Treatment Effects on Annual and Dry Period Streamflow at Cathedral Peak

Abstract

Total annual streamflow and dry season flows of treated catchments at Cathedral Peak, Natal, were compared and related to those of index catchments. Afforestation with Pinus patula Schlech. and Cham, of 74% of a catchment with Themeda triandra Forsk. grass cover reduced streamflow by a maximum of 440 mm in the twenty-second year after planting. The average reduction over a period of twenty-seven years amounted to 257 mm per year. Dry period flow diminished by 15 mm in the twenty-second year after planting. The influence of the trees became evident eight years after planting. Streamflow then diminished markedly until about the nineteenth year whereafter the trend apparently weakened. Streamflow later appeared to rise. Silvicultural treatments of the pine stands showed no detectable effect on streamflow. The exclusion of frequent fires from T. triandra grassland for twenty-five years resulted in seral changes in the vegetation, but no detectable changes in annual and dry period streamflow.