Light-driven growth in Amazon evergreen forests explained by seasonal variations of vertical canopy structure

Light-regime variability is an important limiting factor constraining tree growth in tropical forests. However, there is considerable debate about whether radiation-induced green-up during the dry season is real, or an apparent artifact of the remote-sensing techniques used to infer seasonal changes...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2017-03, Vol.114 (10), p.2640-2644
Main Authors: Tang, Hao, Dubayah, Ralph
Format: Article
Language:English
Subjects:
Biological Sciences
Drought
Forests
Light
Photosynthesis - physiology
Photosynthesis - radiation effects
Plant Leaves - growth & development
Plant Leaves - radiation effects
Precipitation
Radiation
Remote sensing
Rivers
Seasons
Trees - physiology
Tropical Climate
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Summary:Light-regime variability is an important limiting factor constraining tree growth in tropical forests. However, there is considerable debate about whether radiation-induced green-up during the dry season is real, or an apparent artifact of the remote-sensing techniques used to infer seasonal changes in canopy leaf area. Direct and widespread observations of vertical canopy structures that drive radiation regimes have been largely absent. Here we analyze seasonal dynamic patterns between the canopy and understory layers in Amazon evergreen forests using observations of vertical canopy structure from a spaceborne lidar. We discovered that net leaf flushing of the canopy layer mainly occurs in early dry season, and is followed by net abscission in late dry season that coincides with increasing leaf area of the understory layer. Our observations of understory development from lidar either weakly respond to or are not correlated to seasonal variations in precipitation or insolation, but are strongly related to the seasonal structural dynamics of the canopy layer. We hypothesize that understory growth is driven by increased light gaps caused by seasonal variations of the canopy. This lightregime variability that exists in both spatial and temporal domains can better reveal the drought-induced green-up phenomenon, which appears less obvious when treating the Amazon forests as a whole.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1616943114