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Showing 1 - 200 of 3089 Journals sorted alphabetically
A Practical Logic of Cognitive Systems     Full-text available via subscription   (Followers: 7)
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 25, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 22, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 86, SJR: 1.109, h-index: 94)
Accounting Forum     Hybrid Journal   (Followers: 25, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 30, SJR: 2.515, h-index: 90)
Achievements in the Life Sciences     Open Access   (Followers: 4)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 5, SJR: 0.338, h-index: 19)
Acta Astronautica     Hybrid Journal   (Followers: 363, SJR: 0.726, h-index: 43)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Biomaterialia     Hybrid Journal   (Followers: 25, SJR: 2.02, h-index: 104)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 1)
Acta de Investigación Psicológica     Open Access   (Followers: 2)
Acta Ecologica Sinica     Open Access   (Followers: 8, SJR: 0.172, h-index: 29)
Acta Haematologica Polonica     Free   (SJR: 0.123, h-index: 8)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.604, h-index: 38)
Acta Materialia     Hybrid Journal   (Followers: 229, SJR: 3.683, h-index: 202)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.615, h-index: 21)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.442, h-index: 21)
Acta Oecologica     Hybrid Journal   (Followers: 10, SJR: 0.915, h-index: 53)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription   (Followers: 1)
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 3, SJR: 0.311, h-index: 16)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1)
Acta Poética     Open Access   (Followers: 4)
Acta Psychologica     Hybrid Journal   (Followers: 24, SJR: 1.365, h-index: 73)
Acta Sociológica     Open Access  
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.059, h-index: 77)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 4)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 3)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 4, SJR: 0.383, h-index: 19)
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Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 5, SJR: 0.141, h-index: 3)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 4, SJR: 0.112, h-index: 2)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 4)
Acute Pain     Full-text available via subscription   (Followers: 13)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.967, h-index: 57)
Addictive Behaviors     Hybrid Journal   (Followers: 15, SJR: 1.514, h-index: 92)
Addictive Behaviors Reports     Open Access   (Followers: 6)
Additive Manufacturing     Hybrid Journal   (Followers: 7, SJR: 1.039, h-index: 5)
Additives for Polymers     Full-text available via subscription   (Followers: 21)
Advanced Cement Based Materials     Full-text available via subscription   (Followers: 3)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 133, SJR: 5.2, h-index: 222)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.265, h-index: 53)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.739, h-index: 33)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.299, h-index: 15)
Advances in Agronomy     Full-text available via subscription   (Followers: 15, SJR: 2.071, h-index: 82)
Advances in Anesthesia     Full-text available via subscription   (Followers: 26, SJR: 0.169, h-index: 4)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 3)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 6, SJR: 1.054, h-index: 35)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 11, SJR: 0.801, h-index: 26)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 22, SJR: 1.286, h-index: 49)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 16, SJR: 3.31, h-index: 42)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.277, h-index: 43)
Advances in Botanical Research     Full-text available via subscription   (Followers: 3, SJR: 0.619, h-index: 48)
Advances in Cancer Research     Full-text available via subscription   (Followers: 25, SJR: 2.215, h-index: 78)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 0.9, h-index: 30)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 2.139, h-index: 42)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 4)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 12)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 27, SJR: 0.183, h-index: 23)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.665, h-index: 29)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 9, SJR: 1.268, h-index: 45)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 29, SJR: 0.938, h-index: 33)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18, SJR: 2.314, h-index: 130)
Advances in Computers     Full-text available via subscription   (Followers: 16, SJR: 0.223, h-index: 22)
Advances in Dermatology     Full-text available via subscription   (Followers: 12)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 11)
Advances in Digestive Medicine     Open Access   (Followers: 7)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Ecological Research     Full-text available via subscription   (Followers: 45, SJR: 3.25, h-index: 43)
Advances in Engineering Software     Hybrid Journal   (Followers: 26, SJR: 0.486, h-index: 10)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 43, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 8)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 51, SJR: 0.674, h-index: 38)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 16)
Advances in Genetics     Full-text available via subscription   (Followers: 15, SJR: 2.558, h-index: 54)
Advances in Genome Biology     Full-text available via subscription   (Followers: 11)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 2.325, h-index: 20)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 22, SJR: 0.906, h-index: 24)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 0.497, h-index: 31)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 26)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.396, h-index: 27)
Advances in Immunology     Full-text available via subscription   (Followers: 36, SJR: 4.152, h-index: 85)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 1.132, h-index: 42)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 3, SJR: 1.274, h-index: 27)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 4)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.764, h-index: 15)
Advances in Lipobiology     Full-text available via subscription   (Followers: 2)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Marine Biology     Full-text available via subscription   (Followers: 16, SJR: 1.645, h-index: 45)
Advances in Mathematics     Full-text available via subscription   (Followers: 10, SJR: 3.261, h-index: 65)
Advances in Medical Sciences     Hybrid Journal   (Followers: 6, SJR: 0.489, h-index: 25)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.44, h-index: 51)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 22)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 10)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 8, SJR: 0.324, h-index: 8)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 4)
Advances in Oncobiology     Full-text available via subscription   (Followers: 3)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15, SJR: 2.885, h-index: 45)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.148, h-index: 11)
Advances in Parasitology     Full-text available via subscription   (Followers: 7, SJR: 2.37, h-index: 73)
Advances in Pediatrics     Full-text available via subscription   (Followers: 24, SJR: 0.4, h-index: 28)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 13)
Advances in Pharmacology     Full-text available via subscription   (Followers: 15, SJR: 1.718, h-index: 58)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.384, h-index: 26)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.248, h-index: 11)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 8)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 17)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 1.5, h-index: 62)
Advances in Psychology     Full-text available via subscription   (Followers: 62)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5, SJR: 0.478, h-index: 32)
Advances in Radiation Oncology     Open Access  
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 2, SJR: 0.1, h-index: 2)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 5)
Advances in Space Research     Full-text available via subscription   (Followers: 361, SJR: 0.606, h-index: 65)
Advances in Structural Biology     Full-text available via subscription   (Followers: 8)
Advances in Surgery     Full-text available via subscription   (Followers: 7, SJR: 0.823, h-index: 27)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 30, SJR: 1.321, h-index: 56)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 16)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 13)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 1.878, h-index: 68)
Advances in Water Resources     Hybrid Journal   (Followers: 44, SJR: 2.408, h-index: 94)
Aeolian Research     Hybrid Journal   (Followers: 5, SJR: 0.973, h-index: 22)
Aerospace Science and Technology     Hybrid Journal   (Followers: 331, SJR: 0.816, h-index: 49)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.318, h-index: 36)
African J. of Emergency Medicine     Open Access   (Followers: 5, SJR: 0.344, h-index: 6)
Ageing Research Reviews     Hybrid Journal   (Followers: 8, SJR: 3.289, h-index: 78)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 417, SJR: 1.385, h-index: 72)
Agri Gene     Hybrid Journal  
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 16, SJR: 2.18, h-index: 116)
Agricultural Systems     Hybrid Journal   (Followers: 30, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 40, SJR: 1.546, h-index: 79)
Agriculture and Agricultural Science Procedia     Open Access  
Agriculture and Natural Resources     Open Access   (Followers: 2)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 55, SJR: 1.879, h-index: 120)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.434, h-index: 14)
Air Medical J.     Hybrid Journal   (Followers: 5, SJR: 0.234, h-index: 18)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.285, h-index: 3)
Alcohol     Hybrid Journal   (Followers: 11, SJR: 0.922, h-index: 66)
Alcoholism and Drug Addiction     Open Access   (Followers: 8)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.436, h-index: 12)
Alexandria J. of Medicine     Open Access   (Followers: 1)
Algal Research     Partially Free   (Followers: 8, SJR: 2.05, h-index: 20)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.46, h-index: 29)
Allergology Intl.     Open Access   (Followers: 4, SJR: 0.776, h-index: 35)
Alpha Omegan     Full-text available via subscription   (SJR: 0.121, h-index: 9)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 9, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 46, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 4)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 5)
American Heart J.     Hybrid Journal   (Followers: 49, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 48, SJR: 2.063, h-index: 186)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 40, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 9, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 32, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 26, SJR: 1.259, h-index: 81)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 32, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 46, SJR: 2.023, h-index: 189)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 199, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 59, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 6)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.249, h-index: 88)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, h-index: 45)
American J. of Pathology     Hybrid Journal   (Followers: 27, SJR: 2.653, h-index: 228)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 25, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 35, SJR: 1.286, h-index: 125)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.653, h-index: 70)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 6)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.066, h-index: 51)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 58, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 12)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 2, SJR: 0.209, h-index: 27)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription   (SJR: 0.104, h-index: 3)
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 4, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 37, SJR: 1.548, h-index: 152)
Analytical Biochemistry     Hybrid Journal   (Followers: 167, SJR: 0.725, h-index: 154)
Analytical Chemistry Research     Open Access   (Followers: 8, SJR: 0.18, h-index: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 12)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 1)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 22, SJR: 0.421, h-index: 40)
Angiología     Full-text available via subscription   (SJR: 0.124, h-index: 9)
Angiologia e Cirurgia Vascular     Open Access  

