Land use changes in savannas of Central Brazil: The impact of eucalypt plantations and Brachiaria pastures on water fluxes.

A. C. FRANCO, S. J. BUCCI, F. SCHOLZ, W. A. HOFFMANN, M. L. MEIRELLES, G. GOLDSTEIN, F. R. MEINZER.

Viena

Congreso; nternational Botanical Congress; 2005

We compared transpiration in natural savanna, Eucalyptus grandis plantations of two different ages, and grazed and ungrazed pastures of Brachiaria decumbens. Water extraction in the Brachiaria pastures was mostly restricted to the superficial soil layers whereas E. grandis plantations and savanna vegetation accessed deeper soil layers. There was a strong linear relationship between basal area and active xylem area for both E. grandis and savanna trees. Stem cross-sectional area was mostly conducting tissue in E. grandis, but only about 36% in savanna trees. Thus, over a range of 20 to 200 cm2 of basal area, E. grandis maintained daily sap flow rates that were 2 to 3-fold higher than savanna trees in the wet season. Sap flow rates of E. grandis increased in the dry season while savanna trees maintained rates similar to the wet period. Water loss in the ungrazed Brachiaria pasture was higher than that of the savanna groundlayer in the wet season. Water loss in both decreased substantially in the dry season. Thus, these changes in land use have an important impact on the hydrological cycle.