moderate and high rainfall intensity. The total amount of nutrients lost through leaching increased substantially with higher rainfall intensity. The presence of AM fungi reduced phosphorus losses by 50% under both rainfall scenarios and nitrogen losses by 40% under high rainfall intensity. Thus, the presence of AM fungi enhanced the nutrient interception ability of soils, and AM fungi reduced the nutrient leaching risk when rainfall intensity increases. These findings are especially relevant in areas with high rainfall intensity (e.g., such as the tropics) and for ecosystems that will experience increased rainfall due to climate change. Overall, this work demonstrates that soil biota such as AM fungi can enhance ecosystem resilience and reduce the negative impact of increased precipitation on nutrient losses.Arbuscular mycorrhizal (AM) fungi enhance ecosystem resilience to climate change by reducing the negative impact of increased precipitation on nutrient losses. AM fungi enhanced the nutrient perception ability of soils and reduced the nutrient leaching losses. The effects of mycorrhizal fungi were more pronounced under the high rainfall scenario, indicating that these soil fungi could play a role in mitigating the negative consequences of climate change.
      PubDate: 2017-07-11T03:35:42.760739-05:
      DOI: 10.1111/gcb.13785
       
  • Temporal scale dependent interactions between multiple environmental
           disturbances in microcosm ecosystems
    • Authors: Aurélie Garnier; Frank Pennekamp, Mélissa Lemoine, Owen L. Petchey
      First page: 5237
      Abstract: Global environmental change has negative impacts on ecological systems, impacting the stable provision of functions, goods, and services. Whereas effects of individual environmental changes (e.g. temperature change or change in resource availability) are reasonably well understood, we lack information about if and how multiple changes interact. We examined interactions among four types of environmental disturbance (temperature, nutrient ratio, carbon enrichment, and light) in a fully factorial design using a microbial aquatic ecosystem and observed responses of dissolved oxygen saturation at three temporal scales (resistance, resilience, and return time). We tested whether multiple disturbances combine in a dominant, additive, or interactive fashion, and compared the predictability of dissolved oxygen across scales. Carbon enrichment and shading reduced oxygen concentration in the short term (i.e. resistance); although no other effects or interactions were statistically significant, resistance decreased as the number of disturbances increased. In the medium term, only enrichment accelerated recovery, but none of the other effects (including interactions) were significant. In the long term, enrichment and shading lengthened return times, and we found significant two‐way synergistic interactions between disturbances. The best performing model (dominant, additive, or interactive) depended on the temporal scale of response. In the short term (i.e. for resistance), the dominance model predicted resistance of dissolved oxygen best, due to a large effect of carbon enrichment, whereas none of the models could predict the medium term (i.e. resilience). The long‐term response was best predicted by models including interactions among disturbances. Our results indicate the importance of accounting for the temporal scale of responses when researching the effects of environmental disturbances on ecosystems.Global change threatens the stability of goods and services provided by ecosystems. Nevertheless, little is known about 1) whether and how multiple disturbances interact, 2) whether interactions among disturbances change over time and 3) whether predictions change depending on how disturbances interact.We studied the temporal effect of four common disturbances on an integrative measure of ecosystem health, dissolved oxygen, in a microbial aquatic system.Our results highlight the importance of interactions among disturbances in determining long‐term trajectories of stability of ecosystem services, whereas the dominant disturbance best predicted short‐term trajectories of stability.
      PubDate: 2017-07-06T23:55:46.417689-05:
      DOI: 10.1111/gcb.13786
       
  • Linkages of plant stoichiometry to ecosystem production and carbon fluxes
           with increasing nitrogen inputs in an alpine steppe
    • Authors: Yunfeng Peng; Fei Li, Guoying Zhou, Kai Fang, Dianye Zhang, Changbin Li, Guibiao Yang, Guanqin Wang, Jun Wang, Yuanhe Yang
      First page: 5249
      Abstract: Unprecedented levels of nitrogen (N) have entered terrestrial ecosystems over the past century, which substantially influences the carbon (C) exchange between the atmosphere and biosphere. Temperature and moisture are generally regarded as the major controllers over the N effects on ecosystem C uptake and release. N‐phosphorous (P) stoichiometry regulates the growth and metabolisms of plants and soil organisms, thereby affecting many ecosystem C processes. However, it remains unclear how the N‐induced shift in the plant N:P ratio affects ecosystem production and C fluxes and its relative importance. We conducted a field manipulative experiment with eight N addition levels in a Tibetan alpine steppe and assessed the influences of N on aboveground net primary production (ANPP), gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem exchange (NEE); we used linear mixed‐effects models to further determine the relative contributions of various factors to the N‐induced changes in these parameters. Our results showed that the ANPP, GEP, ER, and NEE all exhibited nonlinear responses to increasing N additions. Further analysis demonstrated that the plant N:P ratio played a dominate role in shaping these C exchange processes. There was a positive relationship between the N‐induced changes in ANPP (ΔANPP) and the plant N:P ratio (ΔN:P), whereas the ΔGEP, ΔER, and ΔNEE exhibited quadratic correlations with the ΔN:P. In contrast, soil temperature and moisture were only secondary predictors for the changes in ecosystem production and C fluxes along the N addition gradient. These findings highlight the importance of plant N:P ratio in regulating ecosystem C exchange, which is crucial for improving our understanding of C cycles under the scenarios of global N enrichment.Increasing nitrogen (N) deposition substantially influences the carbon (C) exchange between the atmosphere and terrestrial biosphere. Temperature and moisture are generally regarded as the major controllers over the N effects on ecosystem C uptake and release. Here we present evidence that plant N:phosphorous (P) ratio, too, is tightly linked to ecosystem production and C fluxes under N additions. Using a field experiment with various N addition levels, we found that plant N:P ratio played a dominate role in shaping these C exchange processes, whereas edaphic variables were relatively weaker in predicting the changes in ecosystem production and C fluxes induced by N additions. These findings highlight the importance of plant N‐P stoichiometry in regulating ecosystem C exchange, which is crucial for improving our understanding of C cycles under the scenarios of global N enrichment.
      PubDate: 2017-07-08T02:25:36.980892-05:
      DOI: 10.1111/gcb.13789
       
