**5.4 Grassland Biome affinities**

122 Biodiversity Loss in a Changing Planet

The Afromontane fynbos genera found on Platberg are Passerina, Cliffortia, Erica, Euryops, Helichrysum, Macowania, Metalasia, Muraltia, Pentaschistis, Ischyrolepis, Schoenoxiphium and Watsonia, all of which are endemic taxa typically found in the Cape Floristic Region

The grass-like genus *Restio* is a major component of the Cape flora not found on Platberg or the broader Drakensberg, however, *Ischyrolepis schoenoides,* is found on Platberg and other inselbergs in the Free State (Du Preez & Bredenkamp 1991; Malan 1998) and could be regarded as an ecological equivalent for *Restio*, as its growth form and habitat is similar. Phylogenetically, these two genera are closely related (Haaksma & Linder 2000) and Germishuizen et al., (2006) lists *Restio schoenoides*, *Kunth* (1) as a synonym for *Ischyrolepis schoenoides* (Kunth) H.P. Linder (Brand et al. 2010). The remnants of fynbos vegetation on Platberg may be relicts from cooler periods when more extensive fynbos migrated over lower altitudes starting during the Late Pleistocene and evident up to the last Glacial

Fig. 6. Fynbos *Passerina montana* shrub community on Clarens Sandstone on Platberg.

Pollen taken from sites at Clarens, a town in the semi-arid interior of the Free State, 200km west of Platberg, and the Rose Cave site, near Ladybrand, 500km to the west of Platberg, located at the extreme western footslopes of the DAC, show a similar pattern for fynbos genera *Protea* and *Cliffortia* which were more abundant and are typical of upland vegetation.

Limited affinities are found with the Nana-Karoo flora on Platberg. These are mostly succulents from the Mesembryanthemaceae (2 genera, 4 species) and low shrubs, *Chrysocoms ciliata, Felicia filifolia, F. muricata* the most representative, found on the warm north and west sides of Platberg (Brand et al., 2010), and may represent previous climatic conditions of hotter, drier periods with less seasonal fluctuation (Scott 1988). Succulent evolution and distribution is not favoured by high rainfall and freezing temperatures extended over days (Smith et al., 1998; van Wyk & Smith 2001), which would be the environmental limiting factors responsible for the low numbers of succulents found at altitude (Körner 2003) on

(Goldblatt & Manning 2000).

Maximum (Scott et al., 1997).

**5.3 Nama-Karoo Biome affinities** 

Platberg and DAC.

Grasses, the family Poaceae, is the single most important plant family for humanity (Gibbs-Russell 1991). It is distributed over all seven continents and is the fifth largest plant family on earth and the second largest family for the DAC. Globally, Poaceae comprise some 770 genera and 9 700 species (Gibbs-Russell 1991). Southern Africa there are approximately 194 genera and 967 species of which 329 are endemic (Carbutt & Edwards 2004, 2006). For the Drakensberg Alpine Centre there are 86 genera and 267 species, of which 22 endemic or near-endemic genera comprising 39 endemic or near-endemic species (Carbutt & Edwards 2004, 2006). Grasses, particularly C4 pathway users, are better than plant families in stripping and utilising CO2 from the atmosphere. Grasses store the Carbon below ground in roots and soils (Retallack 2001), and with the Savanna Biome are enormous sinks for Carbon (Table 3).


Table 3. Mean Carbon (C) content in soils under Modern Grasslands and adjacent Woodlands (modified from Retallack 2001)

Platberg and the DAC are within the Grassland Biome, and as such are dominated by grasses. Grassland is a complex mix of graminoids, forbs and geophytes (Mucina & Rutherford 2006). Geophytes are abundant on Platberg, with Amaryllidaceae, Asphodelaceae, Hyacinthaceae, Hypoxidaceae and Iridaceae growing throughout the grassland, fynbos, woody/shrub and wetland communities. These geophyte families are also important fynbos components (Goldblatt & Manning 2000) and are prominent members in the Succulent and Nama Karoo Biomes (Van Wyk & Smith 2001; Pond et al., 2002; Mucina & Rutherford 2006).

On a regional scale, strong floristic affinities exist between Platberg and the Drakensberg grasslands to the south (Bester 1998), which includes Qwa-Qwa (Moffett 2001), the Golden Gate Highlands National Park (Roberts 1969; Kay et al., 1993), the central Cathedral Peak area, and southern Drakensberg (Killick 1963, 1978a, 1978b; Van Zinderen Bakker 1973; Hillard & Burtt 1987), the Stormberg and Eastern Cape Drakensberg (Hill 1996; Carbutt & Edwards 2004), as well as Korannaberg to the western interior of the Free State (Du Preez & Bredenkamp 1991; Du Preez et al., 1991).

The development of high biodiversity and species richness of Poaceae across the Grassland Biome has a number of explanations; these include a combination of weather (Mean Frost Days, and minimum daily temperature) and moisture availability (Mutke et al., 2001), soils, and the effects of fire and grazing (Seabloom & Richards 2003). Moisture availability is an

Biogeography of Platberg, Eastern Free State, South Africa:

Preez & Bredenkamp 1991; Mucina & Rutherford 2006).

2010), but has high species richness with a total of 670 taxa.

al. (1993, 1995), Fuls (1993) and Kay (1993) use 100 m² plot sizes.

**6. Phytogeographic comparison and biodiversity of Platberg** 

The concept of islands having high numbers of endemics (MacArthur & Wilson 2001) associated; generally with low species richness (Linden 2003) is typical of island fauna and flora as well as African mountain regions (Kingdom 1989). Platberg, as an inselberg 'island' does not fully reflect this association; it has high numbers of endemics, 27 (Brand et al.,

On a global scale the United Kingdom (Whales, Scotland, Northern Ireland and England), covers 312 000 km² (a surface area four-orders-of-magnitude larger than Platberg which is 30 km²) with a total vascular plant species count of approximately 1400 of which none are endemic (Preston et al., 2002). In comparison Platberg has 670 species with the 27 endemic. It is problematic trying to compare species richness (alpha-diversity), with turnover between habitats (beta-diversity) and turnover between floras from one landscape to another (gamma-diversity), (Cowling et al., 1992). Similarities in edaphic conditions must take into account and environmental differences minimised to be able to match the differences in habitat gradients (Cowling et al*.*, 1992). For Platberg it is relatively easy to match alphadiversity with sites elsewhere. However, this becomes more problematic with beta and gamma diversity as different researcher use different plot sizes for similar biomes. For grassland Perkins et al., (1999a) uses 25² m, for Platberg plot size is 30 m² while Eckhardt et

**5.5 Wetland affinities** 

Links with Afromontane Regions and South African Biomes 125

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

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 (Pooley 2003).

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