EARLY WATER YIELD EFFECTS OF CONVERSION OF SLOPES OF A EUCALYPT FOREST CATCHMENT TO RADIATA PINE PLANTATION

Between 1975 and 1987 the water yield from three small, contiguous, forested catchments carrying similar vegetation in southeastern Australia was measured. These were located in humid, steep foothill areas subject to a major plantation program. At the project start all catchments carried mature, natural eucalypt forest. In their natural state the catchments exhibited similar annual hydrologic variation and water yields, with a pronounced low-flow period in summer and autumn, and high flows in winter and spring. One catchment was converted from native eucalypt forest to radiata pine by clearing, burning, and planting in December 1979. A 30-m buffer was retained along the stream. The treatment increased the water yield of the catchment by up to 3.5 ML ha-1, a 47% increase on average. The actual yield increase varied from year to year, and appeared to decline slowly with time from the conversion. Most of the increase was as increased storm flow in the early part of winter. The relation between the storm flow, causal rainfall, and antecedent flow did not appear to be changed by the treatment, suggesting that most of the storm flow response is attributable to increased catchment wetness at the end of the dry summer period.