  • Land‐use strategies to balance livestock production, biodiversity
           conservation and carbon storage in Yucatán, Mexico
    • Authors: David R Williams; Fredy Alvarado, Rhys E Green, Andrea Manica, Ben Phalan, Andrew Balmford
      First page: 5260
      Abstract: Balancing the production of food, particularly meat, with preserving biodiversity and maintaining ecosystem services is a major societal challenge. Research into the contrasting strategies of land sparing and land sharing has suggested that land sparing—combining high‐yield agriculture with the protection or restoration of natural habitats on nonfarmed land—will have lower environmental impacts than other strategies. Ecosystems with long histories of habitat disturbance, however, could be resilient to low‐yield agriculture and thus fare better under land sharing. Using a wider suite of species (birds, dung beetles and trees) and a wider range of livestock‐production systems than previous studies, we investigated the probable impacts of different land‐use strategies on biodiversity and aboveground carbon stocks in the Yucatán Peninsula, Mexico—a region with a long history of habitat disturbance. By modelling the production of multiple products from interdependent land uses, we found that land sparing would allow larger estimated populations of most species and larger carbon stocks to persist than would land sharing or any intermediate strategy. This result held across all agricultural production targets despite the history of disturbance and despite species richness in low‐ and medium‐yielding agriculture being not much lower than that in natural habitats. This highlights the importance, in evaluating the biodiversity impacts of land use, of measuring population densities of individual species, rather than simple species richness. The benefits of land sparing for both biodiversity and carbon storage suggest that safeguarding natural habitats for biodiversity protection and carbon storage alongside promoting areas of high‐yield cattle production would be desirable. However, delivering such landscapes will probably require the explicit linkage of livestock yield increases with habitat protection or restoration, as well as a deeper understanding of the long‐term sustainability of yields, and research into how other societal outcomes vary across land‐use strategies.The proportion of bird, dung beetle and tree species showing different responses to agriculture. The solid vertical line shows current production levels, the dashed line the projected 2025 production target. Across all taxa and production levels, land sparing is the least harmful approach.
      PubDate: 2017-07-10T00:30:39.653412-05:
      DOI: 10.1111/gcb.13791
       
  • Modelling the dynamic physical protection of soil organic carbon: Insights
           into carbon predictions and explanation of the priming effect
    • Authors: Zhongkui Luo; Jeff Baldock, Enli Wang
      First page: 5273
      Abstract: The role and significance of physically protected soil organic carbon (SOC) in regulating SOC dynamics remains unclear. Here, we developed a simple theoretical model (DP model) considering dynamic physical protection to simulate the dynamics of protected (Cp) and unprotected SOC (Cu), and compared the modelling results with a conventional two‐pool (fast vs. slow) model considering chemical recalcitrance. The two models were first constrained using extensive SOC data collected from soils with and without fresh carbon (C) inputs under incubation conditions, and then applied to project SOC dynamics and explore mechanisms underpinning the priming effect (PE). Overall, both models explained more than 99% of the variances in observed SOC dynamics. The DP model predicted that Cp accounted for the majority of total SOC. As decomposition proceeds, the proportion of Cp reached >90% and kept relatively constant. Although the similar performance of the two models in simulating observed total SOC dynamics, their predictions of future SOC dynamics were divergent, challenging the predictions of widely used pool‐based models. The DP model also suggested alternative mechanisms underpinning the priming of SOC decomposition by fresh C inputs. The two‐pool model suggested that the PE was caused by the stimulated decomposition rates, especially for the slow recalcitrant pool, while the DP model suggested that the PE might be the combined consequence of stimulated Cu decomposition, the liberation of Cp to decomposition and the inhibition of the protection of unprotected SOC. The model‐data integration provided a new explanation for the PE, highlighting the importance of liberation of initially physically protected SOC to decomposition by new C inputs. Our model‐data integration demonstrated the importance of simulating physical protection processes for reliable SOC predictions, and provided new insights into mechanistic understanding of the priming effect.The role and significance of physically protected soil organic carbon (SOC) in regulating SOC dynamics remains unclear. We constrained a simple model (DP model) to simulate the dynamics of protected (Cp) and unprotected SOC (Cu), and compared the modelling results with a traditional two‐pool (fast vs. slow) model. We found that the majority of SOC was physically protected. Simulating the dynamics of physically protected SOC had significant consequences on the prediction of future SOC dynamics and explanation of underlying mechanisms. Focusing on the priming effect (PE), the modelling results suggested alternative mechanisms underpinning the PE. That is, fresh C inputs did not only increase the decomposition rate of unprotected‐decomposing SOC, but also liberated protected SOC to decomposition. Overall, the results demonstrated the importance of considering physical protection processes in soil C models, providing new insights into understanding of SOC decomposition processes.
      PubDate: 2017-07-08T02:20:40.179183-05:
      DOI: 10.1111/gcb.13793
       
  • Global change and the distributional dynamics of migratory bird
           populations wintering in Central America
    • Authors: Frank A. La Sorte; Daniel Fink, Peter J. Blancher, Amanda D. Rodewald, Viviana Ruiz-Gutierrez, Kenneth V. Rosenberg, Wesley M. Hochachka, Peter H. Verburg, Steve Kelling
      First page: 5284
      Abstract: Understanding the susceptibility of highly mobile taxa such as migratory birds to global change requires information on geographic patterns of occurrence across the annual cycle. Neotropical migrants that breed in North America and winter in Central America occur in high concentrations on their non‐breeding grounds where they spend the majority of the year and where habitat loss has been associated with population declines. Here, we use eBird data to model weekly patterns of abundance and occurrence for 21 forest passerine species that winter in Central America. We estimate species’ distributional dynamics across the annual cycle, which we use to determine how species are currently associated with public protected areas and projected changes in climate and land‐use. The effects of global change on the non‐breeding grounds is characterized by decreasing precipitation, especially during the summer, and the conversion of forest to cropland, grassland, or peri‐urban. The effects of global change on the breeding grounds are characterized by increasing winter precipitation, higher temperatures, and the conversion of forest to peri‐urban. During spring and autumn migration, species are projected to encounter higher temperatures, forests that have been converted to peri‐urban, and increased precipitation during spring migration. Based on current distributional dynamics, susceptibility to global change is characterized by the loss of forested habitats on the non‐breeding grounds, warming temperatures during migration and on the breeding grounds, and declining summer rainfall on the non‐breeding grounds. Public protected areas with low and medium protection status are more prevalent on the non‐breeding grounds, suggesting that management opportunities currently exist to mitigate near‐term non‐breeding habitat losses. These efforts would affect more individuals of more species during a longer period of the annual cycle, which may create additional opportunities for species to respond to changes in habitat or phenology that are likely to develop under climate change.Understanding the implications of global change for highly mobile taxa such as migratory birds requires information on geographic patterns of occurrence across the full annual cycle. We use eBird data to model weekly patterns of abundance and occurrence for 21 forest passerine species that winter in Central America. Our findings indicate that land‐use change and climate change are likely to have more significant implications for these species on their wintering grounds. Our findings also suggest that management opportunities currently exist to mitigate the near‐term loss of wintering habitats, which may provide longer term benefits as climate change progresses.
      PubDate: 2017-07-24T00:30:02.954946-05:
      DOI: 10.1111/gcb.13794
       
