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Publisher: Elsevier   (Total: 3043 journals)

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Showing 1 - 200 of 3043 Journals sorted alphabetically
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 22, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 21, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 84, 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: 351, 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: 238, 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: 2)
Acta Poética     Open Access   (Followers: 4)
Acta Psychologica     Hybrid Journal   (Followers: 23, 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)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 2)
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: 5)
Additive Manufacturing     Hybrid Journal   (Followers: 7, SJR: 1.039, h-index: 5)
Additives for Polymers     Full-text available via subscription   (Followers: 21)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 135, 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: 25, 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 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: 26, 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: 6)
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: 41, SJR: 3.25, h-index: 43)
Advances in Engineering Software     Hybrid Journal   (Followers: 25, 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: 41, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 50, 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 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: 35, 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 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: 7, 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 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: 61)
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: 3, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 353, 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: 17)
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: 43, 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: 325, 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: 405, SJR: 1.385, h-index: 72)
Agri Gene     Hybrid Journal  
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 15, SJR: 2.18, h-index: 116)
Agricultural Systems     Hybrid Journal   (Followers: 30, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 39, SJR: 1.546, h-index: 79)
Agriculture and Agricultural Science Procedia     Open Access  
Agriculture and Natural Resources     Open Access   (Followers: 1)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 54, 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: 10, 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  
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: 8, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 48, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 6)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 5)
American Heart J.     Hybrid Journal   (Followers: 49, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 47, SJR: 2.063, h-index: 186)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 39, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 8, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 15, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 31, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 25, 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: 45, 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: 235, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 57, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5)
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: 26, SJR: 2.653, h-index: 228)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 22, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 34, 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: 5)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.066, h-index: 51)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 57, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 11)
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: 11)
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  
Animal Behaviour     Hybrid Journal   (Followers: 161, SJR: 1.907, h-index: 126)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 5, SJR: 1.151, h-index: 83)
Animal Reproduction Science     Hybrid Journal   (Followers: 5, SJR: 0.711, h-index: 78)
Annales d'Endocrinologie     Full-text available via subscription   (Followers: 1, SJR: 0.394, h-index: 30)
Annales d'Urologie     Full-text available via subscription  
Annales de Cardiologie et d'Angéiologie     Full-text available via subscription   (SJR: 0.177, h-index: 13)
Annales de Chirurgie de la Main et du Membre Supérieur     Full-text available via subscription  
Annales de Chirurgie Plastique Esthétique     Full-text available via subscription   (Followers: 2, SJR: 0.354, h-index: 22)
Annales de Chirurgie Vasculaire     Full-text available via subscription   (Followers: 1)

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Journal Cover Agricultural and Forest Meteorology
  [SJR: 2.18]   [H-I: 116]   [15 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0168-1923
   Published by Elsevier Homepage  [3043 journals]
  • 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)
       
  • 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)
       
  • Physical and biogeochemical controls on soil respiration along a
           topographical gradient in a semiarid forest
    • Authors: Wei-Yu Shi; Sheng Du; Joseph C. Morina; Jin-Hong Guan; Kai-Bo Wang; Ming-Guo Ma; Norikazu Yamanaka; Ryunosuke Tateno
      Pages: 1 - 11
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Wei-Yu Shi, Sheng Du, Joseph C. Morina, Jin-Hong Guan, Kai-Bo Wang, Ming-Guo Ma, Norikazu Yamanaka, Ryunosuke Tateno
      Soil respiration is a dynamic and fundamental process across all terrestrial ecosystems. However, how physical and biogeochemical factors control seasonal variation and annual rates of soil respiration remains poorly understood. A topographical gradient in a semiarid forest was chosen as the study site to assess how both biogeochemical and physical factors control respiration rates. Parameters measured include soil respiration, litterfall, fine root biomass, soil physical and chemical properties, soil bacteria and archaea gene abundance, ectomycorrhizal fungi abundance and richness, and soil carbon isotope signatures. The results showed that increases in soil temperature and moisture exponentially and linearly promoted root activity, driving seasonal variation of total soil respiration. Seasonal variation of heterotrophic respiration was driven by soil moisture in a second-order polynomial pattern. Autotrophic respiration only contributed to 20% of the total soil respiration, and seasonal variation in the soil respiration rate was driven by heterotrophic respiration. Utilizing soil moisture as a scalar, the values of Q10 and R10 in different poisons on the slope indicated soil respiration was controlled by interaction of soil temperature and moisture, and a new transformation of the R10 function inducing soil moisture was proposed. Along the topographical gradient, the long-term average soil temperature and moisture significantly varied from the top to the bottom of a slope. This variation in physical processes induced differences in plant productivity and biomass accumulation, leading to varying organic matter accumulation across the gradient. The topographical position also induced differences in the size of the soil organic matter aggregates, archaea and bacteria gene abundances, and ectomycorrhizal fungi abundance and richness. The aforementioned parameters are interrelated due to their association with the long-term average soil temperature and moisture, and the interrelation of these parameters ultimately affects annual rates of soil respiration.

      PubDate: 2017-07-23T16:00:07Z
      DOI: 10.1016/j.agrformet.2017.07.006
      Issue No: Vol. 247 (2017)
       
  • Estimating wheat green area index from ground-based LiDAR measurement
           using a 3D canopy structure model
    • Authors: Shouyang Liu; Fred Baret; Mariem Abichou; Fred Boudon; Samuel Thomas; Kaiguang Zhao; Christian Fournier; Bruno Andrieu; Kamran Irfan; Matthieu Hemmerlé; Benoit de Solan
      Pages: 12 - 20
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Shouyang Liu, Fred Baret, Mariem Abichou, Fred Boudon, Samuel Thomas, Kaiguang Zhao, Christian Fournier, Bruno Andrieu, Kamran Irfan, Matthieu Hemmerlé, Benoit de Solan
      The use of active remote sensing techniques based on light detection and ranging (LiDAR) was investigated here to estimate the green area index (GAI) of wheat crops. Emphasis was put on the maximum GAI development stage when saturation effects are known to limit the performances of standard indirect methods based either on the gap fraction or reflectance measurements. The LiDAR provides both the three dimensional (3D) point cloud from which the vertical distribution (Z profile) of the interception points is computed, as well as the intensity of the returned signal from which the green fraction (GF) is derived. The data were interpreted by exploiting the 3D ADEL-Wheat model that synthesizes the knowledge accumulated on wheat canopy structure. A LiDAR simulator that accounts for the specific observation configuration used was developed to mimic the actual LiDAR measurements. The in-silico experiments were conducted to generate training and validation dataset. Neural network were then used to estimate GAI from the Z profile and GF derived from the LiDAR measurements. Performances of GAI estimates by the several methods investigated were evaluated using either experimental data with 3<GAI<6 and data simulated with the 3D structure model with 1<GAI<7. Results confirm that using only the GF provides poor estimates of GAI (0.89<RMSE<1.28; 0.22<rRMSE<0.31), regardless of turbid medium or realistic assumptions on canopy 3D structure. The introduction of the Z profile information improved significantly the GAI estimation accuracy (0.48<RMSE<0.55; 0.12<rRMSE<0.13). This study demonstrates the interest of using the third dimension provided by LiDAR to better estimate GAI in crops under high GAI values. However, this requires the use of a realistic 3D structure crop model over which the LiDAR data could be simulated under the observational configuration used.
      Graphical abstract image

