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  Desertification (sometimes referred to as desertization) is one of the most serious environmental problems confronting the world in the late twentieth century. Drylands cover more than one-third of the earth\'s surface, large parts of which are being heavily, and perhaps irreversibly, degraded. Desertification refers to the degradation of lands in these dry areas and conventionally, following the United Nations Conference on Desertification (UNCOD; held in Nairobi in 1977), and is defined as \'the diminution or destruction of the biological potential of the land [which] can lead ultimately to desert-like conditions\'. Desertification is thus a global problem characterized by the deterioration and degradation of soil and vegetative cover, and is not confined to deserts per se but can occur in any dryland region (Glantz, 1977): according to the United Nations Environment Program (UNEP), drylands denote an area with rainfall up to 600 mm per year. While desertification was implicitly understood by UNCOD to be restricted to dry areas, some scientists have expanded the definition to subsume the impoverishment of any terrestrial ecosystem which can be measured in reduced productivity of desirable plants, undesirable alterations in biomass and plant and fauna diversity, and accelerated soil erosion (Dregne, 1985).

Processes of desertification are of great antiquity. The Sumerian civilization which exploited the Tigris and Euphrates river basin suffered the consequences of poor irrigation and salinity-induced desertification six thousand years ago; the deforestation and proliferation of desert-like conditions was noted by Plato 2500 years ago in his account of Attica. Desertification reached the world stage in the 1970s, however, in the aftermath of the great Sahelian drought/famine (1968-73) and the prospect of a global food crisis.

UNCOD brought together scientists, policy-makers, activists and government representatives from more than 100 countries to design a Plan of Action to combat desertification. Their scientific investigations not only suggested that the Sahelian tragedy was not a natural disaster caused by drought but also estimated that 20 million square miles of the earth\'s surface and 281 million people were affected by at least \'moderate desertification\'. UNCOD called desertification \'an aspect of the widespread deterioration of ecosystems under the combined pressure of adverse and fluctuating climate and excessive exploitation\' (cited in Grainger, 1990, p. 33).

Insofar as drylands are in some measure defined by scarcity of water, highly variable precipitation and limited biomass, they are, from the vantage point of human use, always potentially fragile and vulnerable. The causes of desertification are, however, complex both in terms of the physical and biological sciences and in terms of social theory. On the climatic front, there is no question that cycles of drought have a long history in the arid zones. But the nature and impact of global climate change, the impact of biophysical feedback (albedo), the consequences of dust storms and greenhouse effects remain the subject of intense debate and dispute (Grainger, 1990). It is clear, for example, that the Sahelian zone has experienced a decline in annual precipitation since the 1950s but this downturn may still fall within the bounds of statistical expectation. Similarly the ecology of desertification (and its purported irreversibility) is also a subject of debate. Some of the new studies of Sahelian rangelands, for example, suggest that the resiliency and stability of semi-arid savannas may be quite substantial (Leach and Mearns, 1987). In view of the problems over the definition of desertification — there are over 100 — the scale of desertification is itself a thorny question: two recent studies by Mabbutt and Dregne differ by an order of magnitude of 50 per cent! (see Grainger 1990, pp. 141-2). The UNCOD map of desertification estimates 37.6 million sq. km to be at serious risk of desertification (two-thirds of which are in Africa and Asia).

It is widely understood that desertification can only be understood in relation to human practice but there is no agreement on the weighting of social processes which include: agricultural production in marginal areas (overcultivation), overgrazing, poor irrigation practice, deforestation, population growth/ migration, state policies, and surplus extraction/ exploitation (Glantz, 1987). In order to avoid a shopping list approach to questions of desertification dynamics it is important to engage in a sophisticated political ecology which examines the patterns of livelihood (political economy) and ecology in specific places (Watts, 1983, 1987). The revisionist work on desertification among Sahelian pastoral communities is instructive in this regard (Turner, 1993; Watts, 1987; Leach and Mearns, 1997; cf. pastoralism). This scholarship suggests that certain narratives of desertification became dominant (and were encapsulated in the UNCOD report) which were alarmist in their predictions, rooted in limited research, and rested on simple-minded presumptions of drought causality, poor local resource management by farmers and pastoralists, and unregulated population growth. New research starts from a more sophisticated and fine-grained analysis of the ecology of rangelands (which complexifies alarmist positions), and starts from the paradox of why farmers and pastoralists who know a great deal about their environment should self-consciously overexploit it. The starting point here is poverty and the ways in which access to and control over local resources is changing in such a way that sustainability and conservation are undermined, and how situationally rational decisions may induce desertification. Poor pastoralist communities, which are increasingly differentiated economically, are subject to patterns of outmigration, changing terms of trade, and agricultural and state encroachment which produce excessive animal densities around some dry season wells. Degradation is associated therefore with some locations (public access wells) and some places and some seasons. Whether this represents long-term desertification is another matter. The UNCED Conference in Rio in 1992 (Agenda 21) discussed desertification in much less alarmist terms. (MW)

References Dregne, H. 1985: Aridity and land degradation, Environment 27 (8): 18-33. Grainger, A. 1990: The threatening desert. London: Earthscan. Glantz, M. 1977: Desertification. Boulder: Westview. Glantz, M., ed., 1987: Drought and famine in Africa. Cambridge: Cambridge University Press. Leach, M. and Mearns, R. 1997: The lie of the land. London: Currey. Turner, M. 1993: Overstocking the range, Economic Geography 69 (4): 402-22. Watts, M. 1983: Silent violence. Berkeley: University of California Press. Watts, M. 1987: Drought, environment and food security. In M. Glantz, ed., Drought and famine in Africa. Cambridge: Cambridge University Press, 171-212.



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