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Effects of disturbance on biomass, structure and carbon balance in two Amazonian Forests

Elizabeth Hammond Pyle, Harvard University,
Gregory W. Santoni, Harvard University,
Henrique E. M. Nascimento, National Institute for Amazonian Research (INPA),
Lucy R. Hutyra, Harvard University, (Presenting)
Plinio B. Carmago, University of São Paulo,
Simone Vieira, University of São Paulo,
Daniel J. Curran, Harvard University,
Joost van Haren, University of Arizona,
Scott R. Saleska, University of Arizona,
V. Y. Chow, Harvard University,
William F. Laurance, Smithsonian Tropical Research Institute,
Steven C. Wofsy, Harvard University,

Amazon forests are potentially globally significant sources or sinks for atmospheric carbon dioxide. In this study, we characterize the spatial and temporal trends in carbon storage and fluxes in both live and dead biomass in two central Amazonian forests, the Biological Dynamic of Forest Fragments Project (BDFFP), near Manaus, Amazonas, and the Tapajós National Forest (TNF) near Santarém, Pará. We assessed coarse woody debris (CWD) stocks, tree growth, mortality, and recruitment in ground-based plots distributed across the landscapes at both sites. Carbon dynamics were similar within each site, but differed significantly between the sites. The BDFFP had slightly larger live biomass than the TNF (167 +/- 5 MgC/ha vs. 148 +/- 3 MgC/ha, respectively), but stocks of coarse woody debris (CWD) were 2.5 times larger at TNF (16.2 +/- 1.5 MgC/ha at BDFFP, vs. 40.1 +/- 3.9 MgC/haat TNF). A model of current dynamics suggests that the BDFFP was close to carbon balance, and its size class structure approximated a steady state. The TNF by contrast showed rapid carbon accrual in live biomass (3.19 +/- 0.20 MgC/ha/year in TNF, 2.59 +/- 0.11 MgC/ha/year in BDFFP), more than offset by losses from large stocks of CWD, as well as ongoing shifts of biomass among size classes. This pattern suggests recovery from a significant disturbance, which we argue was likely the ENSO-related drought of 1998, shortly before our measurements began. The net loss of carbon from the TNF will likely last 10-15 years after the initial disturbance (controlled by the rate of decay of coarse woody debris), followed by long term, slow uptake of carbon as the forest evens out remaining imbalances in forest size class structure and composition. The data support the view that strong episodic disturbances such as ENSO droughts create a patchwork of agrading forests in Amazonia, interspersed with much smaller areas that emit carbon to the atmosphere.

Science Theme:  CD (Carbon Dynamics)

Session:  2B: Forest Dynamics and Disturbance

Presentation Type:  Oral (view presentation (1349 KB))

Abstract ID: 21

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