The use of integrated remotely sensed and GIS data to determine causes of vegetation cover change in southern Botswana

The characteristics and dynamics of dry savanna vegetation cover are receiving considerable attention from the perspectives of both global change and range degradation studies. Problems include the establishment of major savanna determinants and the floristic response of vegetation cover to given stimuli. Basic work on determinants is required to assess the nature and causes of natural resource depletion, particularly in the Kalahari region. Use of image processing techniques involving the association of pixel values and field data have resulted in the development of a vegetation map indicating floristic content and structure. Results indicate that a clear distinction can be made between classes containing high proportions of taller woodland species and those that contain mainly woody weeds. Degraded areas with sparse vegetation cover and large areas of bare soil were also identified. The GIS technique of buffer analysis was applied to determine the extent to which herbivory (livestock) and the gathering of bush products by the local population were directly involved in the spatial distribution of savanna types. Results indicate that most of the degraded areas are within 2 km of villages and boreholes. Most of the woody weed areas fall within a 2–4-km zone around boreholes. Spatial association indicates that uncontrolled bush product harvesting and goat grazing are primarily responsible for village-centred degradation, while cattle grazing around numerous boreholes is a primary cause of woody weed development. These kinds of savanna adaptive responses are difficult to reverse in rural Botswana because of increasing population pressure and concomitant poverty.