for Journals by Title or ISSN
for Articles by Keywords

Publisher: Elsevier   (Total: 3184 journals)

 A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z  

        1 2 3 4 5 6 7 8 | Last   [Sort by number of followers]   [Restore default list]

Showing 1 - 200 of 3184 Journals sorted alphabetically
Academic Pediatrics     Hybrid Journal   (Followers: 37, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 26, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 100, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 28, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 39, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 6)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 7)
Acta Astronautica     Hybrid Journal   (Followers: 435, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 28, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 3)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 11, SJR: 0.18, CiteScore: 1)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 308, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 25, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access   (Followers: 1)
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 7, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 8)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 18, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 9, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 11, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 23)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 183, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 12, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 17, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 29, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 11, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 11, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 24, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 15, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 33, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 5)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 14)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 29, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 26, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 20, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 13)
Advances in Digestive Medicine     Open Access   (Followers: 12)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 7)
Advances in Drug Research     Full-text available via subscription   (Followers: 26)
Advances in Ecological Research     Full-text available via subscription   (Followers: 43, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 29, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 8)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 51, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 65, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 17)
Advances in Genetics     Full-text available via subscription   (Followers: 21, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 10, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 7, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 26, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 11, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 24)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 3, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 36, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 10, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 9, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 21, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 12, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 8, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 6)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 5, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 24)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 5)
Advances in Oncobiology     Full-text available via subscription   (Followers: 2)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 18, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 27, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 18)
Advances in Pharmacology     Full-text available via subscription   (Followers: 17, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 10)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 6)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 19)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 66)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 1, SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 6)
Advances in Space Research     Full-text available via subscription   (Followers: 421, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 13, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 37, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 20)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 15)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 53, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 383, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 12, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 473, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 18, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 31, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 45, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 4)
Agriculture and Natural Resources     Open Access   (Followers: 3)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 58, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 7, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 12, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 11)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 2, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 11, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 10, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 54, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 6, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 6, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 5)
American Heart J.     Hybrid Journal   (Followers: 58, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 63, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 46, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 12)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 37, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 29, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 36, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 50)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 249, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 66, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 32, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 39, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 7)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 66, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 24, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription   (Followers: 1)
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 44, SJR: 1.512, CiteScore: 5)
Analytica Chimica Acta : X     Open Access  
Analytical Biochemistry     Hybrid Journal   (Followers: 210, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 13, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 14)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 25, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)
Animal Behaviour     Hybrid Journal   (Followers: 221, SJR: 1.58, CiteScore: 3)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 6, SJR: 0.937, CiteScore: 2)
Animal Reproduction Science     Hybrid Journal   (Followers: 7, SJR: 0.704, CiteScore: 2)

        1 2 3 4 5 6 7 8 | Last   [Sort by number of followers]   [Restore default list]

Similar Journals
Journal Cover
Agricultural and Forest Meteorology
Journal Prestige (SJR): 1.818
Citation Impact (citeScore): 5
Number of Followers: 18  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0168-1923
Published by Elsevier Homepage  [3184 journals]
  • Rain and wind affect chamber measurements
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Martin Maier, Samuel Mayer, Thomas LaemmelAbstractChamber methods are widely used to measure soil-atmosphere fluxes of different gases. To obtain reliable flux estimates it is important to avoid changes in the natural soil-atmosphere system as far as possible. While issues like chamber dimensions, closure time and calculation approaches have been intensively discussed, there is still uncertainty about other possible biases like wind and rain affecting the measurement.To study the effect of local airflow and rain on chamber flux measurements, we used inert tracer gas (Tetrafluoromethane, CF4) that was continuously injected into the subsoil and concurrently measured during the automatic soil respiration measurements. While the variability of the CO2 fluxes included the changing signal of the biological source and the physical effect of the changing environment, the CF4 measurements allowed isolating the latter. Finite element modeling of gas transport within the soil-chamber-atmosphere system was used to further analyze the effect of rain and soil moisture.Rain events had a strong effect on the measured CF4 fluxes with a decrease shortly after rainfall which was then super-compensated by elevated fluxes for 1–2 days. This pattern could be addressed as an artefact of automatic chamber measurements that has been overlooked so far. Since the chamber closed automatically, it excluded a part of the rain amount. This resulted in a temporarily preferential venting of soil gas through the chamber surface that remained drier than the surrounding soil outside the chamber. Thus, we recommend leaving automatic chambers open during rain to strictly avoid rain exclusion.Local wind speed near the chamber was generally low since we worked in a forest. Yet, CF4 flux and CO2 flux decreased with increasing wind speed, what can be interpreted as an artefact due to the chamber modifying the natural airflow conditions. The wind effect, however, was weaker than the effect of rain.
  • Nitrogen addition alters photosynthetic carbon fixation, allocation of
           photoassimilates, and carbon partitioning of Leymus chinensis in a
           temperate grassland of Inner Mongolia
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Biao Wang, Jirui Gong, Zihe Zhang, Bo Yang, Min Liu, Chenchen Zhu, Jiayu Shi, Weiyuan Zhang, Kexin YueAbstractAtmospheric nitrogen (N) deposition is sharply increasing, and this may have substantial impact on carbon (C) fixation and allocation of plants. Knowledge of the effect of N addition on C fixation and allocation patterns of assimilated C is therefore critical to understand the effects on C cycles in terrestrial ecosystems. We conducted a field experiment to examine the effects of N addition (0 to 25 g N m−2 yr−1) on photosynthetic C fixation and C allocation by Leymus chinensis using 13CO2 pulse-labeling and measurements of the percentage of assimilation allocated to nonstructural carbohydrates (NSCs), secondary metabolites (SMs), and growth in a temperate semi-arid grassland. Moderate N addition (5 and 10 g N m−2 yr−1) significantly increased the δ13C value and 13C fixation of plant leaves by increasing Pn and biomass of L. chinensis. However, high N addition (25 g N m−2 yr−1) did not result in a further increase in Pn and total biomass, suggesting excess N inputs was harmful to photosynthetic C fixation in plants. Moderate N addition (10 g N m−2 yr−1) also significantly increased the root/shoot ratio and the proportion of assimilated 13C allocated to roots, but decreased the proportion of leaves and stems allocated, indicating more C was allocated to roots with N addition. We further found that moderate N addition increased the overall NSC and SM concentrations, but C allocation to growth decreased with increasing N, possibly indicating the existence of a trade-off between the C allocation to defense and the allocation to storage and growth. Our findings demonstrated that N addition will alter photosynthetic C fixation and the allocation patterns of photoassimilates, and thus will significantly affect the C cycle and C balance of terrestrial ecosystems under predicted future global changes.
  • The eddy-covariance storage term in air: Consistent community resources
           improve flux measurement reliability
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Ke Xu, Natchaya Pingintha-Durden, Hongyan Luo, David Durden, Cove Sturtevant, Ankur R. Desai, Christopher Florian, Stefan MetzgerAbstractIn the widely-used eddy-covariance (EC) technique, it is often assumed that the air storage term, i.e. the change of below-turbulence-sensor scalar abundance, is negligible or comprises a small part of net surface-atmosphere exchange (NSAE). Previous studies have demonstrated that this assumption is often violated where non-turbulent processes prevail, and thus it is important to measure and calculate air storage in flux measurements. However, the implementation of air storage measurement and calculation is not ubiquitous as EC standard turbulent flux. In most cases, air storage is not a standard data product or even neglected in EC flux tower measurements. In other cases, air storage term is calculated simply using only the measurements at the tower top. This gap between the ideal initiative and actual implementation motivates us to derive and release one of the first community resources to facilitate the consistent measurement and calculation of EC air storage across sites. These resources include (i) the standardized air storage term measurement setup design at National Ecological Observatory Network (NEON) sites; (ii) the development and public release of the eddy4R.stor open-source air storage R-package; (iii) the derivation and public release of storage term data products, measured and calculated consistently across 47 NEON sites; and (iv) exploration the scientific usefulness of these resources through example use cases, specifically the exploration of the bias of the air storage term when different measurement level intensity used and exploration of the air storage term pattern. We expect the consistent air storage measurement and calculation can better serve the overall purpose of the EC technique to provide more reliable measurement of NSAE for the community. This can further benefit the community accurate depiction of the sub-daily to diurnal cycle of surface fluxes in doing carbon cycle flux partitioning, land modeling, and studying ecosystem response to weather extremes.
  • When a cuvette is not a canopy: A caution about measuring leaf temperature
           during gas exchange measurements
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Christopher J. Still, Adam Sibley, Gerald Page, Frederick C. Meinzer, Sanna SevantoAbstractPlant gas exchange systems are widely used to study leaf physiological processes and properties such as stomatal function and the maximum carboxylation rate of Rubisco. Increasingly, these systems are used to assess how leaf gas exchange varies with temperature in order to better understand how rising temperature will impact plant function. Examples of such studies include variation in optimal temperatures of photosynthesis as a function of species and growth environment, and respiratory acclimation to higher temperatures. Leaf thermoregulation leading to homeothermy has been reported based on leaf gas exchange measurements spanning a large (∼25 °C) temperature range. However, as we show here, the design of a popular gas exchange system used for temperature-response measurements can lead to biased measurements of leaf temperature. We demonstrate this with an example showing that apparent leaf thermoregulatory behavior can arise even in empty cuvettes. More broadly, our results have implications for other temperature manipulations in similar gas exchange systems.
  • Soil microclimates influence annual carbon loss via heterotrophic soil
           respiration in maize and switchgrass bioenergy cropping systems
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Adam C. von Haden, Erika Marín-Spiotta, Randall D. Jackson, Christopher J. KucharikAbstractHeterotrophic soil respiration (RH) is the primary pathway of carbon (C) loss from litter and soil organic matter, and thus RH partially determines ecosystem C storage. Because RH is sensitive to soil temperature and moisture, aboveground factors that influence soil microclimate, such as plant structure and residue management, may in turn affect belowground C loss via RH, but this relationship has not been quantified. We examined multiyear soil microclimate differences to 1-m depth, measured seasonal trends of RH, and parameterized crop-specific microclimate-RH models to quantify the effect of soil microclimate differences on annual RH in temperate no-till maize and switchgrass bioenergy cropping systems. Summertime soil temperatures were typically warmer in maize compared to switchgrass, likely resulting from lower leaf area index (LAI) in maize. In contrast, winter soil temperatures were usually warmer in switchgrass than maize, due in part to more consistent snow retention within the switchgrass litter stubble. Daily soil temperature ranges were less extreme in the perennial switchgrass system compared to the annual no-till maize system. Soil moisture near the soil surface was usually lower in maize than switchgrass, but the opposite was true below about 50 cm. RH showed strong seasonal trends, with warmer and drier soil conditions generally leading to higher RH in both crops. Modeled scenarios indicated that the differences in crop-specific soil microclimates accounted for 4 to 17% of the annual RH flux, with the dominant soil microclimate effects on RH occurring during the summer. Thus, the soil microclimate serves as a strong coupling between aboveground properties and belowground C loss via RH in temperate agroecosystems. Agricultural management practices such as planting date, plant density, and residue management could be targeted to promote soil microclimates that reduce RH, thereby reducing gaseous belowground C losses and potentially enhancing ecosystem C storage.
  • A stomatal optimization approach improves the estimation of carbon
           assimilation from sap flow measurements
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Yanting Hu, Tomer Duman, Dirk Vanderklein, Ping Zhao, Karina VR SchäferAbstractModeling the carbon uptake process by plants provides the foundation for global vegetation models. We modified the Canopy Conductance Constrained Carbon Assimilation (4C-A) model, a multi-level assimilation model that utilizes sap-flux measurements, based on the stomatal optimization theory. A novel method of calculating optimal stomatal conductance and carbon assimilation (Anet), which considers the co-limitation of Rubisco activity and RuBP regeneration, has now been incorporated into the modified 4C-A model. Results show that the calculated daily average Anet by the modified 4C-A model was lower than that from the original 4C-A and a big-leaf model but agreed well with that from leaf gas exchange measurement. When the marginal water use efficiency (λ) was high, the calculated daily average Anet became lower than that derived from lower λ. Differences in Anet between the modified and original model were larger when the canopy exhibited higher stomatal conductance or VPD was lower. Hence, a more accurate Anet was estimated by the modified model at dawn and dusk or during humid days when low VPD occurred. In addition, the modified 4C-A model performed better on a diurnal timescale for Anet and stomatal conductance estimation compared to the original one. This modified 4C-A model provides a more realistic estimation of Anet on half hourly to daily timescales, and, thus, can be applied to elucidate the coupling between carbon and water cycles and test the responses of carbon assimilation to environmental change.
