Habitat occupation by Aloe ferox Mill. (Liliaceae) in relation to topographic variations in direct beam solar radiation income

This study concerns both the variety of physical habitats occupied by an arid land plant species and the intermeshing of its geographical range with that of the Cape sclerophyll vegetation in South Africa. On the basis of theoretical values for the direct beam solar radiation incomes of slope facets, eight predictions are made of the topographic situations which Aloe ferox, and the named vegetation type, might be expected to occupy in, successively, areas of below-optimum, optimum and above-optimum mean annual rainfall. Good agreement between field observations and these physically-based predictions was obtained for the Cape sclerophyll vegetation, but poorer agreement for those predicitions relevant to the distribution of the aloe. Of the predictions, those dealing with slope azimuth were generally more successful than were those dealing with the slope angles of habitats which were capable of being occupied.