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Journal Cover Agricultural and Forest Meteorology
  [SJR: 2.18]   [H-I: 116]   [16 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0168-1923
   Published by Elsevier Homepage  [3049 journals]
  • Simple models to predict grassland ecosystem C exchange and actual
           evapotranspiration using NDVI and environmental variables
    • Authors: Stephen J. Del Grosso; W.J. Parton; Justin D. Derner; Maosi Chen; Compton J. Tucker
      Pages: 1 - 10
      Abstract: Publication date: 15 February 2018
      Source:Agricultural and Forest Meteorology, Volume 249
      Author(s): Stephen J. Del Grosso, W.J. Parton, Justin D. Derner, Maosi Chen, Compton J. Tucker
      Semiarid grasslands contribute significantly to net terrestrial carbon flux as plant productivity and heterotrophic respiration in these moisture-limited systems are correlated with metrics related to water availability (e.g., precipitation, Actual EvapoTranspiration or AET). These variables are also correlated with remotely sensed metrics such as the Normalized Difference Vegetation Index (NDVI). We used measurements of growing season net ecosystem exchange of carbon (NEE), NDVI from eMODIS and AVHRR, precipitation, and volumetric soil water content (VSWC) from grazed pastures in the semiarid, shortgrass steppe to quantify the correlation of NEE with these driving variables. eMODIS NDVI explained 60 and 40% of the variability in daytime and nighttime NEE, respectively, on non-rain days; these correlations were reduced to 41 and 15%, respectively, on rain days. Daytime NEE was almost always negative (sink) on non-rain days but positive on most rain days. In contrast, nighttime NEE was always positive (source), across rain and non-rain days. A model based on eMODIS NDVI, VSWC, daytime vs. nighttime, and rain vs. non-rain days explained 48% of observed variability in NEE at a daily scale; this increased to 62% and 77%, respectively, at the weekly and monthly scales. eMODIS NDVI explained 50–52% of the variability in AET regardless of rain or non-rain days. A model based on eMODIS NDVI, VSWC, Potential EvapoTranspiration (or PET), and rain vs. non-rain days explained 70% of the observed variability in AET at a daily scale; this increased to 90 and 96%, respectively, at weekly and monthly scales. Models based on AVHRR NDVI showed similar patterns as those using eMODIS, but correlations with observations were lower. We conclude that remotely-sensed NDVI is a robust tool, when combined with VSWC and knowledge of rain events, for predicting NEE and AET across multiple temporal scales (day to season) in semiarid grasslands.

      PubDate: 2017-11-24T07:10:28Z
      DOI: 10.1016/j.agrformet.2017.11.007
      Issue No: Vol. 249 (2017)
  • A steady-state approximation approach to simulate seasonal leaf dynamics
           of deciduous broadleaf forests via climate variables
    • Authors: Qinchuan Xin; Yongjiu Dai; Xia Li; Xiaoping Liu; Peng Gong; Andrew D. Richardson
      Pages: 44 - 56
      Abstract: Publication date: 15 February 2018
      Source:Agricultural and Forest Meteorology, Volume 249
      Author(s): Qinchuan Xin, Yongjiu Dai, Xia Li, Xiaoping Liu, Peng Gong, Andrew D. Richardson
      As leaves are the basic elements of plants that conduct photosynthesis and transpiration, vegetation leaf dynamics controls canopy physical and biogeochemical processes and hence largely influences the interactive exchanges of energy and materials between the land surface and the atmosphere. Given that the processes of plant leaf allocation is highly sensitive to climatological and environmental conditions, developing robust models that simulate leaf dynamics via climate variables contributes a key component to land surface models and coupled land-atmosphere models. Here we propose a new method to simulate seasonal leaf dynamics based on the idea of applying vegetation productivity as a synthesized metric to track and assess the climate suitability to plant growth over time. The method first solves two closed simultaneous equations of leaf phenology and canopy photosynthesis as modeled using the Growing Production-Day model iteratively for deriving the time series of steady-state leaf area index (LAI), and then applies the method of simple moving average to account for the time lagging of leaf allocation behind steady-state LAI. The seasonal LAI simulated using the developed method agree with field measurements from a selection of AmeriFlux sites as indicated by high coefficient of determination (R2 =0.801) and low root mean square error (RMSE=0.924m2/m2) and with satellite-derived data (R2 =0.929 and RMSE=0.650m2/m2) for the studied flux tower sites. Moreover, the proposed method is able to simulate seasonal LAI of deciduous broadleaf forests that match with satellite-derived LAI time series across the entire eastern United States. Comparative modeling studies suggest that the proposed method produces more accurate results than the method based on Growing Season Index in terms of correlation coefficients and error metrics. The developed method provides a complete solution to modeling seasonal leaf dynamics as well as canopy productivity solely using climate variables.

      PubDate: 2017-11-24T07:10:28Z
      DOI: 10.1016/j.agrformet.2017.11.025
      Issue No: Vol. 249 (2017)
  • Water loss by transpiration and soil evaporation in coffee shaded by
           Tabebuia rosea Bertol. and Simarouba glauca dc. compared to unshaded
           coffee in sub-optimal environmental conditions
    • Authors: M.P. Padovan; R.M. Brook; M. Barrios; J.B. Cruz-Castillo; S.J. Vilchez-Mendoza; A.N. Costa; B. Rapidel
      Pages: 1 - 14
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): M.P. Padovan, R.M. Brook, M. Barrios, J.B. Cruz-Castillo, S.J. Vilchez-Mendoza, A.N. Costa, B. Rapidel
      There is increasing concern that due to land pressure and the need to maximize income, smallholder coffee farmers are increasingly being forced to cultivate in areas which are considered to be sub-optimal for coffee. Little is known about optimal coffee and tree combinations in these conditions and the degree to which crops and trees compete or are synergistic. In environmental conditions which were sub optimal for coffee cultivation in Nicaragua (1470mm annual rainfall, 27°C mean annual temperature and 455m altitude compared to optima of 2000mm, 23–24°C and altitude between 1000 and 1400m at that latitude, respectively), coffee and shade tree transpiration and soil evaporation were directly and separately measured in agroforestry (AFS) and full sun systems (FS). AFS was found to be a more efficient water user than FS because a greater proportion of rainfall was used by plant transpiration rather than being lost by soil evaporation. Plant transpiration accounted for 83% and 69% of evapotranspiration while soil evaporation represented 17% and 31%, in AFS and FS respectively. In AFS most of the water transpiration was due to coffee (72.5%) and much less by deciduous Tabebuia rosea (19%) and evergreen Simarouba glauca shade trees (8.5%). Furthermore, the study demonstrated the vastly different behaviour in water use by the shade trees. When in leaf, Tabebuia rosea transpired at four to six times the rate of evergreen Simarouba glauca, although crown sizes were similar. Contrasting precipitation between two consecutive years of study demonstrated that competition for water between coffee and shade tree occurred only in a severe dry season when coffee leaf water potential (LWP) reached its lowest values of −2.33MPa in AFS. It was concluded that in most circumstances there was sufficient water for both coffee and trees, that coffee in AFS was a more efficient user of water than FS coffee, and that evergreen Simarouba glauca was more suitable as coffee shade tree compared to deciduous Tabebuia rosea in the sub optimal environmental condition studied.

      PubDate: 2017-11-11T13:27:10Z
      DOI: 10.1016/j.agrformet.2017.08.036
      Issue No: Vol. 248 (2017)
  • Linked spatial variability of throughfall amount and intensity during
           rainfall in a coniferous forest
    • Authors: Richard F. Keim; Timothy E. Link
      Pages: 15 - 21
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Richard F. Keim, Timothy E. Link
      Routing of rainfall through forest canopies causes spatial variability in throughfall amounts and intensities, but the covariance of these effects has not been investigated. We investigated the relationship between point throughfall amount and intensity reduction in an old-growth seasonal temperate rainforest in southwestern Washington, USA, using tipping bucket rain gauges both under and above the coniferous forest canopy. Mean hydraulic residence time of rainfall in the canopy was 25min, with event means ranging between 4 and 52min. Locations of high throughfall accumulation received throughfall at intensities similar to rainfall, and locations of low accumulation experienced more variable intensities. Drip points funneling water to zones of high accumulation are not typical of this coniferous seasonal temperate rainforest. There was a positive relationship between intensity reduction by the canopy and evaporation during rain events that indicates that refilling of storage made available by evaporation is important for buffering throughfall intensities.

      PubDate: 2017-09-23T18:51:13Z
      DOI: 10.1016/j.agrformet.2017.09.006
      Issue No: Vol. 248 (2017)
  • Intercomparison of surface energy fluxes, soil moisture, and
           evapotranspiration from eddy covariance, large-aperture scintillometer,
           and modeling across three ecosystems in a semiarid climate
    • Authors: Prasanth Valayamkunnath; Venkataramana Sridhar; Wenguang Zhao; Richard G. Allen
      Pages: 22 - 47
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Prasanth Valayamkunnath, Venkataramana Sridhar, Wenguang Zhao, Richard G. Allen
      A comprehensive seasonal and interannual energy partition and flux analyses were conducted to differentiate three ecosystems including sagebrush, cheatgrass, and lodgepole pine in the Snake River Plain of Idaho. The study used 3 years of eddy covariance (EC) and large aperture scintillometer (LAS) flux measurements to evaluate the bio-physical processes that control the surface energy partitioning. A comparison of sensible heat flux (SH) by EC (HEC ) and LAS (HLAS ) showed HEC was slightly underestimated due to wind turbulence and energy balance closure issues. The Noah Land Surface Model (LSM) was configured with NCEP-NARR (NOAHNARR simulation) or meteorological observation from the EC tower (NOAHObs simulation). NOAHNARR simulation showed significantly more RMSE compared to NOAHObs due to biases in downwelling shortwave and longwave radiation and precipitation (P) in the NARR data. Higher leaf area index (LAI) and moderate stomatal resistance (RS) of lodgepole pine resulted in increased evapotranspiration (ET) (472–535mm/year) compared to cheatgrass (261mm to 278mm/year) and sagebrush (229–353mm/year). The Budyko ET analysis showed that all the three sites are water deficient and the evaporative ratio was less for the lodgepole pine ecosystem (0.80) when compared to sagebrush (0.94) and cheatgrass (0.93). The residual (attributed to deep percolation and runoff) from the water budget was higher (15–16%) in the lodgepole pine compared to that of cheatgrass (2–5%) and sagebrush (2–9%). Our results indicate the field-scale distinguishing features of heterogeneous ecosystems in the semi-arid environment and emphasize the need for intercomparison of flux measurements for better understanding of energy budget partitioning and improving the accuracy of simulated fluxes.

