Drylands: Coping with Uncertainty, Thresholds, and Changes in State

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Drylands cover 40% of the terrestrial surface (Table 8.1, Plate 6) and are characterized by high ecological and cultural diversity. Although they are, by definition, of low productivity, they have been a source of biotic, social, and scientific innovation. A third of the global biodiversity hotspots are in drylands, with a diversity of large mammals in savannas, high diversity and endemism of vascular plants in shrublands, and a high diversity of amphibians, reptiles, birds, and mammals in deserts. Succulence, the CAM photosynthetic pathway, and camels’ tolerance of changing blood water content are examples of biological innovations that arose in drylands. Drylands are culturally diverse and account for 24% of the world’s languages (Safriel et al. 2005). Traditionally, many social groups moved both seasonally and in response to prolonged droughts (e.g., Davidson 2006). The need to cope with harsh conditions and repeated episodes of scarcity have given rise to strong cultural traditions such as the invasive effectiveness of the Mongols, the rule base for several major religions, and traditional ecological knowledge backed by powerful sanctions as in Aboriginal cultures in Australia. In ecology, attention to the extreme conditions represented by drylands has helped create paradigm shifts of wider relevance, such as the development of disequilibrium concepts and state-and-transition models (Westoby et al. 1989, Vetter 2005) that were important drivers of the development of resilience theory (Walker 1993). Such concepts are especially pertinent as humans prepare for climatic change.