**5.5 Wetland affinities**

124 Biodiversity Loss in a Changing Planet

important factor in determining species richness (Mutke et al., 2001) particularly for grasses, maximum growth occurs for up to four days after rain (Cavagnora 1988), which allows grasses to outcompete geophytes and forbs with similar morphology (Mucina & Rutherford 2006). The Drakensberg and Platberg have much higher precipitation than the surrounding areas 700-2400 mm (Mucina & Rutherford 2006), this provides for more moisture availability at higher, cooler altitudes. The lower regions of the Grassland Biome have lower rainfall 454 mm average (Mucina & Rutherford 2006), and are more humid. This moisture availability divides the grassland into high altitude Moist grassland dominated by species using C3 metabolism and low, altitude Dry grassland dominated by species using C4 metabolism. Platberg on the cool southern and eastern sides in particular, provide in current times, a similar habitat and climatic conditions reminiscent of both Holocene and Pleistocene with the grassland on the plateau a mix of upland C3 grasses form cooler times, mixed with C4 grasses from corresponding warmer times (Scott & Vogel 2000). On Platberg, the predominance of C4 grasses indicates that it falls within the core of the Grassland Biome, with a species composition similar to that dominated by C4 grasses from the supertribe Andropogonodae which includes *Andropogon, Trachypogon, Heteropogon, Cymbopogon, Diheteropogon, Monocymbium, Tristachya, Schizachyrium, Themeda* and *Hyparrhenia* (Gibbs-Russell et al*.*, 1991; Mucina & Rutherford 2006). The abundant C3 grass *Helictotrichon longifolium*, found on the open plateau area of Platberg, would suggest a link with the predominant high altitude Drakensberg grasses dominated by C3 grasses. The other abundant C3 grass on Platberg is from the smallest of the five Grass subfamilies, Bambusoideae, the mountain bamboo *Thamnocalamus tessellatus*. On Platberg *Thamnocalamus tessellatus* forms dense stands, which grow on the cool, moist, sheltered south slopes of Platberg. These stands occur below the vertical cliffs at about 2000 m, and in some of the gullies which drain the seasonal streams as low as 1980 m (Brand et al., 2009). The *Thamnocalamus tessellatus* vegetation community is dominated by this monotypic, endemic genus, which is a species-poor community with limited presence of the low trees *Buddleja loricata, Searsia divaricata* and *Leucosidea sericea* (Brand et al., 2009). Shading out of competition and the dense rhizomatous, root system inhibits growth of other species. In Africa, Bambusoideae are mainly tropical species confined to the humid forest shade where *Arundinaria alpina* grows in dense stands on mountains between 2 130 m and 3 200 m (White 1983). In South Africa *Thamnocalamus tessellatus* (previously named *Arundinaria tessellatus*) is confined predominantly at high altitudes of 2 700 m in the Stormberg and Drakensberg, but may be found as low as 1450 m (Pooley 2003) on the Ngeli inselberg in KwaZulu/Natal. Where it does occur in South Africa, *Thamnocalamus tessellatus* has a limited range, composed of disjunct populations – it only occurs again in the Himalayas

The almost total dominance of C4 grasses on Platberg is somewhat anomalous as it would have been predicted that for Platberg, with its relatively high altitude of 2 350 m with snow, frost and freezing temperatures, high rainfall between 700 – 1 200 mm per annum and close proximity to the Drakensberg, would be dominated or at least have a higher cover/abundance of C3 grasses. However, despite the cold conditions on Platberg, its altitude may be below the limit for continuous cold for extended periods, and thus below the altitude at which C3 grasses metabolic pathway predominates (Pitterman & Sage 2000; Sage 2001) as with the higher elevations at 3000 m for the Drakensberg (Hillard & Burtt 1987; Mucina & Rutherford 2006). The grassland structure and composition on Platberg may also be a reflection of palaeocological conditions, which started in the Miocene some 20

(Pooley 2003).

million years ago (Scott et al., 1997).

Wetlands form distinct and unique vegetation communities embedded in all eight Biomes in South Africa as well as through out the mountains and associated phytochoria of the Afromontane Region. Consequently, in South Africa, wetlands have been assigned the formal vegetation designation of Azonal units (Mucina & Rutherford 2006). Wetlands on Platberg are embedded in the grassland as playas or pans with semi-permanent, or permanent open water (Figure 7), which is the key factor that determines the common species shared by wetlands (Stock et al., 2004). A total of 13 naturally occupying, different wetland types where identified with 188 species including five alien (weeds) plants. The wetlands are not particularly species rich, with an average of 13.56 species per 30 m² (the lowest for all vegetation types), ranging from 7–29 species per sample plot. This is lower than found for other high altitude wetlands by Fuls (1993) and Malan (1998) who recorded 21 species per plot. Wetland vegetation is dominated by a single species or two to three species mostly hydrophilic grasses, sedges or juncales, which contributes to a low diversity index (Burgoyne et al., 2000). Sedge dominated wetlands occur on inselbergs in West Africa (Porembski & Brown 1995) and are a feature of most, if not all inselbergs (Parmentier et al., 2006). Very few species are endemic to high altitude wetlands, the majority also occurring in low altitude fresh water wetlands (Collins 2005). This inflates the total species richness in wetlands as numerous species will also occur in association with, but not exclusively to wetlands, the status of these species associated with wetlands (wetland indicator status), are classified into 5 categories. Due to the geology on Platberg; it is capped with lava, no vernal pools occur. Vernal pools are abundant on the lower altitude inselbergs (Korannaberg, Thaba Nchu and Thaba Patswa), in the arid interior and north of Platberg where the more resistant igneous capping has been lost and the softer sandstone exposed weathering to form vernal pools. Vernal pools are species poor with a low biodiversity, but contain Obligate Wetland, and Facultative wetland species with a high proportion of endemics (Du Preez & Bredenkamp 1991; Mucina & Rutherford 2006).
