Bushwillow & Large-fruited Bushwillow Woodland Gertenbach Landscapes 3
Location and Geomorphology
This landscape is situated along the upper course of the Mbyamide River in the central southern district between the Sabie and Crocodile Rivers. It covers approximately 540 km/2 which represents 2,8 percent of the KNP. The underlying granite and gneiss is deeply weathered resulting in a undulating landscape with distinct uplands and bottomlands. The area is drained exclusively by the Mbyamide River and its tributaries. The altitude varies between 450 and 550 metres above sea level.
The climate is mild and the absence of frost is an important characteristic. Temperatures of about 40 o/c in the summer is not usual. The average rainfall varies between 600 and 700 mm per year and occurs mainly during the summer. The temperature data for Pretoriuskop (Table 1) is also applicable to this landscape.
Venter (1981) describes the soil of the uplands in this landscape as red, course, fersiallitic sands and loams. Harmse & Van Wyk (1972) classified the soil on the uplands mainly as Hutton and Clovelly Forms with Portsmouth and Paleisheuwel rewspectively as the dominant Series. The soil is deeply leached and has good internal drainage. The soil pattern differs from that of the Lowveld Sour Bushveld (Landscape 1) in that a definite ecotone is present.
There is a definite seepline where the topography changes from convex to concave and superfluous rainwater that has fallen on the uplands move downlands and laterally to appear on the surface. These soils are saturated with water in the rainy season and gleyed horizons are present (Fig.7). It is in this seepline that temporary springs originate during the rainy season. Dominant types of soil under these conditions are Escourt, Kroonstad, Cartref, Wasbank and Longlands. These types of soil are generally classified as duplex soils.
Fig.7. Diagrammatic representation of a granite undulation.
Accumulations of clay and minerals have taken place in the bottomlands. The result is that the bottomland soils are clayey and have a high concentration of mineral salts. Soils commonly present in the bottomlands are Valsriver, Swartland, Sterkspruit, Glenrosa, Wasbank, Cartref and Escourt. On the banks of the spruits, under-developed soils of the Oakleaf and Dundee Forms (Fig.7) can be expected. This sequence of soil types from the upland to the bottomland is referred to as a catenary sequence and is usually constant for a specific landscape. That is why Coetzee (1983) as quoted in the introduction included the phrase “recurrent pattern” in the definition. Expectations to this normal sequence of soil types do occur, but are not sufficiently important to justify the creation of a new “landscape”.
As is indicated by the name of the landscape, the vegetation on the uplands is dominated by Combretum collinum subsp. suluense and C. zeyheri (Fig.8). This is a relatively dense bush savanna between 1 and 5 metres in height with larger trees sparsely dispersed. Other woody species occurring constantly on the uplands are as follows: Terminalia sericea, Combretum apiculatum, Dichrostachys cinerea subsp. Nyassana, Strychnos madagascariensis, Peltophorum africanum, Combretum molle, Pterocarpus rotundifolius, Maytenus heterophylla, Sclerocarya caffra, Acacia exuvialis, Dalbergia melanoxylon and Xeromphis obovata.
The field layer is moderate to dense, less than 1 metre in height and is dominated by Pogonarthria squarrosa, Tricholaena monachne, Hyperthelia dissolute, Setaria flabellate, Loudetia simplex, Eragrositis rigidior, Trichoneura grandiglumis, Perotis patens, Brachiaria nigropedata, Digitaria eriantha subpsp. pentzii, Panicum maximum,
Fig.8. Landscape 3. Upland Combretum collinum / Combretum zeyeri Woodland -page 19
Aristida congesta subsp. Congesta, A. congesta subsp. Barbicollis, Heteropogon contortus and Rhynchelytrum repens. Forbs in the field layer include the following: Waltheria indica, Agathisanthemum bojeri, Kohautia virgata, Tephrosia polystachya, Clerodendrum ternatum and Rhynchosia totta. The vegetation which occurs on the ecotone is dominated by an almost homogeneous stand of Terminalia sericea. The field layer is dense, up to 1 metre high and includes the following species: Eragrostis gummiflua, Pogonarthria squarrosa, Hyperthelia dissolluta and Epaltes gariepina.
Fig.9. Landscape 3. Ecotone and Bottomlands Combretum collinum/ Combretum zeyheri Woodland -page 20
The nutritive clayey bottomlands (Fig.9) are open savannas with a dense grass layer. Because of the sweeter nature of the grass in these bottomland areas, these parts are the first to be overgrazed and therefore are the first to show signs of retrogressive succession. The most important woody species are Acacia nigrescens, A. nilotica subsp. Kraussiana, Ormocarpum trichocarpum, Acacia gerrardii, Combretum hereroense, Grewia bicolor, Euclea natalensis, Ziziphus mucronata, Grewia hexamita, Albizia harveyi, Acacia exuvialis, with Spirostachys Africana, Cassine aethiopica, Euclea divinorum, Schotia brachypetala, Pappea capensis and Diospyros mespiliformis which are limited to the brackish footslopes. The field layer is dense with the following important species: Themeda triandra, Digitaria eriantha subsp. Pentzii, Heteropogon contortus, Cymbopogon plurinodis. Eragrostis superba, Enneapogon cenchroides, Aristida subsp. Barbicollis, Schmidtia papophoroides and Urochloa mosambicensis. On the brackish footslopes Dactyloctenium aegyptium and Sporobolus nitens are dominant. Dominant forbs are Heliotropium steudneri, Abutilon austro-africanum, Ruellia patula, Justicia flava, Blepharis integrifolia and Cyphocarpa angustifolia
The riverine vegetation is very heterogeneous but the most common species are: Diospyros mespiliformis, Spirostachys Africana, Lonchocarpus capassa, Combretum imberbe, Schotia brachypetala, Acacia robusta, Cassine aethiopica and Euclea natalensis. The grass layer is dominated by Panicum maximum.
This landscape is preferred habitat for sable antelope, buffalo, kudu, white rhino, reedbuck and elephant, while smaller antelope like steenbok ( Raphicerus campestris) and duikers occur constantly. Zebra are widely distributed forming groups of four or six individuals while wildebeest are normally absent from this landscape.