34. Rockey Highveld Grassland

Synonyms:

Bankenveld (A61); Moist Cool Temperate Grassland; Rhus leptodictya-Acacia caffra Mountain Bushveld, Loudetia simplex-Trachypogon spicatus Grassland.

Statistics:

24 063 km²; ± 65% transformed; 1.38% conserved.

Locality & Physical Geography:

This is a transitional type between typical grasslands of the high inland plateau, and the bushveld of the lower inland plateau. It stretches from Lichtenburg to Middelburg in the east, including the southern slopes of the Magaliesberg, the ridges of the Witwatersrand and the dolomite plains of Gauteng and North-West Province, mainly between 1 500 to 1 600 m in altitude.

Climate:

Summer rain between 650 to 750 mm per year. Temperatures vary between -12°C and 39°C, with an average of 16°C.

Geology & Soil:

The habitat is rocky mountains, hills, ridges and plains of quartzite, conglomerate, shale, dolomite and sometimes andesitic lava.

Vegetation:

Characteristic grass species are: Giant Speargrass Trachypogon spicatus, Broadleaf Bluestem Diheteropogon amplectens, Red Autumngrass Schizachyrium sanguineum, Andropogon schirensis, Loudetia simplex, Tristachya leucothrix, Panicum natalense, Bewsia biflora, Digitaria tricholaenoides, D. monodactyla and Sporobolus pectinatus. Many dicotyledonous forbs occur in this vegetation type, including Wild Sweetpea Sphenostylis angustifolia, Rough-hair Sage Acrotome hispida, Broom Ragwort Senecio venosus, S. coronatus, Justicia anagalloides, Pentanisia angustifolia, Pearsonia cajanifolia, Indigofera comosa, Xerophyta retinervis, Acalypha angustata, Vernonia oligocephala, the xerophytic Parsley Fern Cheilanthes hirta and the leafy succulent Crassula lanceolata. A Drakensberg (Afromontane) affinity can clearly be seen in the presence, and often abundance, of grass species such as Caterpillar Grass Harpochloa falx, Sickle Grass Ctenium concinnum, Toothbrush Grass Rendlia altera, Alloteropsis semialata and Monocymbium ceresiiforme while non-grassy forbs showing this affinity include Wild Squill Scilla nervosa, Bluntleaf Currant Rhus rehmanniana, Gwarrie R. discolor, Vernonia natalensis, Berkheya setifera and Helichrysum oreophilum. Woody vegetation, of Zambezian and Afromontane affinity, occurs as sheltered islands of temperate mountain bushveld within the Grassland Biome. Typical species include Common Hook Thorn Acacia caffra, Mountain Karee Rhus leptodictya, Common Wild Currant R. pyroides, R. rigida, R. magalismontana, R. zeyheri, Ehretia rigida, Maytenus heterophylla, Euclea crispa, Zanthoxylum capense, Dombeya rotundifolia, Protea caffra, Celtis africana, Ziziphus mucronata, Tapiphyllum parvifolium, Vangueria infausta, Canthium gilfillanii, Englerophytum magalismontanum, Combretum molle, Ancylobotrys capensis, Olea europaea subsp. africana and Grewia occidentalis.

Key Environmental Parameters:

Acocks interpreted Bankenveld as a fire-maintained grassland, which would develop into savanna if fire was excluded. Frosts during winter play the most important role in the distribution of the woody elements in this transitional zone. Grassland vegetation is restricted to exposed sites in the irregular, undulating, high-altitude landscape, especially on the crests of rocky hills and ridges.

Economic Uses:

Maize production is limited due to the shallow, rocky soils. Grazing by cattle is often found in this vegetation type, but the dominance of sour grass species often results in a low nutrient status of the grass during winter.

Conservation Status:

In the Gauteng area the vegetation is highly threatened by urbanization, industrialisation and mining, and, to a lesser degree, agriculture. Poorly conserved in the Suikerbosrand, Rustenburg, Abe Bailey and Boskop Dam Nature Reserves, and several smaller reserves managed by local authorities within the metropolitan area.

Key References:

Morris (1976), Bredenkamp & Theron (1980), Coetzee et al. (1993), Bezuidenhout et al. (1994a), Coetzee et al. (1995).

Authors:

George Bredenkamp & Noel van Rooyen.