Effects of changing forest cover on components of the water balance

A studuy was undertaken of the effects of clearing a native euca­lpt forest, and replanting it with a Pinus radiata [P. radiata) planta­tion, on individual hydrological processes, on the water yield and on the catchment water balance. The objective of the study was to exam­ine the effects of vegetation species change and growth rates on com­ponenst of the water balance. In this study a water balance of the two forests was undertaken for a 27-ear period (1967-1993); 11 years before and 16 years after the forest conversion. Analysis of the rate of vegetative growth and de­velopment of the forest floor litter, combined with data on precipitation, canopy interception, forest floor interception and streamflow, enable investigation of the effects of forest conversion on water balance com­ ponents for the whole period.The age of a P. radiata plantation during the first 16 gears of its growth greatly affected the streanflow and the other water balance components. For the first 4 gears after forest conversion, the rates of evapotranspiration and streamflow changed completely. Transpiration and the evaporation of intercepted rainfall ceased after the forest floor was cleared. The changes in the first 4 ears were followed by a fur­ ther transformation of the whole evapotranspiration and canopy and forest floor interception losses as the plantation grew, with decreases in runoff, was followed b an equilibrium situation in which streamflow and the evapotraspiration from soil water storage were smaller for the native fore.