Of all the global environmental problems, desertification is, perhaps, the most threatening for poor rural people. The most accepted definition of desertification states that it is land degradation in arid, semiarid, and dry sub-humid areas resulting from various factors, including climatic variations and human activities. Drylands cover almost 40 percent of the total land surface of the world and are inhabited by approximately 1 billion humans dispersed over more than 100 countries. These people include many of the world's most vulnerable, marginalized, and politically weak citizens. In spite of the progress in the understanding of the ecological dimension of this phenomenon, few communities' wellbeing has improved by the myriad action plans and activities carried out by local, regional, or national organizations, particularly in Africa. A growing body of evidence suggests that a closer look at the social system and the role of its components is critical to understanding this frequent outcome. Drylands are characterized by water scarcity stemming from the conjunction of low water offer (i.e., precipitation) and high water demand (i.e., water lost to the atmosphere as water vapor from soil via evaporation and from plants through transpiration). Drylands' precipitation is highly variable through the year and occurs in infrequent, discrete, and largely unpredictable events. In turn, the high evaporative demand of the atmosphere, resulting from high air temperatures, low humidity, and abundant solar radiation, determines that water availability is the dominant controlling factor for biological processes such as plant growth and herbivore productivity. Thus drylands, though not barren, are ecosystems of low and highly variable productivity capable of limited human settlement and vulnerable to anthropogenic disturbance. The proximate causes of desertification are complex and vary from region to region. The European Mediterranean region has a long history of human misuse. War, urbanization, farming, and tourism have, over the years, altered vegetation to such an extent that, at present, virtually no natural vegetation exists there and soil erosion is ubiquitous. In contrast, Australian drylands have experienced extensive degradation only recently. The introduction of domestic livestock by Europeans in the late 1880s, together with the fences used to concentrate these animals and the suppression of fire, drastically reduced the abundance of perennial grasses, leaving more soil exposed to erosion by water or wind, and triggered shrub encroachment. In the Sahelian region of Africa, where the concept of desertification was first coined at the beginning of the 20th century, the replacement of the original vegetation by crops, the increase of grazing pressure over the remaining lands, and the collection of wood for fuel resulted in a reduction of the biological or economic productivity of the land. In particular, inappropriate use of heavy machinery, deficient irrigation schemes, and grazing management practices led to soil erosion, salinization, and overgrazing. Any attempt to assess the impact of desertification on human societies should first acknowledge the difference between the ways water-limited ecosystems shape the functioning of social systems and the effects of desertification itself. Desertification imposes an additional constraint on human well-being by further reducing the limited ecosystem goods (e.g., food, timber, water) and services (e.g., soil maintenance, erosion control, carbon sequestration) that drylands provide. Failure to address this difference would lead to an overestimation of the desertification effects. Additionally, the manifestations of desertification vary widely, depending on the capacity of each country to mitigate its impacts. For example, in Africa it resulted in declining productivity and intensifying food insecurity and widespread famines, whereas in the Mediterranean region...
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