  • Recent climatic drying leads to age‐independent growth reductions of
           white spruce stands in western Canada
    • Authors: Edward H. Hogg; Michael Michaelian, Trisha I. Hook, Michael E. Undershultz
      First page: 5297
      Abstract: Since 2001, climatic conditions have been notably drier than normal across large areas of the western Canadian interior, leading to widespread impacts on the forests of this region. This poses a major concern for the future, given climate change projections for continued warming and drying. We conducted tree‐ring analysis in 75 pure stands of white spruce (Picea glauca) across Alberta and west‐central Saskatchewan to examine the effects of recent climatic drying on the growth of this important boreal tree species. Allometric equations were used to calculate annual growth in aboveground tree biomass (GBM) from ring width measurements. Results showed an increasing trend in GBM from the 1960s to the 1990s, followed by a sharp decline during the severe drought of 2001–2002. Of the 75 stands, only 18 recovered sufficiently to cause an increase in mean GBM from the predrought decade of 1991–2000 to the subsequent decade of 2001–2010. The remaining 57 stands exhibited a decline in mean GBM between these decades. Climatic drying was a major cause of the growth decline, as shown by the significant stand‐level relationship between percentage change in decadal mean GBM and the change in decadal mean values of a climate moisture index from 1991–2000 to 2001–2010. Subsequent analyses of boreal stands sampled across Alberta during 2015 revealed that white spruce growth had declined even further as drought conditions intensified during 2014–2015. Overall, there was a 38% decrease in mean GBM between 1997 and 2015, but surprisingly, the percentage decrease was not significantly different for young, productive stands compared with older, less productive stands. Thus, stand ageing cannot explain the observed decline in white spruce growth during the past quarter century, suggesting that these forests are at risk if the trend towards more frequent, severe drought continues in the region.Annual change in (a) average increment of aboveground tree biomass and (b) the climate moisture index during 1960–2015 for 40 white spruce stands sampled in 2015 across northern and west‐central Alberta. Average values are also shown for the youngest and oldest stands within each of 10 study areas. Vertical lines denote drought years having negative average values of the climate moisture index for these 10 study areas.
      PubDate: 2017-07-17T04:21:31.752179-05:
      DOI: 10.1111/gcb.13795
       
  • Thermal buffering capacity of the germination phenotype across the
           environmental envelope of the Cactaceae
    • Authors: Charlotte E. Seal; Matthew I. Daws, Joel Flores, Pablo Ortega-Baes, Guadalupe Galíndez, Pedro León-Lobos, Ana Sandoval, Aldo Ceroni Stuva, Natali Ramírez Bullón, Patricia Dávila-Aranda, Cesar A. Ordoñez-Salanueva, Laura Yáñez-Espinosa, Tiziana Ulian, Cecilia Amosso, Lino Zubani, Alberto Torres Bilbao, Hugh W. Pritchard
      First page: 5309
      Abstract: Recruitment from seeds is among the most vulnerable stage for plants as global temperatures change. While germination is the means by which the vast majority of the world's flora regenerate naturally, a framework for accurately predicting which species are at greatest risk of germination failure during environmental perturbation is lacking. Taking a physiological approach, we assess how one family, the Cactaceae, may respond to global temperature change based on the thermal buffering capacity of the germination phenotype. We selected 55 cactus species from the Americas, all geo‐referenced seed collections, reflecting the broad environmental envelope of the family across 70° of latitude and 3700 m of altitude. We then generated empirical data of the thermal germination response from which we estimated the minimum (Tb), optimum (To) and ceiling (Tc) temperature for germination and the thermal time (θ50) for each species based on the linearity of germination rate with temperature. Species with the highest Tb and lowest Tc germinated fastest, and the interspecific sensitivity of the germination rate to temperature, as assessed through θ50, varied tenfold. A left‐skewed asymmetry in the germination rate with temperature was relatively common but the unimodal pattern typical of crop species failed for nearly half of the species due to insensitivity to temperature change at To. For 32 fully characterized species, seed thermal parameters correlated strongly with the mean temperature of the wettest quarter of the seed collection sites. By projecting the mean temperature of the wettest quarter under two climate change scenarios, we predict under the least conservative scenario (+3.7°C) that 25% of cactus species will have reduced germination performance, whilst the remainder will have an efficiency gain, by the end of the 21st century.Predictions of germination performance were made by comparing the optimum germination temperature (To) with current and projected climate change scenarios (+1.0°C and +3.7°C); a negative impact on germination rate is predicted when the environmental temperature exceeds To (a). The time required to achieve 50% germination under the different scenarios was also calculated (b). Under the +3.7°C scenario, 24 species will have an efficiency gain in germination demonstrating sufficient thermal buffering to cope with global temperature change.
      PubDate: 2017-07-20T00:22:35.050271-05:
      DOI: 10.1111/gcb.13796
       
  • Sea‐ice loss boosts visual search: fish foraging and changing pelagic
           interactions in polar oceans
    • Authors: Tom J. Langbehn; Øystein Varpe
      First page: 5318
      Abstract: Light is a central driver of biological processes and systems. Receding sea ice changes the lightscape of high‐latitude oceans and more light will penetrate into the sea. This affects bottom‐up control through primary productivity and top‐down control through vision‐based foraging. We model effects of sea‐ice shading on visual search to develop a mechanistic understanding of how climate‐driven sea‐ice retreat affects predator–prey interactions. We adapt a prey encounter model for ice‐covered waters, where prey‐detection performance of planktivorous fish depends on the light cycle. We use hindcast sea‐ice concentrations (past 35 years) and compare with a future no‐ice scenario to project visual range along two south–north transects with different sea‐ice distributions and seasonality, one through the Bering Sea and one through the Barents Sea. The transect approach captures the transition from sub‐Arctic to Arctic ecosystems and allows for comparison of latitudinal differences between longitudes. We find that past sea‐ice retreat has increased visual search at a rate of 2.7% to 4.2% per decade from the long‐term mean; and for high latitudes, we predict a 16‐fold increase in clearance rate. Top‐down control is therefore predicted to intensify. Ecological and evolutionary consequences for polar marine communities and energy flows would follow, possibly also as tipping points and regime shifts. We expect species distributions to track the receding ice‐edge, and in particular expect species with large migratory capacity to make foraging forays into high‐latitude oceans. However, the extreme seasonality in photoperiod of high‐latitude oceans may counteract such shifts and rather act as a zoogeographical filter limiting poleward range expansion. The provided mechanistic insights are relevant for pelagic ecosystems globally, including lakes where shifted distributions are seldom possible but where predator–prey consequences would be much related. As part of the discussion on photoperiodic implications for high‐latitude range shifts, we provide a short review of studies linking physical drivers to latitudinal extent.We explore how climate‐driven sea‐ice decline restructures visual search, and thereby predator–prey interactions and distribution of pelagic fish, in a future Arctic Ocean. Less sea ice means increased light, which results in a nonlinear change of visual predation performance. We find that earlier melt dates and longer ice‐free periods during summer month benefit visual predators, but also that sea‐ice independent light constraints on visual foraging remain during the polar night, likely to act as a zoogeographical filter limiting northward range shifts.
      PubDate: 2017-07-31T07:22:17.321259-05:
      DOI: 10.1111/gcb.13797
       
