Vegetation of the south-western arid Kalahari: An overview

The south-western Kalahari, with rainfall of 150-450 mm p.a., can be described as an arid savanna or semi-arid desert. This area includes the southern Kalahari dunefields which is considered by most authors to have phytogeographical affinities with the Sudano-Zambezian Region, while others classify the area as part of the Nama-Karoo Region. Extensive vegetation maps are available for the Kalahari areas of Namibia and Botswana. For the dunefield area of South Africa, a detailed syntaxonomical vegetation classification, description and mapping of plant communities has been completed. Rainfall is clearly the main determinant of forage production in this environment. Although the vegetation and animal numbers of the south-western Kalahari conservation areas show definite changes in the short to medium term, mainly in reaction to rainfall, a long-term ecological balance prevails at present and should continue if the present large sizes of these conservation areas are maintained. The introduction of boreholes into livestock areas has led to vegetation degradation in the arid areas of southern Africa. However, in the Kalahari conservation areas evidence indicates that vegetation changes are largely regulated by natural events such as rainfall, while grazing impacts are localised and controlled by a natural rotational grazing system. A total of 489 flowering plant species representing 218 genera and 56 families, have been recorded in the Kalahari Gemsbok National Park, an area covering 9593 km(2). Preliminary results indicate that only 1.6% of the plant species is endemic to the south-western Kalahari dunefield. The Kalahari is therefore not a "hot-spot" in terms of richness or rarity (endemism). In spite of the low level of endemism the Kalahari merits conservation because, like other desert areas, it is fragile and vulnerable to the pernicious effects of environmental degradation.