Hydrologic effects of conversion of slopes of a eucalypt forest catchment to radiata pine plantation

Summary

Between 1975 and 1987 a multiple catchment project was conducted in the headwaters of Cropper Creek, 22 km southwest of Myrtleford (Victoria). This used three catchments ranging in size from 44 to 113 ha. During summer and autumn the streams carried a low (or zero) flow. Normally, heavy rains in late autumn or early winter led to higher flows until mid-spring. Flows then receded to low summer flows. In summer a clear diurnal variation was apparent. Flows reached a maximum about midnight and a minimum about midday. All three streams had similar water yields while their catchment carried native forest and when stream flows were high. During summer and autumn two of the streams would dry up, limiting their utility as “control catchments.” Clem Creek was converted from native eucalypt forest to radiata pine in December 1979. A 30 m buffer was retained along the stream. The water yield of the treated catchment increased by up to 400 mm per annum and varied from year to year. Most of this increase was as increased storm flow in the early part of the high-flow period. This was due to greater slope water storage because of reduced evapotranspiration from the slope vegetation. The treatment caused a small increase in the amplitude of the observed diurnal variation. This suggested enhanced transpiration from the stream vegetation due to increased groundwater recharge to the bottom-land of the catchment. After eight years the response is diminishing. The project was ended as an economy measure in 1987.