ECOLOGICAL IMPACTS OF GLOBAL CHANGE ON DRYLANDS AND THEIR IMPLICATIONS FOR DESERTIFICATION

Potential impacts of global change on dryland ecosystems are reviewed from four perspectives. First, results are reviewed from recent resear ch on vegetation change, land degradation and desertification. The rol e of disturbances and low recurrence events in triggering non-linear c hanges by driving ecosystems beyond their resilience thresholds is out lined. Particular attention is paid to the development of spatial stru ctures as feedbacks that tend to buffer degradation. Secondly, the syn ergetic operation of climatic and anthropogenic forcing factors of dry land degradation is discussed in the light of some case histories. Cha nges in one group of those factors often render the ecosystems particu larly sensitive to changes of those in the second group. Thirdly, off- site effects of dryland degradation are summarized, including feedback s to the atmosphere, changes in biological diversity and downstream im pacts in river catchments. Finally, the implications of global change for land degradation control policies are outlined. The importance of prevention is emphasized, as well as the need to carefully consider wh ere to apply rehabilitation and restoration. Prevention includes soft and cheap measures based on management practices, while restoration ca lls for massive and expensive interventions on soil or vegetation. (C) 1998 John Wiley & Sons, Ltd.