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Title: Leaf flush drives dry season green-up of the Central Amazon
Authors: Lopes, Aline Pontes
Nelson, Bruce Walker
Wu, Jin
Graça, Paulo Maurício Lima Alencastro de
Tavares, Julia Valentim
Prohaska, Neill
Martins, Giordane Augusto
Saleska, Scott Reid
Keywords: Biology
Evolutionary Algorithms
Chromatic Coordinate
Enhanced Vegetation Index
Leaf Abscission
Leaf Flush
Tropical Forest
Canopy Architecture
Dry Season
Evergreen Forest
Image Analysis
Light Availability
Precipitation Intensity
Tropical Forest
Vegetation Index
Amazon River
Issue Date: 2016
metadata.dc.publisher.journal: Remote Sensing of Environment
metadata.dc.relation.ispartof: Volume 182, Pags. 90-98
Abstract: Understanding how land surface seasonality emerges from individual tree crown phenology is a key challenge of tropical ecology. We used daily images over a full year from a tower-mounted RGB camera to quantify the leaf phenology of 267 individual tree crowns in an evergreen Central Amazon forest. The Green Chromatic Coordinate, an index of each crown's greenness, showed rapid large-amplitude positive and negative changes, each generally occurring once per year. Rapid increase was attributed to leaf flushing and occurred in 85% of all crowns. Rapid negative change occurred in 42% of individuals, caused mostly by massive pre-flush leaf abscission (31% of all crowns). Flushing was concentrated in the five driest months (55% of crowns) compared to the five wettest months (10%). Inter-crown variance of greenness was lowest in the wet season when fewer crowns were abruptly abscising or flushing leaves. With a one month lead, flushing frequency closely tracked seasonal light availability (R = 0.89) and was inversely correlated with rainfall (R = -. 0.88). We linked the post-flush age of each crown's leaf cohort to the Enhanced Vegetation Index (EVI) of crowns at different phenostages on a nadir view QuickBird image. When aggregated to landscape-scale, this camera-based EVI closely followed (R = 0.95) the MODIS MAIAC EVI of the same site, fully corrected for sun-sensor geometry effects. Leaf phenology therefore drives the dry season green-up detected by MODIS in the Central Amazon. It is also consistent with evolutionary strategies to couple photosynthetic efficiency with light availability and to avoid predation and disease on vulnerable young leaves. © 2016 Elsevier Inc.
metadata.dc.identifier.doi: 10.1016/j.rse.2016.05.009
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