14. CLAY THORN BUSHVELD

Synonyms:

Springbok Flats Turf Thornveld (A12), Other Turf Thornveld (A13).

Statistics:

16 302 km²; ± 60% transformed; 0.93% conserved.

Locality & Physical Geography:

Widely distributed on the flat plains with black or red vertic clay soils, south-east of Potgietersrus and Nylstroom in Northern Province, and similar habitats in the northern parts of North-West Province.

Climate:

The summer rainfall is erratic and extremely variable, ranging from 450 to 750 mm per year. Temperatures vary between extremes of -6C and 40C, with an average of 19C.

Geology & Soil:

The soils are characteristically black or red vertic clays, derived from basalt.

Vegetation:

The vegetation is dominated by various Acacia species: Hairy Umbrella Thorn A. tortilis, Scented Thorn A. nilotica, Sweet Thorn A. karroo, A. tenuispina, A gerrardii, A. nigrescens and A. robusta. Other woody species often encountered include Buffalo Thorn Ziziphus mucronata, Sicklebush Dichrostachys cinerea and Wild Raisin Grewia flava. The principal grass species, in a dense sward, are Turf Grass lschaemum afrum, Deck Grass Sehima galpinii, Canary Millet Setaria incrassata and Panicum coloratum. Overgrazing and deterioration of the grass sward causes a serious increase in cover of the woody species, with an associated dominance of Pinhole Grass Bothriochloa insculpta, Three-awn Rolling Grass Aristida bipartita, Sweet Signalgrass Brachiaria eruciformis and Sorghum versicolor.

Key Environmental Parameters:

Extremely clayey soils determine the distribution of this Thornveld.

Economic Uses:

Widely cultivated for crops such as wheat, maize and sunflowers and livestock farming.

Conservation Status:

Poorly conserved in parts of Nylsvley, Mosdene, Potgietersrus and Warmbaths Nature Reserves.

Key References:

Van der Meuien (1979), Van der Meuien & Westfall (1980).

Authors:

Noel van Rooyen & George Bredenkamp.