Acacia welwitschii Thickets on Karoo Sediments Gertenbach Landscape 13 - Ecozone G: Delagoa Thorn Thickets on Eca Shale - Delagoa Lowveld
Ironically the prominent species is now no longer
Acacia welwitschii, but
Senegalia welwitschii.
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A narrow band on the Ecca Shales, sandwiched in between the basalts on the eastern side of the Kruger Park and the granites in the west.
Geologically the Kruger National Park can roughly be divided into granite and gneiss in the western half and basalt in the eastern half. Karoo sediments occur where the granite and basalt make contact and this forms a strip that extends from north to south throughout the KNP. The Karoo sediments consist of Cave Sandstone, Red Beds and Ecca-shales. This landscape is limited to the Ecca-shales. The terrain is concave, low lying and reasonably flat with slight slopes.
It extends as a narrow strip from Crocodile Bridge northwards to the vicinity of the Timbavati picnic spot. The thickets are seldom broader than 4 km. Good examples of this landscape can be seen along the tourist roads at Gomandwane and Leeupan.
The general orientation of the spruits and rivers in the KNP are from west to east. Considering that the shales are prone to weathering and erosion it often happens that the spruits running from west to east through granite, turns north or south when reaching the shales. Examples of such spruits in this landscape are the Vurhami, Salitji, Nwaswitsonto and Nsemani. The soils have a strong structure and poor internal drainage with the result that small pans commonly occur. Examples are Leeupan, Nkayapan and Ngumula pan.
The landscape is unique considering that the vegetation is dominated by
Senegalia welwitschii subsp.
delagoensis, a taxon only found in South Africa, apart from certain stands in Eswatini and in the south of Zimbabwe.
The combination of grasses and the variety of forbs show that this landscape is heavily grazed. The grass cover is therefore usually less dense (between 30 and 60% crown cover) and sometimes disappears altogether with the advent of the dry season. The structure of the woody component is a moderate tree savanna with tall shrubs and sparse low shrubs.
This landscape is differentiated by the following species:
Small trees:
Senegalia senegal var.
rostrata Bushy Three-hook Thorn,
Senegalia welwitschii subsp.
delagoensis Delagoa Thorn,
Albizia petersiana Multi-stemmed False-thorn,
Schotia capitata Dwarf Boer-bean,
Spirostachys africana Tamboti,
Pappea capensis Jacket Plum.
Tall shrubs:
Euclea divinorum Magic Guarri,
Maerua parvifolia Dwarf Bush-cherry,
Boscia mosambicensis Broad-leaved Shepherd Tree,
Dichrostachys cinerea subsp.
africana Small-leaved Sickle Bush,
Ehretia rigida Forest Puzzle-bush,
Flueggea virosa White Berry-bush,
Grewia bicolor White Raisin,
Searsia gueinzii Thorny Karee.
Low shrubs:
Abutilon austro-africanum, Justicia flava, Zanthoxylum humile.
Dominant grass species:
Chloris virgata, Panicum coloratum, Panicum maximum, Sporobolus nitens, Aristida congesta, Chloris roxburghiana, Dactyloctenium aegypteum, Tragus berteronianus.
This landscape carries what is possibly the largest biomass of game in the KNP. As a result of the palatable short grazing and open low shrub layer, a large number of impala, wildebeest and zebra are present.
Senegalia welwitschii is a good fodder tree and therefore giraffe, kudu, steenbok and duiker are all present. Elephant breeding herds prefer the dense tree veld and buffalo are continuously on the move through the thickets. White rhino have a strong association with this landscape and waterbuck are often encountered at the pans between the trees. As a result of the high density of prey species, lion and hyaena are plentiful while cheetah are regularly seen.