      PubDate: 2017-07-23T16:00:07Z
      DOI: 10.1016/j.agrformet.2017.07.007
      Issue No: Vol. 247 (2017)
       
  • 2D profiles of CO2, CH4, N2O and gas diffusivity in a well aerated soil:
           measurement and Finite Element Modeling
    • Authors: M. Maier; B. Longdoz; T. Laemmel; H. Schack-Kirchner; F. Lang
      Pages: 21 - 33
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): M. Maier, B. Longdoz, T. Laemmel, H. Schack-Kirchner, F. Lang
      Soil gas fluxes depend on soil gas concentrations and physical properties of a soil. Taking soil samples for physical analysis into the laboratory strongly modifies soil gas concentrations and also cuts roots that sustain the activity in the rhizosphere. Since microbial processes interact with gas concentrations in soil, we need to study gas transport and production in situ. We developed a method to monitor the transport and production and consumption of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in soils in situ in a two dimensional (2D) profile using tetrafluoromethane (CF4) and sulfur hexafluoride (SF6) as tracer gases and Finite Element Modeling of soil gas transport. Continuous injection of the inert tracer gases and 2D gas sampling in a soil profile allowed for inverse modeling of the 2D profile of soil gas diffusivity. In a second step, the 2D profiles of the production and consumption of CO2, CH4, and N2O were inversely determined. Soil gas concentrations were monitored in a Scots pine stand in South-West Germany during a rain-free week in the fall. The 2D relative (so as to be independent of gas species) soil gas diffusivity profile showed large horizontal variability. Relative soil gas diffusivity was found to be anisotropic with the vertical direction greater by a factor of 1.26. Topsoil moisture decreased slowly over time resulting in an increase in relative soil gas diffusivity. The soil was found to be a source of CO2, and a net sink of CH4 and N2O, with the highest production (CO2) and consumption (CH4, N2O) occurring in the topsoil. The gas concentration and production profiles of CO2 were nearly horizontally homogenous, while those for CH4 showed larger horizontal differences. Net consumption of CH4 and net production of CO2 both increased as the soil dried. This occurred despite reverse trends for these variables in the topsoil (0–8cm depth) which were more than offset by the underlying soil becoming more active. Sensitivity tests showed that the determination of 2D profiles of soil gas diffusivity and production and consumption of CO2 and CH4 were more reliable than the estimates for N2O because the magnitudes of these for N2O were very low. Our method represents a useful tool for the analyses of soil gas flux heterogeneities and associated microbial processes within soil profiles.
      Graphical abstract image

      PubDate: 2017-08-03T10:06:27Z
      DOI: 10.1016/j.agrformet.2017.07.008
      Issue No: Vol. 247 (2017)
       
  • Shifts in cultivar and planting date have regulated rice growth duration
           under climate warming in China since the early 1980s
    • Authors: Xunyu Hu; Yao Huang; Wenjuan Sun; Lingfei Yu
      Pages: 34 - 41
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Xunyu Hu, Yao Huang, Wenjuan Sun, Lingfei Yu
      Climate warming accelerates crop development and shortens growth duration. The adoption of new cultivars and changes in planting date may either retard or amplify this acceleration. However, the extent to which the cultivar and planting date shifts have impacted rice growth duration under climate warming remains largely unknown. Using an up-to-date data series from 82 agro-meteorological stations in China where rice phenology was observed from 1981 to 2012, we quantified the impacts of climate warming, cultivar and planting date shifts on rice growth duration based on a degree-days calculation. The results indicate that climate warming shortened the growth duration length (GDL) between emergence and maturity at rates of 4.2±0.7 (mean±SE), 1.8±0.3 and 3.9±0.5days 10-yr−1 for single, early and late rice. GDL shortening was more pronounced in the vegetative phase than in the reproductive phase for single and early rice, but it was opposite for late rice system. Cultivar shifts prolonged the GDL at rates of 6.1±1.0 and 1.7±0.6days 10-yr−1 for single and early rice but induced GDL shortening of 4.1±1.6days 10-yr−1 for late rice. The effect of planting date shifts (advanced or delayed) on GDL change was variable and depended on the rice cropping system. On average, climate warming accelerated crop development, with a relative contribution to GDL changes of −40% in single rice, −45% in early rice, and −35% in late rice. Cultivar shifts compensated for the GDL shortening induced by climate warming in single and early rice with the relative contribution of 58% and 44%, respectively, but accelerated crop development in late rice with a contribution of −37%. Nevertheless, the planting date at two-thirds of the late rice stations was significantly delayed, which retarded the acceleration by 29% in terms of GDL changes.

      PubDate: 2017-08-03T10:06:27Z
      DOI: 10.1016/j.agrformet.2017.07.014
      Issue No: Vol. 247 (2017)
       
  • Increasing moisture limitation of Norway spruce in Central Europe revealed
           by forward modelling of tree growth in tree-ring network
    • Authors: Jan Tumajer; Jan Altman; Petr Štěpánek; Václav Treml; Jiří Doležal; Emil Cienciala
      Pages: 56 - 64
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Jan Tumajer, Jan Altman, Petr Štěpánek, Václav Treml, Jiří Doležal, Emil Cienciala
      Planted even-aged forests dominated by Norway spruce (Picea abies) progressively replaced mixed natural forests in large parts of Central Europe during past centuries due to the productivity-motivated preferences of forest owners. These managed forests have become vulnerable to climate change, specifically to increasingly severe drought. To evaluate the response of trees to warming, we collected samples from a randomized landscape inventory grid of 7×7km to account for spatial gradients in climate/growth interactions in the entire forested part of the Czech Republic. The purely climate-driven forward growth model − Vaganov-Shashkin “Lite” − was calibrated by real (observed) radial growth series to identify a course of climatic limiting factors on an intra-annual scale. Relative proportions of moisture and temperature limited parts of total tree-ring width were determined as well as trends in limiting conditions over the period 1940–2012 and along the elevation gradient. Significant match between modelled and observed growth was shown in 47% of the grid cells. The coherence between modelled and observed site series was significantly improved when individual grid cells were aggregated into elevation belts. In grid cells below 600m, from 51 to 58% of tree-ring width was formed under moisture-limited conditions, with the proportion of growth under optimal conditions being minimal. The effect of drought stress was outweighed by earlier spring onset of growth, resulting in positive trends in total tree-ring width above 500m. About 26% of tree-ring growth has occurred under optimal climatic conditions at elevations above 800m, where, moreover, 45% of total annual growth was temperature limited. Except for one medium-elevation belt, the proportion of growth under moisture-limited conditions significantly increased during the period analysed. Recent warming and increasing frequency of drought events deepened the divergence in growth trends between low-elevation areas and stands at medium and high elevations.

