Desertification

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Desertification first became a topical issue in the 1930s with the dust bowl of the Great Plains of North America. Since then desertification has become a global problem, particularly with the devastating droughts of 1968-73 in parts

Figure 11.2 Mounted head of European bison Bison bonasus, which was amongst the big-game animals ruthlessly hunted by big-game hunters more interested in the thrill of the chase than conservation. This particular species, however, is no longer in danger of extinction (see also Section 5.8.2). (Drawn by Peter R. Hobson.)

Figure 11.2 Mounted head of European bison Bison bonasus, which was amongst the big-game animals ruthlessly hunted by big-game hunters more interested in the thrill of the chase than conservation. This particular species, however, is no longer in danger of extinction (see also Section 5.8.2). (Drawn by Peter R. Hobson.)

of the Sahel where 100 000 people and 12 million cattle died. The Sahel region is a narrow band of West Africa sandwiched between the Sahara desert to the north and the savannas and tropical forest to the south. The United Nations Conference on Desertification (UNCOD) defined desertification as land degradation in arid, semi-arid and dry subhumid areas resulting mainly from adverse human impact. Despite the definition, the underlying complex causes of desertification also involve climate patterns and long-term climate change. Le Houerou (1997) points out that the Sahara has expanded and shrunk a number of times over the past 1.7 million years. Moreover, the drought in the Sahel (a 20-40% reduction in rainfall over three decades in parts of the Sahel) is similar to a dry episode that occurred during most of the first half of the 1800s (Nicholson, 2001; see Section 11.3.1 also). However, it is readily apparent that human impact on the landscape has aided the decline of forests and other vegetation during these droughts through soil compaction by domestic animals and by gradual clearing of trees for firewood.

As mentioned in Section 3.3, forests, in repeatedly recycling the amount of water passing from the oceans to the land, increase rainfall on a continental scale. This is a major aspect of the reasoning behind present attempts to re-afforest the Sahel region. Mixed plantings of eucalypts (particularly Eucalyptus camaldulensis) and nitrogen-fixing acacias are proving most useful in stabilizing soils and thus helping to bring land back into production, although there is suggestion that the eucalypts can lead to soil acidification. Acacia senegal and A. albida are particularly useful as crops.

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