  • Protected areas offer refuge from invasive species spreading under climate
           change
    • Authors: Belinda Gallardo; David C. Aldridge, Pablo González-Moreno, Jan Pergl, Manuel Pizarro, Petr Pyšek, Wilfried Thuiller, Christopher Yesson, Montserrat Vilà
      First page: 5331
      Abstract: Protected areas (PAs) are intended to provide native biodiversity and habitats with a refuge against the impacts of global change, particularly acting as natural filters against biological invasions. In practice, however, it is unknown how effective PAs will be in shielding native species from invasions under projected climate change. Here, we investigate the current and future potential distributions of 100 of the most invasive terrestrial, freshwater, and marine species in Europe. We use this information to evaluate the combined threat posed by climate change and invasions to existing PAs and the most susceptible species they shelter. We found that only a quarter of Europe's marine and terrestrial areas protected over the last 100 years have been colonized by any of the invaders investigated, despite offering climatically suitable conditions for invasion. In addition, hotspots of invasive species and the most susceptible native species to their establishment do not match at large continental scales. Furthermore, the predicted richness of invaders is 11%–18% significantly lower inside PAs than outside them. Invasive species are rare in long‐established national parks and nature reserves, which are actively protected and often located in remote and pristine regions with very low human density. In contrast, the richness of invasive species is high in the more recently designated Natura 2000 sites, which are subject to high human accessibility. This situation may change in the future, since our models anticipate important shifts in species ranges toward the north and east of Europe at unprecedented rates of 14–55 km/decade, depending on taxonomic group and scenario. This may seriously compromise the conservation of biodiversity and ecosystem services. This study is the first comprehensive assessment of the resistance that PAs provide against biological invasions and climate change on a continental scale and illustrates their strategic value in safeguarding native biodiversity.Protected areas are championed as refugia for native biodiversity and habitats, but we do not know how effective they are in shielding native taxa from biological invasions under projected climate change.Here, we found that only a quarter of Europe's marine and terrestrial areas protected over the last 100 years have been colonized by 100 of the worst terrestrial, freshwater, and marine invaders, with long‐established areas showing the lowest richness of invaders (A).This situation may change in the future, as models anticipate a shift in species distribution toward the north and east of Europe in response to climate change (B).
      PubDate: 2017-07-31T00:30:02.336089-05:
      DOI: 10.1111/gcb.13798
       
  • Marine‐terminating glaciers sustain high productivity in Greenland
           fjords
    • Authors: Lorenz Meire; John Mortensen, Patrick Meire, Thomas Juul-Pedersen, Mikael K. Sejr, Søren Rysgaard, Rasmus Nygaard, Philippe Huybrechts, Filip J. R. Meysman
      First page: 5344
      Abstract: Accelerated mass loss from the Greenland ice sheet leads to glacier retreat and an increasing input of glacial meltwater to the fjords and coastal waters around Greenland. These high latitude ecosystems are highly productive and sustain important fisheries, yet it remains uncertain how they will respond to future changes in the Arctic cryosphere. Here we show that marine‐terminating glaciers play a crucial role in sustaining high productivity of the fjord ecosystems. Hydrographic and biogeochemical data from two fjord systems adjacent to the Greenland ice sheet, suggest that marine ecosystem productivity is very differently regulated in fjords influenced by either land‐terminating or marine‐terminating glaciers. Rising subsurface meltwater plumes originating from marine‐terminating glaciers entrain large volumes of ambient deep water to the surface. The resulting upwelling of nutrient‐rich deep water sustains a high phytoplankton productivity throughout summer in the fjord with marine‐terminating glaciers. In contrast, the fjord with only land‐terminating glaciers lack this upwelling mechanism, and is characterized by lower productivity. Data on commercial halibut landings support that coastal regions influenced by large marine‐terminating glaciers have substantially higher marine productivity. These results suggest that a switch from marine‐terminating to land‐terminating glaciers can substantially alter the productivity in the coastal zone around Greenland with potentially large ecological and socio‐economic implications.Marine productivity is very differently regulated in fjords influenced by land‐terminating or marine‐terminating glaciers. Fjords with marine‐terminating glaciers sustain a much higher productivity due to nutrient upwelling by rising subsurface meltwater. Glacier retreat hence can have large impact on marine productivity and fisheries in the fjords around Greenland.
      PubDate: 2017-08-04T00:30:03.257677-05:
      DOI: 10.1111/gcb.13801
       