      PubDate: 2017-08-03T10:06:27Z
      DOI: 10.1016/j.agrformet.2017.07.015
      Issue No: Vol. 247 (2017)
       
  • Temporal variations and spatial differentiation in the black alder and
           silver birch pollination pattern-the impact of local climate or something
           more'
    • Authors: K. Borycka; B. Ortyl; I. Kasprzyk
      Pages: 65 - 78
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): K. Borycka, B. Ortyl, I. Kasprzyk
      Numerous abiotic factors have an important impact on the phenology of woody plants with temperature as the main driver of their development. Furthermore, the biological factors connected with phenotypic plasticity and genetic heterogeneity might be the cause of differentiation in phenological response to abiotic factors. As objects of our study, we chose black alder and silver birch trees. The main aims of the study were to demonstrate the spatial and temporal diversity in the timing of Alnus glutinosa and Betula pendula pollination as well as to identify factors affecting these variations. We focused on abiotic factors such as thermal conditions: air and surface temperatures, within and between population variability. Phenological observations were carried out in Rzeszów (SE Poland) in a period of four years at over a dozen locations. Stands differed in their thermal conditions and prevalent land use types. The pollination pattern in the study area was presented against the background of local thermal conditions which were described by Land Surface Temperature (LST) and maximum daily air temperature. LST was estimated with a single-channel algorithm using satellite images obtained from Landsat 7 and 8. Our results showed great spatial and temporal diversity in the pollination pattern in the study area. Year-to-year variations in the B. pendula pollination pattern were less pronounced than in the case of A. glutinosa. The pollination pattern was strongly influenced by temperature before and during pollination. In the study area, the variability of LST was greater than that of air temperature but the relationships between the timing of pollination phenophases and LST or land use types were weak. It was observed that the same sites were similar in their pollination pattern − the timing of phenophases was ‘accelerated’ or ‘delayed’ during the whole study period. The same individuals were the first or the last that began to pollinate independently of the year. We concluded that despite the impact of temperature on A. glutinosa and B. pendula development, the phenotype of an individual tree might be as important for phenological variability as local climate.

      PubDate: 2017-08-03T10:06:27Z
      DOI: 10.1016/j.agrformet.2017.07.017
      Issue No: Vol. 247 (2017)
       
  • Impact of canopy representations on regional modeling of
           evapotranspiration using the WRF-ACASA coupled model
    • Authors: Liyi Xu; Rex David Pyles; Kyaw Tha Paw U; Richard Snyder; Erwan Monier; Matthias Falk; Shu-Hua Chen
      Pages: 79 - 92
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Liyi Xu, Rex David Pyles, Kyaw Tha Paw U, Richard Snyder, Erwan Monier, Matthias Falk, Shu-Hua Chen
      In this study, we couple the Weather Research and Forecasting Model (WRF) with the Advanced Canopy-Atmosphere-Soil Algorithm (ACASA), a high complexity land surface model, to investigate the impact of canopy representation on regional evapotranspiration. The WRF-ACASA model uses a multilayer structure to represent the canopy, consequently allowing microenvironmental variables such as leaf area index (LAI), air and canopy temperature, wind speed and humidity to vary both horizontally and vertically. The improvement in canopy representation and canopy-atmosphere interaction allow for more realistic simulation of evapotranspiration on both regional and local scales. The coupled WRF-ACASA model is compared with the widely used intermediate complexity Noah land surface model in WRF (WRF-Noah) for both potential (ETo) and actual evapotranspiration (ETa). Two LAI datasets (USGS and MODIS) are used to study the model responses to surface conditions. Model evaluations over a diverse surface stations from the CIMIS and AmeriFlux networks show that an increase surface representations increase the model accuracy in ETa more so than ETo. Overall, while the high complexity of WRF-ACASA increases the realism of plant physiological processes, the model sensitivity to surface representation in input data such as LAI also increases.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.07.003
      Issue No: Vol. 247 (2017)
       
  • Quantifying and reducing the differences in forest CO2-fluxes estimated by
           eddy covariance, biometric and chamber methods: A global synthesis
    • Authors: Xingchang Wang; Chuankuan Wang; Ben Bond-Lamberty
      Pages: 93 - 103
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Xingchang Wang, Chuankuan Wang, Ben Bond-Lamberty
      Carbon dioxide (CO2) fluxes between terrestrial ecosystems and the atmosphere are primarily measured with eddy covariance (EC), biometric, and chamber methods However, it is unclear why the estimates of the CO2-fluxes, when measured using different methods, converge at some sites but diverge at others. We synthesized a novel global dataset of forest CO2-fluxes to evaluate the consistency between EC and biometric or chamber methods for quantifying the CO2 budget in forest ecosystems. The EC approach, compared with the other two methods, overestimated net ecosystem production (NEP) by 25% (0.52MgCha−1 yr−1), and underestimated ecosystem respiration (Re) by 10% (1.39MgCha−1 yr−1) and gross primary production by 3% (0.48MgCha−1 yr−1). The differences between EC and the other methods were greater at the sites with complex topography and dense canopy than at the sites with flat topography and open canopy. Forest age also influenced the differences mainly through changes in leaf area index. Open-path EC system induced large positive bias in the NEP estimated by EC, presumably due to its surface-heating effect. These results suggest that EC method likely produce biased estimates of NEP and Re in forest ecosystems. A global extrapolation suggests that the differences in the forest CO2-fluxes measured with different methods be consistent with the global overestimation of NEP and underestimation of Re by EC method. Accounting for these differences would substantially improve our estimates of the forest carbon budget. The uncertainties involved in each method were also discussed. To reduce uncertainty in quantifying both local and global carbon budgets, we recommend cross-validation of forest CO2-fluxes measured by different methods with more accurate measurements and careful data processing strategies.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.07.023
      Issue No: Vol. 247 (2017)
       
  • Projection of phenology response to climate change in rainfed vineyards in
           north-east Spain
    • Authors: M.C. Ramos
      Pages: 104 - 115
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): M.C. Ramos
      The aim of this research was to predict the changes in vine phenology of some white grape varieties when rainfed vineyards are subjected to climate change. The research was conducted in the north east of Spain, in an area with a Mediterranean climate. Temperature and precipitation changes under two Representative Concentration Pathway (RCP) scenarios – RCP4.5 and RCP8.5 – were simulated based on an ensemble of models. Water losses by runoff were predicted using the WEPP model and changes in evapotranspiration were estimated according to the predicted changes in temperature, wind speed and solar radiation for the same scenarios. Dates of budbreak, bloom, veraison and harvest of three varieties were evaluated: Chardonnay, during the period 1998–2012; and Parellada and Macabeo during the period 1998–2009. Projections for 2030, 2050 and 2070 were made based on the observed phenological dates and the heat accumulation needed to reach each stage and water available recorded in different periods along the growing cycle. An advance of all phenological dates was predicted, higher for veraison and harvest than for the earlier stages and higher for Parellada than for Macabeo and Chardonnay. These stages may advance up to 10 and 16days, respectively, for 2050 and up to 12 and 20days for 2070 under the RCP4.5 scenario. Under RCP8.5 scenario, the advance by 2070 could be up to 23 and 28days. These changes resulted in a shortening of the periods between phenological dates (>10days), higher for Parellada than for Chardonnay and Macabeo. The results also showed an additional advance of bloom for Chardonnay and Macabeo associated with decreasing water available, and an advance of veraison and harvest for all three varieties, associated with decreasing water available, particularly between budbreak and bloom and between bloom and veraison, depending on the variety.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.07.022
      Issue No: Vol. 247 (2017)
       
