B51D-0455
Sunlight Mediated Seasonality in Canopy Structure and Photosynthetic Activity of Amazonian Rainforests
Friday, 18 December 2015
Poster Hall (Moscone South)
Jian Bi1, Yuri Knyazikhin2, Sungho CHOI3, Taejin Park2, Jonathan Barichivich4, Philippe Ciais5, Rong Fu6, Sangram Ganguly7, Forrest G Hall8, Thomas Hilker9, Alfredo R Huete10, Matthew O Jones11, John S Kimball12, Alexei Lyapustin8, Matti Mottus13, Ramakrishna R Nemani7, Shilong Piao14, Benjamin Poulter15, Scott R Saleska16, Sassan S Saatchi17, Liang Xu18, Liming Zhou19 and Ranga Myneni3, (1)Scripps Institution of Oceanography, Geosciences Research Division, La Jolla, CA, United States, (2)Boston University, Earth & Environment, Boston, MA, United States, (3)Boston University, Boston, MA, United States, (4)University of East Anglia, Climatic Research Unit, School of Environmental Sciences, Norwich, United Kingdom, (5)LSCE Laboratoire des Sciences du Climat et de l'Environnement, Gif-Sur-Yvette Cedex, France, (6)University of Texas at Austin, Geological Sciences, Austin, TX, United States, (7)NASA Ames Research Center, Moffett Field, CA, United States, (8)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (9)Oregon State University, Corvallis, OR, United States, (10)University of Technology Sydney, Plant Functional Biology and Climate Change, Ultimo, Australia, (11)NTSG - University of Montana, Missoula, MT, United States, (12)University of Montana, Numerical Terradynamic Simulation Group, College of Forestry & Conservation, Missoula, MT, United States, (13)University of Helsinki, Helsinki, Finland, (14)Peking University, Beijing, China, (15)Montana State University, Bozeman, MT, United States, (16)University of Arizona, Tucson, AZ, United States, (17)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (18)University of California Los Angeles, Los Angeles, CA, United States, (19)University at Albany, State University of New York, Department of Atmospheric and Environmental Sciences, Albany, United States
Abstract:
Resolving the debate about the nature and controls of seasonal variation in structure and metabolism of Amazonian rainforests is critical to understanding their response to climate change. In situ studies have observed higher photosynthetic and evapotranspiration rates, increased litterfall and leaf flushing during the sunlight-rich dry season. Satellite data also indicated higher greenness level, a proven surrogate of photosynthetic carbon fixation, and leaf area during the dry season relative to the wet season. Some recent reports suggest that rainforests display no seasonal variations and the previous results were satellite measurement artefacts. Therefore, we re-examine here several years of data from three sensors on two satellites under a range of sun positions and satellite measurement geometries and document robust evidence for a seasonal cycle in structure and greenness of wet equatorial Amazonian rainforests. This seasonal cycle is concordant with independent observations of solar radiation. We attribute alternative conclusions to an incomplete study of the seasonal cycle, i.e. the dry season only, and to prognostications based on a biased radiative transfer model. Consequently, evidence of dry season greening in geometry corrected satellite data was ignored and the absence of evidence for seasonal variation in lidar data due to noisy and saturated signals was misinterpreted as evidence of absence of changes during the dry season. Our results, grounded in the physics of radiative transfer, buttress previous reports of dry season increases in leaf flushing, litterfall, photosynthesis and evapotranspiration in well-hydrated Amazonian rainforests.
