Managing riparian zone vegetation to sustain streamflow: results of paired catchment experiments in South Africa

Abstract

The reductions in streamflow associated with timber plantations are of particular concern in South Africa and, as a means of sustaining flows, permits granted by the state for the establishment of plantations have required that plantings should be no closer than 20-50 m from streams and other waterbodies. This paper presents the results of three catchment experiments, analysed by the paired catchment method, that aimed to provide a quantitative evaluation of the water yield savings attributable to this practice. These experiments show conclusively that, for South African conditions, riparian vegetation is a more liberal user of water than vegetation in other parts of a catchment and that the clearing of indigenous forest or exotic trees in the riparian zone of the catchment will result in disproportionately greater gains in water yield than would result from clearing similar vegetation elsewhere in the catchment. First year flow increases from clearing of tall woody vegetation in the riparian zone ranged from 55 to 110 mm (9-44%) per 10% of catchment cleared. In the same catchments, clearing of similar vegetation in upslope (nonriparian positions) led to flow increases ranging from 27 to 35 mm (2.5-14%) per 10% of catchment cleared.