Some hydrological effects of changing forest cover from eucalypts to Pinus radiata

A study of the hydrological effects of clearing a catchment covered by native, dry sclerophyl eucalypt forest, and replanting it with a Pinus radiata plantation was undertaken. The purpose of this study was to examine the effects of vegetation species change and growth rates on streamflow. The water balance of the two forests was observed for a 27-year period; 11 years before and 16 years after the forest conversion. Data on precipitation, canopy interception, forest floor interception and water yield, combined with analysis of the rate of vegetative growth and development of the forest floor litter, enabled investigation of the effects of forest conversion on the water balance components for the whole period (1967-1993). The age of a P. radiata plantation during the first 16 years of its growth greatly affected the streamflow and other water balance components. For the first 4 years after forest conversion, the rates of evapotranspiration and streamflow changed completely. Transpiration and the evaporation of intercepted rainfall ceased after the forest was cleared. The changes in the first 4 years were followed by a further transformation of the whole evapotranspiration process as the pine plantation developed. A trend of increasing evapotranspiration and canopy and forest floor interception losses as the plantation grew, with decreases in runoff, was followed by an equilibrium situation in which streamflow, and the evapotranspiration from soil water storage were smaller than for the native forest. (C)2000 Elsevier Science B.V. All rights reserved.