Environmental change in the Kalahari: Integrated land degradation studies for nonequilibrium dryland environments

Recent decades have seen major intensification of cattle-based agricultural production in semiarid savanna ecosystems. In the Kalahari of Botswana, cattle production now occurs on privatised and fenced ranches. Patterns of ecological change, notably increased bush dominance, have been linked to increased cattle-grazing intensity, but it remains contentious whether these changes represent land degradation. Uncertainty in ecological understanding stems from the dynamic, "nonequilibrium" functioning of semiarid ecosystems. Given the inherent ecological variability of drylands, we argue that degradation assessments should be based, not on ecological observations alone, but on the study of long-term changes in pastoral production figures and on changes in the ecologically determining factors of soil water and soil nutrient availability. Provided here is a framework incorporating soil and ecological changes at a range of scales that can enable us to distinguish drought-induced fluctuations from long-term ecological-state changes. The results demonstrate that increased cattle use and associated ecological changes have not been caused by, nor are they associated with, changes in soil water and nutrient availability. We present a model of ecosystem dynamics that does not display bush encroachment as a definite form of land degradation. Encroachment may also be curtailed by resilience mechanisms found in protected ecological niches and by the resilience of the nutrient-poor sandy soils.