Perspectives on desertification: western Mediterranean

In the western Mediterranean desertification is triggered by climatic variability and demographic disequilibrium, both of which directly and indirectly affect water budgets and land degradation through associated changes in land use patterns. This paper gives a historical perspective by reviewing major findings in climate and land use changes in the area, including information from tree ring, palynological, sedimentological, archaeological and archive analysis, with special emphasis on the past 500 years. This paper discusses the synergies between these changes and their implications to the most vulnerable ecosystems, such as mountain and semiarid ecosystems, and compares current desertification processes in the area's north and south. In both cases rangelands and irrigated zones are the most affected land use systems. In the Maghreb (Algeria, Morocco and Tunisia), rangelands are being destroyed by overgrazing and agricultural encroachment. In northern countries rangelands are increasing at the expense of marginal agriculture. This paper discusses some controversial implications of rangeland vegetation recovery on fire and water regimes and reviews information on the steppes of Stipa tenacissima, paying attention to changes and degradation patterns, irreversible thresholds and implications of their spatial structure. Finally, this paper discusses western Mediterranean irrigated lands as hot spots of desertification; their vulnerability to rainfall variability; the difficulties of relieving them from overexploitation of water resources; and their terminal symptoms, such as soil salinization, exhaustion and deterioration of aquifers, and damage to downstream fluvial and wetland systems. (C)1998 Academic Press Limited.