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Amazon Forests Maintain Consistent Canopy Structure and Greenness During the Dry SeasonThe seasonality of sunlight and rainfall regulates net primary production in tropical forests. Previous studies have suggested that light is more limiting than water for tropical forest productivity, consistent with greening of Amazon forests during the dry season in satellite data.We evaluated four potential mechanisms for the seasonal green-up phenomenon, including increases in leaf area or leaf reflectance, using a sophisticated radiative transfer model and independent satellite observations from lidar and optical sensors. Here we show that the apparent green up of Amazon forests in optical remote sensing data resulted from seasonal changes in near-infrared reflectance, an artefact of variations in sun-sensor geometry. Correcting this bidirectional reflectance effect eliminated seasonal changes in surface reflectance, consistent with independent lidar observations and model simulations with unchanging canopy properties. The stability of Amazon forest structure and reflectance over seasonal timescales challenges the paradigm of light-limited net primary production in Amazon forests and enhanced forest growth during drought conditions. Correcting optical remote sensing data for artefacts of sun-sensor geometry is essential to isolate the response of global vegetation to seasonal and interannual climate variability.
Document ID
Document Type
Reprint (Version printed in journal)
External Source(s)
Morton, Douglas C.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Nagol, Jyoteshwar
(Maryland Univ. College Park, MD, United States)
Carabajal, Claudia C.
(Sigma Space Corp. Lanham, MD, United States)
Rosette, Jacqueline
(Maryland Univ. College Park, MD, United States)
Palace, Michael
(New Hampshire Univ. Durham, NH, United States)
Cook, Bruce D.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Vermote, Eric F.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Harding, David J.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
North, Peter R. J.
(University Coll. Swansea, United Kingdom)
Date Acquired
December 8, 2014
Publication Date
February 13, 2014
Publication Information
Publication: Nature
Volume: 506
Issue: 7487
Subject Category
Meteorology And Climatology
Earth Resources And Remote Sensing
Report/Patent Number
Funding Number(s)
Distribution Limits
Public Use Permitted.
dry season

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