BIOPHYSICAL FEEDBACKS AND THE RISKS OF DESERTIFICATION

The widespread distribution of irreversible degradation in dryland env ironments (desertification), along with recent studies of complex eart h-surface systems, suggests that desertification may be the result of inherent biophysical feedbacks in dryland systems. This notion is test ed by applying qualitative stability analysis of partially-specified s ystems. This analysis shows that a well-known model of biophysical fee dbacks in dryland ecosystems is inherently unstable. Furthermore, the two-way relationships between seven key components in desertification (vegetation, albedo, temperature, precipitation, soil moisture, wind e rosion, and water erosion) result in inherent instability. Stability t heory also shows that any analysis of process-response or cause-effect relationships including those seven components is more likely than no t to reveal an unstable relationship. The latter occur both in the for m of mutually-reinforcing links which result in the growth and persist ence of disturbances and competitive exclusion relationships which cau se one variable to be favored. The inherent instability in the dryland environment means that perturbations such as drought or overgrazing w ill persist or grow, leading to desertification.