  • Insect outbreaks have transient effects on carbon fluxes and vegetative
           growth but longer-term impacts on reproductive growth in a mangrove forest
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Weizhi Lu, Jingfeng Xiao, Xiaowei Cui, Fanghong Xu, Guangxuan Lin, Guanghui LinAbstractMangroves are experiencing frequent severe insect outbreaks, and the bud moth larvae (BML; Lasiognatha cellifera) is one of the most common leaf-feeding insects. However, the effects of insect outbreaks on ecosystem carbon fluxes of mangrove ecosystems are not well understood, and more importantly, the relative effects of these disturbances on vegetative and reproductive growth of mangroves remain unclear. We used measurements of plant litterfall, leaf damage percentage, and insect frass production, satellite-derived normalized difference vegetation index (NDVI), and eddy covariance flux measurements to quantify the impacts of a BML outbreak in 2010 on carbon fluxes and both vegetative and reproductive growth of a mangrove forest. The BML outbreak occurred in 2010 damaged nearly 90% of the foliage, increased the annual leaf litterfall, and decreased the flower and propagule production. Net ecosystem productivity decreased following the insect disturbance and recovered within several months. There were no significant differences in annual carbon fluxes among the four years from 2009 to 2013. In contrast, the flower production significantly decreased and there was nearly no propagule production after the insect outbreak. Reproductive growth did not recover even two years after the insect outbreak. Our results showed that the BML outbreak had asymmetric effects on vegetative and reproductive growth of mangrove forests. Our findings can help us better understand the impacts of insect disturbances on mangrove ecosystems and also have implications for informing mangrove conservation and restoration efforts.
  • In-situ estimation of unsaturated hydraulic conductivity in freezing soil
           using improved field data and inverse numerical modeling
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Qiang Cheng, Qiang Xu, Xianglin Cheng, Song Yu, Zhongyi Wang, Yurui Sun, Xiaofei Yan, Scott B. JonesAbstractHydraulic property determination in freezing soils continues to be a substantial challenge. Our overall objective was to present a novel method for in-situ estimation of unsaturated hydraulic conductivity in freezing soil using a combination of improved field data and a simplified inverse modeling approach. Dielectric sensor readings in the field were corrected using knowledge of ice permittivity, temperature and water redistribution to achieve higher accuracy in determination of liquid soil water content and soil ice content. The equation describing unsaturated hydraulic conductivity in freezing soil with an added impedance parameter was inversely estimated by firstly fitting soil freezing and thawing characteristic curves using the measured liquid soil water content and soil temperature, and then minimizing differences of the measured and simulated total soil water content with a coupled heat- and water-transfer model in frozen soil. Field measurements were made over two winters between 2011 and 2013 (year-1: winter of 2011–2012; year-2: winter of 2012–2013) in Beijing, China. Results suggested that (i) the relative error of liquid soil water content measurement in freezing soil was up to 53% if the knowledge of ice permittivity, temperature and water redistribution was neglected; (ii) the estimated impedance parameter in year-1 (1.152) was an order of magnitude higher than in year-2 (0.117), possibly because a faster freezing rate generated more fine ice in year-2, resulting in reduced tortuosity; (iii) the estimated impedance parameter uncertainty likely comes from the model assumptions, the measurement accuracies of model inputs and the inverse modeling parameter estimates. Based on these results and analysis, we conclude that the impedance parameter in frozen soil is strongly related to both the soil ice content and the size of formed ice, which is affected by the freezing rate and by the size of soil pores related to the soil texture.
  • Tree species classification in a temperate mixed forest using a
           combination of imaging spectroscopy and airborne laser scanning
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Hossein Torabzadeh, Reik Leiterer, Andreas Hueni, Michael E. Schaepman, Felix MorsdorfAbstractKnowledge of the spatial distribution of tree species is important for efficiently managing and monitoring forested ecosystems, especially in mixed forests of the temperate zone. In this study, we fused imaging spectroscopy (IS) data with leaf-on and off small-footprint airborne laser scanning (ALS) data, for tree species identification in a dense temperate forest in Switzerland. In addition to the spectral reflectance of the sunlit part of the tree crowns, structural features computed based on the height, intensity and point distribution of ALS data in both the vertical and horizontal dimensions are used as features. Features were extracted using a pixel-based (1 m × 1 m) and an individual tree crown approach. In addition, applying a floating forward feature selection approach revealed that the ALS-derived features provided relevant structural information for species identification, while IS-derived features added complementary biochemical information. Comparing the accuracies of three different combinations of ALS and IS data, shows the highest classification accuracy (kappa = 90.3%) was obtained by fusing a selected set of features at individual tree crowns (ITC), while the best kappa accuracies resulting from IS or ALS data alone were 74.7% and 75.1%, respectively. Inclusion of the ITC information improved the classification results for all datasets, however, this improvement is significantly higher for ALS derived datasets (+31%). Our results show that accurate ITC information drastically improves classification accuracy of tree species in dense forests and that multi-seasonal ALS structural attributes play a major part in species discrimination.
  • Seasonality of leaf area index and photosynthetic capacity for better
           estimation of carbon and water fluxes in evergreen conifer forests
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Rong Wang, Jing M. Chen, Xiangzhong Luo, Andy Black, Altaf ArainAbstractLeaf area index (LAI), defined as one half the total leaf area per unit ground area, and Vcmax, representing the maximal carboxylation rate of leaves, are two most significant parameters used in most Terrestrial Biosphere Models (TBMs). The ability of TBMs to simulate gross primary productivity (GPP) and evapotranspiration (ET) for evergreen needle-leave forests (ENF) can be significantly hampered by uncertainties in LAI and Vcmax. Remotely sensed (RS) LAI for ENF is generally underestimated in winter, early spring and late autumn. Although constant Vcmax throughout the growing season is often used in TBMs for GPP and ET modeling, it could vary significantly under leaf aging and stressed conditions. There were recent studies that apply seasonal leaf chlorophyll constraints on GPP modeling for croplands and deciduous forests, but little attention is given to the influence of the seasonality of either LAI or Vcmax on GPP or ET estimations for the ENF biome. In this study, we pay special attention to this biome, with the purpose of investigating if the representations of seasonal LAI and Vmax variations are essential in TBMs. To serve this purpose, the University of Toronto LAI product Version 2 was corrected for its seasonal variation using leaf lifespan and in-situ measurements at eight ENF sites in Canada. Seasonal Vcmax variation was derived from the MERIS Terrestrial Chlorophyll Index (MTCI) through downscaling it to the leaf level using a scheme with a general vertical nitrogen distribution within the canopy. Leaf chlorophyll content (LCC) is thus derived from MTCI and converted to Vcmax using empirical equations. Four model cases with and without considerations of the seasonal LAI and Vcmax variations were tested and compared. Validation against eddy covariance measurements indicates that the case with both LAI and Vcmax variations produced the highest R2, lowest root mean square error (RMSE) and lowest mean absolute error (MAE) for both GPP and ET simulations, and thus outperforms all other cases without considering the variations or with consideration of one of the variations only. In this best case, the simulated daily GPP yields R2 of 0.91, RMSE of 0.91 g C m−2 and MAE of 0.65 g C m−2, while the simulated daily ET yields R2 of 0.8, RMSE of 0.52 mm and MAE of 0.34 mm. Most improvements were found in spring and autumn. Not only the correlations between the seasonal trajectories of model simulation and observation were improved, but also the annual total GPP and ET were more accurately estimated. The smallest mean absolute relative bias to eddy covariance measurements is 9% for GPP and 15% for ET, both were found in the best case. Moreover, improvements in GPP were more pronounced than in ET. Our results highlight the significance of considering both seasonal structural and physiological characteristics of leaves in TBMs. Considering the important role that evergreen coniferous forests play in global terrestrial ecosystems, global simulations of GPP and ET in space and time can benefit from the proper representation of seasonal variations in canopy structure and leaf physiology as represented by LAI and Vcmax, respectively.
  • Nonlinear boundaries of land surface temperature–vegetation index space
           to estimate water deficit index and evaporation fraction
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Xiaolong Hu, Liangsheng Shi, Lin Lin, Yuanyuan ZhaAbstractLand surface temperature (Ts)–vegetation index (VI) space is widely used for agricultural drought monitoring. The determination of dry and wet edges is the essential procedure for the construction of this space. However, the universally applied linear boundaries have not been strictly verified. In this study, we aim to: (1) develop and analyze the nonlinear boundaries of Ts–VI space using one-source surface energy balance theory, and (2) validate the improvement of nonlinear boundaries with in-situ measurements in the view of water deficit index (WDI) and evaporation fraction (EF). Results demonstrate the nonlinear characteristics of dry and wet edges and show that the nonlinear boundaries are the single-valley functions of fractional vegetation cover (fc), sharply decreasing with fc in sparse canopies and slowly increasing with fc in dense canopies. The nonlinear feature is controlled by aerodynamic and thermodynamic roughness lengths, which reflect the coupling effect between soil and canopy. In comparison with linear boundaries, nonlinear boundaries lead to significant improvement on estimating WDI but similar performance on estimating EF. The rough estimation of EF using nonlinear boundaries may be attributed to the high uncertainty of aerodynamic resistance. Our analysis suggests that the uncertainty of surface roughness length schemes and energy imbalance issue are the main error sources of nonlinear dry and wet boundaries.
  • Adjustments of leaf traits and whole plant leaf area for balancing water
           supply and demand in Robinia pseudoacacia under different precipitation
           conditions on the Loess Plateau
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Zhongdian Zhang, Mingbin Huang, Xiaofang Zhao, Lianhai WuAbstractThe adjustments of plant traits for balancing water supply and demand are critical for keeping the survival of forests under drought stress. In this study, we aimed to determine the long-term adjustments of leaf traits and whole plant leaf area (PLA) in Robinia pseudoacacia trees under different precipitation conditions, and to provide physiological information for modelling. We characterized the temporal changes of plant traits with simulated different precipitation conditions using three levels of water supply in a controlled growth chamber. The results indicated that increasing transpiration with R. pseudoacacia growth leaded to a decline in soil moisture under each precipitation conditions. As drought progressed, leaves exhibited a coordinated increase in vein and stomatal densities, higher drought tolerance by increasing cell wall elasticity, and higher water storage capacitance. After 60 days, leaf traits were similar among the treatments while PLA decreased considerably with decreasing water supply. The field observation along a precipitation gradient indicated that PLA decreased by 64% as mean annual precipitation declined from 645.9 mm to 421.9 mm, while leaf traits did not exhibit marked differences among different sites. The variation in PLA along the precipitation gradient could be well estimated with the optimal PLA calculated by long-term simulations of soil water balance. In summary, increasing transpiration with plant growth induced similar patterns of soil desiccation under different precipitation conditions, which further resulted in the convergence in leaf traits. The adjustment of PLA achieved an optimal value to maximize plant growth and to prevent severe drought stress by balancing the water supply and demand. These results provided a way to fill the gap between experiments and modelling studies for large-scale predictions of plant traits, and should be helpful for the sustainable management of plantation forests in the Loess Plateau.