  • Tree stomata conductance estimates of a wax myrtle-tree heath
           (fayal-brezal) cloud forest as affected by fog
    • Authors: Axel Ritter; Carlos M. Regalado
      Pages: 116 - 130
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Axel Ritter, Carlos M. Regalado
      Direct transpiration measurements of tree species obtained with Granier’s heat dissipation probes, combined with micrometeorological data were used to derive tree conductance estimates in a cloud-immersed wax myrtle-tree heath forest located in the Garajonay National Park (La Gomera, Canary Islands, Spain). The one-year period time series were analysed distinguishing between foggy and fog-free conditions in order to evaluate the vegetation response to fog. The presence of fog was found to reduce transpiration (T) in both species investigated (E. arborea and M. faya), such that the yearly medians of the hourly T values were 6–15.6 times higher when no fog was present as compared to cloud immersed periods. By contrast the gc estimates exhibit larger values in the afternoon during foggy conditions when compared in terms of the hourly gc medians at each time of the day, and were clearly greater on a daily basis. During foggy conditions, gc followed a monotonically increasing trend. Large variability of conductance estimates was observed across the ranges of micrometeorological conditions explored. The largest conductance values were associated with low solar radiations, air temperatures between 8 and 15°C, low VPD (<0.5kPa), and wind velocities of 2–4ms−1. Laurel forest trees, previously referred as following a profligate water use strategy, may thus profit from the foggy environment by maintaining the stomata opened during the day without significant water losses, while benefiting with the associated carbon gain.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.07.021
      Issue No: Vol. 247 (2017)
       
  • Impact of canopy aerodynamic distance spatial and temporal variability on
           long term eddy covariance measurements
    • Authors: Quentin Hurdebise; Bernard Heinesch; Anne De Ligne; Caroline Vincke; Marc Aubinet
      Pages: 131 - 138
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Quentin Hurdebise, Bernard Heinesch, Anne De Ligne, Caroline Vincke, Marc Aubinet
      Understanding if and how the spatial and temporal variability of the surrounding environment affects turbulence is essential for long-term eddy covariance measurements. It requires characterizing the surrounding environment. One way to achieve this is to analyse the canopy aerodynamic distance (Δ), which is the difference between measurement height (zm ) and displacement height (d). In this work, an original method to estimate the canopy aerodynamic distance at a fine spatial (30° sectors) and temporal (one year) resolution was proposed. It was based on sensible heat cospectra analysis, calibrated on a measurement height change and validated using canopy height inventories. This method was applied to 20 years of eddy covariance measurements from the Vielsalm Terrestrial Observatory (VTO), a site located in a mixed temperate forest. The method allowed Δ spatio-temporal variability due to changes in canopy or measurement height to be detected. Relationships between Δ and turbulence statistics were then analysed: the momentum correlation coefficient (ruw ) was found to be dependent on Δ, confirming that the measurements were made in the roughness sublayer of the atmospheric surface layer. In contrast, no such relationship was found sensible heat, CO2 or water vapour correlation coefficients, suggesting that the Δ variability did not affect significantly these fluxes. There were significant differences, however, between azimuthal directions, suggesting that these scalars were affected by forest heterogeneity in a different way. Various hypotheses were put forward to explain the differences and their relevance was evaluated. This study highlighted the need to consider the spatial and temporal variability of the surrounding environment in order to verify the consistency of long-term eddy covariance datasets.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.07.013
      Issue No: Vol. 247 (2017)
       
  • Effects of short-term N addition on soil C fluxes in alpine Sibiraea
           angustata scrub on the eastern margin of the Qinghai-Tibetan Plateau
    • Authors: Dong Wang; Heliang He; Qiao Gao; Wei He; Chunzhang Zhao; Huajun Yin; Qing Liu
      Pages: 151 - 158
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Dong Wang, Heliang He, Qiao Gao, Wei He, Chunzhang Zhao, Huajun Yin, Qing Liu
      Although knowledge of the impact of N enrichment on soil C fluxes is scant, such information is highly critical for estimating the global C budget under elevated N deposition. To quantify the effects of short-term N addition on soil C sequestration in an alpine scrub ecosystem, we conducted a field experiment for Sibiraea angustata scrub on the eastern margin of the Qinghai-Tibetan Plateau in China. We quantified the soil C pool (0–30cm) and C fluxes in litterfall, fine root (<2mm diameter) production (FRP), and soil CO2 emission (heterotrophic respiration, Rh) over four years with four levels of N addition (N0; control, N20; 20, N50; 50, and N100, 100kgNha−1 year−1). The results showed that at control plots the total C-input (433±33gCm−2 year−1) via FRP (360±34gCm−2 year−1) and litterfall (73±1gCm−2 year−1) was close to the C-output via Rh (466±5gCm−2 year−1), which demonstrates that the S. angustata scrub soil C is at equilibrium status. However, adding N, particularly the N100 treatment, significantly affected the soil C balance; the soil became a C sink (163±46gCm−2 year−1) by increasing FRP (+63%) rather than by increasing litterfall (P >0.05) or reducing Rh (P >0.05). As a result, the soil C pool (0–30cm) increased significantly. In conclusion, these results suggest that fine roots play a dominant role in the C balance of an alpine scrub ecosystem due to large C-inputs to the soil. Moreover, short-term high N enrichment causes sequestration of additional atmospheric CO2, largely because of the stimulation of fine root growth rather than increased inputs of aboveground plant litterfall or reductions in soil CO2 emission.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.07.026
      Issue No: Vol. 247 (2017)
       
