'n Ekologiese studie van die plantegroei van 'n noordelike en suidelike kloof van die Magaliesberge

Abstract

English: The vegetation of the two kloofs in the Magaliesberg range is described. These kloofs are 10 miles west of the Hartebeespoortdam in die Brits district covering an area of approximately 35 morgen. The altitude of the area varies from 4200 to 5200 feet above sea level. Geologically the region is situated within the Pretoria Series of the Transvaal System and consists of Magaliesberg Quartzites and Magaliesberg Shales. The soils conform very closely to the geological structure. They are residual and formed in situ. Owing to the mountainous topography there has been alluvial drift. The average annual rainfall of the area is 696.7 mm. measured at Wolhuterskop, of which 85% falls during the summer months October to March. There is an indication that the precipitation is higher at the top of the mountain than at the base, and also higher on the south side of the mountain than on the north side. The temperatures of the north and south sides of those. the mountain as well as those of the slopes of the kloofs are compared. Maximum temperatures are lower at the top of the mountain than at the base while minimum temperatures are higher at the top. Temperatures in general are higher on the north side. The temperatures of the slopes of the kloofs, receiving the greater insolation, are higher than those of the opposite slopes. The influence of biotic factors on the vegetation is discussed. The vegetation is classified according to the method described by Goodall (1953) into 16 groups. These 16 groups are described as belonging to the following six communities:- 1. Mimusops-Chrysophyllum-community. 2. Rauvolfia-community. 3. Croton-community 4. Chrysophyllum-community 5. Acacia caffra-community 6. Acalypha glabrata-community. The Mimuso-Chrysophyllum-community occupies most of the west slope and small patches of the lower portion of the east slope of the north kloof. The dominant trees are Mimusops zeyheri and Chrysophyllum magalismontanum. The Rauvolfia-community is confined to the streambanks in the north kloof. This community is characterized by the tropical element in the flora. Rauvolfia caffra is the dominant tree, while species such as Trema guineenais, Ilex mitis, Pygeum africanum_and Pittosporum viridiflorum are present. The east slope of the north kloof is occupied by the Croton-community. This is a dry open community with Croton- subgratissimus, Combretum zeyheri and Combretum holosericeum being the dominant trees. The Chrysophyllum-community covers the western slopes of the kloof near the northern top of the mountain. Chrysophyllum magalismontanum is the dominant tree. Trees such as Cornbretum holosericeum and Ochna pulchra are important constituents of the tree layer. The Acacia caffra-community occupies the slopes of the south kloof and small parts of the upper portion of the north kloof. This community is dominated by Acacia caffra. In the parts of the north kloof where the Acacia caffracommunity occurs, some of the associated species show an affinity with the Bushveld flora. Species such as Combretum zeyheri, Crysophyllum magalismontanum and Mimusops zeyheri are found in this community. On the south side the associated species are mostly widely distributed species, such as Dombeya rotundifolia and Euclea,_lanceolata. The Acalypha glabrata-community occupies the streambanks of the south kloof. The dominant tree is Buddle salicifolia, a specie of the Kalahari Thornveld. Calondendrum_capense and Celtis_africana, temperate forest species, form on important consituent of the tree layer. The vegetation of the north side of the range is dominated by Bushveld species, but a number of tropical forest species are present, e.g. Rauvolfia caffra, Pittosporum viridiflorum, Pygeum africanum and Trema guineensis. The vegetation of the south side of the mountain is dominated by widely distributed species, but there are traces of temperate or transitional forest, with species such as Celtis africana, Kiggelaria africana, Halleria lucida, Leucosidea sericea, Buddleja salvifolia and Cassinopsis ilicifolius.