      PubDate: 2017-09-23T18:51:13Z
      DOI: 10.1016/j.agrformet.2017.08.025
      Issue No: Vol. 248 (2017)
  • The challenge of reconciling bottom-up agricultural methane emissions
           inventories with top-down measurements
    • Authors: R.L. Desjardins; D.E. Worth; E. Pattey; A. VanderZaag; R. Srinivasan; M. Mauder; D. Worthy; C. Sweeney; S. Metzger
      Pages: 48 - 59
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): R.L. Desjardins, D.E. Worth, E. Pattey, A. VanderZaag, R. Srinivasan, M. Mauder, D. Worthy, C. Sweeney, S. Metzger
      Agriculture is estimated to produce more than 40% of anthropogenic methane (CH4) emissions, contributing to global climate change. Bottom-up, IPCC based methodologies are typically used to estimate the agriculture sector’s contribution, but these estimates are rarely verified beyond the farm gate, due to the challenge of separating interspersed sources. We present flux measurements of CH4, using eddy covariance (EC), relaxed eddy accumulation (REA) and wavelet covariance obtained using an aircraft-based measurement platform and compare these top-down estimates with bottom-up footprint adjusted inventory estimates of CH4 emissions for an agricultural region in eastern Ontario, Canada. Top-down CH4 fluxes agree well (mean±1 standard error: EC=17±4mg CH4 m−2 d−1; REA=19±3mg CH4 m−2 d−1, wavelet covariance=16±3mgCH4 m−2 d−1), and are not statistically different, but significantly exceed bottom-up inventory estimates of CH4 emissions based on animal husbandry (8±1mgCH4 m−2 d−1). The discrepancy between top-down and bottom-up estimates was found to be related to both increasing fractional area of wetlands in the flux footprint, and increasing surface temperature. For the case when the wetland area in the flux footprint was less than 10% fractional coverage, the top-down and bottom-up estimates were within the measurement error. This result provides the first independent verification of agricultural methane emissions inventories at the regional scale. Wavelet analysis, which provides spatially resolved fluxes, was used to attempt to separate CH4 emissions from managed and unmanaged CH4 sources. Opportunities to minimize the challenges of verifying agricultural CH4 emissions inventories using aircraft flux measuring systems are discussed.
      Graphical abstract image

      PubDate: 2017-09-23T18:51:13Z
      DOI: 10.1016/j.agrformet.2017.09.003
      Issue No: Vol. 248 (2017)
  • Sequestration of atmospheric CO2 in boreal forest carbon pools in
           northeastern China: Effects of nitrogen deposition
    • Authors: Guoyong Yan; Yajuan Xing; Jianyu Wang; Zhenghua Li; Ligong Wang; Qinggui Wang; Lijian Xu; Zhi Zhang; Junhui Zhang; Xiongde Dong; Wenjun Shan; Liang Guo; Shijie Han
      Pages: 70 - 81
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Guoyong Yan, Yajuan Xing, Jianyu Wang, Zhenghua Li, Ligong Wang, Qinggui Wang, Lijian Xu, Zhi Zhang, Junhui Zhang, Xiongde Dong, Wenjun Shan, Liang Guo, Shijie Han
      An increase in nitrogen (N) deposition has been proposed to cause boreal forests to capture and store a globally significant quantity of carbon (C), but the size of the boreal forest C sink remains uncertain after N addition. Therefore, we conducted a N addition experiment using four N addition rates (0, 2.5, 5.0 and 7.5gNm−2 yr−1) in the boreal zone of northeastern China to determine the changes in forest C sequestration and to investigate the mechanisms of the changes in C sequestration after N addition. Our data show that N addition increases the total C sequestration, but the efficiency of this effect is reduced as the N addition rate increases. We also found that the amount and the mechanism of the C sequestration increase in above- and belowground C pools vary with different amounts of N addition. Low- and medium-N addition increased the above- and belowground C sequestration, and the potential mechanisms responsible for such C accumulation include N-induced increases in photosynthesis via a decrease in the foliar C content and increases in root mass via increased plant C allocation in the roots. However, high-N addition decreases aboveground C sequestration by inhibiting photosynthesis and increases belowground C sequestration by inhibiting soil C losses. Our data indicate that the response patterns of above- and belowground C pools to different amounts of N addition may involve several complex biochemical processes and occur by different mechanisms; therefore, separating the effects of N addition on above- and belowground C sequestration will help improve and validate current modeling efforts.

      PubDate: 2017-09-30T08:46:25Z
      DOI: 10.1016/j.agrformet.2017.09.015
      Issue No: Vol. 248 (2017)
  • Temporal photoperiod sensitivity and forcing requirements for budburst in
           temperate tree seedlings
    • Authors: Andrey V. Malyshev; Hugh A.L. Henry; Andreas Bolte; Mohammed A.S. Arfin Khan; Juergen Kreyling
      Pages: 82 - 90
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Andrey V. Malyshev, Hugh A.L. Henry, Andreas Bolte, Mohammed A.S. Arfin Khan, Juergen Kreyling
      Phenological responses to winter and spring warming in trees alter growing season length and can influence productivity. An improved mechanistic understanding of phenology, including temporal changes in budburst forcing requirements (BFR) and photoperiod sensitivity, could improve projections of phenological shifts and changes in tree species composition in response to climate warming. We investigated changes in BFR and photoperiod sensitivities at high temporal resolution from mid-winter to spring in seedlings of eight common deciduous and coniferous temperate tree species. Eight provenances of F. sylvatica, a dominant European species, also were included to examine variability in bud dormancy patterns within a species. Tree seedlings were over-wintered in a common garden and transferred weekly into climate chambers at forcing temperatures (+20°C) from December to April. Budburst was observed under 16 and 8h photoperiods. Across species, as chilling unit sums accumulated, BFR and photoperiod sensitivity decreased. Functions relating chilling and forcing unit sums explained ambient spring budburst accurately. BFR differed strongly among species, but not among provenances of F. sylvatica from similar latitudes. Overall, our results indicate that a precise tracking of BFR and photoperiod sensitivity helps explain species-specific differences in phenotypic sensitivities, which can improve species-specific projections of phenological responses to climate warming.

      PubDate: 2017-09-30T08:46:25Z
      DOI: 10.1016/j.agrformet.2017.09.011
      Issue No: Vol. 248 (2017)
  • The effects of projected climate and climate extremes on a winter and
           summer crop in the southeast USA
    • Authors: Davide Cammarano; Di Tian
      Pages: 109 - 118
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Davide Cammarano, Di Tian
      In this study, we explored how changing climate conditions in the 20th and 21st century affect summer and winter crop yields the southeast United States. An ensemble of 10 global circulation models (GCMs) were utilized and the uncertainties associated to their estimates were calculated. The objectives of this study were to utilize historical and projected climate data to (i) analyse historical and projected precipitation and temperature separately for a winter and a summer crop; (ii) evaluate how these climate factors impact the crop yield and the water use; (iii) quantify for the two crops, and for vegetative vs. reproductive stages, the impacts of climate extremes on crop yield and water use. The daily weather data for both historical and projected periods were obtained from the Multivariate Adaptive Constructed Analogs (MACA) downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) datasets. A series of 16 climate extremes indices mostly selected from the Expert Team on Climate Change Detection and Indices (ETCCDI) was calculated using the MACA downscaled CMIP5 data. The Decision Support System for Agrotechnology Transfer (DSSAT) model was used to simulate the effects of climate on a summer crop (maize, using the CERES-Maize model) and a winter crop (wheat, using the CERES-Wheat model) crop on a silty-clay and on a sandy soil during the historical baseline (1950–1999) and the projected (2006–2055) periods. Overall, the decadal crop-specific growing season temperature trend showed warming of the southeast with little variability across the climate models for the baseline and an increase uncertainty for future conditions. For each 1°C the simulated maize yield would decrease by 4.6% across the different climate projections, while wheat would be reduced by 3.8%. Water use efficiency decreased under future projections by 2.7% on a silty-clay soil, independently of the winter/summer crop, but on a sandy soil the decrease was 4% for maize and 1.7% for wheat. The impacts of projected temperature and rainfall change will be different for a winter than for a summer crop depending on the type of soil on which the crop is grown.

      PubDate: 2017-11-11T13:27:10Z
      DOI: 10.1016/j.agrformet.2017.09.007
      Issue No: Vol. 248 (2017)
  • Acclimation to higher VPD and temperature minimized negative effects on
           assimilation and grain yield of wheat
    • Authors: Muhammad Adil Rashid; Mathias Neumann Andersen; Bernd Wollenweber; Xiying Zhang; Jørgen Eivind Olesen
      Pages: 119 - 129
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Muhammad Adil Rashid, Mathias Neumann Andersen, Bernd Wollenweber, Xiying Zhang, Jørgen Eivind Olesen
      Adapting to climate change and minimizing its negative impact on crop production requires detailed understanding of the direct and indirect effects of different climate variables (i.e. temperature, VPD). We investigated the direct (via heat stress) and indirect effects (through increased VPD) of high temperature on growth, physiology and yield of two wheat cultivars (Taifun and Vinjett) at two watering levels; well-watered: WW (100% evapotranspiration (ET)) and drought stress: DS (50% of WW ET). Three climate treatments were applied for five days, starting at one week after anthesis. Treatments included hot humid (HH: 36°C; 1.96kPa VPD), hot dry (HD: 36°C; 3.92kPa VPD) and normal (NC: 24°C; 1.49kPa VPD). Difference between HH and HD was considered as the indirect effect of temperature through increased VPD. HD increased transpiration by 2–22% and decreased photosynthetic water-use efficiency (WUEp) by 24–64% over HH during stress but whole-plant WUE at final harvest was not affected. HD reduced grainfilling duration (3days), resulted in relatively lower green leaf area (GLA) after the stress and showed a tendency of lower net assimilation rate during the stress compared to HH. However, yield and yield components were not affected under WW conditions due to two reasons (i) acclimation of the photosynthesis, stomatal conductance and rubisco carboxylation efficiency to high temperature and VPD and (ii) translocation of assimilates from stem/leaf to grains after the stress episode. Five days of high temperature stress alone (HH) reduced GLA, grainfilling duration (5days) and thousand-grain weight (17%), which ultimately reduced grain yield by 17%. DS mainly affected GLA, grainfilling duration and reduced grain yield by 7% vis-à-vis WW. Two cultivars differed only for GLA (lower for Vinjett under HH) and WUEp (higher for Vinjett under DS). This indicates that the temperature induced increase in VPD has little effect on growth and yield, if sufficient soil moisture is available, because acclimation and tolerance mechanisms tend to alleviate stress effects. These compensatory mechanisms should also be considered when modelling climate effects on crops. However, heat waves and drought events during sensitive crop developmental stages (i.e. anthesis, grainfilling) are important climate variables that need to be considered for adaption to climate change.

