The impact of an increasing elephant population on the woody vegetation in southern Sabi Sand Wildtuin, South Africa

Abstract

In 1961, a fence was erected between privately owned Sabi Sand Wildtuin (SSW) and the Kruger National Park (KNP), which largely prevented elephants entering the SSW. In 1993, the fence was removed. This lead to a rapid influx of elephants into the SSW during the winter months, most of which move back into the KNP during the wet summer season. In 1993, the SSW elephant population was 1/1045 ha but increased to 1/305.8 ha in 1996. It more than doubled to 1/146 ha in 1998. This study was undertaken on the property Kingston, in southern SSW, to assess the impact of elephants on woody vegetation and determine why they show seasonal dietary preferences for specific tree parts. Vegetation utilisation was recorded on a five kilometer transect of vehicle track in 1996 and repeated in 1998. From the transect, species density was calculated for those trees impacted on. Trees that had been newly bark stripped were recorded in 1996 and 1998. Cambium samples were collected in summer and winter from eight tree species. Field observations of elephants impacting on woody vegetation augmented the data base. Transect analysis showed a strong correlation between tree utilisation and density. The most visual damage was of Combretum apiculatum, Acacia burkei, Pterocarpus rotundifolius and Grewia species. Tree damage increased by 73 from 1996 to 1998. Significantly higher levels of nitrogen, sodium and magnesium were found in the species most regularly bark stripped. Bull elephants were responsible for 94 of the trees seen uprooted. The results suggested that SSW can sustain the present elephant population, but further influx at the present rate of increase, will have a negative impact on the reserve.