  • Risk of genetic maladaptation due to climate change in three major
           European tree species
    • Authors: Aline Frank; Glenn T. Howe, Christoph Sperisen, Peter Brang, J. Bradley St. Clair, Dirk R. Schmatz, Caroline Heiri
      First page: 5358
      Abstract: Tree populations usually show adaptations to their local environments as a result of natural selection. As climates change, populations can become locally maladapted and decline in fitness. Evaluating the expected degree of genetic maladaptation due to climate change will allow forest managers to assess forest vulnerability, and develop strategies to preserve forest health and productivity. We studied potential genetic maladaptation to future climates in three major European tree species, Norway spruce (Picea abies), silver fir (Abies alba), and European beech (Fagus sylvatica). A common garden experiment was conducted to evaluate the quantitative genetic variation in growth and phenology of seedlings from 77 to 92 native populations of each species from across Switzerland. We used multivariate genecological models to associate population variation with past seed source climates, and to estimate relative risk of maladaptation to current and future climates based on key phenotypic traits and three regional climate projections within the A1B scenario. Current risks from climate change were similar to average risks from current seed transfer practices. For all three climate models, future risks increased in spruce and beech until the end of the century, but remained low in fir. Largest average risks associated with climate projections for the period 2061–2090 were found for spruce seedling height (0.64), and for beech bud break and leaf senescence (0.52 and 0.46). Future risks for spruce were high across Switzerland. However, areas of high risk were also found in drought‐prone regions for beech and in the southern Alps for fir. Genetic maladaptation to future climates is likely to become a problem for spruce and beech by the end of this century, but probably not for fir. Consequently, forest management strategies should be adjusted in the study area for spruce and beech to maintain productive and healthy forests in the future.To guide forest management, we investigated potential genetic maladaptation to future climates in Norway spruce, silver fir, and European beech in Switzerland. Based on data from a genecological field test, we project all three species to be adapted to the near‐term climates of 2021 to 2050. Considering the climates of 2061 to 2090 (see figure), fir is projected to be still largely adapted (b), whereas spruce and beech are expected to be maladapted in many regions (a, c). Consequently, spruce and beech deserve greater attention when designing management strategies for maintaining healthy Swiss forests.
      PubDate: 2017-08-10T03:00:33.517756-05:
      DOI: 10.1111/gcb.13802
       
  • Warmer winters increase the rhizosphere carbon flow to mycorrhizal fungi
           more than to other microorganisms in a temperate grassland
    • Authors: Johanna Birgander; Johannes Rousk, Pål Axel Olsson
      First page: 5372
      Abstract: A decisive set of steps in the terrestrial carbon (C) cycle is the fixation of atmospheric C by plants and the subsequent C‐transfer to rhizosphere microorganisms. With climate change winters are expected to become milder in temperate ecosystems. Although the rate and pathways of rhizosphere C input to soil could be impacted by milder winters, the responses remain unknown. To address this knowledge‐gap, a winter‐warming experiment was established in a seminatural temperate grassland to follow the C flow from atmosphere, via the plants, to different groups of soil microorganisms. In situ 13CO2 pulse labelling was used to track C into signature fatty acids of microorganisms. The winter warming did not result in any changes in biomass of any of the groups of microorganisms. However, the C flow from plants to arbuscular mycorrhizal (AM) fungi, increased substantially by winter warming. Saprotrophic fungi also received large amounts of plant‐derived C—indicating a higher importance for the turnover of rhizosphere C than biomass estimates would suggest—still, this C flow was unaffected by winter warming. AM fungi was the only microbial group positively affected by winter warming—the group with the closest connection to plants. Winter warming resulted in higher plant productivity earlier in the season, and this aboveground change likely induced plant nutrient limitation in warmed plots, thus stimulating the plant dependence on, and C allocation to, belowground nutrient acquisition. The preferential C allocation to AM fungi was at the expense of C flow to other microbial groups, which were unaffected by warming. Our findings imply that warmer winters may shift rhizosphere C‐fluxes to become more AM fungal‐dominated. Surprisingly, the stimulated rhizosphere C flow was matched by increased microbial turnover, leading to no accumulation of soil microbial biomass.In a warming‐experiment we tracked carbon from plants to microorganisms. Arbuscular mycorrhizal and saprotrophic fungi got most of the carbon from the plants, but only mycorrhizal fungi benefited from warm (the red curve) compared to ambient (the blue curve) temperatures. These responses were probably caused by earlier onset of flowering, and plant growth during milder winters.
      PubDate: 2017-08-17T03:41:11.706976-05:
      DOI: 10.1111/gcb.13803
       
  • A casualty of climate change' Loss of freshwater forest islands on
           Florida's Gulf Coast
    • Authors: Amy K. Langston; David A. Kaplan, Francis E. Putz
      First page: 5383
      Abstract: Sea level rise elicits short‐ and long‐term changes in coastal plant communities by altering the physical conditions that affect ecosystem processes and species distributions. While the effects of sea level rise on salt marshes and mangroves are well studied, we focus on its effects on coastal islands of freshwater forest in Florida's Big Bend region, extending a dataset initiated in 1992. In 2014–2015, we evaluated tree survival, regeneration, and understory composition in 13 previously established plots located along a tidal creek; 10 plots are on forest islands surrounded by salt marsh, and three are in continuous forest. Earlier studies found that salt stress from increased tidal flooding prevented tree regeneration in frequently flooded forest islands. Between 1992 and 2014, tidal flooding of forest islands increased by 22%–117%, corresponding with declines in tree species richness, regeneration, and survival of the dominant tree species, Sabal palmetto (cabbage palm) and Juniperus virginiana (southern red cedar). Rates of S. palmetto and J. virginiana mortality increased nonlinearly over time on the six most frequently flooded islands, while salt marsh herbs and shrubs replaced forest understory vegetation along a tidal flooding gradient. Frequencies of tidal flooding, rates of tree mortality, and understory composition in continuous forest stands remained relatively stable, but tree regeneration substantially declined. Long‐term trends identified in this study demonstrate the effect of sea level rise on spatial and temporal community reassembly trajectories that are dynamically re‐shaping the unique coastal landscape of the Big Bend.Through long‐term field observations, we investigated the replacement of coastal freshwater forest islands by salt‐tolerant vegetation in response to sea level rise. We found that in forest islands subjected to infrequent tidal flooding during a 22‐year period, live trees and an under story composed of forest vegetation persisted, though tree regeneration and species richness declined. In moderately flooding islands, tidal flooding increased 43%–117%; few live, nonregenerating trees remained by 2014, and under stories became dominated by halophytic shrubs. In frequently flooded islands, tidal flooding increased 22%–33%, and freshwater forest was completely replaced by herbaceous salt marsh. Our study demonstrates how climate change‐driven community reassembly is altering the unique coastal landscape of Florida.
      PubDate: 2017-07-26T04:31:02.85664-05:0
      DOI: 10.1111/gcb.13805
       
