16. EASTERN THORN BUSHVELD

Synonyms:

Eastern Province Thornveld (A7), False Thornveld of Eastern Cape (A21), Invasion of Grassveld by thorn (A22), Eastern Province Grassland (A68); Acacia Savanna, False Thornveld Grasslands.

Statistics:

9 235 km² ; area transformed unknown; 0.45% conserved.

Locality & Physical Geography:

This thornveld occurs along the Eastern Cape coast, extending inland on dry upland ridges above Valley Thicket. It is invaded by thicket and the dominant savanna tree, Sweet Thorn Acacia karroo, is invasive of grasslands.

Climate:

The average annual rainfall ranges from under 450 to 900 mm, chiefly 600 to 750 mm per year, occurring mainly in the summer, but more evenly distributed through the year in the southern parts. Temperatures vary between -2C and 42C, with an average of 18C.

Geology & Soil:

Deep loamy soils derived from shale, mudstone and sandstone of the Beaufort Group of the Karoo Sequence.

Vegetation:

The vegetation is characterised by small (less than 3 m tall) Sweet Thorn Acacia karroo trees and invasive thicket species such as Karoo Bluebush Diospyros lycioides, Karee Rhus spp., Cat-thorn Scutia myrtina, Maytenus polyacantha, and Ehretia rigida. In some rocky areas to the south-west, Fynbos elements such as Flower Rush Bobartia gracilis, Cliffortia linearifolia and Bitter Blombos Selago corymbosa may be present. Grasses are dense and of sourish, mixed type with Redgrass Themeda triandra, Bushveld Dropseed Sporobolus fimbriatus, Fingergrass Digitaria eriantha, Eragrostis curvula, and Tristachya hispida. There is a great variety of herbaceous species including Chamaecrista mimosoides, Mountain Herb Schistostephium crataegifolium, Eriosema kraussianum, Senecio speciosus, Tephrosia macropoda, Monsonia emarginata, Lobelia erinus and Helichrysum odoratissimum. This vegetation type is thus variable, ranging from diverse grasslands with Acacia karroo invasion to dense thickets of A. karroo scrub and depauperate, overgrazed grasslands. In parts of the southern region there is an abundance and diversity of woody species in addition to A. karroo.

Key Environmental Parameters:

Fire and grazing are key determinants of this vegetation type, but soil and climate are also important factors: the summer rainfall in cold, but not very cold, high altitude areas seems to determine the distribution of this vegetation type.

Economic Uses:

Much of this vegetation type is valuable cattle, sheep or goat country.

Conservation Status:

Overgrazing leads to the loss of grass species and the increase of A. karroo and other woody plants. Virtually none of the vegetation is conserved, but with correct farming practices the vegetation type can be considered effectively preserved when grazed.

Key References:

Lubke et al. (1986, 1988).

Authors:

Roy Lubke & George Bredenkamp.