  • Evaluation of modeled actual evapotranspiration estimates from a land
           surface, empirical and satellite-based models using in situ observations
           from a South African semi-arid savanna ecosystem
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Floyd V. Khosa, Gregor T. Feig, Martina R. van der Merwe, Mohau J. Mateyisi, Azwitamisi E. Mudau, Michael J. SavageAbstractEvapotranspiration (ET) plays a crucial role in the land-atmosphere interaction and climate variability, especially in arid and semi-arid areas. Accurate estimates of ET are important in hydrological and climate modeling. This study evaluates eight ET data products from different models used for ET estimation. The data products are classified into three main categories depending on the type of modeling approaches: namely process-based land surface model, empirical models, and satellite data derived estimates. The different model estimates are evaluated against in situ measurements from the Skukuza flux tower which is situated in a semi-arid savanna in South Africa. The correlation score and cantered root mean square error computed on monthly ET averages indicate that the satellite-derived model and land surface model estimates are closer to the observed ET signal for the Skukuza site, both in-phase and magnitude. The empirical models' outputs tend to reflect a relatively pronounced departure from observations in magnitude. The normalised mean bias computed for different seasons reveals that the estimates from all modeling approaches are close to the observed signal during the transition period (March–May) to the austral summer. In general, all models overestimate ET during summer and underestimate it in winter. A qualitative analysis of the year-to-year variation for different seasons reveals that all model estimates are qualitatively consistent with the observed seasonal pattern of the signal. Satellite and process-based land surface models (LSMs) also show a response to extremes events such as drought years. The study identifies satellite-derived model outputs as a candidate for understanding spatio-temporal variability of ET across different landscapes within the study region, and process-based models to potentially be used for climate change impact studies on ET.
  • Correlation-based flux partitioning of water vapor and carbon dioxide
           fluxes: Method simplification and estimation of canopy water use
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Todd M. Scanlon, Daniel F. Schmidt, Todd H. SkaggsAbstractThe partitioning of water vapor and carbon dioxide (CO2) exchange between vegetation and the atmosphere remains a current research priority. A technique that has been proposed to simultaneously partition these fluxes, based on the correlation between their high-frequency concentration time series, has been the subject of recent empirical evaluations and theoretical advances. The method assumes that flux-variance similarity can be applied separately to stomatal exchange (transpiration for water vapor and net photosynthesis for CO2) and non-stomatal exchange (direct evaporation for water vapor and soil and stem respiration for CO2). Here, we present a mathematical simplification of this approach, from which the partitioned fluxes can be derived from routine eddy covariance measurements. The simplification arises from the fact that the transpiration and net photosynthesis fluxes are linearly related in solution space with respect to variable canopy water use efficiency, W. Conditions that are amenable to successful partitioning can now be determined a priori for a given averaging period. The simplified framework also has the benefit of providing a means for estimating W based on optimization theory. This allow for the estimation of W without any preconceptions of how the intercellular CO2 concentration, ci, varies as a function of ambient conditions. The simplified partitioning framework is applied to eddy covariance measurements collected over a mixed deciduous forests for three growing season. Aside from being more computationally efficient, the partitioned results exhibit less scatter compared with prior implementations.
  • Advantage of multi-band solar-induced chlorophyll fluorescence to derive
           canopy photosynthesis in a temperate forest
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Zhunqiao Liu, Xiaoliang Lu, Shuqing An, Mary Heskel, Hualei Yang, Jianwu TangAbstractWhen solar-induced chlorophyll fluorescence (SIF) is developed as a novel approach to quantify gross primary production (GPP), narrow SIF emission spectrum around the atmospheric oxygen absorption windows (˜ 761 nm and ˜687 nm) has been widely used to represent SIF and to derive GPP. As SIF is a continuous spectrum, deriving the full broadband SIF emission spectrum over 640–850 nm provides an opportunity to fully explore the potential of SIF in estimating GPP. Using high-frequency measurements of canopy carbon flux and SIF emissions at the atmospheric absorption bands, we reconstruct the full SIF spectrum from SIF signals at the absorption bands, and then analyze correlations between the GPP and the selected single SIF bands and their combinations using both linear regression (LR) and Gaussian processes regression (GPR). Our results indicate that (1) the red SIF bands (640–700 nm) shows low correlation with GPP due to the strong (re)absorption of red SIF emissions by leaf chlorophyll; (2) the individual bands in near-infrared area (at 720 nm, 740 nm, and 761 nm) can determine about 60% and 62% of the variance in GPP with hourly scale by LR and GPR, respectively, and the combination of those SIF bands provide increased predictive power, explaining 66% and 76% variance in GPP with hourly scale by LR and GPR, respectively; (3) the solar radiation saturation, fraction of direct solar radiation, air temperature and leaf area index may have negative impacts on the SIF-GPP correlations when they are beyond optimal thresholds; and (4) the temporal aggregation of SIF-GPP (daily scale) enhances the correlations as compared with the hourly scale: the daily combination of SIF bands (at 687 nm, 720 nm, and 761 nm) can account for 80% and 93% of variance in daily daytime GPP by LR and GPR, respectively, suggesting that the combination of these three bands of SIF on the daily scale is the best proxy for GPP. Our results provide a new approach to analyze the SIF-GPP correlations using the ground-based full broadband SIF emission, suggesting that multi-bands SIF has a stronger capacity in predicting plant GPP than traditionally used signal band SIF data.
  • Publisher's note
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s):
  • Ecosystem hydrologic and metabolic flashiness are shaped by plant
           community traits and precipitation
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Daniel L. Potts, Greg A. Barron-Gafford, Russell L. ScottAbstractUnderstanding the hydrologic and carbon cycling consequences of precipitation variability in dryland ecosystems requires improved appreciation and accounting of how above- and belowground biophysical processes differ in their response to rainfall. Our objective was to contrast the sensitivity of dryland ecosystem evapotranspiration (ET), gross ecosystem productivity (GEP), and ecosystem respiration (Re) in response to inter- and intra-annual precipitation variability in a nearby grassland, savanna, and shrubland ecosystems in southeastern Arizona. To do this, we modified the Richards-Baker index, which quantifies the flashiness of a stream’s hydrograph, to calculate analogous indices of ecosystem hydrologic and metabolic flashiness. In this way, ecosystem flashiness describes the frequency and rapidity of short-term fluctuations in H2O and CO2 exchange in response to precipitation while preserving the sequence of day-to-day variation in fluxes using tower-based time-series of daily averaged ET, GEP and Re. We calculated annual hydrologic, GEP, and Re flashiness (fET, fGEP and fRe respectively) using 6 years of daily-averaged fluxes estimated from eddy covariance. In contrast to our prediction, annual fGEP was consistently greater than annual fRe. Furthermore, we predicted that increasing rooting depth would correlate with a decline in annual fET and fGEP. In fact, annual fGEP was similar between the grassland, savanna, and shrubland. Whereas the response of annual fET and fGEP to annual precipitation was plant community dependent and generally declined with increasing rainfall, annual fRe did not vary in response to precipitation. The effect of late summer storms on fGEP was plant community dependent such that shrubland fGEP and fRe strongly declined in response to rainfall whereas grassland and savanna fGEP was relatively unresponsive. Conceptually similar to hydrologic flashiness, ecosystem flashiness may provide an additional lens through which to observe the influence of resource availability, shifts in community composition, and disturbance on ecosystem hydrologic and carbon cycling.
  • Weather and trade-offs between growth and reproduction regulate fruit
           production in European forests
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): M.J. Vergotti, M. Fernández-Martínez, S.C. Kefauver, I.A. Janssens, J. PeñuelasAbstractSome tree species have a highly variable year-to-year pattern of reproduction which has repercussions for the entire ecosystem. Links between meteorological variability, fruit production and crown cover, and trade-offs between reproduction and vegetative growth, remain elusive, despite a long history of research. We explored how meteorological conditions determined variations in fruit production and crown cover and how remotely sensed vegetation indices, such as the enhanced vegetation index (EVI), may be used to characterize the fluctuations in fruit production. We used data for fruit production from six European tree species (Abies alba, Picea abies, Pseudotsuga menziesii, Fagus sylvatica, Quercus petraea and Q. robur) growing in monospecific stands, EVI and seasonal meteorological variables (precipitation and temperature) for 2002–2010. Weather accounted for fruit production better than EVI. Deciduous trees were more responsive to weather than evergreens, most notably to different seasonal temperatures, which were positively correlated mainly with crown cover and fruit production in deciduous species. Our results also suggested different patterns of relationships between fruit production, crown cover and weather, indicating different strategies of resource management. These patterns indicated a possible internal trade-off in evergreens, with resources allocated to either growth or reproduction. In contrast, in deciduous species we found no evidence for such a trade-off between vegetative growth and reproduction.
  • Forest wind regimes and their implications on cross-canopy coupling
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Anita Freundorfer, Ingo Rehberg, Beverly E. Law, Christoph ThomasAn analysis of wind regimes across forests of varying density and height is presented. The hockey stick-like dependence of the friction velocity on the mean advective wind speed is used to determine the threshold between the weak-wind and the strong-wind regime for the entire canopy. Such thresholds are compared across four different sites. The height dependence of thresholds within the canopy is inverted compared to the one above grassland sites. This can be understood by extending the accepted interpretation for weak-wind thresholds from grassland sites to forested sites.Even for large fluctuations above the canopy, the fluctuations of the vertical wind velocity in the subcanopy remain small during weak-wind situations. Correspondingly, in the strong-wind regime, turbulence in the subcanopy remains strong in spite of reduced above-canopy turbulence. This fact suggests that previously used methods for determining the degree of coupling across the canopy layer based upon the ratio of the vertical wind variance between the above-canopy and subcanopy may prove erroneous. Furthermore, it emphasizes the significance of mechanisms generating subcanopy turbulence other than above-canopy turbulent transport and shear.The transport of mass and energy between the subcanopy and above-canopy layers is significantly reduced during the weak-wind regime. In particular, the vertical turbulent transport is reduced by more than one order of magnitude. This suggests a decoupling of the subcanopy layer during weak-wind situations and allows for the accumulation of carbon dioxide originating from soil respiration in the subcanopy layer during the weak-wind regime.Graphical abstractGraphical abstract for this article
  • Maize yield under a changing climate: The hidden role of vapor pressure
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Jennifer Hsiao, Abigail L.S. Swann, Soo-Hyung KimAbstractTemperatures over the next century are expected to rise to levels detrimental to crop growth and yield. As the atmosphere warms without additional water vapor input, vapor pressure deficit (VPD) increases as well. Increased temperatures and accompanied elevated VPD levels can both lead to negative impacts on crop yield. The independent importance of VPD, however, is often neglected or conflated with that from temperature due to a tight correlation between the two climate factors. We used a coupled process-based crop (MAIZSIM) and soil (2DSOIL) model to gain a mechanistic understanding of the independent roles temperature and VPD play in crop yield projections, as well as their interactions with rising CO2 levels and changing precipitation patterns. We found that by separating out the VPD effect from rising temperatures, VPD increases had a greater negative impact on yield (12.9 ± 1.8%, increase in VPD associated with 2 °C warming) compared to that from warming (8.5 ± 1.4%, the direct effect of 2 °C warming). The negative impact of these two factors varied with precipitation levels and influenced yield through separate mechanisms. Warmer temperatures caused yield loss mainly through shortening the growing season, while elevated VPD increased water loss and triggered several water stress responses such as reduced photosynthetic rates, lowered leaf area development, and shortened growing season length. Elevated CO2 concentrations partially alleviated yield loss under warming or increased VPD conditions through water savings, but the impact level varied with precipitation levels and was most pronounced under drier conditions. These results demonstrate the key role VPD plays in crop growth and yield, displaying a magnitude of impact comparative to temperature and CO2. A mechanistic understanding of the function of VPD and its relation with other climate factors and management practices is critical to improving crop yield projections under a changing climate.
