BIOPHYSICAL FEEDBACKS AND THE RISKS OF DESERTIFICATION

The widespread distribution of irreversible degradation in dryland environments (desertification), along with recent studies of complex earth-surface systems, suggests that desertification may be the result of inherent biophysical feedbacks in dryland systems. This notion is tested by applying qualitative stability analysis of partially-specified systems. This analysis shows that a well-known model of biophysical feedbacks in dryland ecosystems is inherently unstable. Furthermore, the two-way relationships between seven key components in desertification (vegetation, albedo, temperature, precipitation, soil moisture, wind erosion, and water erosion) result in inherent instability. Stability theory also shows that any analysis of process-response or cause-effect relationships including those seven components is more likely than not to reveal an unstable relationship. The latter occur both in the form of mutually-reinforcing links which result in the growth and persistence of disturbances and competitive exclusion relationships which cause one variable to be favored. The inherent instability in the dryland environment means that perturbations such as drought or overgrazing will persist or grow, leading to desertification.