SOUTH-AFRICA ARID AND SEMIARID RANGELANDS - WHY ARE THEY CHANGING ANDCAN THEY BE RESTORED

Since the mid-19th century settled livestock ranching has been the maj or form of land use in South Africa, occupying 68% of the land surface . Decreases in livestock densities and ranch numbers during the past c entury imply that carrying capacities for domestic herbivores are fall ing. Differences in carbon isotope signals with soil depth and abrupt shifts in dominant plant species across ranch boundaries reveal that s outhern African rangelands are changing. Case studies suggest ways to control altered grassland composition, bush encroachment in arid savan na, and dominance by toxic and halophytic shrubs in arid shrublands. B ut climatic and biological factors constrain rates of passive recovery , and guidelines for active restoration are poor and techniques costly . Moreover, conservation of remaining good rangeland is seldom enforce d, and economic considerations usually outweigh the land user's desire to sustain diversity and productivity.