  • Assessing causes of yield gaps in agricultural areas with diversity in
           climate and soils
    • Authors: Juan I. Rattalino Edreira; Spyridon Mourtzinis; Shawn P. Conley; Adam C. Roth; Ignacio A. Ciampitti; Mark A. Licht; Hans Kandel; Peter M. Kyveryga; Laura E. Lindsey; Daren S. Mueller; Seth L. Naeve; Emerson Nafziger; James E. Specht; Jordan Stanley; Michael J. Staton; Patricio Grassini
      Pages: 170 - 180
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Juan I. Rattalino Edreira, Spyridon Mourtzinis, Shawn P. Conley, Adam C. Roth, Ignacio A. Ciampitti, Mark A. Licht, Hans Kandel, Peter M. Kyveryga, Laura E. Lindsey, Daren S. Mueller, Seth L. Naeve, Emerson Nafziger, James E. Specht, Jordan Stanley, Michael J. Staton, Patricio Grassini
      Identification of causes of gaps between yield potential and producer yields has been restricted to small geographic areas. In the present study, we developed a novel approach for identifying causes of yield gaps over large agricultural areas with diversity in climate and soils. This approach was applied to quantify and explain yield gaps in rainfed and irrigated soybean in the North-Central USA (NC USA) region, which accounts for about one third of soybean global production. Survey data on yield and management were collected from 3568 producer fields over two crop seasons and grouped into 10 technology extrapolation domains (TEDs) according to their soil, climate, and water regime. Yield potential was estimated using a combination of crop modeling and boundary functions for water productivity and compared against highest producer yields derived from the yield distribution in each TED-year. Yield gaps were calculated as the difference between yield potential and average producer yield. Explanatory factors for yield gaps were investigated by identifying management practices that were concordantly associated with high- and low-yield fields. Management×TED interactions were then evaluated to elucidate the underlying causes of yield gaps. The chosen spatial TED framework accounted for about half of the regional variation in producer yield within the NC USA region. Across the 10 TEDs, soybean average yield potential ranged from 3.3 to 5.3 Mgha−1 for rainfed fields and from 5.3 to 5.6Mgha−1 for irrigated fields. Highest producer yields in each TED were similar (±12%) to the estimated yield potential. Yield gap, calculated as percentage of yield potential, was larger in rainfed (range: 15–28%) than in irrigated (range: 11–16%) soybean. Upscaled to the NC USA region, yield potential was 4.8Mgha−1 (rainfed) and 5.7Mgha−1 (irrigated), with a respective yield gap of 22 and 13% of yield potential. Sowing date, tillage, and in-season foliar fungicide and/or insecticide were identified as explanatory causes for yield variation in half or more of the 10 TEDs. However, the degree to which these three factors influenced producer yield varied across TEDs. Analysis of in-season weather helped interpret management×TED interactions. For example, yield increase due to advances in sowing date was greater in TEDs with less water limitation during the pod-setting phase. The present study highlights the strength of combining producer survey data with a spatial framework to measure yield gaps, identify management factors explaining these gaps, and understand the biophysical drivers influencing yield responses to crop management.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.07.010
      Issue No: Vol. 247 (2017)
       
  • Contrasting responses of heterotrophic and root-dependent respiration to
           soil warming in a subtropical plantation
    • Authors: Hui Wang; Shirong Liu; Jingxin Wang; Dejun Li; Zuomin Shi; Yanchun Liu; Jia Xu; Pizheng Hong; Haolong Yu; Zhang Zhao; Angang Ming; Lihua Lu; Daoxiong Cai
      Pages: 221 - 228
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Hui Wang, Shirong Liu, Jingxin Wang, Dejun Li, Zuomin Shi, Yanchun Liu, Jia Xu, Pizheng Hong, Haolong Yu, Zhang Zhao, Angang Ming, Lihua Lu, Daoxiong Cai
      The most advanced global land models remain highly uncertain in their predictions of the magnitude and direction of the effects of global warming on soil respiration. To better understand how soil respiration responds to warming, we conducted a three-year soil warming experiment in a subtropical Castanopsis hystrix plantation. Soil respiration (Rs) is considered the sum of root-dependent respiration (Rrd) and heterotrophic respiration (Rh). We estimated root-dependent respiration using the difference in soil respiration between trenched (100cm deep) and non-trenched plots. Our results showed that soil moisture was significantly higher in the trenched than non-trenched subplots in the second year, but not in the third year. Soil warming increased Rh, and suppressed Rrd. The responses of Rh and Rrd to soil warming varied with the seasons, being greater in the dry–cool than in the wet–warm season. The elevated Rh levels may have resulted from the increased soil temperature and decreased soil moisture due to warming. The decline in soil total nitrogen (STN) content attributed to soil warming decreased arbuscular mycorrhizal fungi (AMF) biomass, which led to the reduced Rrd. The decreased Rrd and increased Rh appear to have offset each other, resulting in unaltered Rs levels under the warming treatment. Our study shows that mycorrhizal colonization can have similar effects on soil carbon as it does abiotic environmental factors such as temperature and moisture, and affects Rs dynamics.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.07.025
      Issue No: Vol. 247 (2017)
       
  • Grassland types and season-dependent response of ecosystem respiration to
           experimental warming in a permafrost region in the Tibetan Plateau
    • Authors: Tao Zhang; Genxu Wang; Yan Yang; Tianxu Mao; Xiaopeng Chen
      Pages: 271 - 279
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Tao Zhang, Genxu Wang, Yan Yang, Tianxu Mao, Xiaopeng Chen
      Information regarding the response of ecosystem respiration (ER) to various warming levels, especially in different grassland types and seasons, is scarce at the field scale in the permafrost region of the Tibetan Plateau (TP). In this study, we examined how different warming levels during different seasons affected ER in Tibetan alpine meadow and swamp meadow after 6 years experimental warming. The interpolated annual ER of swamp meadow (387.0gCm−2) was higher than that of alpine meadow (284.5gCm−2) in natural conditions. A moderate warming of 2.4°C increased ER by 62.2% and 36.6%, and a high warming of 5.3°C increased ER by 101.3% and 52.0% in alpine meadow and swamp meadow, respectively. The warming effects on ER were greater in the non-growing season compared with the growing season; this significantly increased the contribution of non-growing season emissions to annual ER from 25% in natural conditions to 31% in high warming treatments. ER was significantly affected by soil temperature, aboveground biomass and the duration of thaw days. The temperature sensitivity of ER (Q 10) was higher in the non-growing season (3.02–5.02) than in the growing season (2.11–2.75) and decreased with increasing temperature. Our results indicated that the magnitude of warming-induced increases in ER differed by grassland type and season, and there was strong potential for the non-growing season to serve as a positive feedback to annual carbon balance.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.08.010
      Issue No: Vol. 247 (2017)
       
