EFFECT OF CLEARFELLING PINES ON WATER YIELD IN A SMALL EASTERN TRANSVAAL CATCHMENT, SOUTH-AFRICA

A catchment afforested partially with exotic pines in the Witklip experimental catchment area near White River in the Eastern Transvaal (South Africa), was clearfelled to test the effects of deforestation on catchment water yield. Water yield is an important issue in the Eastern Transvaal as the highest percentage of afforestation in South Africa takes place in this area and it is also an area of intense competition for water resources. The effects of treatment were assessed using the paired catchment approach. Simple regression analysis results revealed that clearing the forest led to a significant increase in catchment water yield of approximately 280 mm/a (S.E. +/- 55.4) during the first 4 years after completion of treatment. Maximum seasonal streamflow increases were approximately 250 mm/a during the high-flow period (summer) and 140 mm/a during the low-flow period (winter). The results from this study are in accordance with results obtained in several other catchment studies world-wide, verifying results from other parts of the world under South African conditions.