Desertification

Drylands cover more than 40% of the terrestrial land surface of the globe. Climatically, with low precipitation and high evapotranspiration, drylands are classified as arid, semiarid, and dry subhumid zones. Current estimates suggest that 10% to 20% of global drylands suffer from some form of acute land degradation, or desertification, which is the reduction or loss of biological or economic productivity. The environmental and socioeconomic costs of desertification are enormous, impacting the livelihoods of some 250 million people. This is likely to become much worse in the future, as 38% of the total human population of over 6.5 billion reside in drylands, which also have the highest human population growth of any other region of the world.

The United Nations Convention to Combat Desertification (UNCCD) defines desertification as land degradation in dryland areas resulting from various factors, including human activities (e.g., overgrazing by domestic animals, poor cultivation practices) and climatic factors (e.g., drought, increasing air temperature). The Millennium Ecosystem Assessment frames the concept of desertification in terms of decreases in the potential of the land to continue to provide the essential ecosystem goods and services needed to sustain human livelihoods (e.g., crops, woody fuels, forage for grazing animals, and sufficient water). Importantly, both the UNCCD and Millennium Ecosystem Assessment focus explicitly on the linkages between humans (H) and their environments (E) and how this affects human welfare. Desertification is intimately linked to global environmental change through human populations (food and water security, poverty, loss of biodiversity, sustainable livelihoods, and the like) and the environment (trace gas emissions to the atmosphere, dust storms, land use change, and similar matters).

In spite of its importance as a major global problem, the concept of desertification historically has been viewed quite differently by different stakeholders, which has hindered progress in finding solutions. Farmers, conservationists, social workers, ecologists, land managers, and local politicians have legitimate but different perspectives that rarely converge. Why? First, “land degradation” per se does not lend itself to easy quantification: It is usually a slow, continuous process, and the environmental (ecological, biogeochemical, hydrological) changes occurring may not result in an immediate reduction or loss of biological or economic productivity. Second, local areas have a unique set of coupled human-environment (H-E) interactions, so the drivers and consequences of land degradation vary from location to location and, importantly, change over time and spatial scales. Lastly, there are many indirect factors (national economic policies, international trade) that interact with localized direct factors (precipitation, soil [Page 395]fertility, cultivation practices, livestock grazing rates, culture), all of which lead to a complex suite of nonlinear interactions in H-E systems that are difficult to understand and generalize. For these reasons (and others), no focused international science program has emerged to assist the UNCCD in guiding policymakers and scientists.

As an initial step to achieving this goal, James F. Reynolds, D. Mark Stafford Smith, and others proposed the Drylands Development Paradigm (DDP), an integrated framework built around the behavior of coupled H-E systems. It draws heavily from a convergence of insights and key advances drawn from research in desertification, vulnerability, poverty alleviation, and community development. The DDP consists of five principles that, when implemented as a whole, provide a strategy for analyzing causes and consequences of desertification.

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