latitudi-Conservation value of the Egoli Granite Grassland, an endemic grass-land in Gauteng, South Africa

Gauteng is the most densely populated province in South Africa. Its remaining natural areas are constantly under threat from urban development and the associated impacts. Presently, the natural areas of Gauteng support a large diversity of ecosystems. One such ecosystem is the Egoli Granite Grassland, endemic to the province, poorly conserved and therefore highly threatened. This paper describes the original Egoli Granite Grassland and the anthropogenic Hyparrhenia hirta dominated grassland that has replaced it in many of the remnant areas. Human impacts on this sensitive ecosystem have resulted in an altered species composition, loss of many species, and a change from a species-rich grassland with high conservation value to a species-poor grassland with low conservation value. The conservation of the last remaining relicts of original Egoli Granite Grassland is essential.


Introduction
The Egoli Granite Grassland is a type of grassland and a mapping unit (Gm10) classified under the Mesic Highveld Grassland Bioregion according to the new Vegetation Map of South Africa, Lesotho and Swaziland (Mucina et al. 2005).This grassland was mapped as Bankenveld (veld type 61) by Acocks (1988), and Rocky Highveld Grassland (Vegetation Type 34) by Bredenkamp & Van Rooyen (1996).Acocks (1988) describes the Bankenveld as a False Grassveld Type.The climax vegetation of this veld type should be, according to Acocks, an open savanna, that is a bushveld vegetation, but it has been changed to, and maintained as grassveld by regular veld fires.However, Bredenkamp & Brown (2003) consider Bankenveld vegetation as a mosaic of grassland and woodland communities controlled by (micro-)climatic conditions that exist in the topographically heterogeneous landscape in the transition zone between the Grassland and Savanna biomes.
From a conservation planning or urban development viewpoint, the range of structural and floristic variation is considered too large to define Bankenveld as a single unit, even on the reconnaissance level of vegetation investigation.Bredenkamp & Brown (2003) recognised 16 major vegetation types within Bankenveld.The Egoli Granite Grassland is considered as mainly belonging to the Hyparrhenia hirta Anthropogenic Grassland (Bredenkamp & Brown 2003).
Egoli Granite Grassland is restricted to the Gauteng Province of South Africa and is located north of the Roodepoort / Krugersdorp ridge complex and stretches over a distance of approximately 35 km to Centurion in the north.This grassland stretches over a distance of approximately 50 km in a westerly direction from the R21 highway in the east.The 28º longitude and 26 º latitudi-Conservation value of the Egoli Granite Grassland, an endemic grassland in Gauteng, South Africa G.J. Bredenkamp, L.r. Brown and m.F.pFaB Bredenkamp, G.J., L.R. Brown and M.F. Pfab. 2006.Conservation value of the Egoli Granite Grassland, an endemic grassland in Gauteng, South Africa.Koedoe 49(2): 59-66.Pretoria.ISSN 0075-6458.
Gauteng is the most densely populated province in South Africa.Its remaining natural areas are constantly under threat from urban development and the associated impacts.Presently, the natural areas of Gauteng support a large diversity of ecosystems.One such ecosystem is the Egoli Granite Grassland, endemic to the province, poorly conserved and therefore highly threatened.This paper describes the original Egoli Granite Grassland and the anthropogenic Hyparrhenia hirta dominated grassland that has replaced it in many of the remnant areas.Human impacts on this sensitive ecosystem have resulted in an altered species composition, loss of many species, and a change from a species-rich grassland with high conservation value to a species-poor grassland with low conservation value.The conservation of the last remaining relicts of original Egoli Granite Grassland is essential.
G.J. Bredenkamp, African Vegetation and Plant Diversity Research Centre, University of Pretoria;L.R. Brown, Applied Behavioural Ecology and Ecosystem Research Unit, University of South Africa;M.F. Pfab, Bioregional Planning, Gauteng Department of Agriculture, Conservation and Environment, Johannesburg, 2001 South Africa.nal lines cross in the centre of this grassland (Fig. 1).
Due to high demand for developable land in Gauteng, and especially the Johannesburg / Pretoria corridor, the Egoli Granite Grassland is under extreme pressure.Large areas are already developed for residential, industrial and commercial purposes.This has led to the destruction of vast tracts of this grassland.At least 61 % of Egoli Granite Grassland has been permanently transformed: 27 % by urban development (Fig. 2); 17 % by smallholdings; 12 % by agriculture (cultivated lands); and 5 % by other impacts such as exotic plantations, mining and planted pastures.An estimated additional 17 % of Egoli Granite Grassland is degraded due to overgrazing and the influence of edge effects associated with a highly fragmented landscape (Fahrig 2003).Other effects, such as trampling, increased pollutants and the infestation of weeds and alien species also contribute to degradation of this grassland.It is therefore highly likely that the national target for conservation of this grassland type, i.e., 25 % of the total extent, will never be realised.
Egoli Granite Grassland is extremely poorly conserved, with only 0.02 % (26 ha) of the vegetation type currently protected, includ-ing 3 ha in Glen Austin Bird Sanctuary, 3 ha in Melville Koppies Nature Reserve, 9 ha in Ruimsig Nature Reserve, and 11 ha in the Walter Sisulu Botanical Gardens (Fig. 2).The current protection status of Egoli Granite Grassland is therefore completely inadequate, with only 0.1 % of the national target actually achieved.In order to meet South Africa's international obligations, it is imperative that the Gauteng provincial government put in place measures to improve the conservation status of Egoli Granite Grassland.
Any viable remnant patch of original Egoli Granite Grassland must therefore be protected from transforming land uses.In order to assess whether a valuable remnant patch will be affected by a proposed development, environmental consultants involved in vegetation impact assessments are required by the Gauteng Department of Agriculture, Conservation and Environment (GDACE) to assess the presence and condition of Egoli Granite Grassland on any site proposed for development.
As this grassland was only recently defined with the development of the new Vegetation Map of South Africa, Lesotho and Swaziland (Mucina et al. 2005), very little information on its floristic composition, condition, the extent of the grassland, and the management thereof exists, causing some confusion among nature conservationists, environmental consultants and local authorities.The aim of this paper is therefore to provide an ecological overview of this grassland.