  • Deep peat warming increases surface methane and carbon dioxide emissions
           in a black spruce‐dominated ombrotrophic bog
    • Authors: Allison L. Gill; Marc-André Giasson, Rieka Yu, Adrien C. Finzi
      First page: 5398
      Abstract: Boreal peatlands contain approximately 500 Pg carbon (C) in the soil, emit globally significant quantities of methane (CH4), and are highly sensitive to climate change. Warming associated with global climate change is likely to increase the rate of the temperature‐sensitive processes that decompose stored organic carbon and release carbon dioxide (CO2) and CH4. Variation in the temperature sensitivity of CO2 and CH4 production and increased peat aerobicity due to enhanced growing‐season evapotranspiration may alter the nature of peatland trace gas emission. As CH4 is a powerful greenhouse gas with 34 times the warming potential of CO2, it is critical to understand how factors associated with global change will influence surface CO2 and CH4 fluxes. Here, we leverage the Spruce and Peatland Responses Under Changing Environments (SPRUCE) climate change manipulation experiment to understand the impact of a 0–9°C gradient in deep belowground warming (“Deep Peat Heat”, DPH) on peat surface CO2 and CH4 fluxes. We find that DPH treatments increased both CO2 and CH4 emission. Methane production was more sensitive to warming than CO2 production, decreasing the C‐CO2:C‐CH4 of the respired carbon. Methane production is dominated by hydrogenotrophic methanogenesis but deep peat warming increased the δ13C of CH4 suggesting an increasing contribution of acetoclastic methanogenesis to total CH4 production with warming. Although the total quantity of C emitted from the SPRUCE Bog as CH4 is 50% of seasonal C emissions in the highest‐warming treatments when adjusted for CO2 equivalents on a 100‐year timescale. These results suggest that warming in boreal regions may increase CH4 emissions from peatlands and result in a positive feedback to ongoing warming.Belowground warming increased both CO2 and CH4 emission, but CH4 production was more sensitive to warming which decreased the CO2:CH4 of the respired C. Although the total quantity of C emitted from the bog as CH4 is small, CH4 represents >50% of seasonal C emissions in the highest warming treatments when adjusted for CO2 equivalents. These results suggest that high‐latitude warming may increase the contribution of CH4 to total ecosystem C losses and make peatlands a positive feedback to additional warming.
      PubDate: 2017-07-28T05:36:44.051594-05:
      DOI: 10.1111/gcb.13806
       
  • Multidate, multisensor remote sensing reveals high density of
           carbon‐rich mountain peatlands in the páramo of Ecuador
    • Authors: John A. Hribljan; Esteban Suarez, Laura Bourgeau-Chavez, Sarah Endres, Erik A. Lilleskov, Segundo Chimbolema, Craig Wayson, Eleanor Serocki, Rodney A. Chimner
      First page: 5412
      Abstract: Tropical peatlands store a significant portion of the global soil carbon (C) pool. However, tropical mountain peatlands contain extensive peat soils that have yet to be mapped or included in global C estimates. This lack of data hinders our ability to inform policy and apply sustainable management practices to these peatlands that are experiencing unprecedented high rates of land use and land cover change. Rapid large‐scale mapping activities are urgently needed to quantify tropical wetland extent and rate of degradation. We tested a combination of multidate, multisensor radar and optical imagery (Landsat TM/PALSAR/RADARSAT‐1/TPI image stack) for detecting peatlands in a 2715 km2 area in the high elevation mountains of the Ecuadorian páramo. The map was combined with an extensive soil coring data set to produce the first estimate of regional peatland soil C storage in the páramo. Our map displayed a high coverage of peatlands (614 km2) containing an estimated 128.2 ± 9.1 Tg of peatland belowground soil C within the mapping area. Scaling‐up to the country level, páramo peatlands likely represent less than 1% of the total land area of Ecuador but could contain as much as ~23% of the above‐ and belowground vegetation C stocks in Ecuadorian forests. These mapping approaches provide an essential methodological improvement applicable to mountain peatlands across the globe, facilitating mapping efforts in support of effective policy and sustainable management, including national and global C accounting and C management efforts.Tropical mountain peatlands contain extensive peat soils that have yet to be mapped or included in global carbon estimates. Our map displayed a high coverage of peatlands containing large belowground soil carbon storage within the Ecuadorian Andes. These mapping approaches provide an essential methodological improvement applicable to mountain peatlands across the globe, facilitating mapping efforts in support of effective policy and sustainable management, including national and global carbon accounting and C management efforts.
      PubDate: 2017-07-26T04:12:20.38519-05:0
      DOI: 10.1111/gcb.13807
       
  • Increasing temperature cuts back crop yields in Hungary over the last 90
           years
    • Authors: Zsolt Pinke; Gábor L. Lövei
      First page: 5426
      Abstract: The transformation of climatic regime has an undeniable impact on plant production, but we rarely have long enough date series to examine the unfolding of such effects. The clarification of the relationship between crop plants and climate has a near‐immediate importance due to the impending human‐made global change. This study investigated the relationship between temperature, precipitation, drought intensity and the yields of four major cereals in Hungary between 1921 and 2010. The analysis of 30‐year segments indicated a monotonously increasing negative impact of temperature on crop yields. A 1°C temperature increase reduced the yield of the four main cereals by 9.6%–14.8% in 1981–2010, which revealed the vulnerability of Eastern European crop farming to recent climate change. Climate accounted for 17%–39% of yield variability over the past 90 years, but this figure reached 33%–67% between 1981 and 2010. Our analysis supports the claim that the mid‐20th century green revolution improved yields “at the mercy of the weather”: during this period, the impact of increasing fertilization and mechanisation coincided with climatic conditions that were more favourable than today. Crop yields in Eastern Europe have been stagnating or decreasing since the mid‐1980s. Although usually attributed to the large socio‐economic changes sweeping the region, our analysis indicates that a warming climate is at least partially responsible for this trend. Such a robust impact of increasing temperatures on crop yields also constitutes an obvious warning for this core grain‐growing region of the world.The analysis of 90 year weather and yield data indicated that grain yields in Hungary are increasingly sensitive to climatic factors, esp. to drought. The figure shows the effect of deviations from the mean in precipitation (left), temperature (middle) and drought index (right) on yields of the four major grains in Hungary, during three 30‐year periods between 1921 and 2010. Note that the slope of the last period, 1981‐2010, is usually steeper than the others, indicating an increasing impact of climate deviations on yields.
      PubDate: 2017-08-08T06:25:37.460781-05:
      DOI: 10.1111/gcb.13808
       
  • Multi‐century tree‐ring precipitation record reveals increasing
           frequency of extreme dry events in the upper Blue Nile River catchment
    • Authors: Mulugeta Mokria; Aster Gebrekirstos, Abrham Abiyu, Meine Van Noordwijk, Achim Bräuning
      First page: 5436
      Abstract: Climate‐related environmental and humanitarian crisis are important challenges in the Great Horn of Africa (GHA). In the absence of long‐term past climate records in the region, tree‐rings are valuable climate proxies, reflecting past climate variations and complementing climate records prior to the instrumental era. We established annually resolved multi‐century tree‐ring chronology from Juniperus procera trees in northern Ethiopia, the longest series yet for the GHA. The chronology correlates significantly with wet‐season (r = .64, p 
      PubDate: 2017-08-23T06:56:14.433002-05:
      DOI: 10.1111/gcb.13809
       