  • Testing an energy exchange and microclimate cooling hypothesis for the
           effect of vegetation configuration on urban heat
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Jingli Yan, Weiqi Zhou, G. Darrel JeneretteAbstractWhile an effect of urban vegetation configuration on land surface temperature (LST) has been identified worldwide, the mechanism underlying configuration-LST relationships remains unclear as most urban LST data only resolve to neighborhood scales. Here we ask: does urban vegetation provide more cooling arranged in fewer and larger patches or more numerous but smaller patches in the Phoenix metropolitan area, Arizona, USA' We hypothesized the combination of energy exchanges between adjacent patches and microclimate cooling induced by vegetation are key processes determining how configuration affects LST. Using high resolution thermal data (7 m), we evaluated predictions from this hypothesis through a multiple scale analysis spanning from within individual patches to among neighborhoods. We found tree cover is the dominant factor influencing urban cooling and that tree and grass configurations also substantially affect cooling, with effects generally exceeding 40% that of tree cover. The effects of tree and grass cover and configuration on LST were scale-dependent and reflect differences from within individual patches to among neighborhoods. In general, greater edge density and shape complexities of vegetation patches cool the landscape but may warm individual vegetation patches. Conversely, increasing individual vegetation patch size and reducing shape complexity may lead to cooler vegetation patches but a hotter landscape. Our findings suggest more edge area strengthens energy exchanges between vegetation and surroundings and more vegetation core area lead to greater cooling within individual patches. Through applications of high resolution thermal remote sensing, we are able to more directly connect effects of land cover composition and configuration to LST distributions that can help cities plan and evaluate local climate adaptation strategies.
  • Optimization of a remote sensing energy balance method over different
           canopy applied at global scale
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Xuelong Chen, Zhongbo Su, Yaoming Ma, Elizabeth M. MiddletonAbstractParameterization methods which calculate turbulent heat and water fluxes with thermal remote sensing data were evaluated in the revised remote sensing surface energy balance system (SEBS) model (Chen et al., 2013). The model calculates sensible heat (H) based on the Monin-Obukhov similarity theory (MOST) and determines latent heat (LE) as the residual of energy balance. We examined the uncertainties of H and LE in the SEBS model due to five key parameters at the local station point scale. Observations at 27 flux towers located in seven land cover types (needle-leaf forest, broadleaf forest, shrub, savanna, grassland, cropland, and sparsely vegetated land) and an artificial intelligence particle swarm optimization (PSO) algorithm was combined to calibrate the five parameters (leaf drag coefficient, leaf heat transfer coefficients, roughness length for soil, and two parameters for ground heat calculation) in the SEBS model. The root-mean-square error at the site scale was reduced by 9 Wm−2 for H, and 92 Wm−2 for LE, and their correlation coefficients were increased by 0.07 (H) and 0.11 (LE) after using the calibrated parameters. The updated model validation was further conducted globally for the remotely sensed evapotranspiration (ET) calculations. Overestimation of SEBS global ET was significantly improved by using the optimized values of the parameters. The results suggested PSO was able to consistently locate the global optimum of the SEBS model, and appears to be capable of solving the ET model optimization problem.
  • Unraveling the impacts of droughts and agricultural intensification on the
           Altiplano water resources
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Frédéric Satgé, Yawar Hussain, Alvaro Xavier, Ramiro Pillco Zolá, Leandro Salles, Franck Timouk, Frédérique Seyler, Jérémie Garnier, Frédéric Frappart, Marie-Paule BonnetAbstractDuring the last decades, agriculture has drastically increased over the South American Andean Plateau (Altiplano), resulting in extensive changes in land cover from native vegetation to essentially Quinoa crop. Along with climatic variability, these land use changes appear as a catalyst in worsening the already existing drought events and water scarcity processes. Hence, understanding their relative contributions to the regional desertification process is crucial for sustainable water-use adaptation, but also is quite ambiguous because of water resource data scarcity over the Altiplano. Therefore, in the present study, an attempt to measure the impact of severe droughts and agricultural intensification on the water resources has been made using remote sensing datasets. The first step was dedicated to the validation of newly released CHIRPS v.2 precipitation and GLEAM v.3 potential evapotranspiration products by comparing their estimates with the results obtained from gauges data. Then, the Standardized Precipitation Index (SPI) was used to describe past hydro-meteorological drought events in terms of their spatial extent, duration, intensity and their impacts on the regional water resources. Finally, the dynamic trends in the spatial extent of the Quinoa crop and the meteorological conditions derived from CHIRPS v.2 and GLEAM v.3 were compared with the Vegetation Condition Index (VCI) and the Total Water Storage (TWS) derived from AVHRR and GRACE data respectively, to observe the respective influence of agriculture and climate variability on the regional hydrological system. A significant increase in Quinoa crop extent is observed from 2001 which corresponds to a significant decrease in regional VCI and TWS. Based on this trend, agriculture appears as a contributing factor in the water scarcity process over the Altiplano. The outcomes of this study will contribute to local decision making for a better water management and hydro-meteorological monitoring system.
  • Modeling rainfall interception components of forests: Extending drip
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Návar JoséAbstractAssessment of forest interception, I, and its components; the average evaporation rate during the storm, E¯, and canopy storage, S, are essential for simulating the contribution of forests to the water cycle and the climate system. The objectives of this study were to: (i) propose a new model to predict I, E¯, and S, as well as rainfall duration, RD and rainfall intensity, R¯ ; (ii) correlate E¯, RD, and R¯ assessments; and (iii) quantify the role plant surfaces play on the generation of interception from four forests in Mexico. Based on extended drip equations, the model was calibrated using field measurements from forty-five forest interception case studies (N = case studies, n = number of rains) in tropical dry, TDF (N = 21, n = 347), arid/semi-arid, A&SF (N = 15, n = 659), temperate, TF (N = 4, n = 258), and tropical montane cloud, TMCF, forests (N = 6, n = 658) and validated using field measurements from sprinkling experiments in ne Mexico. The model performed very good in predicting both individual and cumulative I values, with average errors, ME%, as a function of precipitation, P, smaller than 4% and Nash-Sutcliffe, NSE, values> 0.33 for three out of four forests. E¯ assessments accounted for between 65% and 93% of I in these forests. Higher E¯ and I figures were found in individual trees (3.78A mm h−1, 27%) in contrast to forest plots (2.24B mm h−1, 14%). E¯ assessments decreased as a function of RD but increased as a function of R¯ for all forests (p ≤ 0.05). Leaf area index, LAI, significantly explained part of the I variance in complex non-linear fashions (p ≤ 0.05). The novel independent assessments of I, E¯, S, RD, and R¯, the significant relationships between I components, and the complex role plant surfaces play on the generation of I fill an important scientific gap in this area of forest hydrology.
  • Divergent vegetation responses to extreme spring and summer droughts in
           Southwestern China
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Lisheng Song, Yan Li, Yanghang Ren, Xiuchen Wu, Bo Guo, Xuguang Tang, Weiyu Shi, Mingguo Ma, Xujun Han, Long ZhaoAbstractIn the winter and spring of 2009–2010 and summer of 2011, Southwestern China was hit by two severe drought events that are unprecedented over the past three decades with substantial economic damage. The understanding of how vegetation growth responds to extreme drought events in different seasons is inadequate, and underlying mechanisms are unclear. Here, we investigated the impacts of the 2009–2010 winter-spring drought and 2011 summer drought on vegetation growth and productivity in Southwestern China, using multiple remote sensing vegetation indexes including Normalized Difference Vegetation Index, Enhanced Vegetation Index, gross primary productivity/net primary productivity and vegetation optical depth. Our analyses reveal that severe soil moisture deficit in 2009–2010 winter-spring drought resulted in reduction in evapotranspiration, Enhanced Vegetation Index (0.047) and gross primary productivity (1.833 P cg) /net primary productivity in 2010 spring, worse decreased Normalized Difference Vegetation Index (0.135) and decreased vegetation optical depth in summer. By contrast, the 2011 summer drought led to enhanced vegetation greenness and higher summer gross primary productivity (1.272 P cg) /net primary productivity (0.546) compared with normal years (2007–2008), due to increased solar radiation over forests region. Our study highlights the divergent responses of vegetation to extreme drought events occurred in different seasons.
  • Study on the throughfall, stemflow, and interception of two shrubs in the
           semiarid Loess region of China
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Shengqi Jian, Caihong Hu, Guodong Zhang, Jinping ZhangAbstractThe Loess Plateau, China, has been subject to 40 years of re-vegetation predominantly with the xerophytic shrubs Caragana korshinskii and Hippophae rhamnoides. Throughfall, stemflow, canopy interception, and water storage capacity experiments for the two shrubs were conducted from May to September during the period 2009–2013. The results showed that the throughfall percentages averaged 62.4% and 70.1% of gross rainfall for H. rhamnoides and C. korshinskii, respectively, while stemflow accounted for 2.4% and 6.7% of the gross rainfall for the two shrubs. The rainfall threshold for stemflow generation was 2.46 and 1.06 mm for H. rhamnoides and C. korshinskii, respectively. The wetting front depths for the two shrubs in the area around the stems were deeper than away from the shrubs. The averaged percentages of interception loss in H. rhamnoides and C. korshinskii were 35.2% and 23.2%. Additionally, H. rhamnoides had greater water storage capacity per leaf area for each simulated rainfall intensity (mean, 0.59 mm; range, 0.28–0.88 mm) than C. korshinskii (mean, 0.44 mm; range, 0.26–0.52 mm). Canopy water storage varied temporally with the eight simulated rainfall intensities. For all the tested rainfall intensities, H. rhamnoides could store more water per dry biomass (mean, 0.72 g−1; range, 0.39–1.06 g−1) than C. korshinskii (mean, 0.49 g−1; range, 0.31–0.69 g−1). The present study can inform re-vegetation projects, water budget analyses, and modeling efforts aimed at understanding rainfall water movement within shrub communities in the semiarid Chinese Loess Plateau, China.
  • From tree to stand-level structural complexity — Which properties make a
           forest stand complex'
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Dominik Seidel, Martin Ehbrecht, Peter Annighöfer, Christian AmmerAbstractManagement for complexity has become an important paradigm for European and North American forestry. Recent advancements in data processing allow for a detailed, three-dimensional and objective quantification of structural complexity in forests based on terrestrial laser scanning data. In our study, we used such 3D data from an exemplary temperate broad-leaved forest in Thuringia, Germany, to gain insights to the relationship between tree-level structural complexity and stand-level structural complexity. From our study site, which was 80 by 80 m in extent with a total of 215 trees growing in it, we created a dataset that contained each tree as an independent point cloud. Random sample plots of varying size (10 × 10 m; 15 × 15 m; 20 × 20 m) where used to create sub-plots (sampling with replacement) and to enable for the investigation of effects of scale. Our study revealed that plot-level complexity of plots up to 20 × 20 m is largely determined by the complexity of the most complex-structured tree individual. Furthermore, a high tree complexity and variability thereof in the stand was generally beneficial to stand structural complexity. Other individual tree characteristics, such as a large crowns, were also identified to have positive effects on plot-level complexity. We conclude that management for complexity should focus on large-crowned, highly-complex tree individuals as key elements of stand structural complexity. This indicates that large and old trees may not only be of great importance as habitat trees potentially increasing biodiversity, but also due to their contribution to the overall stand-level complexity.
  • Regeneration origin affects radial growth patterns preceding oak decline
           and death – insights from tree-ring δ13C and δ18O
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Marcin Zadworny, Andrzej M. Jagodziński, Piotr Łakomy, Joanna Mucha, Jacek Oleksyn, Jesús Rodríguez-Calcerrada, Krzysztof UfnalskiAbstractOak trees (Quercus spp.) develop a taproot system which extends several meters deep and enables them to survive periods of water deficit that occur during their long lifespan. Regeneration forestry practices disturb the natural development and proportion of oak root systems by repeated undercutting of the taproots of seedlings in nurseries, or the repeated cutting of stems in coppice systems. Thus, regeneration practices may affect tree growth and susceptibility to environmental stresses, including increasingly frequent and severe droughts. To test this hypothesis, tree-ring dendroclimatological and stable isotope data were used to assess the physiological responses of acorn-sown, planted, and coppiced Quercus robur trees of different health classes (healthy, defoliated and recently dead) to interannual climatic variations over the last 41 years. Annual basal area increment (BAI) was negatively and positively related with δ13C and δ18O, respectively; although the intensity of these relations depended on tree regeneration origin and current vigor. Compared to healthy oaks, dead acorn-sown oaks exhibited significantly higher BAI, and lower δ13C and intrinsic water use efficiency (iWUE) during drought periods, but not during non-drought periods; in contrast, dead coppiced oaks showed lower BAI, δ13C, iWUE and δ18O irrespective of climatic conditions. Acorn-sown and planted oaks growing fast at early stages of regeneration exhibited sudden decreases in BAI before dying following a severe drought period. In comparison, growth decline preceding the death of coppiced stems was progressive, suggesting that long-term C limitations to increasingly weakened trees underline drought-induced decline and eventual dieback. Different climate sensitivity of Q. robur trees of different regeneration origin suggests that regeneration forestry practices should be taken into account when adapting forest management plans to climate change.
