Sunlight mediated seasonality in canopy structure and photosynthetic activity of Amazonian rainforests

Jian Bi, Boston University (now at UCSD), bijian.bj@gmail.com (Presenter)
Yuri Knyazikhin, Boston University, jknjazi@bu.edu
Sungho Choi, Boston University, gkattack@gmail.com
Taejin Park, Boston University, taejin1392@gmail.com
Jonathan Barichivich, University of East Anglia, j.barichivich@leeds.ac.uk
Philippe Ciais, Laboratoire des Sciences du Climat et de l'Environnement, philippe.ciais@lsce.ipsl.fr
Rong Fu, The University of Texas at Austin, rongfu@jsg.utexas.edu
Sangram Ganguly, Bay Area Environmental Research Institute, sangramganguly@gmail.com
Forrest Hall, NASA Goddard Space Flight Center, forrest.g.hall@nasa.gov
Thomas Hilker, Oregon State University, thomas.hilker@oregonstate.edu
Alfredo Huete, University of Technology Sydney, ahuete@icloud.com
Matthew Jones, The University of Montana, matt.jones@ntsg.umt.edu
John Kimball, The University of Montana, johnk@flbs.umt.edu
Alexei I. Lyapustin, NASA Goddard Space Flight Center, alexei.i.lyapustin@nasa.gov
Matti Mõttus, University of Helsinki, matti.mottus@helsinki.fi
Ramakrishna R. Nemani, NASA Ames Research Center, rama.nemani@nasa.gov
Shilong Piao, Peking University, slpiao@pku.edu.cn
Benjamin Poulter, Montana State University, benjamin.poulter@montana.edu
Scott R. Saleska, University of Arizona, saleska@email.arizona.edu
Sassan S. Saatchi, Jet Propulsion Laboratory, California Institute of Technology, sasan.s.saatchi@jpl.nasa.gov
Liang Xu, University of California, Los Angeles, bireme@gmail.com
Liming Zhou, University at Albany, State University of New York, lzhou@albany.edu
Ranga B. Myneni, Boston University, ranga.myneni@gmail.com

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 claim that undisturbed 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 intact wet equatorial Amazonian rainforests. This seasonal cycle is concordant with independent observations of solar radiation. We trace the contrarian findings to an incomplete study of the seasonal cycle, i.e. the dry season only, and an unorthodox approach, i.e. these forests must conform to the prognostications of a poorly performing 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.

Presentation Type:  Poster

Session:  General Contributions   (Tue 4:35 PM)

Associated Project(s): 

• Myneni, Ranga: Modest Maintenance of Terra and Aqua MODIS LAI/FPAR Products and Transitioning to Core Production ...details

Poster Location ID: 141