      PubDate: 2017-11-11T13:27:10Z
      DOI: 10.1016/j.agrformet.2017.09.018
      Issue No: Vol. 248 (2017)
  • Influence of climate variability and length of rainy season on crop yields
           in semiarid Botswana
    • Authors: Jimmy Byakatonda; B.P. Parida; Piet K. Kenabatho; D.B. Moalafhi
      Pages: 130 - 144
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Jimmy Byakatonda, B.P. Parida, Piet K. Kenabatho, D.B. Moalafhi
      Climate variability and change is expected to affect agricultural productivity among other sectors. Studying the influence of this variability on crop production is one measure of generating climate change resilience strategies. In this study, the influence of climate variability on crop yield is investigated by determining the degree of association between climatic indices and crop yields of maize and sorghum using spearman’s rank correlation. The climatic indices used in this study are aridity index (AI), standardised precipitation evapotranspiration index (SPEI) at timescales of 1, 3, 6 and 12 months and southern oscillation index (SOI) representing El Niño southern oscillation (ENSO) influence on local climate. Local rainfall characteristics are expressed through length of the rainy season (LRS). Results reveal that ENSO influence is the most dominant across Botswana accounting for 85% and 78% variations in maize and sorghum yields respectively. Whereas AI and SPEI accounts for 70% and 65% variations in maize and sorghum respectively, LRS accounts for only 50% and 62% respectively. To facilitate agricultural planning, crop yield projections have been made using artificial neural network (ANN) models. The ANN projections indicate a likelihood of maize and sorghum yields declining by 51% and 70% respectively in the next 5 years. The high association between ENSO and crop yields in Botswana could further facilitate yield projections. Information generated from this study is useful in agricultural planning and hence strengthens farmers’ strategies in mitigating impacts of climate variability and change in semiarid areas.

      PubDate: 2017-11-11T13:27:10Z
      DOI: 10.1016/j.agrformet.2017.09.016
      Issue No: Vol. 248 (2017)
  • Species-specific tree growth and intrinsic water-use efficiency of
           Dahurian larch (Larix gmelinii) and Mongolian pine (Pinus sylvestris var.
           mongolica) growing in a boreal permafrost region of the Greater Hinggan
           Mountains, Northeastern China
    • Authors: Xuanwen Zhang; Xiaohong Liu; Qiuliang Zhang; Xiaomin Zeng; Guobao Xu; Guoju Wu; Wenzhi Wang
      Pages: 145 - 155
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Xuanwen Zhang, Xiaohong Liu, Qiuliang Zhang, Xiaomin Zeng, Guobao Xu, Guoju Wu, Wenzhi Wang
      Increasing air temperature and atmospheric CO2 concentrations (C a) can profoundly affect photosynthesis and intrinsic water-use efficiency (iWUE). However, the response of trees in boreal permafrost regions to rapid warming and C a increases is poorly constrained by prior research. Here, we evaluated long-term changes in growth (using regional curve standardization [RCS]) and iWUE of Dahurian larch (Larix gmelinii) and Mongolian pine (Pinus sylvestris var. mongolica) in the boreal permafrost region of northeastern China and species-specific responses to increasing C a and temperature. From 1930–2010, RCS growth of Dahurian larch and Mongolian pine decreased, while iWUE increased by 25.5 and 21.1%, respectively. RCS growth of both species was negatively correlated with winter temperatures, but Mongolian pine depended most strongly on previous December to current February temperatures and Dahurian larch depended most strongly on March temperatures. Moisture conditions only weakly influenced growth. We found similar long-term changes of tree-ring δ13C in the two species. Carbon isotopic discrimination of Dahurian larch and Mongolian pine was determined mainly by growing season temperature (positive) and moisture (negative), but with different signal strengths, suggesting that stomatal conductance influenced tree-ring δ13C. Commonality analysis showed that RCS growth was affected mainly by temperature, but also by the combined effect (interaction) of iWUE and temperature. However, the contribution of iWUE alone was lower for Mongolian pine. Our results suggest that the increased iWUE caused by increasing C a will not improve tree growth sufficiently to compensate for temperature-induced water stress. The rate of temperature increase has slowed around 1990, which would have stabilized the degree of temperature-induced water stress, and this could be helpful to tree growth recovery in the permafrost region of northeastern China.

      PubDate: 2017-09-30T08:46:25Z
      DOI: 10.1016/j.agrformet.2017.09.013
      Issue No: Vol. 248 (2017)
  • Incorporating leaf chlorophyll content into a two-leaf terrestrial
           biosphere model for estimating carbon and water fluxes at a forest site
    • Authors: Xiangzhong Luo; Holly Croft; Jing M. Chen; Paul Bartlett; Ralf Staebler; Norma Froelich
      Pages: 156 - 168
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Xiangzhong Luo, Holly Croft, Jing M. Chen, Paul Bartlett, Ralf Staebler, Norma Froelich
      Chlorophyll is the main light-harvesting pigment in leaves, facilitating photosynthesis and indicating the supply of nitrogen for photosynthetic enzymes. In this study, we explore the feasibility of integrating leaf chlorophyll content (Chlleaf) into a Terrestrial Biosphere Model (TBM), as a proxy for the leaf maximum carboxylation rate at 25°C ( V max 25 ), for the purpose of improving carbon and water flux estimation. Measurements of Chlleaf and V max 25 were made in a deciduous forest stand at the Borden Forest Research Station in southern Ontario, Canada, where carbon and water fluxes were measured by the eddy covariance method. The use of Chlleaf-based V max 25 in the TBM significantly reduces the bias of estimated gross primary productivity (GPP) and evapotranspiration (ET) and improves the temporal correlations between the simulated and the measured fluxes, relative to the commonly employed cases of using specified constant V max 25 , leaf area index (LAI)-based V max 25 or specific leaf area (SLA)-based V max 25 . The biggest improvements are found in spring and fall, when the mean absolute errors (MAEs) between modelled and measured GPP are reduced from between 2.2–3.2 to 1.8gCm−2 d−1 in spring and from between 2.1–2.8 to 1.8gCm−2 d−1 in fall. The MAEs in ET estimates are reduced from 0.7–0.8mmd−1 to 0.6mmd−1 in spring, but no significant improvement is noted in autumn. A two-leaf upscaling scheme is used to account for the uneven distribution of incoming solar radiation inside canopies and the associated physiological differences between leaves. We found that modelled V max 25 in sunlit leaves is 34% larger than in the shaded leaves of the same Chlleaf, which echoes previous physiological studies on light acclimation of plants. This study represents the first case of the incorporation of chlorophyll as a proxy for V max 25 in a two-leaf TBM at a forest stand and demonstrates the efficacy of using chlorophyll to constrain V max 25 and reduce the uncertainties in GPP and ET simulations.

      PubDate: 2017-09-30T08:46:25Z
      DOI: 10.1016/j.agrformet.2017.09.012
      Issue No: Vol. 248 (2017)
  • A new consistent sap flow baseline-correction approach for the stem heat
           balance method using nocturnal water vapour pressure deficits and its
           application in the measurements of urban climbing plant transpiration
    • Authors: Marie-Therese Hoelscher; Martin Andreas Kern; Gerd Wessolek; Thomas Nehls
      Pages: 169 - 176
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Marie-Therese Hoelscher, Martin Andreas Kern, Gerd Wessolek, Thomas Nehls
      The stem heat balance (SHB) method is a widely used sap flow technique to determine the transpiration and the water demands of herbaceous and woody plants, especially those with small diameters (e.g. climbers). The accuracy of the sap flow derived by this method (QS ) depends on correction of the total measured heat input (Qt ) by subtracting unintended heat losses; these heat losses are referred to as “fictitious flow” (Q fic) (QS = Qt − Qfic). We developed a physically consistent baseline-correction approach using minimum nocturnal water vapour pressure deficits (VPD). This VPD approach was compared to the so-called “night value subtraction” (NVS) approach and direct gravimetric determination for potted climbing plants and an outdoor climbing plant stand. In addition, performance tests were also conducted on artificial model stems and cut plant stems. In the tests with the outdoor climbing plant stand, sap flow corrected by the NVS approach underestimated daily transpiration by up to 33% compared to direct gravimetric determination. In contrast, the newly developed VPD approach underestimated or overestimated transpiration by only 5%–10%. The VPD approach makes use of the direct dependence of sap flow on VPD during zero-radiation conditions (night). This means, Qfic is the constant of the linear regression of the VPD and the lowest recorded Qt at night. Therefore, the correction is based on all recorded sap flow data from the measurement period itself, which in turn accounts for all factors influencing Qfic RH , including RH and T air; these latter parameters are often recorded in any case. This also means that this method can be subsequently applied to currently available data sets in order to improve their quality. Our results suggest that when the raw data are corrected appropriately, the SHB method is viable when attempting to determine transpiration rates of climbing plants. This is especially true for urban areas, with their illumination, typically high VPDs and increased Tair at night.

