Bushwillow & Mopane Woodland: Timbavati Gertenbach Landscapes 6
Location and Geomorphology
This landscape is located in the triangle formed by the Olifants River, Timbavati River and the western boundary of the KNP. The substratum is mainly granite and gneiss intersected by numerous intrusions of dolerite. This landscape is also intersected by a large gabbro-body which is classified as a separate landscape (Landscape 19). Amphibolite from the Swaziland System occur extensively throughout this landscape (Schutte 1982) and have an important influence on the soil and vegetation. The terrain is undulating and is drained by the tributaries of the Timbavati River of which the Shisakashanghondo, Chalons, Brak, Mbhanswe and Mshatu spruits are the most important.
The altitude of this landscape varies between 300 and 500 metres and it occupies 469.3 km/2 or 2.4 percent of the KNP.
This landscape is subject to a temperate climate with hot summers and cool winters with frost as an exception in the low lying areas. Compare Table 3 for temperature data. Rainfall varies between 450 and 550 mm per year (Kingfisherspruit 582.3mm, Letaba 462.2mm) (Gertenbach 1980).
The soil pattern of the Combretum spp. /Colophospermum mopane Woodland of the Timbavati-area is, to a limited extent, similar to that of the Mixed Combretum spp. /Terminalia sericea Woodland (Landscape 5). As a result of the lower rainfall and the influence of the Swaziland System the uplands are less sandy with Hutton/ - Zwartfontein. Clovelly/Denhere and Glenrosa/Dunvegan as the dominant soils. The seepline is usually absent and the soil becomes increasingly more clayey with the movement towards the bottomlands. The common soils for the middleslopes are glenrosa, but the more clayey series occur in the bottomlands viz, Dothole and Ponda.
At the footslopes Valsrivier and Sterkspruit soils can be expected. Escourt soils occur very rarely. Alluvial soils of the Oakleaf and Dundee Forms can be expected on the banks of the spruits. The occurrence of dolerite intrusions in the granite result in changes in soil type over short distances. Soil Forms normally found on the dolerite intrusions are Hutton/Shigalo, Hutton/Hardap, Swartland/Nyoka and soils with a melanic A-horizon such as Mayo/Tshipise and Milkwood/Sunday. As a result of the presence of materials originating from amphibolite from the Swaziland System (Schutte 1982) in the granite, the soils in certain catenas are redder and more clayey. The presence or absence of amphibolite in a specific catena can thus determine the formation of the soil Form. There are indications (Gertenbach in prep.) that the occurrence of Colophospermum mopane can be correlated with the presence of weathered products of amphibolite in the soils.
On the sandy uplands of pure granite and gneiss in the southern areas of the landscape, Terminalia sericea/Combretum apiculatum communities occur that are very similar to those in landscapes 5, 8 and 11 except in one important aspect and that is the absence of Combretum zeyheri (Fig.15). Normally the vegetation on the uplands is open bush savanna dominated by Combretum apiculatum and Terminalia sericea with the odd individual Colophospermum mopane. The relationship between these two species is very important because as the soil becomes more clayey Combretum apiculatum becomes less dominant and Colophospermum mopane more dominant. Other woody species occurring on the uplands are Albizia harveyi, Dalbergia melanoxylon, Sclerocarya caffra, Cissus cornifolia, Acacia exuvialis, A. burkei, Dichrostachys cinerea subsp. Africana, Commiphora africana and Lannea stuhlmannii.
Fig. 16. Landscape 6. Bottomland Combretum spp. / Colophospermum mopane Woodland of the Timbavati-area. –page 33
Woody species typical of the middle-and footslopes are again Colophospermum mopane (Fig.16) with less Combretum apiculatum and species such as Ormocarpum trichocarpum, Acacia gerrardii, A. nigrescens, Euclea divinorum, Bolusanthus speciosus, Combretum hereroense, C. imberbe, Terminalia prunioides, Grewia bicolor, Maerua parvifolia and Ximenia caffra.
Herbaceous plants in the Field layer which are common for the uplands and bottomlands of this landscape are Pogonarthria squarrosa, Eragrostis rigidior, Aristida congesta subsp. Barbicollis, Digitaria eriantha var. pentzii, Panicum maximum, Enneapogon cenchroides, Heteropogon contortus, Schmidtia pappophoroides, Urochloa mosambicensis, Indigofera floribunda, Rhinacanthus rotundifolius, Cyphocarpa angustifolia, Rhynchosia totta, Indigofera bainesii, Tephrosia polystachya, Ruellia patula, Asparagus plumosus, Corchorus asplenifolius and Hibiscus micranthus. Species associated with the above-mentioned plants and occurring only on the uplands are Tricholaena monachne, Rhynchelytrum repens, Brachiaria serrata, Trichoneura grandiglumis, Waltheria indica, Evolvulus alsinoides, Euphorbia neopolycnemoides, Kohautia virgata, Agathisanthemum bojeri and Fimbristylis complanata. Characteristic herbaceous species for the bottomlands are Themeda triandra, Cymbopogon plurinodis, Eragrostis gummiflua, E. superba, Panicum coloratum, Bothriochloa radicans, Dyschoriste rogersii, Pavonia patens, Vernonia fastigiata and Abutilon austro-africanum.
Riverine vegetation is comparable from landscape to landscape and the following plant species are typical of spruits for landscapes 6, 8, 9, 10 and 11 (Fig. 17): Colophospermum mopane, Combretum imberbe, C. hereroense, Lonchocarpus capassa, Acacia robusta, Albizia harveyi, Diospyros mespiliformis, Schotia brachypetala, Euclea natalensis, Ziziphus mucronata, Dalbergia melanoxylon, Lannea stuhlmannii and Euclea diviorum. Dominant plants in the field layer are Panicum maximum, Urochloa mosambicensis, Cenchrus ciliaris, Abutilon ramosum, A. guineense, Justicia flava, Pupalea lappacea and Achyranthes aspera.
Fig. 17. Landscape 6. Stream bank Combretum spp. / Colophospermum mopane Woodland of the Timbavati-area. – page 34
The dolerite intrusions that occur in the granite are not very broad, but as a result of the mixing of the weathered material of dolerite and granite the influence of the dolerite is sometimes bigger than can be expected. The vegetation structure on these soils derived from dolerite and amphibolite are much the same. It is usually an open savanna with large Colophospermum mopane trees, a moderate shrub layer of 1 to 1.5 metres high and a dense grass cover of Bothriochloa radicans, Themeda triandra, Cymbopogon plurinodis, Heteropogon contortus and Eragrostis superba. The vegetation on the dolerite intrusions are also comparable to that of the granitic bottomlands.
The landscape is suitable habitat for sable antelope, elephant, buffalo, kudu and impala close to the spruits. Zebra occur regularly but in smaller groups of about six individuals. Giraffe are not very common in the mopane-veld, but do occur where the veld is more mixed. Due to the density of the woody vegetation there is a relatively low density of plains preferring game.