  • On the relationship between continuous measures of canopy greenness
           derived using near-surface remote sensing and satellite-derived vegetation
           products
    • Authors: Luke A. Brown; Jadunandan Dash; Booker O. Ogutu; Andrew D. Richardson
      Pages: 280 - 292
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Luke A. Brown, Jadunandan Dash, Booker O. Ogutu, Andrew D. Richardson
      Over the last two decades, satellite-derived estimates of biophysical variables have been increasingly used in operational services, requiring quantification of their accuracy and uncertainty. Evaluating satellite-derived vegetation products is challenging due to their moderate spatial resolution, the heterogeneity of the terrestrial landscape, and difficulties in adequately characterising spatial and temporal vegetation dynamics. In recent years, near-surface remote sensing has emerged as a potential source of data against which satellite-derived vegetation products can be evaluated. Several studies have focussed on the evaluation of satellite-derived phenological transition dates, however in most cases the shape and magnitude of the underlying time-series are neglected. In this paper, we investigated the relationship between the green chromatic coordinate (GCC) derived using near-surface remote sensing and a range of vegetation products derived from the Medium Resolution Imaging Spectrometer (MERIS) throughout the growing season. Moderate to strong relationships between the GCC and vegetation products derived from MERIS were observed at deciduous forest sites. Weak relationships were observed over evergreen forest sites as a result of their subtle seasonality, which is likely masked by atmospheric, bidirectional reflectance distribution function (BRDF), and shadowing effects. Temporal inconsistencies were attributed to the oblique viewing geometry of the digital cameras and differences in the incorporated spectral bands. In addition, the commonly observed summer decline in GCC values was found to be primarily associated with seasonal variations in brown pigment concentration, and to a lesser extent illumination geometry. At deciduous sites, increased sensitivity to initial increases in canopy greenness was demonstrated by the GCC, making it particularly well-suited to identifying the start of season when compared to satellite-derived vegetation products. Nevertheless, in some cases, the relationship between the GCC and vegetation products derived from MERIS was found to saturate asymptotically. This limits the potential of the approach for evaluation of the vegetation products that underlie satellite-derived phenological transition dates, and for the continuous monitoring of vegetation during the growing season, particularly at medium to high biomass study sites.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.08.012
      Issue No: Vol. 247 (2017)
       
  • Patch size of trees affects its cooling effectiveness: A perspective from
           shading and transpiration processes
    • Authors: Min Jiao; Weiqi Zhou; Zhong Zheng; Jia Wang; Yuguo Qian
      Pages: 293 - 299
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Min Jiao, Weiqi Zhou, Zhong Zheng, Jia Wang, Yuguo Qian
      Increasing urban greenspace, particularly trees, has been widely recognized as an effective means for urban heat mitigation. Lots of uncertainty, however, occurs on how spatial configuration of trees affects their cooling effectiveness. A frequently asked question from urban planners is that whether a large greenspace patch has better cooling effects than several smaller ones, or vice versa. Here, we attempted to address this question by investigating the effects of patch size of trees on the two key cooling processes: shading and transpiration. We chose two typical tree species, Ginkgo biloba and Populus tomentosa, with 4 different patch sizes, and conducted the research in Beijing. We integrated field measurements of air temperature, relative humidity and transpiration rate with model simulation, and conducted the analysis at both the patch and within-patch level. We found: (1) Smaller patches had higher temperature, lower humidity and greater within-patch variations in temperature and humidity than larger ones. (2) With a fixed area of tree cover, a number of small patches can provide more shade than a single large patch, suggesting a monotonic increase of shade provision with the division of a large patch into smaller ones. (3) There was a non-linear relationship between patch size and transpiration rate, suggesting a maximum transpiration rate might occur at certain patch size. By considering the joint effects of shading and transpiration, an optimal size of patch might occur, at which the joint effects of shading and transpiration are maximized.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.08.013
      Issue No: Vol. 247 (2017)
       
  • Evaluating AquaCrop model for simulating production of amaranthus
           (Amaranthus cruentus) a leafy vegetable, under irrigation and rainfed
           conditions
    • Authors: Z.A. Bello; S. Walker
      Pages: 300 - 310
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Z.A. Bello, S. Walker
      Amaranthus (Amaranthus spp.), a leafy vegetable in South Africa, has the potential to be cultivated as a crop, but is rarely cultivated because it easily grows naturally on any waste land. The crop tolerates adverse environmental conditions, but performs better with application of water and soil organic or inorganic fertilizers. The AquaCrop crop model was calibrated and validated for amaranthus under irrigation and rainfed conditions for this study. Field experiments were carried out during the 2008–09 and 2009–10 seasons under line source sprinkler system while pot experiment was carried out during the 2010–11 season. The pot and field data sets were used for parameterisation, calibration and validation of the model. The model was adequately calibrated for biomass and cumulative evapotranspiration (ET) for amaranthus under irrigation and rainfed conditions. However, pooled data across irrigation and rainfed conditions showed canopy cover (CC) was moderately simulated (root-mean-square error (RMSE) =20.8%; model efficiency (ME)=0.11; R2 =0.577; d index of agreement (d)=0.746; mean absolute percentage error (MAPE)=43.4%). During validation, the model was able to adequately predict biomass and cumulative evapotranspiration (ET) for amaranthus for pooled data of irrigation (Full irrigation=W5 & Moderate irrigation=W3) and rainfed (W1) with RMSE of 1.96tha−1 and 75.64mm, ME of 0.89 and 0.76, R2 of 0.92 and 0.91, d index of agreement of 0.91 and 0.91 and MAPE of 24.1 and 37.6% respectively. The prediction of soil water content by the model was moderate (RMSE=50.62mm; ME=0.19; R2 =0.30; d=0.67; MAPE=40.09) and needs improvement. It is recommended that datasets from other agro-ecological regions be used to improve calibration and validation for this crop.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.08.003
      Issue No: Vol. 247 (2017)
       
  • Responses of different physiological parameter thresholds to soil water
           availability in four plant species during prolonged drought
    • Authors: Weiming Yan; Yangquanwei Zhong; Zhouping Shangguan
      Pages: 311 - 319
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Weiming Yan, Yangquanwei Zhong, Zhouping Shangguan
      Large-scale vegetation restoration on the Loess Plateau in China has been performed by the central government in recent decades; however, the planting of incompatible vegetation during these efforts has resulted in serious environmental problems, such as dry soil layers, that are widespread and difficult to ameliorate. To determine the proper evaluation indices for plant available soil water content (PASWC) in commonly reforested plants and crops, we examined the physiological responses of Robinia pseudoacacia (tree), Amorpha fruticosa (shrub), Medicago sativa (perennial leguminous herb) and Zea mays (crop) to prolonged drought; these plants were planted widely in the semiarid Loess Plateau region of China. Leaf water status, gas exchange and fluorescence parameters did not show marked changes at the beginning of the prolonged drought but changed rapidly as PASWC continued to decrease. These data were fitted with a sigmoid function (P< 0.0001). In addition, different physiological parameters showed different PASWC thresholds; the fluorescence parameters exhibited the lowest PASWC threshold among the four species, with an upper threshold that was less than 50% of the PASWC for all but Z. mays. In this study, the photosynthesis rate was a better indicator of the PASWC, and the upper and lower thresholds of PASWC of the normalized photosynthesis rate were 64.1% and 47.6%, 83.0% and 44.1%, 82.7% and 35.2%, 82.9% and 39.3% for R. pseudoacacia, A. fruticosa, M. sativa and Z. mays, respectively. The current study also suggests that R. pseudoacacia is a suitable afforestation species in areas with higher levels of rainfall. These results provide important information for determining the PASWC and the supply capacity of soil water on the Loess Plateau.