Physical Environment
This area is generally characterised by rocky undulating plains representing crests, slopes and valley bottoms with shallow, nutrientpoor soils.Shallow drainage lines and vleilike wetland areas occur in the valley bottoms.Rockiness of the soil surface is a further common characteristic shared by most Bankenveld areas.
Mean monthly temperature in the study area is 16.8 º C with a mean maximum of 22.6 º C and a mean minimum of 10.8 º C. The mean winter temperature is 13.8 º C and mean summer temperature, 25.6 º C (Weather Bureau 2000; Grobler et al. 2002).Mean annual rainfall in Gauteng is 670 mm (Gauteng 1997).
Old granitic and gneissic rocks at least 2 400 million years old (Kerfoot 1987) are exposed in the Egoli Granite Grassland area.The Halfway House Granites (Fig. 3) of the Johannesburg Dome are intensively weathered with deep drainage lines resulting in a gently rolling topography, with shallow, coarse, nutrient-poor, well-drained soils.The granite areas are mostly covered by grassland vegetation though patches of woodland vegetation are found at sheltered sites on hillslopes and rocky outcrops within this veld type (Grobler 2000;Grobler et al. 2002Grobler et al. , 2006)).
The Bb land type predominates over the entire region (Land Type Survey Staff 1984, 1985, 1987) (Fig. 3).The residual granitic soils are very shallow and poorly drained.The A horizon is often sandy and light in colour with little organic matter and with an increase in clay content with depth.The soils are invariably acid and very rich in silica (Kerfoot 1987).

Current vegetation
This tall grassland occurs over vast areas, usually on shallow, leached soils on the Johannesburg Granite Dome.Disturbed grassland or other disturbed areas such as road reserves or old fields, not cultivated for some years, are also usually Hyparrhenia species-dominated and low in species richness.Although some of these tall grasslands appear to be quite natural, they are mostly associated with an anthropogenic influence from recent or even iron-age times.

