Protea Atlas Logo
  Home
  Mission
  Overview of Project
  Project Staff
  Sponsors
  Achievements
  Checking, Illustrations
  Upcoming Activities
  Id and  Species Lists
  Protea Information
  Protea Gallery
  Growing Proteas
  Interim Dist. Maps
  Publications
  Afrikaanse Inligting

  SANBI

Protea Landscapes in the Bewaarkloof Mountain, Transvaal


Protea Atlas LogoThe Bewaarkloof area is situated 40 km south-east of Pietersburg in the northern Transvaal (24o02'-15'S and 29o41'-53'E), just outside the tropics (Figure 1). It thus sits west of the Wolkberg Wilderness Area and the Lekgalameetse Nature Reserve on the Drakensberg Escarpment in the Olifants River catchment area. In total an area of 24 600 ha has been earmarked for conservation use.

Fig. 1: Locality of Bewaarkloof BWK in relation to Wolkberg Wilderness Area WWA, Lekgalameetse Nature Reserve LNR, the Great Escarpment ESC, Strydpoort Mountains STRM, Olifants River OLIF and Tzaneen TZ.

The entire area is characterized by an extremely broken topography and deeply incised valleys. The lowest point is at 780 masl and the highest point is 2055 masl, a relief of 1275 m. Geologically, the region can be divided into two zones. The northern half consists mainly of dolomites. The southern half is characterized by asbestos-bearing ironstone from which asbestos was mined until 1984.

Most of the soils are extremely leached (i.e. the important plant minerals have been washed out) due to the steep topography and relatively high annual rainfall - about 500 mm in the valleys and 1000 mm in the northern peaks. The low-lying southern parts also differ considerably in temperature from the north-eastern plateau where frosts are frequent. The predominant vegetation is North-eastern Mountain Sourveld and Sourish Mixed Bushveld (Acocks Veld Types 8 and 19).

During our vegetation survey of the area it became apparent that the proteas were replacing one another with altitude on the dolomite slopes. So we collected leaf cover values for the nine most common woody plants from 60 plots in the area. We carefully positioned our plots so that they included both the dolomite and banded-ironstone slopes for a variety of altitudes and aspects. We used an gradient analysis programme (CCA-Canoco for the experts) which places the species along a theoretically standard slope (Figure 2).

Fig. 2: Schematic species relay along an imaginary slope in the Bewaarkloof area. Species are listed in the text.

From our results the species are arranged in a progression from the Mountain Syringa Kirkia wilmsii Kw on the lower slopes, being replaced by Red and Velvet Bushwillows Combretum apiculatum and C. molle Ca, Common Hook-thorn Acacia caffra Ac and Transvaal Beechwood Faurea saligna Fs until finally the Protea spp replace them at the higher elevations. This progression can clearly be observed in the field.

This species sequence can be observed on both the north and the south slopes. The main difference between these two slopes is that on the south slopes the species are located some 200 m lower. Thus Protea caffra Pc which occurs at 1700 m on the north slope occurs between 1300-1600 m on the south slopes (Figure 3). The actual altitude at which a species occurs depends not only on the aspect, but also on the steepness of the slope and the width of the valley between the ridges. The steeper the slope and the more enclosed the valley, the moister the southern slope will be and the lower down the species will occur.

Fig 3: Schematic positions of species illustrating the combined influence of aspect and altitude of the dolomitic slopes in the Bewaarkloof area. Communities were identified from a larger data set for the entire area. At: Acacia tortilis Umbrella Thorn, Dc Dichrostachys cinerea Sickle Bush.

At altitudes of 1700 m, pockets of Protea rubropilosa Pr and P. roupelliae roupelliae Prr were observed. These species tend to form monospecific stands, in which they are the only woody plants present. It appears that P. rubr is only found at very high elevations, whereas P. roup r tends to favour the more exposed localities just below the high crests.

It thus appears that altitude is not influencing the plants. Rather, altitude acts so as to increase rainfall and mist, and to reduce temperatures and evaporation. Southern slopes receive less sunshine and thus the temperature and evaporation are much lower than for northern slopes. Our gradient analyses shows that available moisture is the environmental factor most influencing the distributions of the plant species on the slopes. This is why the species can be seen (Figure 3) to occur in parallel belts across a mountain, skewed so that they occur at lower altitudes in the south.

The predictable sequence of species on the dolomite slopes in the Bewaarkloof area offers a powerful tool for mapping plant communities and planning conservation and management strategies. Rather than requiring expensive detailed surveys of many slopes, the plant communities of these slopes can readily be predicted based on altitude, aspect and slope.

We thank the sub-directorate Nature Conservation of the Department of Development Aid for permission to make this study. Sakkie Schabort contributed to our understanding the local vegetation pattern. This work was done whilst being a member of the Wits Resource Ecology Group. More detailed results are available from the authors.

Mark Stalmans, Nelspruit & Gideon de Klerk, Pietersburg


Back PAN 14