Location and General Description
The ecoregion draws its name from the high interior plateau known as the Highveld, and the expansive cover of species-rich communities of grasses. The ecoregion is bordered by the Drakensberg in the east, the arid Karoo and Kalahari in the west, and the low-lying bushveld to the north. The Highveld Plateau is fairly flat with elevations varying from 1,400 m to 1,800 m. The flat topography means that the landscape is traversed by many meandering rivers, with the grassland community historically playing an important role in natural water purification of the westward flowing rivers that originate on the Drakensberg escarpment (Davies and Day 1998). The functioning of this ecosystem has been disrupted in many areas by water transfer projects that have been built to supply greater Johannesburg with water (Davies and Day 1998).
The dominant vegetation comprises grasses, with geophytes and herbs also being well represented. Dominant and diagnostic grass species are Hyparrhenia hirta and Sporobolus pyramidalis. Non-grassy forbs include Acacia sieberiana, Rhus rehmanniana, Walafrida densiflora, Spermacoce natalensis, Kohautia cynanchica, and Phyllanthus glaucophyllus (Bredenkamp et al. 1989; Coetzee et al. 1993; Eckhardt et al. 1993; Fuls et al. 1993; Cowling et al. 1997).
Relatively high rainfall maintains the grasslands during the summer months, with the mean annual range between 400 to 900 mm. Frequent fires, frost, and heavy grazing - formerly by wild animals and now by cattle and sheep – suppress the presence of shrubs and trees (Low and Rebelo 1998). Mean maximum temperatures range from 21 to 24oC, and mean minimums range from 3 to 6o C, with temperatures sometimes reaching 38o C in the summer and –11oC in the winter. Summer rainfall is not evenly distributed throughout the region, resulting in several different habitat types. Differences in habitat types are further accentuated by the variable soil characteristics of the region. Over most of the area sandstones and shales of the Karoo sequence are dominant. Deep red sand-loam soils dominate towards the cooler and wetter northeast, and transition to shallower lithosols in the extreme northeast (Low and Rebelo 1998).
Some dissention surrounds the number of diagnostic habitat types that comprise Highveld Grasslands. Several authors (White 1983; Acocks 1988; Low and Rebelo 1998) prefer detailed subdivision, and others advocate the aggregation of habitat types (Rutherford and Westfall, 1986). Here, the Highveld Grassland ecoregion is divided into three habitat types: (1) Kalahari/Karoo-highveld transition zone; (2) sweet grasslands; and (3) sour grasslands (see also Harrison et al. 1997). In the western half of the ecoregion, a gradual transition occurs from the Karoo/Kalahari-highveld transition zone to the grassland habitats of the Highveld. Shrubs and trees grow in the transition zone, although grasses still dominate. This ecotone borders the sweet grasslands, which occur predominately in areas with lower rainfall. They have low fiber content and retain nutrients in their leaves during the winter. In contrast, sour grassveld species are short and dense, have a high fiber content, and retain nutrients in the roots during the winter, making them largely unpalatable (Rutherford and Westfall 1986).
Although highly fragmented, the Highveld contains the greatest expanse of remaining grassland in southern Africa. Analyses of pollen spores from the Winterberg escarpment suggest that grasses have dominated the floral community since at least the early Holocene (Meadows and Meadows 1988; Meadows and Linder 1993). At times, Highveld grassland types have expanded or contracted in response to climate change. During the Quaternary, grassland expanded in response to glacial events to the north. Global climate change may again alter the ecotonal nature of the Karoo/Kalahari-highveld grassland in the extreme west of the ecoregion, with arid-adapted species of the Karoo/Kalahari ecoregions encroaching onto sweet grassland. Despite the severely degraded nature of the once pristine Highveld Grassland, this ecoregion provides the last remaining stronghold of several grassland species that have suffered major reductions in abundance in the grassland biome (e.g. the blue crane (Anthropoides paradisea) (Allan 1992).
Bird species richness is relatively high within this ecoregion (Harrison et al. 1997). However, Botha’s lark (Spizocorys fringillaris) is the only bird species strictly endemic to the ecoregion, where it inhabits heavily grazed grassland. An additional six species of birds are near-endemics including whitewinged flufftail (Sarothrura ayresii), blue korhaan (Eupodotis caerulescens), southern whitebellied korhaan (Eupodotis cafra), Rudd’s lark (Heteromirafra ruddi), melodious lark (Mirafra cheniana), buff-streaked chat (Oenanthe bifasciatai), and yellow-breasted pipit (Hemimacronyx chloris) (Harrison et al. 1997).