  • Summer drought and spring frost, but not their interaction, constrain
           European beech and Silver fir growth in their southern distribution limits
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Antonio Gazol, J. Julio Camarero, Michele Colangelo, Martín de Luis, Edurne Martínez del Castillo, Xavier Serra-MaluquerAbstractClimate warming has lengthened the growing season by advancing leaf unfolding in many temperate tree species. However, an earlier leaf unfolding increases also the risk of frost damage in spring which may reduce tree radial growth. In equatorward populations of temperate tree species, both late frosts and summer droughts impose two constraints to tree growth, but their effects on growth are understudied. We used a tree-ring network of 71 forests to evaluate the potential influence of late frosts and summer droughts on growth in two tree species that reach their southern distribution limits in north-eastern Spain: the deciduous European beech (Fagus sylvatica L.) and the evergreen Silver fir (Abies alba Mill). The occurrence of late frost events and summer drought was quantified by using a high-resolution daily temperature and precipitation dataset considering the period 1950–2012. Late frosts were defined as days with average temperature below 0 °C in the site-specific frost-free period, whereas drought was quantified using the 18 month-long August Standardized Precipitation Evapotranspiration Index (SPEI). The growth of European beech and Silver fir was reduced by the occurrence of both late frost events and summer drought. However, we did not find a significant interaction on growth of these two climate extremes. Beech was more negatively impacted by late frosts, whereas Silver fir was more impacted by summer drought. Further studies could use remote-sensing information or in situ phenological records to refine our frost index and better elucidate how late frosts affect growth, whether they interact with drought to constrain growth, and how resilience mechanisms related to post-frost refoliation operate in beech.
  • Moderate chilling requirement controls budburst for subtropical species in
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Yanjun Du, Yuanqi Pan, Keping MaAbstractIt is well known that spring phenology has advanced in temperate regions over the last few decades in response to climate change. However, we understand much less about climate-driven changes in phenology within subtropical and tropical regions, where the timing of events is less predictable and has not been well-studied. It is not known whether subtropical plants have a similar winter chilling requirement to what has been well-documented in temperate species. To explore this possibility, we established a climate chamber experiment to test the effects of photoperiod and chilling on the timing of budburst within 37 subtropical woody species. We found that both moderate and strong chilling treatments advanced budburst and reduced forcing requirements, relative to plants subjected to a low chilling treatment. Longer photoperiod enhanced budburst rate for only two species, suggesting that chilling is more important for regulating budburst for most species. With respect to future climate change, the spring phenology of subtropical species is expected to be delayed further because species could lack the ability to meet their fundamental chilling requirement. These results have important implications for the conservation and management of tropical and subtropical plant populations under future climate change scenarios.
  • Consequences of environmental heterogeneity for the photosynthetic light
           environment of a tropical forest
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Geoffrey G. Parker, David R. Fitzjarrald, Irene Cibelle Gonçalves SampaioAbstractWe studied the interplay of atmospheric and canopy structure factors driving the canopy light environment (Photosynthetic Photon Flux Density, PPFD) in primary moist tropical forest in the Tapajós National Forest, Brazil. We quantified the temporal and spatial length scales that characterize intact rain forest inhomogeneities, asking: Are seasonal changes in the canopy radiation balance evident at these scales' We sought to describe the components of intensity, duration and spatial variation of within-canopy PPFD in light of these inhomogeneities. Do fluctuating atmospheric conditions, especially the presence of clouds and precipitation, affect the radiative inputs at both the canopy top and the forest floor'We examined the characteristic scales of heterogeneity in the vertical and the horizontal using a two-part approach. For radiation we combined long-term continuous high-frequency measurements of down- and up-welling short-wave and visible wavebands above the canopy with similarly frequent observations from a dense sensor network at forest floor. Vertical variations in canopy structure, obtained with a ground-based LIDAR, similarly combined intensive observations at the sensor network with occasional large-scale transects along the forest floor. Close similarities in both radiation and canopy structure at both scales support the representativeness of local observations of the wider area.A composite broadband measure similar to the Normalized Difference Vegetation Index (denoted cbNDVI) was constructed from above-canopy observations to compare with reports of remotely sensed canopy reflectivity at this site. We estimated the canopy Leaf Area Index (LAI) by combining observations of the variation in understory transmittance by solar elevation with a commonly-used algorithm. We obtained the conventional whole-canopy extinction coefficient, by applying the Beer-Lambert law.Over the course of a year this forest receives 11,795 mol m−2, only 62% of potential clear-day PPFD – atmospheric transmissivity is reduced by clouds, precipitation, smoke and haze. Very little PAR (≈ 2%) is reflected from the canopy and only 5.7% penetrates to 1 m above the forest floor - overall 92% of PAR is absorbed by the canopy. All radiation balance components closely tracked the dynamics of incoming light, showing little seasonal variation.Understory light observations across the 7.5–28.5 m spanning the understory array sensors showed essentially constant correlation between sensor pairs over time. There was a high degree of local persistence in the understory spatial pattern that varied slowly and directionally with the changing geometry of the sun and canopy structure. Over larger distances (to 1000 m), the patterns of spatial autocorrelation of understory PPFD and outer canopy structure were remarkably similar in shape, both declining rapidly to a more-or-less constant level around 15–20 m, a scale consistent with the dimensions of outer canopy crowns.The vertical pattern of transmission and absorption was estimated by combining understory transmittance with the distribution of canopy surface area obtained from the ground-based LIDAR system. It showed the maximum absorption relatively low in the canopy (8–19 m above ground). Although rather tall (canopy height is at 41.5 m), the extremely elaborate outer surface of the forest suggests the layers highest above ground are of little consequence to the PAR absorption budget.The cbNDVI measure exhibited seasonal variation consistent with other reports (somewhat higher in the wet season) but in contrast to a recent argument that the forest ‘greens up’ during the early dry season. However, except for the variations caused by the angle and intensity of incoming light modulated by atmospheric effects, there was little seasonality in the forest light environment at km67, including: canopy reflectances in several wavebands, all PPFD radiation budget components, the estimated LAI and mid-day PAR extinction coefficient and the length scales of understory PPFD. Canopy transmission was somewhat greater (6.4%) under diffuse skies compared to the least diffuse conditions (6.0%), and slightly more PPFD was absorbed under diffuse (92.7%) versus the least diffuse conditions (92.3%), but was not a significant contribution to the budget.The large diurnal variations in the extinction coefficient seriously affects its utility as a descriptor of canopy radiative properties. We propose an alternative approach for transmitted light: the canopy behaves as: 1.) a constant fraction filter under diffuse conditions, combined with 2.) a variable filter depending on solar elevation for sunfleck conditions. These regimes may be described with simple parameters each having mechanistic relations to canopy structure. In summary, we demonstrate that obtaining the radiation signal at forest floor at high data rate for long periods exploits seasonal sun angle changes to probe canopy structure. Combined with occasional long transect information, temporal and vertical sampling spatially allow improved definition of characteristic scales to describe both the understory light environment and canopy structure.
  • Determination of phloem sap flow rate using a combination of the heat
           balance method and girdling in citrus
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Yuki Nakano, Naoto IwasakiAbstractSugars accumulated in fruits are synthesized in leaves and translocated into the fruits. Quantitative measurement of phloem sap flow would enhance our understanding of the phenomenon and would facilitate efforts to ensure the production of high-quality fruits. The influence of girdling, which cuts off phloem, on sap flow rate determined using the heat balance method, was investigated in citrus. The present study aimed to measure the flow rates in phloem and xylem sap separately and to investigate the effect of gauge temperature on gauge output accuracy. When the gauge temperature was kept constant, the flow rate was consistent with the amount of water transpired from the branch. Immediately after girdling, the sap flow rate increased in a non-bearing branch, but decreased in a bearing branch. We conclude that the phloem sap flowed basipetally in the non-bearing branch and acropetally toward the fruits in the bearing branch. Regression lines for the sap flow before and after girdling were almost parallel, and the difference in the intercept of the two regression lines can be regarded as the flow rate change caused by girdling. Our results indicate that it is possible to determine separate flow rates for phloem and xylem sap by combining the heat balance method with girdling.
  • Associations between large-scale climate oscillations and land surface
           phenology in Iran
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Alireza Araghi, Christopher J. Martinez, Jan Adamowski, Jørgen Eivind OlesenAbstractVariations in land surface phenology arising from large-scale and regional climatic oscillations are important determinants for environmental and ecological conditions. Spearman’s correlation coefficient was employed to delineate, within the geographical territory of Iran, the relationship between phenological metrics [cumulative NDVI (cumNDVI), start of growing season (SOS), and end of growing season (EOS)], which were obtained using the Normalized Difference Vegetation Index (NDVI) derived from the AVHRR Global Inventory Modeling and Mapping Studies (GIMMS), and six large-scale climate oscillations [the Arctic Oscillation (AO), the Dipole Mode Index (DMI), the Multivariate El Niño Southern Oscillation Index (MEI), the North Atlantic Oscillation (NAO), the North Sea-Caspian Pattern (NCP), and the Pacific Decadal Oscillation (PDO)]. Results showed that the NCP and NAO had the greatest association, while the AO and MEI had the least association, with the studied phenological metrics for the different types of vegetation in Iran. The NCP was significantly correlated with 25–41% of the pixels for the different vegetation types. The climate oscillations that dominated the relation to phenological metrics differed depending on whether relations with current or previous year climatic oscillation indices were used. The results have implications for environmental and ecological forecasting and analysis, especially for vegetation trends in Iran’s arid to semi-arid climate.
  • Mechanisms of mitigating nitrous oxide emissions from vegetable soil
           varied with manure, biochar and nitrification inhibitors
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Pengpeng Duan, Qianqian Zhang, Xi Zhang, Zhengqin XiongA clear understanding of the effects of manure, biochar and nitrification inhibitors (NI, nitrapyrin-SNI and Sorghum bicolor L.-BNI) amendment on nitrous oxide (N2O) production pathways and consumption remains elusive under field conditions. A field experiment using an isotopocule mapping approach (δ15NSPN2O and δ18ON2O/H2O map) in conjunction with molecular techniques were conducted to understand the mechanisms of these options for N2O mitigation in a Tung choy (Ipomoea aquatic Forssk.) vegetable soil. The manure substitution and biochar not only decreased nitrification/fungal denitrification and bacterial denitrification/nitrifier denitrification-derived N2O emission, but also stimulated N2O reduction to N2 during the denitrification process as evidenced from the decrease of ammonia-oxidizing bacteria (AOB) amoA and the increase of nirS, nosZⅠ, nosZⅡ and fungal nirK transcripts. Biochar had a greater potential to enhance this reduction with decrease of ammonia-oxidizing archaea (AOA) amoA transcripts. NIs mitigated the N2O derived from nitrification and/or bacterial denitrification/nitrifier denitrification demonstrated from the simultaneous decrease of soil NO2− and NO3− and increase of soil NH4+ intensity together with the lower AOB amoA transcripts in NIs than in the urea. These results helped explain the observed differences in N2O emissions among these mitigation options, and laid the foundation for a better understanding of N2O production and reduction under field conditions.Graphical abstractGraphical abstract for this article
  • Long-term variations in energy partitioning and evapotranspiration in a
           semiarid grassland in the Loess Plateau of China
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Ping Yue, Qiang Zhang, Liang Zhang, Hongyu Li, Yang Yang, Jian Zeng, Sheng WangAbstractEstimating seasonal and interannual variations in energy partitioning and actual evapotranspiration (ET) distributions in semiarid grasslands is essential for improving the understanding of interactions between the land and atmosphere, and is useful for land surface parameterization in grasslands of the Loess Plateau. In this study, energy fluxes and ET values over a semiarid grassland site and their environmental and biological controls were investigated over multiple years (2007–2012) using the eddy covariance method. The seasonal and interannual variations in the partitioning of the net radiation (Rn) into sensible (H) and latent (LE) heat fluxes were primarily controlled by precipitation through changes in the soil water content (SWC) and vegetation growth. During relatively wet and warm periods, LE was the dominant component of the energy balance, whereas H was the dominant component of energy partitioning in dry periods. Annual ET was higher than annual P (except in 2007), with a better closure of surface energy balance during the drier years. The total annual ET and its daily maximum varied from 278.2 to 460.3 mm and from 3.45 to 4.95 mm day−1, respectively. The daily Priestley-Taylor coefficient (ET/ETeq, where ETeq is the equilibrium evaporation) decreased sharply when the SWC in the 5-cm soil layer decreased below 0.15 m3 m-3 during the growing seasons. The average ET for sixteen days was linearly correlated with the normalized difference vegetation index (NDVI). ET/ETeq increased nonlinearly with an increase in Gs but was insensitive to the increases in Gs greater than 6.52 mm s−1 in the driest year (2011) and 9.17 mm s−1 in the wettest year (2007). Additionally, there is good correlation between the threshold of Gs and the annual mean NDVI. On an annual scale, the low Gs (3.07-6.77 mm s−1), ET/ETeq (0.28-0.42), and higher Bowen ratio (β) (2.07–4.19) collectively represented the overall water-limited conditions for ET in the semiarid grassland of the Loess Plateau. Our data indicate that ET and its biophysical controls vary in response to interannual changes in annual P. These results contribute to an understanding of the driving mechanisms for long-term variations in energy partitioning and biophysical controls on ET in the Loess Plateau of China.
