Investigating long-term (> 35 year) woody vegetation change around watering points in the Kalahari Gemsbok National Park

By Dr Helga van der Merwe (SAEON) and Dr Hugo Bezuidenhout (SANParks) Tweet

From 1978 onwards, numerous surveys have been conducted in the Kalahari Gemsbok National Park to gain insight into the medium- and long-term changes in the vegetation, in particular within the piosphere surrounding artificial watering points.

The hypothesis is that provision of artificial watering points generally promotes heavy concentrations of wildlife around the watering point, resulting in the degradation of herbaceous vegetation and bush densification.

Woody species most commonly associated with bush densification in the Kalahari environment are Senegalia mellifera (Ξ Acacia mellifera), Rhigozum trichotomum and Grewia flava. Vachellia erioloba (Ξ Acacia erioloba) is also often mentioned as a plant species that could densify in this region.

Artificial watering points have been provided in the Kalahari Gemsbok National Park since the 1930s and the long-term impact of these watering points on the vegetation is unknown for such a large conservation area (9 600 km^²).

Piosphere (area denuded of vegetation) around an artificial watering point in the Kalahari Gemsbok National Park (Photo: Helga van der Merwe) Undisturbed Kalahari vegetation away from an artificial watering point (Photo: Helga van der Merwe)

Investigating changes in the vegetation

This study aimed to establish whether densification in the park occurred over time at the Dankbaar artificial watering point, opened in 1959, compared to two sites about 5 km from the watering point. Additionally, change in woody species composition and density was investigated to determine whether any directional trends were evident after nearly four decades.

The study found that regardless of distance from the watering point, the density of large Vachellia erioloba and Vachellia luederitzii (Ξ Acacia luederitzii) individuals decreased with successive surveys. This long-term study over more than 35 years shows that no evidence of bush densification was found at the artificial watering point for any of the species known to densify in the southern Kalahari.

Vegetation dynamics in this large conservation area therefore differ from those found in agricultural landscapes, where bush densification is common. Additionally, it was determined that after nearly four decades, woody vegetation composition showed only a slight directional trend at one site away from the watering point.

Good collaboration

The good collaboration between SANParks and SAEON has enabled the renewal of existing datasets, allowing for the analysis and interpretation of data to better understand vegetation dynamics in the Kalahari environment.