RESERVE - Barberton Centre of Plant Endemism

Regional centres of endemism have at least 50% of their species confined to them, as well as having more than 1000 endemic species. Two regions of Plant Endemism are recognized within Mpumalanga. These are the high lying Drakensberg Afromontane Region (DAR) and the more tropical Maputaland-Pondoland Region (MPR). The number of plant species restricted to the DAR is not known, but species endemism is high. This region incorporates a number of distinct centers such as the Barberton, Wolkberg and Lydenburg centers within Mpumalanga.

The Barberton Center of Plant Endemism (BCPE) is shared with Swaziland and is largely a result of the surface-outcrops of volcanic sedimentary rocks belonging to the Barberton Supergroup. Outcrops of serpentinite occur throughout the BCPE, and these rocks give rise to soils with unusually high magnesium : calcium ratios. These soils, together with those derived from ultramafic rocks, are also associated with high concentrations of heavy metals, which are potentially toxic to plants. At least 30 plant species of the BCPE are edaphic (influenced by soil) specialists, adapted to the serpentine soils.

MAP: The biodiversity value of the Barberton Mountainlands World Heritage Site and (Mountainlands Nature Reserve) is indicated by the Barberton Centre of Plant Endemism relative to areas of conserved and transformed land (Source: World Heritage Site Tentative Listing Submission - adapted from Lotter and Ferrar, 2006).

Two subcentres can be identified within the BCPE, based on the distribution of endemic or near endemic plant species recorded for each of these areas. The fundamental bases on which the endemics have evolved is markedly different between the two subunits and warrant separation. Firstly, the Makonjwa subcentre occurs throughout the BCPE wherever ultramafic (incorporating serpentine) derived soils are absent. Secondly, the Komati/De Kaap subcentre occurs on the serpentine and ultramafic derived soils, extending over a range of altitudes. Approximately 30 species are strictly endemic to this subcentre.

Most of the BCPE’s endemics are confined to the grassland areas, with a few woody serpentine endemic plants in the lower lying areas. The endemics are largely herbaceous with endemism notably high in the Iridaceae, Lamiaceae, Liliaceae and Asteraceae.

The Barberton Afromontane forest is situated within the BCPE and is characterized by the occurrence of the following plant species unique and endemic or near endemic to this area: Pavetta barbertonensis, Psoralea glabra, Ochna gamostigmata, Allophylus chaunostachys, Pavetta galpinii, Cola greenwayi, Garcinia gerrardii, Sapium integerrimum, Bersama lucens, Cassinopsis tinifolia, Encephalartos pucidentatus, Encephalartos Henanii, Aphloia theiformis, Micrococca capensis, Chionanthus peglerae, Heterosamara galpinii (= Polygala galpinii), Aloe thorncroftii, and Clivia miniata.

Cycad species, found in BCPE, include Encephalartos paucidentatus and in particular E. heenanii, which is virtually confined to a small corner of Songimvelo adjacent to Mountainlands. The Barberton Sugarbush (Protea curvata) is only found on a few rocky slopes in the Kaap Valley. The largest population of the Saddleback Sugar bush (Protea comptonii) is found in Mountainlands with only a small population occurring further south.

Threats identified include fire misuse, alien plant infestation, over-grazing, timber plantations, uncontrolled bark-harvesting and firewood collection.