  • Soil water response of plant functional groups along an artificial legume
           grassland succession under semi-arid conditions
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Gao-Lin Wu, Ze Huang, Yi-Fan Liu, Zeng Cui, Yu Liu, Xiaofeng Chang, Fu-Ping Tian, Manuel López-Vicente, Zhi-Hua ShiAbstractDrought can cause and accelerate the degradation of planted legume grassland, and the changes in plant community composition can further influence soil physical properties. Here, the soil water response of different plant functional groups (legumes, grass, and forbs) were studied along a legume grassland degradation succession according to the above-ground biomass and the proportion of each functional group. In particular, changes in the soil water storage (SWS), soil properties (soil capillary porosity (CP), and soil organic matter) and plant traits (proportion of functional groups and below-ground biomass) were quantified in a continuously cultivated legume grassland for fifteen, sixteen, eighteen, and twenty-two years, without any tillage. The experimental plots were located in the semi-arid region of the Chinese Loess Plateau, in a flat area without runoff contribution. All plant and soil samples, and measurements, were obtained in a few days to minimize the temporal variability. SWS increased at 50–150 cm soil depth when the proportion of legume functional group (LFG) decreased from 70% to 5%, and this increment was ca. 20% at 50–100 cm soil layers. The Shannon-Wiener diversity index (H), the species richness (R), LFG, CP, and the non-capillary porosity (NCP) were significantly correlated with SWS (P 
  • Do indigenous forecasts and scientific forecasts influence arable
           farmers’ and agro-pastoralists’ estimation of onset and cessation of
           rains' Empirical evidence from Rwenzori region, Western Uganda
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Michael Robert Nkuba, Raban Chanda, Gagoitseope Mmopelwa, Akintayo Adedoyin, Margaret Najjingo Mangheni, David. Lesolle, Edward KatoAbstractThis study investigated the influence of indigenous forecasts (IF) and scientific forecasts (SF) on arable farmers’ and pastoralists’ estimation of onset and cessation of rains in the Rwenzori region of Western Uganda. Daily rainfall data (1970–2010) from 3 weather stations in different agro-ecological zones was used to determine mean onset and cessation dates using the Sivakaumar method. After obtaining the household survey of number of farmers and pastoralists whose estimation of onset and cessation dates were in agreement with the stations’ dates, the relationship between forecast type used and estimation of the dates was investigated using the Pearson correlation coefficient. The results indicate that onset dates for the 1st season were on 11th, 17th, 19th March while cessation was 8th, 11th, 21st June for lowlands, mountainous and forested areas, respectively. For the 2nd season, forested and mountainous areas had their onsets on 3rd and 20th August, respectively but the lowland area their onset on 3rd September. The cessation date for 2nd season for forested areas was on 8th December, while dates for lowland and mountainous areas were 17th and 24th November, respectively. The results suggest that there is positive relationship between using both IF and SF and estimation of onset and cessation dates but negative relationship with IF had for arable farmers. There was strong negative relationship between using both IF and SF and estimation of onset dates for the 2nd season for arable farmers in forested areas, but strong positive relationship with those using IF only season. The coefficients of variation for the rain onsets were high implying climate variability. The adopted Sivakaumar method is easy to operationalize by farmers and pastoralists with primary level of education, and access to daily rainfall data from established institutions like schools, local clinics and facilities provided by agricultural extension workers.
  • Landscape-level vegetation classification and fractional woody and
           herbaceous vegetation cover estimation over the dryland ecosystems by
           unmanned aerial vehicle platform
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Haozhou Wang, Dong Han, Yue Mu, Lina Jiang, Xueling Yao, Yongfei Bai, Qi Lu, Feng WangThe change of fraction vegetation cover (FVC) is the key ecological index for vegetation dynamics of dryland ecosystem. However, it is difficult to directly map woody vegetation and herbaceous vegetation in the dryland from the satellite images due to the mixture of their distribution at small scale. Emerging UAV remote sensing provides a good opportunity to capture and quantify the distribution of the sparse vegetation in the drylands ecosystem. In this study, we proposed a new method to classify woody vegetation and herbaceous vegetation and calculate their FVC based on the high-resolution orthomosaic generated from UAV images by the machine learning algorithm of classification and regression tree (CART). This proposed method was validated and evaluated by visual interpretation, the detailed ground measurement dataset of 4832 trees and 18,798 shrubs and three popular machine learning algorithms of Support Vector Machine(SVM), Random Forest(RF), Gradient Boosting Decision Tree(GBDT). The overall assessments showed good overall accuracy (0.78), average accuracy (0.76), and the Kappa coefficient (0.64). The FVC of woody vegetation calculated from orthomosaic agreed well with that estimated from ground measurements. Both group of FVC have a stable linear relationship over different spatial scales. The proposed method showed higher efficiency of 166%, 111% and 290% than SVM, RF, GBDT respectively. A new optimized model was developed to reduce the workload of vegetation investigation and to design more efficient sampling strategies. The proposed method was incorporated into an interactive web-based software “UAV- High Resolution imagery Analysis Platform” (UAV-HiRAP, Our study demonstrates that UAV-HiRAP combined with UAV platform can be a powerful tool to classify woody vegetation and herbaceous vegetation and calculate their FVC for sparse vegetation in the drylands. The new optimization model will inspire researchers to design more effective sampling strategies for future field investigation.Graphical abstractGraphical abstract for this article
  • Rapid recovery of thermal environment after selective logging in the
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Manoela M. Mollinari, Carlos A. Peres, David P. EdwardsAbstractSelective logging is one of the most widespread pattern of disturbance in tropical forests but has a much lower detrimental impact on forest structure than wildfires and conversion to farmland. Thus, logged tropical forest represents critical strongholds of global biodiversity. The ability of these forests to rapidly recover their baseline thermal environmental conditions will markedly influence their conservation value, particularly under global climate change. We investigated the impacts of commercial selective logging on the forest thermal environment in the Brazilian Amazon by relating canopy disturbance from logging to ambient understorey and ground surface temperatures. Specifically, we assessed the impact of selective logging on the forest thermal heterogeneity; how much post-harvest time is required for the thermal environment of logging gaps and logging roads return to unlogged primary forest levels; and the spatial availability of surface microclimates considering time of recovery since logging. Logging gaps following 1 year of recovery had a hotter understorey ambient than all other environments, especially during peak midday temperatures. Compared to the unlogged understorey, logging gaps after 3 years of recovery were only marginally warmer, and logging gaps after 5 years of recovery were slightly cooler. Older wide roads (5 years; 6 m) experienced very similar understorey thermal conditions than both narrow roads (3 m) after 1-5 years of recovery, and unlogged forest. Ground surface temperatures exhibited the largest discrepancies among all environments. The temperature range spanned by surface microclimates notably increased during peak midday heat in logging gaps following 1 year of recovery. Additionally, the proportion of cool area was smaller in younger logging gaps, but the average size of cool patches and their spatial aggregation was similar to that in unlogged forest. Although commercial selective logging can severely damage tropical forest structure, we found that the forest can fairly rapidly regain its thermal environment. Post-logging forest management should carefully focus on preventing fire incursions and illegal activities with special attention to those 3-5 years post-harvest. Thermal homeostasis in selectively logged tropical forests can be vital for long-term maintenance of global biodiversity under contemporary scenarios of climate change.
  • Aridity change and its correlation with greening over drylands
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Bin He, Shuren Wang, Lanlan Guo, Xiuchen WuAbstractA drying trend and an expansion of drylands through history, as well as an expectation to continue under the future climate, have been inferred by recent studies. However, this seems to conflict with observed greenness over drylands. In this study, the changes in aridity over drylands from 1982 to 2011 were examined using the aridity index (ratio of precipitation and potential evapotranspiration), precipitation minus actual evapotranspiration, and soil moisture derived from a combination of observation and modelling. In addition, corresponding changes in vegetative greenness and their relationships with aridity changes were explored. The results show that above three indicators all point to a little change in aridity of drylands over the past three decades, and their trends in spatial patterns agree well each other. Simultaneously, significant greening (p 
  • On the specific water holding capacity of litter for three forest
           ecosystems in the eastern foothills of the Alps
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Katalin Anita Zagyvai-Kiss, Péter Kalicz, József Szilágyi, Zoltán GribovszkiAbstractForest ecosystems typically have a large leaf-area index both within the crown level and on the ground as litter, making interception a very important element of the forest water balance. Broad information exists about crown interception, but relatively few data are available regarding litter interception. The litter layer is able to change the quantities of water available for soil infiltration and runoff, so the water holding capacity of the litter is an important parameter for hydrological modelling. In this study the water holding capacity of the litter for three species (spruce, beech, sessile oak) was determined under field conditions in the eastern foothills of the Alps. Litter data were produced through a collection of about 450–500 samples over two years (2003–2005). Although the litter oven-dry weights of the forest stands were different, the specific water holding capacities [litres per kg oven-dry weight] of the litter were near-identical for needle-leaf and broad-leaf forest ecosystems. According to our measurements, the specific water holding capacity of the litter is about 2.0–2.1 litres kg−1 oven-dry weight, regardless of the tree species.
  • Joint multifractal analysis of air temperature, relative humidity and
           reference evapotranspiration in the middle zone of the Guadalquivir river
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): A.B. Ariza-Villaverde, P. Pavón-Domínguez, R. Carmona-Cabezas, E. Gutiérrez de Ravé, F.J. Jiménez-HorneroAbstractPrevious works have analysed the relationship existing between reference evapotranspiration (ET0) and other climatic variables under a one-at-a-time perturbation condition. However, due to the physical relationships between these climatic variables is advisable to study their joint influence on ET0. The box-counting joint multifractal algorithm describes the relations between variables using relevant information extracted from the data singularities. This work investigated the use of this algorithm to describe the simultaneous behaviour of ET0, calculated by means of Penman–Monteith (PM) equation, and the two main climatic variables, relative humidity (RH) and air temperature (T), influencing on it in the middle zone of the Guadalquivir river valley, Andalusia, southern Spain. The studied cases were grouped according to the fractal dimension values, obtained from the global multifractal analysis, which were related to their probability of occurrence. The most likely cases were linked to smooth behaviour and weak dependence between variables, both circumstances were detected in the local multifractal analysis. For these cases, the rest of Penman Monteith (PM) equation variables, neither the T nor the RH, seemed to influence on ET0 determination, especially when low T values were involved. By contrast, the least frequent cases were those with variables showing high fluctuations and strong relationship between them. In these situations, when T is low, the ET0 is affected by the rest of PM equation variables. This fact confirmed T as main driver of ET0 because the higher T values the lesser influence of other climate variables on ET0. This condition could not be extended to RH because the variability in ET0 singularities was not significantly influenced by low or high values of this variable. These results show that the joint multifractal analysis can be regarded as a suitable tool for describing the complex relationship between ET0, T and RH, providing additional information to that derived from descriptive statistics.Although, joint multifractal analysis shows some limitations when it is applied to large number of variables, the results reported are promising and suggest the convenience of exploring the relationships between ET0 and other climatic variables not considered here with this framework such as wind speed and net radiation.