      PubDate: 2017-10-08T16:07:58Z
      DOI: 10.1016/j.agrformet.2017.09.014
      Issue No: Vol. 248 (2017)
  • A comparative analysis of the spatio-temporal variation in the phenologies
           of two herbaceous species and associated climatic driving factors on the
           Tibetan Plateau
    • Authors: Wenquan Zhu; Zhoutao Zheng; Nan Jiang; Donghai Zhang
      Pages: 177 - 184
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Wenquan Zhu, Zhoutao Zheng, Nan Jiang, Donghai Zhang
      Studying the differences in phenology among plant species is important for understanding their physiological and reproductive responses to climate change and complex inter-species interactions. This study conducted a comparative analysis of the spatio-temporal variation in the phenologies of two herbaceous species (Plantago asiatica and Taraxacum mongolicum) and associated climatic driving factors on the Tibetan Plateau (TP) based on ground-observed phenology data during 2000–2012. The results indicated that both spring and autumn phenology of the two species showed strong dependences on altitude, latitude and longitude, although the magnitudes of the variation with geographical factors were different among species. Change in altitude contributed the most to the spatial variation in phenology for both species. In addition, strong dependences on altitude were also observed for the phenological differences between the two species. With the increase of altitude, the same phenophases of the two species tended to occur synchronously at first and then the chronological order of the same phenophases between the two species changed. Spring and autumn phenophases showed significant negative correlations with the growing degree-days (GDD) and the cold degree-days (CDD) (p< 0.001), respectively. Moreover, the phenophases of T. mongolicum were more sensitive than those of P. asiatica in response to GDD or CDD, which explained the spatial variation in the phenological difference between the two species. The divergent phenological responses to climate change and the spatial variation in phenological differences between P. asiatica and T. mongolicum may alter the inter-species interactions between the two species.

      PubDate: 2017-10-08T16:07:58Z
      DOI: 10.1016/j.agrformet.2017.09.021
      Issue No: Vol. 248 (2017)
  • Potential rice exposure to heat stress along the Yangtze River in China
           under RCP8.5 scenario
    • Authors: Lei Zhang; Bingyun Yang; Sen Li; Yingyu Hou; Dapeng Huang
      Pages: 185 - 196
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Lei Zhang, Bingyun Yang, Sen Li, Yingyu Hou, Dapeng Huang
      Along with the global warming, heat events will tend to heighten and should be a matter of concern to rice production. Spatiotemporal changes in single-season rice exposure to heat stress along the Yangtze River during 1971–2100 were evaluated using datasets of single-season rice phenology observation and downscaled daily temperature projections from the 21 models. The results from top two best models which performed well in reproducing daily and seasonal temperatures were compared with that from all 21 models using the ensemble mean method under RCP8.5 scenario. It was found that obvious advances of the date of inflorescence emergence and ripening occurred in most parts of the study region through the period of 2021–2050 and 2071–2100. Duration of exposure to heat stress which was defined as an event of at least 3 successive days with daily mean temperature ≥30°C or maximum temperature ≥35°C tended to increase although length of crucial phenology period subjected to heat stress shortened. Mid-eastern Hubei, central Anhui, western Jiangsu, northern Zhejiang and northeastern Hunan were hot spots prone to heat stress. Heat stress for the entire region in the two future periods of 2021–2050 and 2071–2100 increased significantly, with an upward trend of 0.13 and 0.09%d per year for all 21 models and top two best models from 1971 to 2100 respectively. Understanding the potential exposure to heat stress can help decision makers to develop mitigation strategies to ensure rice production security.

      PubDate: 2017-11-11T13:27:10Z
      DOI: 10.1016/j.agrformet.2017.09.020
      Issue No: Vol. 248 (2017)
  • Parametric study of the influence of environmental factors and tree
           properties on the transpirative cooling effect of trees
    • Authors: Lento Manickathan; Thijs Defraeye; Jonas Allegrini; Dominique Derome; Jan Carmeliet
      Pages: 259 - 274
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Lento Manickathan, Thijs Defraeye, Jonas Allegrini, Dominique Derome, Jan Carmeliet
      Vegetation can provide transpirative cooling in cities and is therefore being increasingly integrated as an essential part of Urban Heat Island (UHI) mitigation strategies. However, the behaviour of vegetation must be accurately understood to determine the effectiveness of vegetation based solutions. In this study, vegetation is modelled as a porous medium in a computational fluid dynamics model for flow of moist air, where a leaf energy balance model is used to determine the heat fluxes. We study the cooling effect of a single row of trees at noon with solar altitude at 90° for various environmental factors (wind speed, air temperature, relative humidity and solar radiation intensity) and tree properties (leaf size, stomatal resistance and leaf area density). Furthermore, the influence of tree height and number of tree rows on the cooling effect are studied. The Universal Thermal Climate Index (UTCI) around the trees is estimated to determine the impact of transpirative cooling on pedestrian thermal comfort. The study shows that, at low wind speeds, pedestrians would only perceive a local benefit of transpirative cooling. However, vegetation extracts overall more heat from the flow at higher wind speeds. A study on the influence of environmental conditions quantifies to which extent a single row of trees provide maximum cooling during hot and dry conditions. The shading provided by trees improves thermal comfort more that transpirative cooling of a single row of trees. Furthermore, taller trees are more beneficial as the vegetation canopy with high leaf temperatures is further away from the pedestrian level.

      PubDate: 2017-10-21T01:45:38Z
      DOI: 10.1016/j.agrformet.2017.10.014
      Issue No: Vol. 248 (2017)
  • Effects of thinning a forest stand on sub-canopy turbulence
    • Authors: Eric S. Russell; Heping Liu; Harold Thistle; Brian Strom; Mike Greer; Brian Lamb
      Pages: 295 - 305
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Eric S. Russell, Heping Liu, Harold Thistle, Brian Strom, Mike Greer, Brian Lamb
      The density of a forest canopy affects the degree of influence of vegetation on the mean and turbulence flow fields. Thinning a forest in situ is difficult and expensive therefore many studies investigating the effects of changing canopy density have been done in wind tunnels or with modeling. Here, we analyze data collected at 0.13h, 0.83h, and 1.13h (canopy height; h=21m) as the surrounding loblolly pine stand was progressively thinned three times. The first thinning removed the understory and the two subsequent thinnings removed whole trees leading to a 60% reduction in the overall stand density. As the forest was thinned, turbulence and wind speed near the surface (0.13h) increased and became more connected with above the canopy (1.13h). The variation of the three-dimensional wind components increased for 0.13h when the understory was thinned. Turbulence at 0.83h and 1.13h increased when whole trees were removed (2nd and 3rd thinning). An increase in the peak spectral power of the 0.13h vertical velocity indicated an increase in the influence of larger eddies surviving through the canopy, but these did not affect the vertical turbulence or momentum transfer.

      PubDate: 2017-10-21T01:45:38Z
      DOI: 10.1016/j.agrformet.2017.10.019
      Issue No: Vol. 248 (2017)
  • Wavelet-based coupling of leaf and canopy reflectance spectra to improve
           the estimation accuracy of foliar nitrogen concentration
    • Authors: Junjie Wang; Yiyun Chen; Fangyuan Chen; Tiezhu Shi; Guofeng Wu
      Pages: 306 - 315
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Junjie Wang, Yiyun Chen, Fangyuan Chen, Tiezhu Shi, Guofeng Wu
      The leaf or canopy reflectance spectra of vegetation have been widely employed in estimating foliar nitrogen (N) concentration; however, they alone may not actually reflect the spectral and detailed information at a sampling plot. In this study, the potential spectral details of Carex (C. cinerascens) at a plot scale were derived using discrete wavelet transform, in which a simple operation of addition was employed to combine the reconstructed leaf and canopy reflectance at the fourth decomposition level (named “leaf-canopy d4 reflectance”). Partial least squares regression (PLSR), successive projections algorithm-based multiple linear regression (SPA-MLR) and random forest regression (RFR) models with leaf, canopy and leaf-canopy d4 reflectance were established and validated for foliar N estimation, respectively. The results showed that the PLSR (R2 CV =0.718, determination coefficient of cross-validation; R2 Val =0.743, determination coefficient of independent validation; RPD=1.91, residual prediction deviation), SPA-MLR (R2 CV =0.709, R2 Val =0.747, RPD=1.97) and RFR (R2 CV =0.714, R2 Val =0.783, RPD=2.16) models with leaf-canopy d4 reflectance outperformed their corresponding models with leaf or canopy reflectance. We conclude that the wavelet-based coupling of leaf and canopy reflectance spectra has great potential in the accurate estimation of foliar N concentration. This proposed strategy helps to understand the spectral details of vegetation at a plot scale, providing the potential for improving the plot-based estimation of plant nutrients in grassland, precision agriculture or forestry.

      PubDate: 2017-10-21T01:45:38Z
      DOI: 10.1016/j.agrformet.2017.10.017
      Issue No: Vol. 248 (2017)
  • Assessment of canola crop lodging under elevated temperatures for
           adaptation to climate change
    • Authors: Wei Wu; Bao-Luo Ma
      Pages: 329 - 338
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Wei Wu, Bao-Luo Ma
      With temperatures rising due to global climate change, many endeavors have been looking into how this will affect crop production and food security. Lodging, which is the permanent displacement of crop plants from upright position, is one of the main causes of yield loss and quality reduction in canola/oilseed rape. However, there has been little research to date on how the mechanisms of crop lodging might be affected by high temperature. The objectives of this study were to examine the effect of high temperature on the structural features of lodging resistance in four canola genotypes, to determine what kind of lodging (stem or root) was more prevalent, and to identify corresponding mechanistic traits associated with lodging under high temperature conditions. The experiment was carried out in controlled growth facilities with the genotypes tested under normal (23/17°C; CK) and high temperature (27.01/24.3°C) regimes. The results showed that high temperature reduced root lodging resistance significantly, as indicated by a dramatic reduction in both root anchorage and safety factor (against anchorage failure). These were attributable to the large suppression on lateral root growth (32%), and thereby reduction in root bending resistance (33%), root–soil cone dimension (13%), and its shear strength (33%). High temperature showed an inconsistent effect on stem lodging resistance, which was in alignment with the engineering mechanics theory and supported by the anatomical observations. These results indicated that canola genotypes were more prone to anchorage failure than stem buckling. Consequently, root lodging resulted from anchorage failure would become a critical aspect under rising temperatures with the global warming. The present study indicates that root lodging should be targeted as a priority to improve crop lodging resistance through breeding selection for a root system with high anchorage strength, especially when the crop plants are expected to encounter inevitable high temperature stress.

