15. SUBARID THORN BUSHVELD

Synonyms:

Invasion of Grassland by Acacia karroo (A22); Acacia Savanna.

Statistics:

7 708 km²; area transformed unknown; 0.22% conserved.

Locality & Physical Geography:

Found in the relatively low-lying valleys in the drainage basin of the White and Black Kei

Rivers in the Eastern Cape. Acocks considered the area to be Dry Cymbopogon-Themeda Veld, invaded by Sweet Thom Acacia karroo, and a seral stage to Valley Bushveld. Those grasslands which have been invaded, and are now recognized as savanna, occur along the upper Kei Valley around Queenstown, Cathcart and Tarkastad, and on undulating country at the foot of the mountains, in a broad band below the Amatola-Winterberg escarpment, in the vicinity of Somerset East, Bedford and Alice. These valleys are, however, similar to those dominated by Acacia karroo, which occur northwards into KwaZulu-Natal.

Climate:

Rainfall is 500 to 600 mm per year, occurring in summer. Temperatures vary between extremes of -8C and 40C, with an average of 17C.

Geology & Soil:

Clayey loam soil derived from shale, mudstone and sandstone of the Beaufort Group of the Karoo Sequence.

Vegetation:

Sweet Thorn Acacia karroo bushclumps or individuals characterize this type, but the grass layer mostly remains intact, except where severely overgrazed. The most prominent grass species include Redgrass Themeda triandra, Bushveld Turpentinegrass Cymbopogon plurinodis, Weeping Lovegrass Eragrostis curvula, Sporobolus fimbriatus, Heteropogon contortus, Digitaria eriantha and Eustachys paspaloides.

Key Environmental Parameters:

Fire and grazing are ecological processes within this vegetation type. This is a summer rainfall grassland which is invaded by Sweet Thorn Acacia karroo.

Economic Uses:

Mainly grazing.

Conservation Status:

Poorly conserved, mainly in the Ciskei region.

Key References:

Lubke et al. (1986, 1988).

Authors:

Roy Lubke & George Bredenkamp.