  • Response of wheat grain quality to low temperature during jointing and
           booting stages—On the importance of considering canopy temperature
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Leilei Liu, Hang Song, Kejia Shi, Bing Liu, Yu Zhang, Liang Tang, Weixing Cao, Yan ZhuAbstractMaintaining grain quality under climate change is critical for human nutrition, end-use functional properties and the commodity value. Climate change has resulted in a continuous increase in the frequency, intensity, and duration of extreme low-temperature events, which have affected both the yield and quality of wheat production. To better understand the effects of low temperature on wheat grain quality two-year temperature-controlled experiments were conducted in phytotrons with two different cold-sensitive winter wheat cultivars at four daily maximum/minimum temperature levels and three temperature durations—2, 4 and 6 days—at both jointing and booting stages. In general, low temperature had a positive effect on the protein concentrations and processing quality of wheat but a negative effect on the starch concentrations and appearance quality. Compared with the low temperature duration, low temperature level had a more significant effect on the wheat grain quality, and wheat grain quality was more sensitive to low temperature during the booting than the jointing stage. In addition, significant linear relationships were observed between most of the grain quality indices and cold degree days (CDD) at both stages, which indicated that CDD could be used to quantify the effect of low temperature on crop grain quality well. Furthermore, a comparison of the relationships between the grain quality indices and CDDa (air temperature-based cold degree days) and CDDc (canopy temperature-based cold degree days) indicated stronger correlations between CDDc and nutritional quality. In addition, a relatively stronger positive relationship between CDDa and the processing quality and a negative relationship between CDDc and the appearance quality were observed in the low temperature environment. These results could assist in high quality wheat breeding under future climate conditions.
  • Comparison of GLUE and DREAM for the estimation of cultivar parameters in
           the APSIM-maize model
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Meiling Sheng, Junzhi Liu, A-Xing Zhu, David G. Rossiter, Haoran Liu, Zhangcong Liu, Liming ZhuAbstractProcess-based crop models are popular scientific tools to study the impacts of environmental conditions and management decisions on crop growth. Some cultivar parameters in crop models cannot be measured directly and need to be estimated. In this research, two most popular Bayesian methods, namely generalized likelihood uncertainty estimation (GLUE) and Differential Evolution Adaptive Metropolis (DREAM), were used for the first time to estimate parameters of the maize module of the Agricultural Productions Systems sIMulator model (APSIM-maize). Both theoretical and real-world evaluations were conducted to compare the performances of these two methods. The maize yields from 2003 to 2006 were used for model calibration, and the yields from 2007 to 2013 were used for model validation. Both GLUE and DREAM performed well in the theoretical and real-world evaluation. During the validation period (2007–2013), when the heteroscedastic model error assumption was adopted in DREAM, on average approximate 90% of observed yield values were captured in the 95% confidence band of DREAM (P-factor = 90.47%), which was larger than that using GLUE (P-factor = 80.93%). Meanwhile the uncertainty bands of DREAM (R-factor = 4.42) were wider than those of GLUE (R-factor = 2.32). If only one parameter set was allowed to be used in the simulation, the weighted mean parameter values according to the likelihood of each parameter set performed better than the parameter set with maximum likelihoods for GLUE while the opposite is true for DREAM. But considering future analysis in the real-world evaluation, the moderate performance of these two methods suggests that a single parameter set obtained by neither GLUE nor DREAM is satisfactory and ensemble simulation is needed. Overall, GLUE and DREAM had similar performance, but GLUE is more convenient and simpler to use than DREAM. So we think GLUE is a better choice than DREAM for estimating cultivar parameters of APSIM-maize.
  • Assessment of global drought propensity and its impacts on agricultural
           water use in future climate scenarios
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Yejia Lu, Huanjie Cai, Tingting Jiang, Shikun Sun, Yubao Wang, Jinfeng Zhao, Xiang Yu, Jingxin SunDrought is the most widespread and most influential natural disaster in the world, especially a threat to agricultural production. In future climate scenarios, the meteorological elements such as precipitation and temperature in each region will change, which will affect the distribution and characteristics of global drought in the future. In this paper, the global drought propensity was evaluated by reformulated Standardized Precipitation Evapotranspiration Index (SPEI-PM) based on Penman-Monteith equation in three future climate scenarios (RCP2.6, RCP4.5 and RCP8.5) of 9 General Circulation Models (GCMs). Mann-Kendall (MK) trend test and empirical orthogonal function (EOF) analysis were used to assess the spatial-temporal distribution and evolution characteristics of the future global drought. Taking reference evapotranspiration (ET0) of crops as the index, potential effects of global drought on agricultural water use were assessed. The results showed that under the influence of the changes of future temperature, precipitation and other meteorological factors, the global drought has presented regional difference characteristics. In three climate scenarios, the trend of severe drought was detected in Africa, North America, South America and Oceania in three climate scenarios. Spatial distribution of SPEI is consistent and intensified drought was detected in southern, northern and northeast of Africa in three decades in all scenarios. EOF analysis showed that there were more positive time coefficients in RCP8.5 scenario than other scenarios, then parts of South America and Africa would face intensified drought in all climate scenarios. The evolution of future global drought would pose a threat on global water use for agricultural production. The annual average ET0 of three decades in major grain producing countries would be on the rise compared to the baseline (1976–2005), among which RCP8.5 scenario was most obvious. Large increase rate of ET0 would occur in Ukraine, Turkey, Russia and Canada in the 2080s in three scenarios. In the future, major grain producing countries would face serious threats of drought, which would pose a great challenge to regional agricultural water use. The study will provide forward-looking information to alleviate the adverse effects of drought on agricultural water use.Graphical abstractSpatial distribution of decadal average SPEI in the 2030s, 2050s, and 2080s in (a) RCP 2.6 Scenario; (b) RCP 4.5 Scenario; (c)RCP 8.5 Scenario.Graphical abstract for this article
  • Error characterization of methane fluxes and budgets derived from a
           long-term comparison of open- and closed-path eddy covariance systems
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): M. Julian Deventer, Timothy J. Griffis, D. Tyler Roman, Randall K. Kolka, Jeffrey D. Wood, Matt Erickson, John M. Baker, Dylan B. MilletAbstractWetlands represent the dominant natural source of methane (CH4) to the atmosphere. Thus, substantial effort has been spent examining the CH4 budgets of global wetlands via continuous ecosystem-scale measurements using the eddy covariance (EC) technique. Robust error characterization for such measurements, however, remains a major challenge. Here, we quantify systematic, random and gap-filling errors and the resulting uncertainty in CH4 fluxes using a 3.5 year time series of simultaneous open- and closed path CH4 flux measurements over a sub-boreal wetland.After correcting for high- and low frequency flux attenuation, the magnitude of systematic frequency response errors were negligible relative to other uncertainties. Based on three different random flux error estimations, we found that errors of the CH4 flux measurement systems were smaller in magnitude than errors associated with the turbulent transport and flux footprint heterogeneity. Errors on individual half-hourly CH4 fluxes were typically 6%–41%, but not normally distributed (leptokurtic), and thus need to be appropriately characterized when fluxes are compared to chamber-derived or modeled CH4 fluxes.Integrated annual fluxes were only moderately sensitive to gap-filling, based on an evaluation of 4 different methods. Calculated budgets agreed on average to within 7% (≤1.5 g−CH4 m−2 yr−1). Marginal distribution sampling using open source code was among the best-performing of all the evaluated gap-filling approaches and it is therefore recommended given its transparency and reproducibility.Overall, estimates of annual CH4 emissions for both EC systems were in excellent agreement (within 0.6 g−CH4 m−2 yr−1) and averaged 18 g−CH4 m−2 yr−1. Total uncertainties on the annual fluxes were larger than the uncertainty of the flux measurement systems and estimated between 7–17%. Identifying trends and differences among sites or site years requires that the observed variability exceeds these uncertainties.
  • On the applicability of maximum overlap discrete wavelet transform
           integrated with MARS and M5 model tree for monthly pan evaporation
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Alireza Ghaemi, Mohammad Rezaie-Balf, Jan Adamowski, Ozgur Kisi, John QuiltyAbstractAccurate pan evaporation (Epan) prediction is a critical issue in water resources management, particularly when designing and managing rural water resource systems, and when assessing water utilization and demand. In this study, Multivariate Adaptive Regression Spline (MARS) and M5 Model Tree (MT) models were coupled with a maximum overlap discrete wavelet transform (MODWT) to create MARSMODWT and MTMODWT models for the prediction of monthly pan evaporation for Turkey’s Siirt and Diyarbakir meteorological stations. The performance of the standalone MARS and MT models was compared to the corresponding MODWT-based hybrid models. Furthermore, the developed hybrid models were combined with (Epan) Mallow’s coefficient (Cp) to minimize the number of predictor variables needed to predict monthly Epan. The models used preprocessed input data, including temperature (T), wind speed (W), relative humidity (RH), and solar radiation (SR). The performance of each approach was evaluated using standard statistical measures (i.e., correlation coefficient (R), root mean square error (RMSE), Nash-Sutcliffe efficiency (NSE) and mean absolute error (MAE)). The results showed that the MARSCpMODWT model improved the MARS accuracy with respect to lower percentages of RMSE (29.46%) and MAE (24.53%) in the validation phase for the Siirt station. In case of the Diyarbakir station, the MARSCpMODWT improvements decreased the RMSE (17.91%) and MAE (16.49%) values in comparison to standalone MARS model. The overall results indicated that the use of both MODWT and Cp as pre-processing techniques improves prediction accuracy, and thus, they are both recommended for use in further studies.
  • Subtropical mangrove wetland is a stronger carbon dioxide sink in the dry
           than wet seasons
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Jiangong Liu, Derrick Y.F. LaiCoastal mangrove wetlands have an excellent potential in sequestrating atmospheric carbon dioxide (CO2) owing to their high primary productivity as well as slow anaerobic decomposition of organic matter. Yet, there is hitherto a paucity of researches examining the temporal variations and environmental controls of ecosystem-scale CO2 fluxes in subtropical mangroves using quasi-continuous, high temporal resolution measurements. In this study, we measured the net ecosystem CO2 exchange (NEE) between the atmosphere and a subtropical estuarine mangrove dominated by Kandelia obovata using an eddy covariance system for two full years to investigate the seasonal variability and key biophysical drivers of NEE. During the wet seasons, the magnitude of increase in ecosystem respiration (Re) was greater than that in gross primary productivity (GPP) owing to a combination of higher temperature and lower percentage of inundation, tidal height and water salinity, which subsequently resulted in an overall decrease in net CO2 uptake as compared to the dry seasons. Our results of path analysis showed that temperature was a dominant control of the temporal variations in CO2 flux during the wet seasons, while its influence became weaker during the dry seasons. On the other hand, an increase in water salinity during the dry seasons had a positive influence on GPP, which was likely related to a greater availability of ions (mainly Cl− and Na+) in supporting photosynthesis by mangrove trees in this coastal wetland with relatively low salinity (∼5–15 ppt). Our subtropical mangrove wetland was shown to be a significant carbon (C) sink, with annual C uptake rates of 890 and 758 g CO2-C m-2 yr−1 in the two years of study. We found a strong control of mangrove CO2 fluxes by biophysical factors such as temperature and salinity, implying that global warming and a reduction in water salinity in response to a greater river discharge could potentially reduce the C sink strength of estuarine mangroves in the subtropical regions.Graphical abstractGraphical abstract for this article
  • Publisher's note
    • Abstract: Publication date: Available online 19 August 2019Source: Agricultural and Forest MeteorologyAuthor(s):
  • The observed and model-simulated response of southern African vegetation
           to drought
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Shakirudeen Lawal, Christopher Lennard, Christopher Jack, Piotr Wolski, Bruce Hewitson, Babatunde AbiodunAbstractDrought is a frequent disturbance in many regions of the globe and can have a particularly severe impact on vegetation. Over southern Africa, where drought is a regular occurrence, relatively little is known about how quickly vegetation responds to droughts. We characterized the meteorological drought occurrence in southern Africa from 1981 to 2005 and examined the impacts on vegetation productivity, as derived from satellite data. The spatio-temporal extent and severity of droughts were assessed at different timescales (1- to 18-month timescales) using the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI). Thereafter, we examined the impacts of droughts on southern African vegetation using the Normalized Difference Vegetation Index (NDVI). The results of this study show that southern African vegetation responds differently to drought over the different timescales. During the 1981–2005 period, droughts had extensive impacts over central parts of South Africa, Namibia and western areas of Botswana and the responses of vegetation varied according to season and biome, likely due to the differences in the levels of water needed by vegetation during various growth/phenological phases. In addition, the magnitude of the drought’s impact on vegetation is sensitive to the type of drought index that is used to characterize its severity.We further investigated the response of vegetation as simulated by an Earth System Model (the Community Earth Systems Model, CESM) over the same period. The intensity of drought impacts on vegetation is underestimated by CESM, while the timescales at which vegetation responds to droughts are overestimated by it. Different model ensemble members show a substantial spread in the simulation of vegetation response across different biomes and seasons, which may be due to inherent errors and biases in the land component of the model (CLM4.5), or in the atmospheric model and/or the parameterizations. However, we demonstrate that the land component of the CESM (CLM4.5) does provide an adequate representation of the response of vegetation to drought and would provide useful information about the response of vegetation to future drought. If the uncertainties we identified could be reduced, a more realistic simulation of the vegetation response to drought could be realized.
