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Drought induced reductions in the Aboveground NPP of a east-central Amazon forest: results from a large-scale partial throughfall exclusion experiment.

Brando Monteiro Brando, IPAM, (Presenting)
Daniel Curtis Nepstad, WHRC/IPAM,
David Ray, WHRC/University of Maine,
Gina Cardinot, IPAM,

Global and regional climatic changes are predicted to reduce precipitation in Amazonia, potentially reducing the net primary productivity (NPP) of extensive areas of moist tropical forests. However, the nature of these responses and their underlying mechanisms are poorly understood. Our investigation sought to clarify the issue by posing the following questions: (1) How will tropical moist forests respond to increased drought? (2) What are the limits of this forest ability to cope with drought? And, (3) To what extent will the forest be able to recover after the drought stress is removed? To address these questions we established a large-scale throughfall reduction experiment located in the Tapajos National Forest, which comprised two 1-ha parcels: a “dry” plot from which approximately 50% of the incoming precipitation was diverted from the soil during five wet seasons from January 2000 to August 2004, and a “wet” plot that received natural rainfall inputs. The forests capacity to recover was assessed on the basis of measurements collected over a 1.5-yr period after the removal of drought stress. Following the second partial throughfall exclusion period NPP was reduced by 50% in the dry plot relative to the wet plot. The greatest difference in NPP between parcels (67%) was observed in 2003, during the period of lowest soil moisture levels. The component of NPP most affected by the drought was stem growth. However, after the drought stress was removed, NPP in the dry plot recovered substantially, being only 14% lower in the dry plot; mainly due to increased stem growth. These results suggest that increased drought has the potential to greatly reduce the NPP of moist tropical forests, yet the surviving trees also appear to exhibit some resilience following cessation of drought.

Science Theme:  CD (Carbon Dynamics)

Session:  1C: Carbon Fluxes in Upland Ecosystems

Presentation Type:  Oral

Abstract ID: 84

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