Original vegetation
The original vegetation is thought to be typical Bankenveld (Acocks 1988) or Rocky Highveld Grassland (Bredenkamp & Van Rooyen 1996).Bredenkamp & Brown (1998) found a few relict sites which indicate that the original vegetation on the shallow granitic soils of the Johannesburg Granite Dome could have been a variant of the Monocymbium ceressiforme-Loudetia simplex Grassland (Bredenkamp & Brown 2003).This vegetation is found in areas where little or no disturbance is evident.
The woody layer consists mainly of a few scattered individuals of the trees Rhus pyroides, R. leptodictya, Ziziphus mucronata, the dwarf shrubs Protea welwitschii, Lopholaenia coriifolia, and the geoxylophyte Parinari capensis that are locally prominent.The grasses Panicum natalense, Urelytrum agropyroides, Tristachya leucothrix, Cymbopogon excavatus and Elionurus muticus are also abundant together with the forbs Cyanotis speciosa, Bulbostylis burchellii, Crabbea acaulis, Anthospermum hispidulum and Senecio venosus.The grass Hyparrhenia hirta is often present and may become more prominent at disturbed sites.This grassland is characterised by a high species richness with a patchy dominance of

Origin of the current vegetation
The shallow, nutrient-poor soils provide a habitat suited to the climax vegetation as discussed previously.Some nutrients are available in the topsoil, supplemented from fallen leaf litter and decomposition, and also from ashes of burned herbaceous layer (if there was a fire).Nutrients are quickly utilised by plants and are furthermore also quickly leached from the very coarse sandy soils.Nutrient cycling is therefore very rapid.
The system is quite stable and fairly predictable without much change caused by normal droughts or grazing.However, if overgrazed or disturbed to such an extent that degradation proceeds beyond a threshold, then recovery is very slow, due to reduced nutrient cycling and decreased nutrient availability and the vegetation may change to another domain of attraction (Bosch 1989), different from the original climax vegetation, representing a plagioclimax (Fig. 4).A change back to the original domain of attraction is unlikely if not impossible in the short and medium term.Due to the granitically derived shallow nutrient poor soils these systems are sensitive and intolerant to frequent impacts such as heavy grazing, ploughing, trampling and general domestic activities.Thus degradation occurs easily resulting in a change from the climax (high species richness) vegetation to an anthropogenic Hyparrhenia hirta (low species richness) dominated vegetation type.
Very often Hyparrhenia species-dominated grasslands occur on ancient lands in the Central Variation of the Bankenveld (Acocks 1988) and in the surroundings of archaeological sites (Bredenkamp & Brown 2003), where the inhabitants had a mosaic of cultivated lands and grazing of domestic stock.
The more recent European settlers also had a profound effect on the natural vegetation as they developed the cities of Johannesburg and Pretoria following the discovery of gold more than a century ago.It seems that the degraded sites developed into Hyparrhenia species-dominated grasslands, which tend to be stable for a very long time.Moll (1965) and Smits et al. (1999) also indicated that Hyparrhenia species-dominated tall grasslands are anthropogenic in origin.

Importance
The substrate of the Johannesburg Granite Dome (Halfway House Granites, Fig. 3) is suitable for development.The area is well situated between Johannesburg, the economic powerhouse of South Africa, and Pretoria the administrative capital of the country.
There is an enormous demand for developable land in this area, which has resulted in the loss of large tracts of the original Egoli Granite Grassland.A mixture of various grasses and high forb diversity renders the original Egoli Granite Grassland with a high conservation value and conservation of remnant areas is especially important since it is unlikely that the transformed anthropogenic grassland will return to the original climax vegetation.
Since Egoli Granite Grassland is endemic to Gauteng, its protection is both a provincial and national priority.It also forms part of a global ecoregion in crisis, an area where biodiversity and ecosystem services are at greatest risk and focused on-the-ground conservation action are required (Hoekstra et al. 2005).