  • Unexpected stasis in a changing world: Lake nutrient and chlorophyll
           trends since 1990
    • Authors: Samantha K. Oliver; Sarah M. Collins, Patricia A. Soranno, Tyler Wagner, Emily H. Stanley, John R. Jones, Craig A. Stow, Noah R. Lottig
      First page: 5455
      Abstract: The United States (U.S.) has faced major environmental changes in recent decades, including agricultural intensification and urban expansion, as well as changes in atmospheric deposition and climate—all of which may influence eutrophication of freshwaters. However, it is unclear whether or how water quality in lakes across diverse ecological settings has responded to environmental change. We quantified water quality trends in 2913 lakes using nutrient and chlorophyll (Chl) observations from the Lake Multi‐Scaled Geospatial and Temporal Database of the Northeast U.S. (LAGOS‐NE), a collection of preexisting lake data mostly from state agencies. LAGOS‐NE was used to quantify whether lake water quality has changed from 1990 to 2013, and whether lake‐specific or regional geophysical factors were related to the observed changes. We modeled change through time using hierarchical linear models for total nitrogen (TN), total phosphorus (TP), stoichiometry (TN:TP), and Chl. Both the slopes (percent change per year) and intercepts (value in 1990) were allowed to vary by lake and region. Across all lakes, TN declined at a rate of 1.1% year−1, while TP, TN:TP, and Chl did not change. A minority (7%–16%) of individual lakes had changing nutrients, stoichiometry, or Chl. Of those lakes that changed, we found differences in the geospatial variables that were most related to the observed change in the response variables. For example, TN and TN:TP trends were related to region‐level drivers associated with atmospheric deposition of N; TP trends were related to both lake and region‐level drivers associated with climate and land use; and Chl trends were found in regions with high air temperature at the beginning of the study period. We conclude that despite large environmental change and management efforts over recent decades, water quality of lakes in the Midwest and Northeast U.S. has not overwhelmingly degraded or improved.The United States (U.S.) has faced major environmental changes in recent decades, and it is unclear whether or how water quality in lakes across diverse ecological settings has responded. We studied nitrogen, phosphorus, and chlorophyll trends from 1990–2013 in lakes across the U.S. We concluded that despite large environmental change and management efforts over recent decades, water quality of lakes in the Midwest and Northeast U.S. has not overwhelmingly degraded or improved.
      PubDate: 2017-08-23T09:30:01.626717-05:
      DOI: 10.1111/gcb.13810
       
  • The spatial distribution of soil organic carbon in tidal wetland soils of
           the continental United States
    • Authors: Audra L. Hinson; Rusty A. Feagin, Marian Eriksson, Raymond G. Najjar, Maria Herrmann, Thomas S. Bianchi, Michael Kemp, Jack A. Hutchings, Steve Crooks, Thomas Boutton
      First page: 5468
      Abstract: Tidal wetlands contain large reservoirs of carbon in their soils and can sequester carbon dioxide (CO2) at a greater rate per unit area than nearly any other ecosystem. The spatial distribution of this carbon influences climate and wetland policy. To assist with international accords such as the Paris Climate Agreement, national‐level assessments such as the United States (U.S.) National Greenhouse Gas Inventory, and regional, state, local, and project‐level evaluation of CO2 sequestration credits, we developed a geodatabase (CoBluCarb) and high‐resolution maps of soil organic carbon (SOC) distribution by linking National Wetlands Inventory data with the U.S. Soil Survey Geographic Database. For over 600,000 wetlands, the total carbon stock and organic carbon density was calculated at 5‐cm vertical resolution from 0 to 300 cm of depth. Across the continental United States, there are 1,153–1,359 Tg of SOC in the upper 0–100 cm of soils across a total of 24 945.9 km2 of tidal wetland area, twice as much carbon as the most recent national estimate. Approximately 75% of this carbon was found in estuarine emergent wetlands with freshwater tidal wetlands holding about 19%. The greatest pool of SOC was found within the Atchafalaya/Vermilion Bay complex in Louisiana, containing about 10% of the U.S. total. The average density across all tidal wetlands was 0.071 g cm−3 across 0–15 cm, 0.055 g cm−3 across 0–100 cm, and 0.040 g cm−3 at the 100 cm depth. There is inherent variability between and within individual wetlands; however, we conclude that it is possible to use standardized values at a range of 0–100 cm of the soil profile, to provide first‐order quantification and to evaluate future changes in carbon stocks in response to environmental perturbations. This Tier 2‐oriented carbon stock assessment provides a scientific method that can be copied by other nations in support of international requirements.In the tidal wetlands across the United States, there is 1,152–1,359 Tg of soil organic carbon (SOC), which is twice as much carbon as the most recent national estimate. The average area‐weighted carbon density is 0.040 g cm‐3 at the 100 cm depth. Approximately 75% of the carbon is found in herbaceous estuarine emergent wetlands with freshwater tidal wetlands holding about 19%. Standardized values can be used to provide a first‐order valuation of sequestration potential.
      PubDate: 2017-08-17T01:41:19.284058-05:
      DOI: 10.1111/gcb.13811
       
  • A reversal of the shift towards earlier spring phenology in several
           Mediterranean reptiles and amphibians during the 1998–2013 warming
           slowdown
    • Authors: Roger Prodon; Philippe Geniez, Marc Cheylan, Florence Devers, Isabelle Chuine, Aurelien Besnard
      First page: 5481
      Abstract: Herps, especially amphibians, are particularly susceptible to climate change, as temperature tightly controls many parameters of their biological cycle—above all, their phenology. The timing of herps’ activity or migration period—in particular the dates of their first appearance in spring and first breeding—and the shift to earlier dates in response to warming since the last quarter of the 20th century has often been described up to now as a nearly monotonic trend towards earlier phenological events. In this study, we used citizen science data opportunistically collected on reptiles and amphibians in the northern Mediterranean basin over a period of 32 years to explore temporal variations in herp phenology. For 17 common species, we measured shifts in the date of the species’ first spring appearance—which may be the result of current changes in climate—and regressed the first appearance date against temperatures and precipitations. Our results confirmed the expected overall trend towards earlier first spring appearances from 1983 to 1997, and show that the first appearance date of both reptiles and amphibians fits well with the temperature in late winter. However, the trend towards earlier dates was stopped or even reversed in most species between 1998 and 2013. We interpret this reversal as a response to cooling related to the North Atlantic Oscillation (NAO) in the late winter and early spring. During the positive NAO episodes, for certain species only (mainly amphibians), the effect of a warm weather, which tends to advance the phenology, seems to be counterbalanced by the adverse effects of the relative dryness.The date of first appearance in spring of the Mediterranean snake Malpolon monspellulanus shifted about 55 days earlier from 1983 to 1997, but this trend was reversed afterwards. This shift, that was observed in several amphibian and reptile species, mirrors the temperature changes in the February–March period, in relation with the North Atlantic Oscillation.
      PubDate: 2017-09-01T05:30:51.085329-05:
      DOI: 10.1111/gcb.13812
       
