**2. Study area**

The study area is located on the eastern escarpment of South Africa. The South African sites are located on the Platberg plateau, while the Lesotho sites are at Khalong-la-Lithunya (Gunns pass), Koti Sepola (near Sani pass) and the Sugar bowl (Figure 2), an extinct volcano, near the Kao diamond mine. The Platberg sites are located in South Africa and above 2,300 m.a.s.l. while the Lesotho sites are all above 3,200 m.a.s.l.

Fig. 2. Location of the study areas.

The climate is temperate cool to cold with dry winters and hot, wet summers. The climate of Lesotho is characterized by warm moist summers, from November to March; and cold dry winters from May to July. The mean monthly maximum measured at Barkley East is 31.4C. The rainfall is mainly in the form of thunderstorms. The mean annual precipitation (MAP) for Mokhotlong is 575mm. The relatively low MAP can be ascribed to a rain shadow effect. The winters are cold with frost. The mean monthly minimum measured at Barkley East is -10.5C. Higher elevations above 3,000 m.a.s.l. receive enough snow during winter to cover the ground for several months with sub-freezing temperatures. On rare occasions snowfalls have been recorded in summer as well. Frost-heaving of the soil is a common phenomenon in these areas and occurs especially on barren patches. The ice crystals which are formed during frost-heaving cause the soil to lift. This kind of disturbance prevents seedlings to establish. The barren patches are therefore kept in state by the frost-heaving activities. The frost-heaving phenomenon is probably also the cause of the thufur (hummocks) which occur on peatlands (Van Zinderen Bakker & Werger, 1974).

As far as the geology is concerned the entire Lesotho highland is underlain by basalt of the Lesotho formation and, to a lesser extent, dolerite and gabbro. The basalt is an igneous rock that covered the Clarens Formation about 120 million years ago when Gondwana begun to breakup. Basaltic colluvium and alluvium are the geologic material for the deep soils of the mountain valleys and accumulation glacis (Schmitz & Rooyani, 1987). The soils, at altitude, are mostly shallow and have more or less even proportions of gravel, coarse sand, fine sand, silt and clay particles. The breakdown of organic matter is a slow process due to the long periods of very low temperatures. Especially in the peatlands the accumulation of peat is the result of the decaying roots of the various plants species present on these wetlands. The peat has a high water-retention.
