Sunlight mediated seasonality in canopy structure & photosynthetic activity of Amazonian rainforests
Date
2015-06Author
Bi, Jian
Knyazikhin, Yuri
Choi, Sungho
Park, Taejin
Barichivich, Jonathon
Ciais, Philippe
Fu, Rong
Ganguly, Sangram
Hall, Forrest
Hilker, Thomas
Huete, Alfredo
Jones, Matthew
Kimball, John S.
Lyapustin, Alexei
Mottus, Matti
Nemani, Ramakrishna R.
Piao, Shilong
Saleska, Scott R.
Saatchi, Sassan S.
Xu, Liang
Zhou, Liming
Myneni, Ranga B.
Metadata
Show full item recordAbstract
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.
Citation
Bi, Jian, Yuri Knyazikhin, Sungho Choi, Taejin Park, Jonathon Barichivich, Philippe Ciais, Rong Fu, Sangram Ganguly, Forrest Hall, Thomas Hilker, Alfredo Huete, Matthew Jones, John Kimball, Alexei I Lyapustin, Matti Mottus, Ramakrishna R. Nemani, Shilong Piao, Benjamin Poulter, Scott R. Saleska, Sassan S. Saatchi, Liang Xu, Liming Zhou, and Ranga B. Myneni. "Sunlight mediated seasonality in canopy structure & photosynthetic activity of Amazonian rainforests." Environmental Research Letters 10 (June 2015): 064014. DOI:https://dx.doi.org/10.1088/1748-9326/10/6/064014.