Bushwillow Woodlands: Puple Pod, Silver Terminalia Sericea Gertenbach Landscapes 5
Location and Geomorphology… see map below
This landscape is discontinuous due to the fact that it consists of two areas which are separated by Landscape 4 viz, the thickets of the Sabie and Crocodile Rivers. One portion of this landscape occurs in the southern district and the remainder forms the south western part of the Central District as far north as the Orpen / Timbavati area. The geological substrata are granite and gneiss with numerous dolerite intrusions which never exceed 10 metres in breadth (Schutte 1974). This landscape occurs mainly on or close to the watersheds and therefore includes only the upper courses of most spruits viz, the Mbyamite, Mlambane, Nwatimhiri and Nwatimwambu in the southern sub-region and the Nwatindlopfu, Nwaswitsonto, Sweni and Nwanedzi in the northern sub-region. The landscape is undulating with distinct uplands, ecotones and bottomlands. The altitude varies between 350 and 500 m and the landscape occupies 1578 km/2 or 8.1 percent of the KNP.
The landscape has a temperate climate with the occurrence of sporadic frost confined strictly to the bottomlands. The phenomenon of temperature inversions (Oosting 1956) is very distinct in this undulating landscape. During daytime higher temperatures are experienced in the bottomlands than on the uplands, but at night it becomes colder in the bottomlands. Table 3 gives the temperature data for Satara which is also applicable to this landscape. Rainfall varies between 550 and 600 mm per year with the average annual rainfall for Skukuza, Tshokwane and Kingfisherspruit 546.3, 561.3 and 582.3 mm respectively.
Temperature data for Satara … (Data collected since September 1981) …Temperature Degrees C
|Absolute Maximum||Average Daily
This landscape has an interesting and most unique centenary sequence of soils that correspond strongly with position in the topography. The upland soils are sandy with between 6 and 15 percent clay and the dominant soil forms are Hutton and Clovelly with Portsmouth / Swartfontein and Danhere / Makuya respectively as the dominant Series.
Where the slopes become steeper Glenrosa soils can be expected.
Venter (1981) shows a diagrammatic representation of a cantena on granite which explains the situation in this landscape .
Where the convex topography changes into a concave topography conditions of temporary water saturation prevail and gleyed sandy soils are present (Cartref and Fernwood).
Over a period of time an accumulation of clay has taken place in the bottomlands and therefore the soil in the bottomlands has become clayey, often sodium saturated with a massive prismacutanic structure in the underground horizons.
Dominant soil Forms are:
Chemical and mechanical analysis of typical soils in the different positions in the topography are shown in Table 4.
Chemical and mechanical analysis of soils in Landscape 5
The banks of the spruits are formed by recent alluvial soils of which Oakleaf, Dundee and Inhoek are the most important Forms.
The frequent occurrence of dolerite intrusions in the granite of this landscape sometimes has the potential to obscure the catenary sequence, as described above. The soil on the dolerite intrusions is darker in colour (Mayo, Milkwood, Bonheim) and usually much more clayey (15 to 35 percent for the A-horizons). In the vicinity of a dolerite intrusion the weathered material from the dolerite and granite blends and it sometimes happens that the A-horizon originates from dolerite but the B-horizon from granite. These soils accommodate a heterogeneous vegetation that does not always fit in with the recurrent pattern (Mayo, Glenrosa).
The vegetation of this landscape is described under the following names: Combretum-veld (Van der Schijff 1957), Mixed Combretum Savanna Woodland (Pienaar 1963) Combretum-veld on Granite Undulations (Van Wyk 1973). Tropical Semi-Arid Granitic Lowveld(Coetzee 1983) and Arid Lowveld(Acocks 1975). It is an area with dense bush savanna vegetation on the uplands, open tree savanna in the bottomlands and with dense riverine vegetation on the banks of spruits and rivers. The vegetation on the deep sandy soils of the uplands consist of a Terminalia sericea/ Combretum Zeyheri / Combretum apiculatum –community with a dense low and high shrub layer and few or no trees (Fig.13). Dominant woody species are Combretum apiculatum, C. zeyheri, Terminalia sericea, Strychnos madagascariensis, Commiphora africac, Cissus cornifolia, Dischrostachys cinerea subsp. Africana, Sclerocarya caffra, Acacia exuvialis, Dalbergia melanoxylon, Lannea stuhlmannii, Pterocarpus rotundifolius, Acacia burkei, Peltophorum africanum, Ormocarpum trichocarpum and Ziziphus mucronata.