      PubDate: 2017-10-21T01:45:38Z
      DOI: 10.1016/j.agrformet.2017.09.017
      Issue No: Vol. 248 (2017)
  • Climate-smart agroforestry: Faidherbia albida trees buffer wheat against
           climatic extremes in the Central Rift Valley of Ethiopia
    • Authors: Tesfaye Shiferaw Sida; Frédéric Baudron; Haekoo Kim; Ken E. Giller
      Pages: 339 - 347
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Tesfaye Shiferaw Sida, Frédéric Baudron, Haekoo Kim, Ken E. Giller
      Faidherbia albida parklands cover a large area of the Sudano-Sahelian zone of Africa, a region that suffers from soil fertility decline, food insecurity and climate change. The parklands deliver multiple benefits, including fuelwood, soil nutrient replenishment, moisture conservation, and improved crop yield underneath the canopy. Its microclimate modification may provide an affordable climate adaptation strategy which needs to be explored. We carried out an on-farm experiment for three consecutive seasons in the Ethiopian Central Rift Valley with treatments of Faidherbia trees with bare soil underneath, wheat grown beneath Faidherbia and wheat grown in open fields. We tested the sensitivity of wheat yield to tree-mediated variables of photosynthetically active radiation (PAR), air temperature and soil nitrogen, using APSIM-wheat model. Results showed that soil moisture in the sub-soil was the least for wheat with tree, intermediate for sole tree and the highest for open field. Presence of trees resulted in 35–55% larger available N close to tree crowns compared with sole wheat. Trees significantly reduced PAR reaching the canopy of wheat growing underneath to optimum levels. Midday air temperature was about 6°C less under the trees than in the open fields. LAI, number of grains spike−1, plant height, total aboveground biomass and wheat grain yield were all significantly higher (P<0.001) for wheat associated with F. albida compared with sole wheat. Model-based sensitivity analysis showed that under moderate to high rates of N, wheat yield responded positively to a decrease in temperature caused by F. albida shade. Thus, F. albida trees increase soil mineral N, wheat water use efficiency and reduce heat stress, increasing yield significantly. With heat and moisture stress likely to be more prevalent in the face of climate change, F. albida, with its impact on microclimate modification, maybe a starting point to design more resilient and climate-smart farming systems.
      Graphical abstract image

      PubDate: 2017-10-21T01:45:38Z
      DOI: 10.1016/j.agrformet.2017.10.013
      Issue No: Vol. 248 (2017)
  • Subsurface water-use strategies and physiological responses of subtropical
    • Authors: L.J. Gow; D.J. Barrett; A.P. O’Grady; L.J. Renzullo; S.R. Phinn
      Pages: 348 - 360
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): L.J. Gow, D.J. Barrett, A.P. O’Grady, L.J. Renzullo, S.R. Phinn
      This study investigated subsurface water-use strategies and physiological responses of subtropical remnant eucalypt woodlands in south-eastern Queensland, Australia. A land surface temperature (LST) model-data approach was used to detect daily use of subsurface water (i.e. soil moisture obtained from depths >30cm and aquifer groundwater) by woody vegetation to a confidence level of 95%. Vegetation subsurface water use was quantified over a 13-year period (2000–2012) coinciding with a series of wet and dry climatic periods. Land surface temperature and subsurface water use time-series data were compared to local meteorological (vapour pressure deficit, rainfall, and soil water availability) and vegetation (leaf area index, stomatal resistance and latent heat loss) data to determine vegetation strategies to declining shallow (<30cm depth) soil water availability. Different vegetation subsurface water-use strategies and physiological response to changes in water availability were identified at inter- and intra-annual time-scales. At the intra-annual scale, frequency of subsurface water use by vegetation was strongly influenced by availability of shallow soil water. From January–September in this landscape, frequency of subsurface water use by vegetation remained relatively constant, supplementing decreasing shallow soil water availability and/or increasing evaporative demand. From October–December, the vegetation opportunistically utilised more abundant shallow soil water arising from more frequent, intense rainfall events, rather than relying on subsurface water. At the inter-annual scale, vegetation increased frequency of subsurface water use and decreased leaf area to reduce latent heat loss in response to dry conditions. Then, during wet years, subsurface water use by vegetation decreased in frequency as water was increasingly sourced from shallow soil layers. However, despite preceding dry periods of different severity, and exhibiting different average annual rainfall, air temperatures and reduction in the frequency of subsurface water use by vegetation, leaf area increased by approximately the same amount for both ‘recovery’ years. This suggests that investment in canopy leaf growth by this vegetation was more sensitive to the onset of increased water availability after drought rather than the overall volume of water made available by rainfall.

      PubDate: 2017-10-21T01:45:38Z
      DOI: 10.1016/j.agrformet.2017.10.005
      Issue No: Vol. 248 (2017)
  • Stand age amplifies greenhouse gas and NO releases following conversion of
           rice paddy to tea plantations in subtropical China
    • Authors: Zhisheng Yao; Xunhua Zheng; Chunyan Liu; Rui Wang; Baohua Xie; Klaus Butterbach-Bahl
      Pages: 386 - 396
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Zhisheng Yao, Xunhua Zheng, Chunyan Liu, Rui Wang, Baohua Xie, Klaus Butterbach-Bahl
      Increasing demand of commercial markets for tea products is driving the conversion from rice paddies to tea plantations in subtropical China. So far, however, little is known on how this land-use change, along with the age of plantation establishment, will affect the fluxes of greenhouse gases (GHG) methane (CH4) and nitrous oxide (N2O) and the air-pollutant nitric oxide (NO). Thus, we measured CH4, N2O and NO fluxes over an entire year from two tea plantations (one- and five-year-old plantations) and a native rice-fallow system under two system-specific nitrogen fertilizer options. On an annual scale, comparable or higher GHG emissions were measured for tea plantations as compared to the rice-fallow system. Besides the pollution swapping from CH4 being the dominating GHG in rice paddies to N2O in tea plantations, annual NO emissions increased significantly. Annual direct emission factors of N2O and NO in tea plantations were 2.47–5.80% and 2.00–3.99%, respectively, significantly higher than in the rice-fallow system (N2O: 1.05–2.05%; NO: 0.033–0.051%). Differences in N fertilizer inputs and soil environmental conditions (e.g., soil water regime, pH and organic carbon) due to contrasting managements of these systems and their interactions are clearly driving the stimulation of N2O and NO emissions and contributing to the significant CH4 reductions. Furthermore, we observed that increasing tea stand age, particularly under organic fertilization, further stimulated N2O and NO emissions that varied significantly intra-annually. Nevertheless, the higher N2O and NO emissions of tea plantations and the increasing emission strength with stand age deserve further research attention and consideration for future land-use conversions.
      Graphical abstract image

      PubDate: 2017-10-28T18:03:30Z
      DOI: 10.1016/j.agrformet.2017.10.020
      Issue No: Vol. 248 (2017)
  • Fine-scale perspectives on landscape phenology from unmanned aerial
           vehicle (UAV) photography
    • Authors: Stephen Klosterman; Eli Melaas; Jon Wang; Arturo Martinez; Sidni Frederick; John O’Keefe; David A. Orwig; Zhuosen Wang; Qingsong Sun; Crystal Schaaf; Mark Friedl; Andrew D. Richardson
      Pages: 397 - 407
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Stephen Klosterman, Eli Melaas, Jon Wang, Arturo Martinez, Sidni Frederick, John O’Keefe, David A. Orwig, Zhuosen Wang, Qingsong Sun, Crystal Schaaf, Mark Friedl, Andrew D. Richardson
      Forest phenology is a multi-scale phenomenon, arising from processes in leaves and trees, with effects on the ecology of plant communities and landscapes. Because phenology controls carbon and water cycles, which are commonly observed at the ecosystem scale (e.g. eddy flux measurements), it is important to characterize the relation between phenophase transition events at different spatial scales. We use aerial photography recorded from an unmanned aerial vehicle (UAV) to observe plant phenology over a large area (5.4ha) and across diverse communities, with spatial and temporal resolution at the scale of individual tree crowns and their phenophase transition events (10m spatial resolution, ∼5day temporal resolution in spring, weekly in autumn). We validate UAV-derived phenophase transition dates through comparison with direct observations of tree phenology, PhenoCam image analysis, and satellite remote sensing. We then examine the biological correlates of spatial variance in phenology using a detailed species inventory and land cover classification. Our results show that species distribution is the dominant factor in spatial variability of ecosystem phenology. We also explore statistical relations governing the scaling of phenology from an organismic scale (10m) to forested landscapes (1km) by analyzing UAV photography alongside Landsat and MODIS data. From this analysis we find that spatial standard deviation in transition dates decreases linearly with the logarithm of increasing pixel size. We also find that fine-scale phenology aggregates to a coarser scale as the median and not the mean date in autumn, indicating coarser scale phenology is less sensitive to the tails of the distribution of sub-pixel transitions in the study area. Our study is the first to observe forest phenology in a spatially comprehensive, whole-ecosystem way, yet with fine enough spatial resolution to describe organism-level correlates and scaling phenomena.

