**1.1 African phytochoria and species richness**

The phytochoria of Africa have been formally classified by White (1983), who defined eighteen major phytochoria for Africa. The two phytochoria of interest for this work as are the *Afromontane* archipelago-like regional centre of endemism (VIII), and embedded within the *Afromontane* phytochoria is the *Afroalpine* archipelago-like centre of extreme floristic impoverishment (IX). The basis of White's work was to produce a vegetation map for Africa, using two criteria: the physiognomy of the most extensive vegetation type, and floristic composition. This produced a useful, broad scale map of regional biodiversity, but did not have the resolution to show species richness on the local or community level.

Biogeography of Platberg, Eastern Free State, South Africa:

**3. Results** 

physiognomic equivalents.

result in there being a lower number of species per hectare.

Links with Afromontane Regions and South African Biomes 117

the lower lying regions, in which the vegetation of Platberg is embedded. The disadvantage of the PRECIS list is that very few of the common species are normally recorded which will

The vegetation on Platberg is dominated by grasses and shows an intergrade of floristic associations and habitat features in common with several other major vegetation types of the Grassland, Fynbos, Afrotemperate Forest and Nana-Karoo Biomes. Fynbos as well as succulents, particularly Mesembryanthemaceae from the Nama-Karoo Biome grow on Platberg. These floristic elements also extend to the DAC. Woody shrubs and forest remnants grow in the specalised ecological niches in sheltered gullies, boulder beds and rocky terrain. Numerous wetlands occur, forming distinct hygrophilous communities. Geophytes and forbs add significantly to the biodiversity of all vegetation types and grow in all habitats. Only two Gymnosperms occur, the indigenous, forest emergent tree *Podocarpus latifolius*, and the exotic *Pinus patula*, established in timber plantations at lower altitudes, which have now invaded and are replacing the indigenous vegetation on the cool southern slopes. Pterdophyte diversity is relatively low, comprising a total of 16 species, 10 genera and 8 families. Ferns are widespread and occur throughout all habitats, on all aspects – hot northern, cool southern and at all altitudes. Three of the ferns, *Dryopteris dracomontana, Mohria rigida* and *Polystichum dracomontanum* are endemic to the DAC. All but one species (*Pellaea calomelanos*) occur at altitude throughout the Afromontane region. The exotic bracken, *Pteridium aquilinum* occurs on the lower footslopes with *Searsia pyroides* subsp *gracilis*. The prostrate fern, *Selaginella caffrorum* is a mat forming species, which forms unique communities that contribute to inselberg vegetation structure. *Selaginella* communities are found on open, sheet rock on Platberg, Korannaberg, Thaba Nchu and other inselbergs as well in the DAC. *Afrotrilepis pilosa* mats occurring on granite inselbergs of west Africa are

Of the 974 species, in the PRECIS database, collected in the 2828AC Harrismith grid, about 670 (68.8%) species occur on Platberg above 1 900m. The rest (31.2%) occur on the surrounding lowlands. The 670 species found on Platberg were correlated with DAC species lists of Van Zinderen Bakker (1973), Killick (1963, 1978a, 1979b), Hill (1996), Low & Rebelo (1996), Carbutt & Edwards (2004, 2006), Hoare & Bredenkamp (2001), (Moffett 2001), Smith & Van Wyk (2001) and Mucina & Rutherford (2006). A strong genus level correlation of over 80% was found between Platberg and the DAC, which includes exotic angiosperm taxa such

Of the 670 species recorded on Platberg, several species are new records for the Free State and represent range extensions, or have only been collected once before (Brand et al., 2010). One of these species *Struthiola angustiloba*, a rare KwaZulu-Natal species was collected on Platberg. Two Asteraceae species also collected on Platberg, *Helichrysum harveyanum* and *H. truncatum* are Northwest/Gauteng and Mpumalanga endemics, giving new range extensions of 400-500 km south to Platberg. These new range extensions are not totally unexpected, given that mountain chains act as routes of migration (Körner 2003) and with similar altitude and ecological conditions, distance is not a critical factor (400-500 km), but

Of the 670 vascular plants recorded on Platberg, there are 305 genera in 96 families (Table 1). Of these 27 are endemic or near-endemic species also found in the Drakensberg Alpine Centre

similarity in live zones determines speciation, rarity and endemism (Körner 2003).

as *Pinus, Acacia,* Bidens, Tagetes, etc. (Carbutt & Edwards 2004).

A map showing continental wide African sites of high biodiversity using both the taxonbased approach and the geographical or inventory-based approach are presented by Mutke et al., (2001). This Global Information System (GIS) approach to map African phytodiversity shows good correlation with climatic, edaphic and biotic parameters for African phytodiversity for the Drakensburg/Natal Area – analogous to White's *Afromontane* archipelago-like regional centre of endemism. This study has improved on White's broad scale map, but being a desktop study still does not provide detailed information of species richness on the local community scale.

Regional mapping of the biodiversity by Van Wyk and Smith (2001) and Mucina & Rutherford (2006) provides a more detailed pattern of plant diversity, which correlates well with the geological map of the African land surface (White 1983; Hillard & Burtt 1987). The South African Drakensberg is shown within this archipelago-like regional endemic centre, which Hillard & Burtt (1987) called the *Eastern Mountain Region* (EMR), first used by Phillips in 1917 (Carbutt & Edwards 2004).

The use of the EMR has not been followed as it shows a broader, topographically less welldifferentiated area and is a loose correlation with the more precise geographical/ topographical designation of the Drakensberg Alpine Centre (DAC) (Van Wyk & Smith 2001). However, what Hillard & Burtt (1987) where alluding to, in using the term 'EMR', was to differentiate the Drakensberg and surrounding high altitude areas from the rest of the continental wide *Afromontane* region due to its unique and rich floristic composition. Biogeographically, the DAC and Platberg also show relatively strong floristic affinities with the Cape Floristic Region (Linder 2003; Carbutt & Edwards 2004, 2006) or the Fynbos Biome as defined by Mucina & Rutherford (2006). Other biogeographical links are shared with Nama-Karoo Biome found in the drier interior of the sub-continent and further north the sub tropical African and Eurasian flora (Mutke et al., 2001). It is within this broader Afromontane biogeographical context, including being one of an 'island-like' archipelago of inselbergs that Platberg's biological diversity is considered.
