Climatic variability, carbon exchange and vegetation vulnerability in Amazonia
Lucy
R.
Hutyra, Harvard University, lhutyra@fas.harvard.edu
(Presenting)
James
W.
Munger, Harvard University, jwm@io.as.harvard.edu
Scott
R.
Saleska, University of Arizona, saleska@email.arizona.edu
Plinio
B.
de Camargo, University of Sao Paulo, pcamargo@cena.usp.br
Steven
C.
Wofsy, Harvard University, scw@io.harvard.edu
The stability of Amazonian equatorial forests, and the fate of their immense stores of organic carbon, depend on the ecosystem response to climate and weather. This study presents 4+ years of eddy covariance measurements of carbon and water fluxes and their response to environmental conditions in an Amazonian old-growth tropical forest. Contrary to expectations, this forest does not show signs of seasonal water limitation on growth despite a 5-month dry season. CO¬2 uptake responds primarily to light on hourly time scales, but photosynthesis overall maximizes in the middle of the dry season, responding to ecophysiological (flushing of new leaves) and atmospheric (high aerosol loading) changes. Annual carbon balance was very sensitive to weather anomalies, particularly the timing of the dry-to-wet seasonal transition, with mean net loss of 939 kg C ha-1 yr-1 (observed range of -221 (uptake) to 2677 (loss) kg C ha-1 yr-1). The climatic sensitivity has significant implications for Amazonian carbon balances on annual to decadal time scales.
We also assessed the vulnerability and resilience of Amazonian vegetation to climate change by analyzing observed climate-vegetation relationships using climate data, observed vegetation distributions, and evapotranspiration rates inferred from eddy flux data. We found that drought frequency is an excellent predictor of the forest-savanna boundary, indicating the key role of extreme climatic events for inducing vegetation change, and highlighting particularly vulnerable regions of Amazonia.