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Amazon forest hidden water stress

Gina Knust Cardinot, IPAM, cardinot@ipam.org.br (Presenting)
Daniel Curtis Nepstad, WHRC/IPAM, dnepstad@whrc.org

Over the past 6 years we have been monitoring changes in whole-tree water use in 27 tree individuals per plot, plant available soil water (PAW) and leaf area index (LAI) in the rainfall exclusion experiment (Santarem, Para, Brazil). The study consists of two 1-ha plots, a control and treatment plot from which rainfall wet season (6-mos) water inputs have been reduced by 50% since 2000. Transpiration was estimated on the basis of sap-flow measuring (Granier-type sensors) and tree fluxes were scaled to stand level using the circumference quotients. The daily treatment plot transpiration was correlated with LAI and PAW (p<.0.01). Control plot didn’t have significant correlation for any variable. After 3 years of exclusion in the 2003 dry season the treatment plot released 77% less water to the atmosphere. The match of LAI and transpiration is remarkable because of the related importance of canopy integrity to maintenance of transpiration patterns. A big lesson from this study is the hidden water stress nature, where forest with 25% less LAI can saturate the vegetation index satellite sensors (as “Normalized Difference Vegetation Index”) must be with high transpiration and photosynthesis restriction. Those findings will provide a better tropical rain forest land-cover and vegetation model parameterization.

Science Theme:  CD (Carbon Dynamics)

Session:  2A: Evapotranspiration and Precipitation

Presentation Type:  Oral

Abstract ID: 92

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