Correlates of stocking rate and overgrazing in the Leliefontein Communal Reserve, central Namaqualand

Abstract

We investigate the correlates of stocking rate in the Leliefontein communal reserve and attempt to provide a mechanistic explanation of the controlling factors. We further speculate on how high stocking rates are maintained in relation to the current state of the rangeland and grazing practices in the region. Stepwise regression revealed that over 80% of the variance in stocking rate could be explained by the mean maximum temperature during the hottest month, February. Deeper investigation revealed that the proximity of the West Coast played an important role in moderating temperature across the reserve. Areas further inland were not only hotter in summer, but were also colder in winter. We speculate that despite large differences in rainfall, the temperature gradient results in a shorter growing season and hence lower productivity of areas further inland. Mean annual rainfall was a very poor predictor of stocking rate and explained less than 5% of the variance in stocking rate across the reserve. Within a single village district, the stocking rate over time was, however. correlated with rainfall over the same period, indicating that stocking rates are determined by primary productivity and are at, or close to, the ecologioal carrying capacity. We further argue that continuous grazing of the lowlands during the growing season has resulted in the lowlands becoming dominated by annuals and unpalatable shrubs. Due to the shallow-rooted nature of annuals, the vegetation has become more sensitive to temperature efficts. The reliability and seasonality of the rainfall in Namaqualand are seen as important factors contributing to the seasonal abundance of annuals and the viability of the current grazing system in the region.

African Journal of Range & Forage Science 17(1, 2&3): 36-45