Resolving the debate surrounding the nature and controls of seasonal variation in the 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, here we re-examine 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 the 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.
Department of Earth and Environment, Boston University, Boston, MA 02215, USA;Department of Earth and Environment, Boston University, Boston, MA 02215, USA;Department of Earth and Environment, Boston University, Boston, MA 02215, USA;Department of Earth and Environment, Boston University, Boston, MA 02215, USA;Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK;Laboratoire des Sciences du Climat et de l’Environnement, IPSL-LSCE, CEA-CNRS-UVSQ, 91191 Gif sur Yvette Cedex, France;Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, USA;Bay Area Environmental Research Institute, NASA Ames Research Center, Moffett Field, CA 94035, USA;Biospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA;College of Forestry, Oregon State University, Corvallis, OR 97331, USA;Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, New South Wales 2007, Australia;Numerical Terradynamic Simulation Group, The University of Montana, Missoula, MT 59812, USA;Numerical Terradynamic Simulation Group, The University of Montana, Missoula, MT 59812, USA;Climate and Radiation Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA;Department of Geosciences and Geography, University of Helsinki, FI-00014, Helsinki, Finland;NASA Advanced Supercomputing Division, Ames Research Center, Moffett Field, California 94035, USA;Department of Ecology, Peking University, Beijing 100871, People’s Republic of China;Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, People’s Republic of China;Department of Ecology, Montana State University, Bozeman, MT 59717, USA;Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA;Institute of the Environment and Sustainability, University of California, Los Angeles, CA 90095, USA;Radar Science and Engineering section, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA;Institute of the Environment and Sustainability, University of California, Los Angeles, CA 90095, USA;Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, New York 12222, USA;Department of Earth and Environment, Boston University, Boston, MA 02215, USA
Recommended Citation:
Jian Bi,Yuri Knyazikhin,Sungho Choi,et al. Sunlight mediated seasonality in canopy structure and photosynthetic activity of Amazonian rainforests[J]. Environmental Research Letters,2015-01-01,10(6)