Large Numbers of Kudu, Sable Antelope Present | Dwarf Acacia nigrescens ( Knob Thorn Tree) Savanna Landscape
Dwarf Acacia nigrescens ( Knob Thorn Tree) Savanna Favours Kudu Herds
Location and Geomorphology
The basalts in the vicinity of the watershed between the Olifants and Nwanedzi Rivers north of Satara contain a lot of amygdales and olivine and decompose to form dark coloured soils. The area is reasonably flat to concave, high lying plains and is drained by the Mtomeni, Mapetane and Gudzane spruits, Shitsalaleni is a well known pan in this area. The altitude varies between 250 and 300 metres and the landscape is relatively small (356 km/2 or 1.8 percent of the KNP).
The largest concentration of kudu in the KNP is present in this landscape and the role they play in stunting the small knobthorn trees should not be disregarded. A few groups of sable antelope occur in this part of the KNP. Zebra, impala, wildebeest, giraffe, waterbuck and warthog occur regularly but in lower densities.Elephants are relatively scarce but herds of buffalo are constantly moving through this area. Lion, hyaena and cheetah occur regularly but not in large numbers.
According to Gertenbach (1980) this area receives between 500 and 550 mm of rain annually and the temperature is comparable to that of Satara which is given in Table 3.
The catenary sequence of soils in this landscape include the occurrence of darkly coloured clayey soils on the uplands with dominant Forms Swartland, Bonheim, Milkwood and Mayo. The percentage of clay in the A- horizons varies between 15 and 35 percent and the pH between 5.6 and 6.8 (Coetzee 1983). The B-horizons contain between 35 and 55 percent clay and the pH varies between 6.1 and 7.7. In situations where there is a concave topography clayey soil of the Arcadia Form can be expected. These are soils with dark coloured vertic characteristics that sometimes granulate spontaneously on the surface.
The vegetation of this landscape varies from a pure grass veld on the vertisols and calcrete soils, to a stunted Acacia nigrescens savanna on the middleslopes (Fig. 42). Where pure grass veld occurs on the uplands it is dominated by Themeda triandra, Bothriochloa radicans, Digitaria eriantha var. pentzii, Panicum coloratum, P. maximum, Enneapogon cenchroides, Ischaemum brachyatherum, Sorghum versicolor, Schmidtia pappophoriodes, Urochloa mosambicensis and Cenchrus ciliaris. Shrubs that sporadically occur are Acacia nigrescens, Ehretia rigida, Cordia sinensis, Ormocarpum trichocarpum, Securinega virosa, Acacia tortilis, Dichrostachys cinerea subsp. africana and Ziziphus mucronata.
On the slopes where the soil is less clayey the above-mentioned woody plants occur more commonly and a dense low tree savanna dominated by Acacia nigrescens is characteristic. These small trees have a single stem and are usually between two and four metres high. The stunted growth form of the trees can be attributed to slow growth as a result of high moisture retention in the soil, combined with the high grass cover and regular occurrence of hot fires. The same limiting factors probably
Fig. 42. Landscape 18. Dwarf Acacia nigrescens Savanna. – page 70
play a role in Colophospermum mopane becoming a shrub in Landscape 23. A characteristic of this landscape is the occurrence of many upright dead tree trunks. The reason for this phenomenon is not clear, but drought probably played an important role.
Vertisols of the Arcadia Form develop in the bottomlands and they contain a large amount of soluble salts. Grasses such as Setaria woodii, Ischaemum brachyatherum, Panicum maximum, Digitaria eriantha var. pentzii, Brachiaria eruciformis and Urochloa mosambicensis usually occur here. Close to the spruit Sporobolus consimilis occur generally and can reach a height of two metres. A unique component of this landscape are stands of Acacia borleae which occur on the brackish vertisols. The dense stands are approximately one to two metres high and almost impenetrable. Acacia borleae is the sole dominant and the following woody species occur sporadically: Azima tetracantha, Cadaba natalensis, Maerua parvifolia, Capparis tomentosa, Boscia mossambicensis and Cordia ovalis. The following plants occur in the field layer: Canchrus ciliaris, Sporobolus smutsii, Sanseviera hyacinthoides, Cyathula crispa, Neuracanthus africanus, Asparagus minutiflorus, Abutilon guineense and Cienfuegosia hildebrandtii.