49. Bushmanland Nama Karoo

Synonyms:

Arid Karoo (A29), False Succulent Karoo (A39).

Statistics:

83 195 km²; area transformed unknown; 0.03% conserved.

Locality & Physical Geography:

Occurring in some of the most arid parts of South Africa where the topography is generally flat and most of the region lies at about 900 m. The gently sloping gradients, from the escarpment in the south to the Orange River in the north, result in numerous brack, silty flats ("vloere") such as Groot Vloer or Verneuk Pan.

Climate:

Rainfall is between 50 and 200 mm, occurring predominantly in autumn.

Geology & Soil:

Quaternary sands and Karoo Sequence shales which give rise to weak and structureless clay and sandy soils.

Vegetation:

Structurally Bushmanland Nama Karoo is dominated by annuals and non-succulent shrubs - this type has the highest proportion of annuals of all the Nama Karoo types. In the more sandy parts of this region the vegetation is dominated by Cauliflower Ganna Salsola tuberculata and after good summer rains by Small Bushman Grass Stipagrostis obtusa and Tall Bushman Grass S. ciliata. In more rocky areas, Thorny Kapokbush Eriocephalus spinescens, Thorn Vygie Eberlanzia spinescens, and especially Threethorn Rhigozum trichotomum, are important species. Annuals, such as Pentzia annua and Brakspekbos Zygophyllum simplex, are common and together with geophytes comprise nearly 50% of the total number of species in the region.

Key Environmental Parameters:

The low, unpredictable rainfall is highly patchy, occurring under the paths of the rare summer thunderstorms. Historically, Springbok and other game moved between the "green spots" where grasses grew following these rains. Winter cyclonic rain from cold fronts is low, and favours shrub growth rather than grasses.

Economic Uses:

This was one of the last vegetation types to be colonized by Europeans. There was a rapid increase in stock in the region around the First World War, so that the long-term effects of heavy grazing are probably still to be discovered. It is used mainly for small-stock farming: almost exclusively Dorpers and Karakul Sheep, and Boer Goats.

Conservation Status:

Very poorly conserved - no major conservation areas occur within this type, but sustainable grazing should result in almost all the species being effectively conserved. Unfortunately, there is evidence of overgrazing in many areas. Riverine areas are seriously invaded by Mesquite Prosopis glandulosa and Threethorn Rhigozum trichotomum, mainly in areas which are heavily grazed.

Key Reference:

Acocks (1988).

Author:

Timm Hoffman.