Where the slopes become steeper and the soils more shallow, Strychnos madagascariensis disappears and larger trees such as Sclerocarya caffra, Albizia harveyi and Albizia nigrescens are found. The difference between the two variations of vegetation on the uplands is mainly due to the composition of the field layer. The field layer on the uplands of the landscape is dominated by Pogonarthria squarrosa, Tricholaena monachne, Eragrostis rigidor, Rhynchelytrum repens, Trichoneura grandiglumis, Perotis patens, Brachiaria nigropedata, B. serrata, Aristida argentea, Digitaria eriantha var. pentzii, Panicum maximum, Aristida congesta subsp.barbicollis, A. meridionalis, Schmidtia pappophoroides, Urochloa mosambecensis, Enneapogon cenchroides and Heteropogon contortus. The dominant forbs are Tephrosia polystachya, Commelina bengalensis, Rhynchosia totta, Clerodendrum ternatum, Leucas glabrata, Evolvulus alsinoides, Cassia mimosoides, Waltheria indica, Indigofera filipes, Agathisanthemum bojeri, Kohautia virgata, Cassia absus, Merremia tridentate and Stylosanthus fruticosa. The two variations of the community on the uplands are distinguished by the absence of Strychnos madagascariensis in the Sclerocarya caffra-variation and the following herbaceous plants are limited to the last named variation: Ceratotheca triloba, Cyperus rupestris, Andropogon gayanus, Crotalaria virgulata, Hibiscus micranthus, Phyllanthus asperulatus,
Fig.13. Landscape 5. Upland Mixed Combretum spp. / Terminalia sericea Woodland. –page 29
Fig.14. Landscape 5. Bottomland Mixed Combretum spp. / Terminalia sericea Woodland- page 29
Brachiaria xantholeuca, Cucumis africanus, Tragia dioica and Hermannia boraginiflora.
On the ecotone or seepline where the convex topography changes to a concave topography, a dense fringe of Terminalia sericea trees occur. Other woody species present in this association are Combretum zeyheri, C. apiculatum, Sclerocarya caffra, Maytenus heterophylla, Peltophorum africanum, Albizia harveyi and Acacia gerrardii. The field layer is very similar to that of the uplands except that the following species are also present: Eragrostis gummiflua, Hyperthelia dissolute, Sporobolus fimbriatus, Cyperus sp., Fimbristylis complanata and Epaltes gariepina.
The bottomlands of this landscape are open tree savanna with a dense grass cover if not overgrazed (Fig.14). Gertenbach (in prep.) classifies it as an Acacia nigrescens / Combretum apiculatum association which is comparable to the vegetation of Landscape 4. Depending on the clay content of the soil and the degree of overgrazing the following two sub-associations in the bottomlands of this landscape can be differentiated viz. Aristida barbicollis /Acacia nigrescens / Combretum apiculatum-sub-association and the Acacia gerrardii / Acacia nigrescens / Combretum apiculatum-sub-association.
Dominant woody species for both these sub-associations are Combretum apiculatum, Acacia nigrescens, Combretum hereroense, Dichrostachys cinerea subsp. Africana, Grewia bicolor, Acacia gerrardii, Dalbergia melanoxylon, Lannea stuhlmannii, Ziziphus mucronata, Acacia tortilis, Pterocarpus rotundifolius, Cissus cornifolia, Combretum imberbe, Commiphora africana, Ormocarpum trichocarpum, Ehretia rigida, Albizia harveyi and Bolusanthus speciosus. The difference between the two sub-associations is mainly determined by the composition of the field layer. Grasses normally present in both these sub-associations are Digitaria eriantha var. pentzii, Panicum maximum, Aristida congesta subsp. Barbicollis, Scmidtia pappophoroides, Urochloa mosambicensis, Heteropogon contortus and Enneapogon cenchroides, but more specifically Cymbopogon plurinodis, Eragrostis superba, Bothriocloa radicans and Eragrostis rigidior. In the Aristida barbicollis-sub-association Aristida congesta subsp. Barbicollis, Pogonarthria squarrosa and Andropogon gayanus are more dominant, while Themeda triandra, Urochloa brachyuran and Panicum coloratum are more dominant in the Acacia gerrardii-sub-association.
Characteristic forbs of both the sub-associations of the bottomlands of this landscape are Waltheria indica, Asparagus plumosus, Blepharis integrifolia, Pavonia patens, Hibiscus micranthus, Phyllanthus asperulatus, Tragia dioica, while more common species such as Tephrosia polystachya, Commelina bengalensis, Rhynchosia totta, Clerodendrum ternatum, Cyphocarpa angustifolia and Leucas glabrata also occur. The banks of the spruits have a dense, mostly evergreen, forest community with the following dominant species:Diospyros mespiliformis, Combretum imberbe, Acacia robusta, Euclea divinorum, Lonchocarpus capassa, Schotia brachypetala, Cassine aetiopica and Spirostachys africana. Dominant grasses are Panicum maximum, Digitaria eriantha var. pentzii, Sporobolus fimbriatus with Abutilon guineense as the most common forb.
On the numerous dolerite intrusions that occur in the granite, the woody vegetation immediately becomes more sparse with a denser grass cover. Acacia nigrescens usually occurs in denser stands and Bolusanthus speciosus is a good indicator of doleritic soils. Dominant grasses are Themeda triandra, Bothriochloa radicans and Cymbopogon plurinodis. The plant communities on dolerite can be compared to that of Landscape 19 viz. Thornveld on Gabbro and it is also similar to that occurring in the bottomlands of the landscape.
Time has shown this landscape to be ideal habitat for sable antelope, while kudu and giraffe are well represented. Zebra occur in smaller groups but wildebeest are restricted to dolerite intrusions or brackish soils with sparse grass cover. Elephant and buffalo are commonly found and impala are limited to the spruits where water is available. Small game such as steenbok and duiker are dispersed throughout the landscape. Warthogs(Phacochoerus aethiopicus) are plentiful in the brackish bottomlands where surface water is available. Carnivores such as lion and leopard are present.