This ecoregion contains a higher number of mammals, although only the orange mouse (Mus orangiae) is restricted to the ecoregion, and the rough-haired golden mole (Chrysospalax villosa) is near-endemic. The ecoregion also supports populations of several large mammal species, some of which are rare in southern Africa (Stuart and Stuart 1995). Among these are the brown hyena (Hyaena brunnea), African civet (Civettictis civetta), leopard (Panthera pardus), sable (Hippotragus niger), pangolin (Manis temminckii), honey badger (Mellivora capensis), striped weasel (Poecilogale albinucha), aardwolf (Proteles cristatus), oribi (Ourebia ourebi), and mountain zebra (Equus zebra hartmannae). Herds of large mammals, including black wildebeest (Connochaetes gnou) and white rhino (Ceratotherium simum), used to occur here, but were extirpated by early settlers.
Relatively few reptile species occur within the ecoregion, mainly due to its cool climate. However, the ecoregion supports some of Africa’s most characteristic reptile species, including Nile crocodile (Crocodylus niloticus), African rock-python (Python sebae), water monitor (Varanus niloticus) and veld monitor (Varanus exanthematicus albigularis). There are also two strict endemic reptiles: giant girdled lizard (Cordylus giganteus), and Agama distanti (Branch 1998). Several additional reptile species are near-endemics, including Drakensberg rock gecko (Afroendura niravia), giant spinytail lizard (Cordylus giganteus), and Breyer's whiptail (Tetrodactylus breyeri) (Branch 1998). Twenty-nine amphibians occur within the ecoregion but none are endemic (Passmore and Carruthers 1995).
The grassland habitat that has remained in a near-pristine state is found mostly in nature reserves. The main protected areas are Valei, Nooitgedacht Dam, Bronkhortspruitdam, Vaal Dam, Willem Pretorius, Rustfontein Dam and Koppies Dam Nature Reserves, and the Ermelo Game Park. Together with a number of smaller reserves, these currently conserve only 0.5 percent of the ecoregion. Even the areas of grassland habitat that have remained in a near-natural state are declining steadily in area and quality. The present state of fragmentation, together with anthropogenic changes planned for the coming years may lead to the extinction or near-extinction of some larger animal species, such as the blue crane (Anthropoides paradisea) (Allan 1992).
Types and Severity of Threats
The Highveld Grassland has suffered extensive degradation. Because it is one of the best areas for farming in South Africa, large tracts of land have already been converted to agriculture, mainly for corn production. Urban expansion, fire, and overgrazing have led to increased fragmentation, as has coal mining and afforestation for stands of exotic trees, especially by species of Eucalyptus (Low and Rebelo, 1998; Cowling et al. 1997). Over several hundred years, particularly around towns, planted wattle (Acacia mearnsii) has become invasive, and is prone to rapid expansion up river watersheds. In the future, expanded surface activity associated with mining below the grassland may become a greater concern as companies develop new technology to make deep mining of coal more profitable (Mallett 1999).
The Highveld plays an important role in natural water purification, as the peat formed here has been shown to filter out 90 percent of the harmful chemicals in herbicides. Peat is also useful in absorbing various other pollutants, as a source of fuel, in horticulture, and for medicinal purposes. In South Africa, where clean water resources are already particularly valuable, this natural filter is being extracted from the Highveld at an unprecedented rate. Approximately 60 percent of locally extracted peat is used to grow mushrooms, while the remaining 40 percent comprises "environmentally friendly" potting soil and compost. Peat has an extremely slow regeneration rate, increasing between 0.7 mm to 1.2 mm per year depending on environmental conditions (Dada 1999). Given its slow formation process, it is unlikely this resource will recover from the damage caused by its rapid removal. Hence, the Highveld’s role as a natural filtration element for scarce water resources could be in danger. The preservation of this resource is imperative, and could be fulfilled by moderating or halting the use of peat for gardening purposes.
Justification of Ecoregion Delineation
This ecoregion, distinguished from surrounding ecoregions by its higher elevations on the Highveld Plateau, follows Low and Rebelo’s (1998) highveld grasslands. These include ‘rocky highveld grassland,’ moist clay highveld grassland,’ ‘dry clay highveld grassland,’ ‘moist sandy highveld grassland,’ ‘ moist cool highveld grassland,’ and ‘moist cold highveld grassland.’ The lumping of these finer units corresponds closely to the ‘Highveld grassland’ vegetation unit of White (1983).
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Prepared by: Rauri Bowie, Aliette Frank
Reviewed by: In progress