  • The quantitative impact of different leaf temperature determination on
           computed values of stomatal conductance and internal CO2 concentrations
    • Abstract: Publication date: 15 December 2019Source: Agricultural and Forest Meteorology, Volume 279Author(s): Lingling Zhang, Sheng ZhangAbstractThe LI-COR 6400 portable photosynthesis system is the most widely used and cited instrument for measuring leaf gas exchange in plant physiology. The focus of this paper is to evaluate three ways of computing/measuring leaf temperature: the LI-COR energy budget computation, the LI-COR leaf thermocouple (T/C), and an infra-red (IR) sensor chip (MLX90615) incorporated into the LI-6400 leaf chamber. The IR-sensor was calibrated against known targets, and then used to cross check the other two methods. The results showed that the IR-sensor was superior to the LI-COR thermocouple and agreed closer with the energy budget values of leaf temperature. The magnitudes of the errors were quantified in terms of °C difference in leaf temperature measured by T/C (as control) and IR sensor versus percentage difference in stomatal conductance (gs) and intercellular CO2 concentration (Ci) computed from leaf temperature. The temperature difference (IR versus other methods) in the range of -1.89 to 1.58 °C resulted in relative errors in gs from 14.7% to -18.0% and Ci from 16.5% to -7.8% of the values reported by the standard LI-6400 calculations depending on species and temperature. Reasons are given for trusting the IR-sensor over the other methods and it is suggested that the next generation LI-COR photosynthesis system include an IR-sensor.
  • Light interception in experimental forests affected by tree diversity and
           structural complexity of dominant canopy
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Kaisa Rissanen, Marc-Olivier Martin-Guay, Anne-Sophie Riopel-Bouvier, Alain PaquetteAbstractBiodiversity affects ecosystem functioning in forests by, for example, enhancing growth and altering the forest structure towards greater complexity with cascading effects on other processes and trophic levels. Complexity in forest canopy could enhance light interception and form a link between diversity and productivity in polyculture forests, but the effect of canopy structure on light interception is rarely directly measured.We modelled the canopy surface structure of a tree diversity experiment by photographing it using unmanned aerial vehicle (UAV) and combining the photos into a digital elevation model with photogrammetry tools. We analysed the effects of tree diversity and functional diversity on canopy structural complexity and light interception with a structural equation model.Our results show that: a) increased structural complexity of the canopy reduces light interception, whereas b) tree diversity increases the structural complexity of the canopy, and has a dual impact on light interception. Tree diversity decreased light interception through the structural complexity of the canopy but increased it probably through canopy packing and crown complementarity. However, the effects of both tree diversity and structural complexity of canopy were smaller than the effect of the functional identities of the tree species, especially the differences between deciduous and evergreen trees.We conclude that more complexity in canopy structure can be gained through increased tree diversity, but complex canopy structure does not increase light interception in young forests.
  • Responses of ecosystem water use efficiency to meteorological drought
           under different biomes and drought magnitudes in northern China
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Hao-jie Xu, Xin-ping Wang, Chuan-yan Zhao, Xiao-xiao ZhangAbstractFuture climate change scenarios predict that warming may increase drought stress over northern China, causing ecological deterioration and food insecurity. Water use efficiency (WUE) is an important indicator to understand the response of ecosystem productivity to water availability. At present we lack a clear picture of how ecosystem WUE responds to drought magnitude across a broad range of vegetation types and environments. Here, we applied Moderate Resolution Imaging Spectrometer (MODIS) satellite images and meteorological data to obtain a regional estimation of gross primary production (GPP) and evapotranspiration (ET) during the period of 2000–2014. We then investigated the relationships between WUE (GPP/ET) and drought magnitude (based on the Standardized Precipitation Evapotranspiration Index, SPEI) for different climate zones and biomes. The mean annual WUE decreased with increasing Aridity Index (AI) in arid regions. However, the relationships between WUE and AI followed a logarithmic function across semi-arid and humid regions. In hype-arid, sub-humid and humid regions, a drying trend resulted in increased WUE. Contrasting responses of WUE to drought were found in arid and semi-arid regions. The negative effect of drought that caused decreased WUE was most significant in the transition zone between arid and semi-arid lands. Besides, the relationships between relative changes in WUE and drought magnitude followed a logarithmic function of SPEI. Severe and extreme drought resulted in WUE reductions regardless of different hydroclimatic conditions and biomes. The ecosystem resistant to drought can be evaluated by the magnitude of WUE reductions during drought, together with the WUE-SPEI correlations. Forests were most resistant to drought, followed by croplands, grasslands, and deserts. Differences in the ecosystem resistance to water stress were attributed to diversities in drought survival traits and strategies. Given that hydroclimatic conditions break down ecosystem resistance under severe and extreme drought, we highlight an urgent need to formulate adaptation strategies aimed at reducing drought risk in the eastern and central portions of northern China.
  • Measuring ammonia emissions from vegetable greenhouses with an inverse
           dispersion technique
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Wenhua Liao, Sen Wang, Chunjing Liu, Zhiling Gao, Thomas K. FleschAbstractChina’s greenhouse vegetable production is considered an important contributor to the national ammonia (NH3) inventory because of the excess nitrogen (N) application rate (normally over 1000 N kg ha−1 yr−1) and large N consumption (approximately 10% of the N fertilizer in China). However, the previously measured emission rates are still in question because of the inherent limits of the commonly used techniques (e.g., non-flow-through chamber technique) and the exclusion of the impact of the greenhouse opening/enclosing scheme on NH3 loss from greenhouse soil to the atmosphere over a growing season. This study examines the ability of an inverse dispersion technique, in combination with an open-path laser system, for measuring NH3 emissions from vegetable greenhouses. The NH3 concentrations over the greenhouse areas greatly exceeded the laser’s detectable limit and showed a clear diel variation pattern. Determination of the area and height of the greenhouse sources are critical to emission estimates, while removing the periods with inaccurate wind simulations has minimal effect on the daily and total emission estimations since the omitted periods mainly occurred during nighttime (low emission periods). With the application of our findings, the observed diel NH3 emission patterns are found in good agreement with the air temperature. The NH3-N losses during the measurements in terms of proportions to the N fertilization (40.02% in spring, 7.83% in summer) are generally comparable to those of previous studies. Overall, the inverse dispersion technique can be used to provide good NH3 emission estimates as well as to assess NH3 emission factors along the opening/enclosing scheme across a growing season of greenhouse vegetables in the future.
  • Soil organic carbon in Italian forests and agroecosystems: Estimating
           current stock and future changes with a spatial modelling approach
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Antonio Caddeo, Serena Marras, Lorenzo Sallustio, Donatella Spano, Costantino SircaAbstractThe soil organic carbon (SOC) is the largest carbon pool in the terrestrial biosphere, second only to oceans, containing twice as much carbon as the atmosphere and three times that stored in global vegetation. Climate change (CC) is expected to impact this carbon pool. To date, large uncertainties still persist on the effects of CC on SOC stocks. In addition, a shortage of data related to regional SOC quantities of tree-covered areas and future changes under CC conditions is recognized. In this work, we used a spatial-explicit modelling approach to estimate the current SOC stock (at 2005) and future changes (at 2095) under CC conditions of the whole forest, tree crop, grassland, and pasture covered areas of Italy. A methodology was preliminarily implemented to obtain spatialized SOC estimates at a regional scale by using the CENTURY 5 model coupled with spatialized vegetation, soil, and climate data. We ran both moderate (RCP4.5) and extreme (RCP8.5) climatic scenarios, and used three Global Circulation Models for each one of the four ecosystems described above. The current SOC stock estimates range from 51.3 (orchards) to 129.5 Mg carbon ha−1 (coniferous forests) and we found an overall SOC stock in Italy ranging from 1320.1 to 1425.1 Tg. SOC projections under CC showed a moderate carbon loss suggesting that forest, grassland, and permanent crop soils could provide an important contribution to climate change mitigation.
  • Biochar amendment reduced greenhouse gas intensities in the rice-wheat
           rotation system: six-year field observation and meta-analysis
    • Abstract: Publication date: 15 November 2019Source: Agricultural and Forest Meteorology, Volume 278Author(s): Zhen Wu, Xi Zhang, Yubing Dong, Bo Li, Zhengqin XiongBiochar amendment to cropland has been recommended as a potential strategy to mitigate climate change. However, estimations of the long-term greenhouse gas (GHG) emissions, namely, the methane (CH4) and nitrous oxide (N2O) mitigation potential, from agricultural systems are limited. Here, a six-year field experiment was conducted to simultaneously monitor the CH4 and N2O emissions and the yield from a rice-wheat rotation system with nitrogen application (0 and 250 kg ha-1) and biochar incorporation (0, 20 and 40 t ha-1) in southeastern China. The results showed that nitrogen application significantly increased CH4 and N2O emissions and the yield compared to the control, while no significant differences were detected among the treatments with no nitrogen. In contrast, biochar amendment resulted in significant decreases in CH4 and N2O emissions by 11.2–17.5% and 19.5–26.3%, respectively, with increases in yield by 7.9-9.2%, on average. In addition, considering the GHG emissions, the soil organic carbon sequestration rate and the yield, biochar significantly decreased the net global warming potential and greenhouse gas intensity over the six-year observation period. Our results were further supported by a meta-analysis, which showed that biochar amendment in the field strongly decreased CH4 and N2O emissions by 9.3% and 18.7%, respectively, and increased the yield by 9.0% under various complex soil environments. Based on our results, biochar application would increase carbon stock by 10.3% and decrease GHG emissions by 10.4% for Chinese rice and wheat production. Our findings suggest that the application of biochar to cropland is a viable option to combat climate change over the long term by soil carbon sequestration and GHG mitigation.Graphical abstractGraphical abstract for this article
  • Corrigendum to “Intercomparison of surface energy fluxes, soil
           moisture, and evapotranspiration from eddy covariance, large-aperture
           scintillometer, and modeling across three ecosystems in a semiarid
           climate” [Agric. For. Meteorol. 248 (2018) 22–47]
    • Abstract: Publication date: Available online 4 July 2019Source: Agricultural and Forest MeteorologyAuthor(s): Prasanth Valayamkunnath, Venkataramana Sridhar, Wenguang Zhao, Richard G. Allen
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
About JournalTOCs
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-