  • Long‐term changes in abundances of Sonoran Desert lizards reveal complex
           responses to climatic variation
    • Authors: Aaron D. Flesch; Philip C. Rosen, Peter Holm
      First page: 5492
      Abstract: Understanding how climatic variation affects animal populations and communities is essential for addressing threats posed by climate change, especially in systems where impacts are projected to be high. We evaluated abundance dynamics of five common species of diurnal lizards over 25 years in a Sonoran Desert transition zone where precipitation decreased and temperature increased across time, and assessed hypotheses for the influence of climatic flux on spatiotemporal variation in abundances. We repeatedly surveyed lizards in spring and summer of each year at up to 32 sites, and used hierarchical mixture models to estimate detection probabilities, abundances, and population growth rates. Among terrestrial species, abundances of a short‐lived, winter–spring breeder increased markedly by an estimated 237%–285% across time, while two larger spring–summer breeders with higher thermal preferences declined by up to 64%. Abundances of two arboreal species that occupy shaded and thus sheltered microhabitats fluctuated but did not decline systematically. Abundances of all species increased with precipitation at short lag times (1–1.5 years) likely due to enhanced food availability, but often declined after periods of high precipitation at longer lag times (2–4 years) likely due to predation and other biotic pressures. Although rising maximum daily temperatures (Tmax) are expected to drive global declines of lizards, associations with Tmax were variable and weak for most species. Instead, abundances of all species declined with rising daily minimum temperatures, suggesting degradation of cool refugia imposed widespread metabolic or other costs. Our results suggest climate warming and drying are having major impacts on lizard communities by driving declines in species with traits that augment exposure to abiotic extremes and by modifying species interactions. The complexity of patterns we report indicates that evaluating and responding to the influence of climate change on biodiversity must consider a broad array of ecological processes.We evaluated abundance dynamics of five lizard species over 25 years in the Sonoran Desert, and assessed the effects of climatic flux. Abundances of terrestrial species varied across time; a winter–spring breeder increased nearly threefold across time, whereas two spring–summer breeders declining by up to 64%. Abundances of arboreal species that occupy shaded, sheltered microhabitats fluctuated but did not decline. Increasing minimum but not maximum temperatures had marked effects on abundances, suggesting degradation of cool refugia‐imposed metabolic costs. Climate warming and drying are driving declines in species with traits that augment exposure to abiotic extremes and modifying species interactions.
      PubDate: 2017-08-17T03:49:18.43998-05:0
      DOI: 10.1111/gcb.13813
       
  • Warming drives a front of white spruce establishment near western
           treeline, Alaska
    • Authors: Amy E. Miller; Tammy L. Wilson, Rosemary L. Sherriff, James Walton
      First page: 5509
      Abstract: Regional warming has led to increased productivity near the boreal forest margin in Alaska. To date, the effects of warming on seedling recruitment have received little attention, in spite of forecasted forest expansion. Here, we used stand structure and environmental data from 95 white spruce (Picea glauca) plots sampled across a longitudinal gradient in southwest Alaska to explore factors influencing spruce establishment and recruitment near western treeline. We used total counts of live seedlings, saplings, and trees, representing five life stages, to evaluate whether geospatial, climate, and measured plot covariates predicted abundance, using current abundance distributions as a surrogate for climate conditions in the past. We used generalized linear models to test the null hypothesis that conditions favorable for recruitment were similar along the environmental gradient represented by longitude, by exploring relationships between per‐plot counts of each life stage and the covariates hypothesized to affect abundance. We also examined the relationship between growing degree days (GDD) and seedling establishment over a period of three decades using tree‐ring chronologies obtained from cores taken at a subset of our sites (n = 30). Our results indicated that seedling, sapling, and tree abundance were positively correlated with temperature across the study area. The response to longitude was mixed, with earlier life stages (seedlings, saplings) most abundant at the western end of the gradient, and later life stages (trees) most abundant to the east. The differential relationship between longitude and life‐stage abundance suggests a moving front of white spruce establishment through time, driven by changes in environmental conditions near the species’ western range limit. Likewise, we found a positive relationship between periods of seedling establishment and GDD, suggesting that longer summers and/or greater heat accumulation might enhance establishment, consistent with the positive relationship we found between life‐stage abundance and temperature.We evaluated the effect of geospatial, climate, and plot covariates on the abundance of five life stages of white spruce from stands in southwest Alaska, and the relationship between growing season conditions and seedling establishment. We found a positive relationship between abundance and temperature that was consistent across all life stages, but a mixed response to longitude, with earlier life stages (seedlings, saplings) most abundant at the western end of the gradient, near the current range margin, and later life stages (trees) most abundant to the east. Likewise, white spruce establishment was positively associated with longer summers and/or greater heat accumulation, as inferred from growing degree days. Together, our results suggest a moving front of white spruce establishment, toward the species’ western range limit.
      PubDate: 2017-08-17T04:20:45.118644-05:
      DOI: 10.1111/gcb.13814
       
  • Aquatic export of young dissolved and gaseous carbon from a pristine
           boreal fen: Implications for peat carbon stock stability
    • Authors: Audrey Campeau; Kevin H. Bishop, Michael F. Billett, Mark H. Garnett, Hjalmar Laudon, Jason A. Leach, Mats B. Nilsson, Mats G. Öquist, Marcus B. Wallin
      First page: 5523
      Abstract: The stability of northern peatland's carbon (C) store under changing climate is of major concern for the global C cycle. The aquatic export of C from boreal peatlands is recognized as both a critical pathway for the remobilization of peat C stocks as well as a major component of the net ecosystem C balance (NECB). Here, we present a full year characterization of radiocarbon content (14C) of dissolved organic carbon (DOC), carbon dioxide (CO2), and methane (CH4) exported from a boreal peatland catchment coupled with 14C characterization of the catchment's peat profile of the same C species. The age of aquatic C in runoff varied little throughout the year and appeared to be sustained by recently fixed C from the atmosphere (
      PubDate: 2017-09-01T06:00:42.689272-05:
      DOI: 10.1111/gcb.13815
       
 
 
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