Seasonal patterns of water utilization by savanna ecosystems with different proportion of herbaceous and woody plants.

SANTANA OTACILIO, HOFFMANN WILLIAM, SCHOLZ FABIÁN G., BUCCI SANDRA J., GIAMBELLUCA THOMAS, GOLDSTEIN GUILLERMO, MEINZER FREDERICK C.

Edinburgo

Conferencia; International Conference Tropical Savannas & Seasonally dry forest; 2003

The partitioning of soil water between trees and herbaceous plants is considered to be one of the main determinants of the structure and function of savanna ecosystems.  To quantify the effects of tree density on water use by herbaceous plants in the Brazilian savannas (Cerrado), evapotranspiration (ET) of the herbaceous layer (including small woody plants) was measured in five savanna physiognomies along a tree density gradient: cerradão, cerrado denso, cerrado sensu strictu, campo cerrado and campo sujo.  Monthly measurements of ET of the herbaceous layer were performed with an open-top chamber from May 2002 to February 2003.  Total ecosystem evapotranspiration, including both the woody and herbaceous layers, was measured simultaneously with an eddy covariance system at the campo cerrado and cerrado denso sites.  Average evapotranspiration from the herbaceous component was highest during the wet season (2.3 ± 0.6 mm day-1) and lowest during the dry season (0.12 ± 0.04 mm day-1). Total ET ranged from 3.75 ± 0.51 mm day-1 in the rainy season and 1.17 ± 0.06 mm day-1 in the dry season.  The contribution of herbaceous plants to total ET was greatest during the wet season (about 75%), than during the dry season (about 15%).Tree density significantly affected the seasonality of groundlayer ET; in the dry season, groundlayer  ET was greatest in the denser physiognomies, while in the wet season, it was greater in the more open physiognomies. Hydraulic lift may partially explain the greater groundlayer ET in dense sites relative to open sites in the dry season.