Forest Management Influence On Hydric Production in a Temperate Rain Forest: a Comparative Study of Small Watersheds

In this work we compare hydric production between two micro-watersheds (surface area less than 10 hectares) covered with Nothofagus oblicua and Nothofagus alpina saplings. One of the watersheds was subject to management by thinning on 2002, and contains 23% less trees, which is equivalent to 33% less basal surface respect to the unmanaged control basin. It is expected that differences be solely related to land use differences given that both watersheds have similar geomorphology. Four years (April 2003 through Jun 2007) of hourly streamflow and precipitation data collected on each watershed are analyzed by separating base flow and direct runoff for specific storms selected to represent different conditions of initial soil moisture. Several hydrograph- separation algorithms are tested in order to increase the robustness of our conclusions. Variations in rainfall- runoff coefficients are analyzed in relation to differences in soil cover and antecedent moisture. Preliminary results show that managed watersheds produce more direct runoff, albeit subject to initial moisture conditions. On the other hand a greater fraction of precipitation becomes baseflow for natural forests. This has important implications for ecosystem hydrologic services valuation and management.