      PubDate: 2017-08-27T13:34:58Z
      DOI: 10.1016/j.agrformet.2017.08.017
      Issue No: Vol. 247 (2017)
       
  • 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
       
  • Validating canopy clumping retrieval methods using hemispherical
           photography in a simulated Eucalypt forest
    • Authors: William Woodgate; John Armston Mathias Disney Lola Suarez Simon Jones
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): William Woodgate, John D. Armston, Mathias Disney, Lola Suarez, Simon D. Jones, Michael J. Hill, Phil Wilkes, Mariela Soto-Berelov
      The so-called clumping factor (Ω) quantifies deviation from a random 3D distribution of material in a vegetation canopy and therefore characterises the spatial distribution of gaps within a canopy. Ω is essential to convert effective Plant or Leaf Area Index into actual LAI or PAI, which has previously been shown to have a significant impact on biophysical parameter retrieval using optical remote sensing techniques in forests, woodlands, and savannas. Here, a simulation framework was applied to assess the performance of existing in situ clumping retrieval methods in a 3D virtual forest canopy, which has a high degree of architectural realism. The virtual canopy was reconstructed using empirical data from a Box Ironbark Eucalypt forest in Eastern Australia. Hemispherical photography (HP) was assessed due to its ubiquity for indirect LAI and structure retrieval. Angular clumping retrieval method performance was evaluated using a range of structural configurations based on varying stem distribution and LAI. The CLX clumping retrieval method (Leblanc et al., 2005) with a segment size of 15° was the best performing clumping method, matching the reference values to within 0.05Ω on average near zenith. Clumping error increased linearly with zenith angle to >0.3Ω (equivalent to a 30% PAI error) at 75° for all structural configurations. At larger zenith angles, PAI errors were found to be around 25–30% on average when derived from the 55–60° zenith angle. Therefore, careful consideration of zenith angle range utilised from HP is recommended. We suggest that plot or site clumping factors should be accompanied by the zenith angle used to derive them from gap size and gap size distribution methods. Furthermore, larger errors and biases were found for HPs captured within 1m of unrepresentative large tree stems, so these situations should be avoided in practice if possible.

      PubDate: 2017-10-08T16:07:58Z
       
  • Inter-comparison of three models for δ13C of respiration with four
           regression approaches
    • Authors: Changhua Chen; Jiaping Pang Jie Wei Xuefa Wen Xiaomin Sun
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Changhua Chen, Jiaping Pang, Jie Wei, Xuefa Wen, Xiaomin Sun
      The carbon isotopic composition of ecosystem carbon pools and fluxes is a useful tracer in the carbon cycle. In this study, the carbon dioxide mixing ratio ([CO2]) and its δ13C were measured in-situ by wavelength-scanned cavity ring-down spectrometry in a subtropical coniferous plantation. We determined δ13C of respiration in the understory (δRs) using three models (i.e., Keeling plots (KP), Miller-Tans plots (MT), and flux ratio method (FR)) with four regressions (i.e., ordinary least squares (OLS), geometric mean regression (GMR), least-squares bisector regression (LSB), and orthogonal distance regression (ODR)). The selection of regression approaches affected KP and MT rather than FR. No significant differences were observed among the three models using OLS (p> 0.05). The systematic bias and uncertainty of δRs would increase with the decrease of the [CO2] ranges (KP and MT) and the d13CO2/dz gradients (FR). The bias of δRs among the four regression approaches could be explained by the Pearson’s correlation coefficient of linear fit at small [CO2] ranges and low d13CO2/dz gradients. The uncertainty of δRs was primarily related to the δ13C measurement error based on a Gaussian noise simulation, and OLS was less sensitive to the δ13C measurement error. A threshold criterion for the [CO2] ranges or the d13CO2/dz gradients should be established to remove the δRs values with relatively large errors and improve the overall reliability of estimating δRs.

      PubDate: 2017-10-08T16:07:58Z
       
  • Projecting tree-growth responses into future climate: A study case from a
           Danish-wide common garden
    • Authors: Weiwei Huang; Patrick Fonti Larsen Anders Ingeborg Callesen Nanna Bjerregaard
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Weiwei Huang, Patrick Fonti, Jørgen Bo Larsen, Anders Ræbild, Ingeborg Callesen, Nanna Bjerregaard Pedersen, Jon Kehlet Hansen
      Assessing growth responses to climate variations from common garden experiments is vital to identify a species portfolio matching future climate. In the present study we make use of a 50 years old common garden experiment spanning six sites with different soil types across Denmark to (i) analyse climate-growth responses and resilience to drought and (ii) model future growth predictions for six non-native conifers and two native broadleaved tree species. Species-specific response-functions and Superposed Epoch Analysis of drought events are used to assess differences in sensitivity to drought. The results show that the growth of all species, except for Quercus robur L., are significantly (P <0.05) and negatively correlated with summer drought from June-August in at least one of the sites, whereby Larix kaempferi (Lamb.) Carr, Abies grandis (Dougl.) Lindl., Picea sitchensis (Bong.) Carr., and Picea abies (L.) Karst. are the less resilient. Negative effects of previous warm autumn or late summer were found for P. abies, A. grandis, Abies alba Mill. and Pseudotsuga menziesii (Mirb.) Franco. Moreover, independently of the site conditions, our model projections of growth responses under future climate prediction (RCP4.5 emission scenario) forecast that growth of L. kaempferi, A. grandis, P. abies and Fagus sylvatica L. will be reduced by up to 10–16% by 2100. Minor changes in growth responses are expected for P. sitchensis, A. alba and P. menziesii, while Q. robur will increase by 12%. This study demonstrates how such projections based on old common garden experiments could be used as inputs to today’s forest management decisions.

      PubDate: 2017-10-08T16:07:58Z
       
  • Seasonality of albedo and FAPAR in a boreal forest
    • Authors: Aarne Hovi; Petr Miina Rautiainen
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Aarne Hovi, Petr Lukeš, Miina Rautiainen
      Satellite data are continuously used to monitor albedo and fraction of absorbed photosynthetically active radiation (FAPAR), which are key components in determining the energy balance and productivity of forests. However, due to the mismatch between spatial resolution of the satellite data and forest stand size, coarse resolution satellite products cannot capture the fine-scale variations in forest structure. Therefore, forest radiation budget models are important tools in quantifying albedo and FAPAR at stand scale. However, due to the lack of suitable input data, simulations are often restricted to summer conditions only and the seasonal patterns are not considered. We modeled the time series of albedo and FAPAR for an entire growing season for 20 forest plots in the boreal zone in Finland (61°50′N, 24°17′ E) using an exceptional ground reference data set. Canopy gap fractions and the spectra of forest floor were monitored in the plots throughout the growing season. Data on the seasonality of spectra of tree foliage were also available. The modeled albedo and FAPAR were upscaled and compared against albedo and FAPAR derived from MODIS satellite data. We showed that forest radiation budget models capable of adequately taking into account foliage clumping and its effects on multiple scattering are the most appropriate for simulating albedo of boreal coniferous forests. Our results also indicated negative albedo-productivity relations in boreal coniferous forests. In addition, we demonstrated that not only the overall level, but also the seasonal patterns of albedo and FAPAR differ between tree species. Therefore, the use of only peak growing season albedo or FAPAR values when estimating climate impacts of forest management can be misleading.

