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 associat ed changes in land use patterns. This paper gives a historical perspec tive by reviewing major findings in climate and land use changes in th e area, including information from tree ring, palynological, sedimento logical, 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 desertifica tion processes in the area's north and south. In both cases rangelands and irrigated zones are the most affected land use systems. In the Ma ghreb (Algeria, Morocco and Tunisia), rangelands are being destroyed b y overgrazing and agricultural encroachment. In northern countries ran gelands are increasing at the expense of marginal agriculture. This pa per discusses some controversial implications of rangeland vegetation recovery on fire and water regimes and reviews information on the step pes of Stipa tenacissima, paying attention to changes and degradation patterns, irreversible thresholds and implications of their spatial st ructure. Finally, this paper discusses western Mediterranean irrigated lands as hot spots of desertification; their vulnerability to rainfal l variability; the difficulties of relieving them from overexploitatio n of water resources; and their terminal symptoms, such as soil salini zation, exhaustion and deterioration of aquifers, and damage to downst ream fluvial and wetland systems. (C)1998 Academic Press Limited.