Long-term vegetation change in the Succulent Karoo, South Africa following 67 years of rest from grazing

Abstract

Changes in species richness and vegetation composition in the diverse semi-arid Succulent Karoo vegetation of South Africa were investigated after 67 (1937–2004) years of rest from livestock grazing at the Worcester Veld Reserve (WVR). This 72 ha reserve lies in the Worcester-Robertson Valley, 140 km east of Cape Town, South Africa (33°39′S and 19°27′E). Vegetation change in 35 plots located on termitaria and 35 plots located in the insterstices between termitaria was assessed using field survey data and multivariate ordination techniques. Changes in plant cover and species composition on termitaria sites were consistently greater than for adjacent off termitaria sites. In addition, the north-facing slopes changed more than the south-facing slopes. There was a higher increase in diversity for off termitaria sites than for on termitaria sites. On termitaria, there was a general decrease in stem succulents, particularly Euphorbia mauritanica and an increase in long-lived evergreen shrubs and trees such as Pteronia incana and Rhus undulata. Most sites had similar compositional shifts primarily determined by their association with termitaria and secondarily with aspect. These findings suggest that a consistent directional change in vegetation composition has taken place as a result of protection from grazing. Contrary to the widely held view that a release from grazing has little benefit in degraded semi-arid vegetation, we find that a significant and predictable directional response to rest has occurred at this site over the study period.