      PubDate: 2017-10-08T16:07:58Z
       
  • Hydrology and microtopography control carbon dynamics in wetlands:
           Implications in partitioning ecosystem respiration in a coastal plain
           forested wetland
    • Authors: Guofang Miao; Asko Noormets Jean-Christophe Domec Montserrat Fuentes Carl Trettin
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Guofang Miao, Asko Noormets, Jean-Christophe Domec, Montserrat Fuentes, Carl C. Trettin, Ge Sun, Steve G. McNulty, John S. King
      Wetlands store a disproportionately large fraction of organic carbon relative to their areal coverage, and thus play an important role in global climate mitigation. As destabilization of these stores through land use or environmental change represents a significant climate feedback, it is important to understand the functional regulation of respiratory processes that catabolize them. In this study, we established an eddy covariance flux tower project in a coastal plain forested wetland in North Carolina, USA, and measured total ecosystem respiration (Re) over three years (2009–2011). We evaluated the magnitude and variability of three respiration components – belowground (Rs), coarse woody debris (RCWD), and aboveground plant (Ragp) respiration at the ecosystem scale, by accounting microtopographic variation for upscaling and constraining the mass balance with Re. Strong hydrologic control was detected for Rs and RCWD, whereas Ragp and Re were relatively insensitive to water table fluctuations. In a relatively dry year (2010), this forested wetland respired a total of about 2000g CO2-C m-2 y-1 annually, 51% as Rs, 37% as Ragp, and 12% as RCWD. During non-flooded periods Rs contributed up to 57% of Re and during flooded periods Ragp contributed up to 69%. The contribution of Rs to Re increased by 2.4% for every cm of decrease in water level at intermediate water table level, and was nearly constant when flooded or when the water level more than 15cm below ground. The contrasting sensitivity of different respiration components highlights the need for explicit consideration of this dynamic in ecosystem and Earth System Models.

      PubDate: 2017-10-08T16:07:58Z
       
  • Repackaging precipitation into fewer, larger storms reduces ecosystem
           exchanges of CO2 and H2O in a semiarid steppe
    • Authors: W.J. Liu; L.F. J.A. Biederman Y.B. Hao Zhang X.M. Kang
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): W.J. Liu, L.F. Li, J.A. Biederman, Y.B. Hao, H. Zhang, X.M. Kang, X.Y. Cui, Y.F. Wang, M.W. Li, Z.H. Xu, K.L. Griffin, C.Y. Xu
      General circulation models predict that precipitation will become more extreme, i.e. rainfall events of larger size but reduced frequency. Studies in North American grasslands have shown that such repackaging of precipitation into fewer, larger events enhanced above ground net primary productivity (ANPP), likely due to deeper soil moisture infiltration favoring plant water use over evaporation. However, ANPP responses in other regions remain poorly understood, and responses of carbon and water exchanges with the atmosphere remain unknown. Here we manipulated rainfall in a steppe ecosystem of northern China over 4 years to investigate how temporal packaging of precipitation impacts ANPP, evapotranspiration (ET), net ecosystem CO2 exchange (NEE) and the component fluxes gross primary productivity (GPP) and ecosystem respiration (RE). Experimental plots received precipitation equivalent to the 60-year growing-season average of 240 mm, variously packaged into 6, 10, 16, or 24 events representing extreme (P6) to historical average (P24) rainfall frequency. Extraordinarily extreme frequency (6 large events) reduced NEE, GPP, RE, ET and water use efficiency (WUE =  NEE /ET). The average NEE, GPP and RE declined 35%, 45% and 48% respectively in the P6 treatment as compared to P16, which showed maximum ET and CO2 exchange. After peaking in the 16-event treatment, GPP and WUE in P24 were not distinguishable from P6. These peaks suggest that P16 was optimal for photosynthesis, with sufficiently frequent rain to maintain unregulated plants and adequately deep soil moisture infiltration to favour transpiration, with associated carbon uptake, over evaporation. Path analysis indicated the lower CO2 fluxes were influenced by reduced soil water content and leaf area index and higher soil temperature, with ET regulating the effects of these microclimatic drivers. ANPP showed a monotonic but non-significant decline with decreasing precipitation frequency, consistent with reduced CO2 fluxes. We found an increase in ANPP of xerophyte plants partially compensated for the ANPP decline in the dominant eurytopic xerophyte plants. Our results suggest that extreme temporal repackaging of precipitation into few events with correspondingly long dry intervals may reduce the capacity of steppe ecosystems to assimilate atmospheric CO2, although community diversity may moderate impacts.

      PubDate: 2017-10-08T16:07:58Z
       
  • Retrieving vegetation canopy water content from hyperspectral thermal
           measurements
    • Authors: Elnaz Neinavaz; Andrew Skidmore Roshanak Darvishzadeh Thomas Groen
      Abstract: Publication date: 15 December 2017
      Source:Agricultural and Forest Meteorology, Volume 247
      Author(s): Elnaz Neinavaz, Andrew K. Skidmore, Roshanak Darvishzadeh, Thomas A. Groen
      The retrieval of vegetation canopy water content using thermal hyperspectral (TIR, 8–14μm) measurements is investigated in this study. Vegetation water content indicators such as fuel moisture content (FMC, %, mass-based) and equivalent water thickness (EWT, gcm−2, area based) play significant roles in plant physiology, as well as in the modelling of fire risk and behavior, particularly in forests. Although retrieval of these parameters, in particular EWT, has been demonstrated from optical and TIR measurements, to our knowledge their prediction at canopy level in the thermal part of the electromagnetic spectrum has not yet been investigated. Therefore, the application of hyperspectral TIR data for predicting FMC and EWT parameters at canopy level is explored here. The emissivity of spectral data in the TIR region is measured for four species (Azalea japonica, Buxus sempervirens, Euonymus japonicus, and Ficus benjamina) under controlled laboratory conditions, using a portable MIDAC Fourier transform infrared spectrometer. EWT, FMC, and their corresponding canopy emissivity measurements are assessed by destructive sampling of the leaves. Leaf area, as well as fresh and dry mass of the harvested leaves, is determined for all four species. Partial least square regression and artificial neural networks, using various spectral subsets, are used to predict the two variables of interest. Higher estimation accuracies have been obtained for both FMC and EWT at canopy level using artificial neural networks. Unexpectedly, the FMC at canopy level, as a mass-based variable, more accurately retrieved using either method. This is contrary to previous findings using multispectral and hyperspectral data. Our results suggest that plant mass may play a greater role in determining spectral emissivity than plant area does.

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