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Afrotropic Deserts

The Afrotropic deserts (Figure 4.1) comprise four large lowland desert ecoregions (Ethiopian xeric grassland and shrublands, Nama Karoo, Somali Acacia-Commiphora bushlands and thickets, and Southwestern Arabian foothills savanna); eight ecoregions occupying coastal desert fringes (Arabian Peninsula coastal fog desert, Eritrean coastal desert, Gulf of Oman desert and semidesert, Madagascar spiny thickets, Namib desert, Northern Namib's Skeleton Coast, Red Sea coastal desert, and Succulent Karoo), and four montane Pleistocene relict ecoregions, or desert "skyislands" (Al Hajar montane woodlands, Ethiopian montane forests, Somali montane xeric woodlands, and Southwestern Arabian montane woodlands). They cover in total 2.7 million square kilometres, of which some 10 per cent is under environmental protection. Their mean population density is 21 persons per square kilometre, and their mean human footprint (20) is relatively high, especially in the Horn of Africa and Madagascar.

Among the plants that are unique to these deserts are Welwitschia mirabilis of the Namib and a great variety of woody legumes and succulentstemmed species such as baobabs (Adansonia), commiphoras (Commiphora), bottle-trees (Pachypodium), phantom-trees (Moringa), and kokerbooms (Aloe dichotoma). The Succulent Karoo, which is home to many of these plants, is the world's only plant hotspot (Mittermeier and others 1999) that is entirely found within the desert biome and is entirely arid. The Madagascar thorny thickets represent a unique, very diverse assemblage of plants and animals, most of them found nowhere else - such as the local baobabs and the octopus tree (Didierea madagascariensis). Much of the Namib is protected but some significant areas are at risk because of prospecting and mining of diamonds and copper. In contrast, very little of the Madagascar thorny thickets are protected; more than 90 per cent of the original habitat has disappeared through extraction of wood for firewood and charcoal, grazing and clearance for farming. Livestock browsing and human firewood collection also threaten the deserts around the Horn of Africa and in the southern Arabian Peninsula, from the Red Sea to the Gulf of Oman.


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