TY - JOUR
T1 - Sunlight mediated seasonality in canopy structure and photosynthetic activity of Amazonian rainforests
AU - Bi, Jian
AU - Knyazikhin, Yuri
AU - Choi, Sungho
AU - Park, Taejin
AU - Barichivich, Jonathan
AU - Ciais, Philippe
AU - Fu, Rong
AU - Ganguly, Sangram
AU - Hall, Forrest
AU - Hilker, Thomas
AU - Huete, Alfredo
AU - Jones, Matthew
AU - Kimball, John
AU - Lyapustin, Alexei I.
AU - Mõttus, Matti
AU - Nemani, Ramakrishna R.
AU - Piao, Shilong
AU - Poulter, Benjamin
AU - Saleska, Scott R.
AU - Saatchi, Sassan S.
AU - Xu, Liang
AU - Zhou, Liming M.
AU - Myneni, Ranga B.
PY - 2015
Y1 - 2015
N2 - 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.
AB - 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.
UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000356835600016&KeyUID=WOS:000356835600016
U2 - 10.1088/1748-9326/10/6/064014
DO - 10.1088/1748-9326/10/6/064014
M3 - Article
SN - 1748-9326
VL - 10
JO - Environmental Research Letters
JF - Environmental Research Letters
IS - 6
M1 - 064014
ER -