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, ca ttle production now occurs on privatised and fenced ranches. Patterns of ec ological change, notably increased bush dominance, have been linked to incr eased cattle-grazing intensity, but it remains contentious whether these ch anges represent land degradation. Uncertainty in ecological understanding s tems from the dynamic, "nonequilibrium" functioning of semiarid ecosystems. Given the inherent ecological variability of drylands, we argue that degra dation assessments should be based, not on ecological observations alone, b ut on the study of long-term changes in pastoral production figures and on changes in the ecologically determining factors of soil water and soil nutr ient availability. Provided here is a framework incorporating soil and ecol ogical changes at a range of scales that can enable us to distinguish droug ht-induced fluctuations from long-term ecological-state changes. The result s demonstrate that increased cattle use and associated ecological changes h ave not been caused by, nor are they associated with, changes in soil water and nutrient availability. We present a model of ecosystem dynamics that d oes not display bush encroachment as a definite form of land degradation. E ncroachment may also be curtailed by resilience mechanisms found in protect ed ecological niches and by the resilience of the nutrient-poor sandy soils .