      PubDate: 2017-10-28T18:03:30Z
      DOI: 10.1016/j.agrformet.2017.10.015
      Issue No: Vol. 248 (2017)
  • Vegetation phenology on the Qinghai-Tibetan Plateau and its response to
           climate change (1982–2013)
    • Authors: Qiang Zhang; Dongdong Kong; Peijun Shi; Vijay P. Singh; Peng Sun
      Pages: 408 - 417
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Qiang Zhang, Dongdong Kong, Peijun Shi, Vijay P. Singh, Peng Sun
      Using NDVI3g vegetation index, we defined 18 phenology metrics to investigate phenological change on the Tibetan Plateau (TP). Considering the heterogeneity of vegetation phenology, we divided TP into 8 vegetation clusters according to a 1:1000000 vegetation cluster map. For regions where phenology is highly sensitive to climate, we investigated the impact of climate variables, such as temperature, precipitation, and solar radiation on phenology using the partial least squares regression (PLS) method. Results indicated (1) that turning points of the starting date of the growing season (SOS) metrics were in 1997–2000, before which SOS metrics advanced 2–3d/10a. The ending date of the growing season (EOS) and the length of growing season metrics (LOS) turning points were 2005 and 2004–2007, respectively. Before the turning points, the EOS metrics had a delayed tendency of 1–2d/10a, and the LOS metrics also had a prolonging tendency of 1–2d/10a. After the turning points, the significant levels of SOS and EOS metrics’ tendency only reached 0.1, and LOS’s tendency was insignificant at the 0.1 level. (2) Alpine meadows and alpine shrub meadows changed most intensely on TP. Advanced SOS and delayed EOS were the main reasons of the alpine meadow LOS extension. Advance SOS mainly contributed to the alpine shrub meadow LOS extension. (3) We used meteorological variables, such as temperature, precipitation and solar radiation, to analyze the drastic change of the phenology of alpine meadows and alpine shrub meadows through the PLS method. Temperature was found to be the dominant meteorological variable impacting phenology. In those regions, the previous year autumn and early winter temperature had a positive effect on the SOS phenology. The high temperature in this period would postpone previous year EOS, indirectly delaying SOS in the current year. On the other hand, warming autumn and early winter may slow the fulfilment of chilling requirements and lead to later SOS, which would have a delayed effect on SOS. Except summer, the minimum temperature had a similar effect on vegetation phenology, as average and maximum temperature. Furthermore, the effect of precipitation on phenology fluctuated widely across different months. The previous year autumn and winter precipitation had a negative effect on the SOS phenology, and early spring precipitation had a positive effect. The main factor limiting vegetation development in August was precipitation, and during this month precipitation had a positive impact on the EOS phenology. The influence of solar radiation was mainly during summer and early fall. This study will contribute toward vegetation phenology model improvement.

      PubDate: 2017-11-11T13:27:10Z
      DOI: 10.1016/j.agrformet.2017.10.026
      Issue No: Vol. 248 (2017)
  • Energy balance closure at a variety of ecosystems in Central Europe with
           contrasting topographies
    • Authors: Ryan McGloin; Ladislav Šigut; Kateřina Havránková; Jiří Dušek; Marian Pavelka; Pavel Sedlák
      Pages: 418 - 431
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Ryan McGloin, Ladislav Šigut, Kateřina Havránková, Jiří Dušek, Marian Pavelka, Pavel Sedlák
      A long-standing problem in micrometeorology is that at most eddy covariance sites around the world, the sum of the sensible and latent heat flux measurements is less than the available energy, resulting in the so-called energy balance closure problem. This study utilised the national network of eddy covariance towers in the Czech Republic to examine the degree of energy balance closure at sites covering a wide variety of vegetation types and terrain complexities. The degree of energy balance closure at each site varied depending on the method used to calculate the closure fraction. When the closure was computed using linear regressions of half-hourly sums of turbulent heat fluxes against half-hourly available energy values, closure ranged from 0.68 (beech forest) to 0.81 (spruce forest). However, when closure was computed using the bulk energy balance ratio method, values ranged from 0.61 to 0.73. Highest closure occurred in moderately unstable atmospheric conditions, while closure also increased with increases in the correlation coefficients for vertical wind velocity and water vapour, and vertical wind velocity and sonic temperature. Lowest closure was found at a beech forest in the Carpathian Mountains, where evidence suggested that the complex topography to the south of the eddy covariance tower was influencing the airflow and resulting in poor energy balance closure results. Energy balance closure was also particularly low at a rapeseed cropland, and this was attributed to the low frequency of moderately unstable to strongly unstable conditions at the site.

      PubDate: 2017-11-11T13:27:10Z
      DOI: 10.1016/j.agrformet.2017.10.003
      Issue No: Vol. 248 (2017)
  • A regional evaluation of plastic film mulching for improving crop yields
           on the Loess Plateau of China
    • Authors: Feng Zhang; Wenjuan Zhang; Jiaguo Qi; Feng-Min Li
      Pages: 458 - 468
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Feng Zhang, Wenjuan Zhang, Jiaguo Qi, Feng-Min Li
      The plastic film mulching (PM) management is being increasingly adopted in the vast rainfed farming regions of China, especially in the Loess Plateau, to obtain high yields. Although many studies have confirmed that PM increases yields and water use efficiency of crops, identifying the most suitable areas for PM and evaluating its performance in improving crop yields on a regional scale have received little attention. A process-based model using 30 years of historical climate data (1980–2010) was applied to evaluate PM crop production improvement in the Loess Plateau, where the annual average air temperature is −9 to 15°C and precipitation is 100–1000mm among study points. The well-calibrated and validated model explained 62% of maize production variance. PM showed increases of 4%–254%, with an average 58% increase, in comparison with unmulched management (CK) yields across the study area. Maize production showed a marked increase in the cold and dry western Loess Plateau and only a slight increase in the warm and wet south-eastern Loess Plateau where soil temperature and moisture conditions are already conducive to crop production. When compared with CK inside study area, the average yield using PM increased 66% in the area with precipitation less than 600mm versus only 20% in the area with precipitation greater than 600mm. Similarly, PM increased the yield by 73% and 37% over CK in areas with annual average air temperature less than 9°C and greater than 9°C, respectively. PM not only increases yield in existing cultivation areas; it also extends the maize suitable arable land. Specifically, PM enabled 2.77% of this study area to produce mature maize where no yield was achieved through CK. PM also led to lower interannual variation and stable yields of maize in 87.75% of the area. However, 9.52% of the area with low precipitation (average precipitation 230mm) and higher temperatures (average temperature 8.0°C) showed higher interannual yield variation in PM than CK. Among the areas studied, those with precipitation between 300 and 600mm, annual average temperatures of 3–9°C or an aridity index of 0.2–0.4 (semiarid zone) were determined as the most suitable for PM management. Thus, PM offers a potential solution to the problem of food security in areas with similar conditions.

      PubDate: 2017-11-11T13:27:10Z
      DOI: 10.1016/j.agrformet.2017.10.030
      Issue No: Vol. 248 (2017)
  • Incorporating diffuse radiation into a light use efficiency and
           evapotranspiration model: An 11-year study in a high latitude deciduous
    • Authors: Sheng Wang; Andreas Ibrom; Peter Bauer-Gottwein; Monica Garcia
      Pages: 479 - 493
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Sheng Wang, Andreas Ibrom, Peter Bauer-Gottwein, Monica Garcia
      The fraction of diffuse photosynthetic active radiation (PAR) reaching the land surface is one of the biophysical factors regulating carbon and water exchange between terrestrial ecosystems and the atmosphere. This is especially relevant for high latitude ecosystems, where cloudy days are prevalent. Without considering impacts of diffuse PAR, traditional ‘top-down’ models of ecosystem gross primary productivity (GPP) and evapotranspiration (ET), which use satellite remote sensing observations, are biased towards clear sky conditions. This study incorporated a cloudiness index (CI), an index for the fraction of diffuse PAR, into a joint ‘top-down’ model that uses the same set of biophysical constraints to simulate GPP and ET for a high latitude temperate deciduous forest. To quantify the diffuse PAR effects, CI along with other environmental variables derived from an eleven-year eddy covariance data set were used to statistically explore the independent and joint effects of diffuse PAR on GPP, ET, incident light use efficiency (LUE), evaporative fraction (EF) and ecosystem water use efficiency (WUE). The independent and joint effects of CI were compared from global sensitivity analysis of the ‘top-down’ models. Results indicate that for independent effects, CI increased GPP, LUE, ET, EF and WUE. Analysis of joint effects shows that CI mainly interacted with the radiation intercepted in the canopy (PAR, net radiation and leaf area index) to influence GPP, ET and WUE. Moreover, Ta and vapor pressure saturation deficit played a major role for the joint influence of CI on LUE and EF. In the growing season from May to October, variation in CI accounts for 11.9%, 3.0% and 7.8% of the total variation of GPP, ET and transpiration, respectively. As the influence of CI on GPP is larger than that on ET, this leads to an increase in WUE with CI. Joint GPP and ET model results showed that when including CI, the root mean square errors (RMSE) of daily GPP decreased from 1.64 to 1.45gCm−2 d−1 (11.7% reduction) and ET from 15.79 to 14.50 Wm−2 (8.2% reduction). Due to the interaction of diffuse PAR with plant canopies, the largest model improvements using CI for GPP and ET occurred during the growing season and for the transpiration component, as suggested by comparisons to sap flow measurements. Furthermore, our study suggests a potential biophysical mechanism, not considered in other studies: under high diffuse PAR conditions, due to the increased longwave emission from clouds, canopy temperature gets higher and enhances GPP and transpiration in this temperature-limited high latitude ecosystem.

