Changing predictors of spatial and temporal variability in stocking rates in a severely degraded communal rangeland

Abstract

Changes in vegetation and soils under heavy continuous grazing have been widely documented, but the effects of these on secondary production are debated. Sterkspruit is one of South Africa's most degraded districts, and soil erosion in the district increased substantially over the twentieth century. Despite this, records dating to the late-1800s show no decline in livestock numbers. This study explores how high stocking rates have been maintained despite an apparent deterioration in the natural resource base. Multiple regression analyses were used to determine the best predictors of stocking rates in 1974, the 1980s and 1997 to determine whether the relative importance of mean annual rainfall and winter temperature (indicative of primary production), the percentage of area on nutrient-poor sandstone-derived soils (representing a dry season nutritional bottleneck), the percentage of an area on steep slopes (which make areas less accessible to livestock) and human population density and availability of arable land (indicative of potential inputs) had changed over time. While mean annual rainfall was the best predictor of stocking rates in 1974, stocking rates in the 1980s and 1997 were best predicted by human population densities. This suggests that a qualitative shift in how livestock populations are maintained has taken place. © 2010 John Wiley & Sons, Ltd..