      PubDate: 2017-11-11T13:27:10Z
      DOI: 10.1016/j.agrformet.2017.10.023
      Issue No: Vol. 248 (2017)
  • Influence of El Niño-Southern Oscillation and the Indian Ocean Dipole on
           winegrape maturity in Australia
    • Authors: C. Jarvis; R. Darbyshire; R. Eckard; I. Goodwin; E. Barlow
      Pages: 502 - 510
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): C. Jarvis, R. Darbyshire, R. Eckard, I. Goodwin, E. Barlow
      Seasonal timing of winegrape maturity is influenced by weather conditions. Significant changes to day-of-year-of-maturity (DOYM), both earlier and later than average, causes logistical problems during harvest, impacting on grape and wine quality. Shifts in climate circulation patterns resulting from atmospheric teleconnections to changes in sea surface temperature (SST) anomalies associated with El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) events can alter seasonal weather across Australia. Events tend to peak in the austral spring (IOD) and summer (ENSO), when vine and berry development is susceptible to anomalous weather. To investigate the impacts of ENSO and IOD on the Australian winegrape growing sector, SST data and annual grape maturity data from a variety of wine growing regions were collected and analysed. Mean DOYM values during IOD events were significantly (P <0.05) different for the largest number of vineyard blocks, with IOD positive (IOD+) events linked to earliest mean DOYM and IOD negative (IOD−) events linked to latest mean DOYM. ENSO and IOD combined events (ENSOIOD) had the largest difference between earliest mean DOYM and latest mean DOYM (42 days). Results for ENSO only grouped events were mixed, with no clear pattern emerging. This finding suggests that the IOD had more impact on DOYM than ENSO and that the IOD superseded the ENSO signal in combined events for the regions included in this study. The results indicate that improved seasonal forecasting of IOD, ENSO, and combined events would allow the Australian winegrape sector to better plan for changes to timing of grape maturity and associated impacts on grape and wine quality, vineyard management, and harvest logistics.

      PubDate: 2017-11-11T13:27:10Z
      DOI: 10.1016/j.agrformet.2017.10.021
      Issue No: Vol. 248 (2017)
  • Inside Front Cover - Editorial Board Page
    • Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248

      PubDate: 2017-11-11T13:27:10Z
  • Water and energy fluxes over northern prairies as affected by chinook
           winds and winter precipitation
    • Authors: Matthew MacDonald; John Pomeroy Richard L.H. Essery
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Matthew K. MacDonald, John W. Pomeroy, Richard L.H. Essery
      Chinooks are the North American variety of foehn: strong, warm and dry winds that descend lee mountain slopes. The strong wind speeds, high temperatures and substantial humidity deficits have been hypothesized to remove important prairie near-surface water storage from agricultural fields via evaporation, sublimation and blowing snow, as well as change the phase of near surface water via snowmelt and ground thaw. This paper presents observations of surface energy and water balances from eddy covariance instrumentation deployed at three open sites in southern Alberta, Canada during winter 2011–2012. Energy balances, snow and soil moisture budgets of three select chinook events were analysed in detail. These three events ranged in duration from two to nine days, and are representative of winter through early spring chinooks. Precipitation data from gauges and reanalyses (CaPA and ERA-interim) were used to assess water balances. Variations in precipitation and snowpacks caused the greatest differences in energy and water balances. Cumulative winter precipitation varied by a factor of two over the three sites: heaviest at the more northern site immediately east of the Rocky Mountains and lightest at the easternmost and southernmost site. The temporal progression of chinook-driven surface water loss is explained, beginning with strong blowing snow events through to evaporation of meltwater as snowpacks disappear. At the two sites with considerable winter precipitation and snowcover, large upward latent heat fluxes, often exceeding 100Wm−2, were driven by downward sensible heat fluxes but were unrelated to net radiation. Conversely, at the southernmost site with little snowcover, upward latent heat fluxes were much smaller (less than 50Wm−2) and were associated with periods of positive net radiation. Upward sensible heat fluxes during periods of positive net radiation were observed at this site throughout winter, but were not observed at the more northerly sites until March when the snowcovers ablated. Daily sublimation plus evaporation rates during chinooks at the sites with heaviest and lightest precipitation were 1.3–2.1mm/day and 0.1–0.3mm/day, respectively. Evaporation of soil water occurred while soils were partially to fully unfrozen in November. There was little change in soil water content between fall freeze-up and spring thaw (December through most of March), indicating that over-winter infiltration was balanced by soil water evaporation and both terms were likely to be small. Winter precipitation resulted in only 2% to 4% increases in near-surface water storage at the more northern sites with greater precipitation, whereas there was a net loss over winter at the southernmost site.

      PubDate: 2017-10-21T01:45:38Z
  • A robust leaf area index algorithm accounting for the expected errors in
           gap fraction observations
    • Authors: Alemu Gonsamo; Jean-Michel Walter Jing Chen Petri Pellikka Patrick Schleppi
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Alemu Gonsamo, Jean-Michel Walter, Jing M. Chen, Petri Pellikka, Patrick Schleppi
      The leaf area index, LAI, representing the physiological and structural functions of vegetation canopies, can be estimated from gap fraction measurements obtained at different zenith angles. Earlier works have provided practical and convenient theoretical solution to retrieve LAI based on the integration of contact numbers (a projected area of leaves on a plane perpendicular to the view or solar zenith angle) over zenith angles as obtained by a linear regression, i.e., LAI=2(A + B), where A and B are the coefficients of the regression of contact numbers against zenith angles. This graphical procedure is equivalent to the more accurate method of LAI retrieval by integrating gap fraction measurements from nadir through horizon angles. However, using an ordinary least-squares regression on inherently unsteady relationship between contact numbers and zenith angles limited the use of a simple graphical procedure for LAI estimation. In this study, we introduce the use of robust procedure to retrieve regression coefficients (i.e., A and B), and assess the performance of the new procedure using numerically derived hypothetical data, computer simulated and real measurements of hemispherical photographs. Our results indicated, the new procedure not only outperformed the ordinary least-squares solution for graphical procedure, but also outperformed all existing LAI methods We conclude from analyses using numerically derived hypothetical data, computer simulated and real measurements of hemispherical photographs that estimating A and B (where LAI=2(A + B)) using a robust procedure is a convenient and sufficiently accurate method for estimating LAI from field measurements of gap fractions at different zenith angles.

      PubDate: 2017-10-08T16:07:58Z
  • Do ring-porous oaks prioritize earlywood vessel efficiency over
           safety' Environmental effects on vessel diameter and tyloses formation
    • Authors: Gonzalo Vicente; Rozas Rosa Ana Ignacio
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Gonzalo Pérez-de-Lis, Vicente Rozas, Rosa Ana Vázquez-Ruiz, Ignacio García-González
      The impact of climate on xylem structure and function has been profusely studied for a variety of species in the last decades, but the ecological role of ring porosity under increasing levels of environmental stress has been scarcely assessed. In this study, we analyse the timing of earlywood vessels occlusions by tyloses in two ring-porous species with contrasting ecological strategies (Quercus robur and Q. pyrenaica) along a seasonal drought gradient, and relate it to variations in earlywood vessel diameter and radial growth obtained from tree-ring series. The number of trees showing tyloses increased in summer as a result of more frequent cavitation events under drier conditions, and was more reduced for the more drought-tolerant Q. pyrenaica, which had a higher hydraulic diameter (D h) but lower latewood increments. D h values decreased towards the wettest sites, and were negatively related to warm and rainy conditions in winter. Our results showed that large earlywood vessel diameters are not necessarily accompanied by high rates of tyloses formation or limited growth in summer. We hypothesize that trees in seasonal environments can take advantage from large earlywood vessels, because benefits from a more efficient hydraulic system during favourable periods are higher than the risk of xylem impairment in summer.

      PubDate: 2017-10-08T16:07:58Z
  • Impact of CO2 storage flux sampling uncertainty on net ecosystem exchange
           measured by eddy covariance
    • Authors: Giacomo Nicolini; Marc Aubinet Christian Feigenwinter Bernard Heinesch Anders Lindroth
      Abstract: Publication date: 15 January 2018
      Source:Agricultural and Forest Meteorology, Volume 248
      Author(s): Giacomo Nicolini, Marc Aubinet, Christian Feigenwinter, Bernard Heinesch, Anders Lindroth, Ossénatou Mamadou, Uta Moderow, Meelis Mölder, Leonardo Montagnani, Corinna Rebmann, Dario Papale
      Complying with several assumption and simplifications, most of the carbon budget studies based on eddy covariance (EC) measurements quantify the net ecosystem exchange (NEE) by summing the flux obtained by EC (FC) and the storage flux (SC). SC is the rate of change of a scalar, CO2 molar fraction in this case, within the control volume underneath the EC measurement level. It is given by the difference in the quasi-instantaneous profiles of concentration at the beginning and end of the EC averaging period, divided by the averaging period. The approaches used to estimate SC largely vary, from measurements based on a single sampling point usually located at the EC measurement height, to measurements based on profile sampling. Generally a single profile is used, although multiple profiles can be positioned within the control volume. Measurement accuracy reasonably increases with the spatial sampling intensity, however limited resources often prevent more elaborated measurement systems. In this study we use the experimental dataset collected during the ADVEX campaign in which turbulent and non-turbulent fluxes were measured in three forest sites by the simultaneous use of five towers/profiles. Our main objectives are to evaluate both the uncertainty of SC that derives from an insufficient sampling of CO2 variability, and its impact on concurrent NEE estimates.Results show that different measurement methods may produce substantially different SC flux estimates which in some cases involve a significant underestimation of the actual SC at a half-hourly time scales. A proper measuring system, that uses a single vertical profile of which the CO2 sampled at 3 points (the two closest to the ground and the one at the lower fringe of the canopy layer) is averaged with CO2 sampled at a certain distance and at the same height, improves the horizontal representativeness and reduces this (proportional) bias to 2–10% in such ecosystems. While the effect of this error is minor on long term NEE estimates, it can produce significant uncertainty on half-hourly NEE fluxes.

      PubDate: 2017-10-08T16:07:58Z
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