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Alien invasive species of plants and animals are causing massive disturbance in natural ecosystems across Africa. In Southern Africa, the introduction of alien tree species, originally for plantation, is of greatest concern. The Catalogue of Problem Plants in Southern Africa (Wells, Balsinhas, Joffe, Engelbrecht, Harding & Stirton 1986) lists 789 species some of which, like Acacia saligna and Hakea sericea, have dominated areas to the extent that natural vegetation has been almost completely lost. Others, for example pine and eucalyptus trees, present a threat to water availability because they use greater amounts of water than the natural vegetation, and therefore reduce the amount of run-off reaching streams and rivers. Other species form dense stands that reduce the amount of light reaching the understorey, physically strangle native species and inhibit regeneration of native seeds. These impacts reduce the diversity and cover of indigenous plant species, and thus alter functioning of the ecosystem.
In South Africa, where the problem of alien invasive species has been well quantified and documented, about 180 species of trees and shrubs have invaded, covering 10 million hectares (8 per cent of the land area) (Versveld, Le Maitre & Chapman 1998). The plant diversity of the Cape Floral Region is particularly threatened by invasive species, with an estimated 33 of 70 threatened plant species being potential extinction victims of invasions of alien woody plants (Hall, De Winter & Van Oosterhout 1980). As in other subregions, the water hyacinth (Eichornia crassipes) is a problematic invasive plant in Southern Africa, forming dense mats that block water channels, disrupting flow patterns, reducing light and nutrients reaching below the surface of the water, and thus creating an undesirable habitat for native plants and animals. Decaying mats of the weed generate unpleasant odours and lead to eutrophication of the water body. Areas afflicted by the water hyacinth include Lake Kariba and Lake Chivero (Zambia/Zimbabwe).
There is a marked lack of information available on most invertebrates, algae, bacteria and fungi in Southern Africa, including on their genetic diversity. It is therefore thought that many species in the sub-region as elsewhere) become extinct before they can be named and described. Lack of knowledge of biodiversity issues has also been compounded by the fact that indigenous knowledge has not been accepted or documented by research institutes or in publications. As a result, protected areas, many of which were established more than three decades ago without consultation of local people, were set aside without accurate assessment of the biological richness within their boundaries. Thus some areas that have little significance in terms of biodiversity are protected while many others with significant biodiversity lack protection. In addition, farmers, who have custody of much of the sub-region's biological diversity, are rarely invited to share their knowledge it, even though that knowledge extends to crop and animal genetic diversity and includes wild plant and animal species that serve humanity as biological resources. The lack of comprehensive knowledge of biodiversity in Southern Africa also contributes to growing discontent about unauthorized access to biodiversity and lack of reciprocity in benefit sharing, mainly on the part of the rich developed countries. For example, while acknowledging that developing drugs is costly, it is also important to attain goals of wealth creation that will provide substantial benefit to those who conserve biodiversity through a culture of bio-partnership, rather than indulging in bio-piracy.
In spite of the numerous pressures on Southern Africa's biological resources, only one species of mammal (the Blue Antelope) has become extinct in recent times, but several sub-species have been lost. The demise of the Blue Antelope has been blamed on competition for grazing from sheep farming, and on subsistence hunting. The African Wild Dog is also an endangered species in Southern Africa, surviving only in large protected areas (Ledger 1990). Similarly the Bearded Vulture has undergone serious population declines in the sub-region and is now restricted to the Drakensberg Mountain range of South Africa and Lesotho. Declines in the Bearded Vulture's population have often been blamed on reduced prey, changing animal husbandry practices and direct persecution-in Lesotho, for example, the bird is killed for its plumage which is used in traditional ceremonies. The number of threatened plant species in Southern Africa continues to grow. Estimates show that 58 species had become extinct by 1995 compared to 39 in 1980, while the number of endangered plant species grew from 105 to 250 during the same period (Hilton-Taylor 1996). The numbers of threatened species in Southern Africa are shown in Table 2b.9. In terms of area, Southern Africa has the highest concentration of threatened plant species in the world (Cowling and Hilton-Taylor 1994). A large percentage of these are in the Cape Floral Region, and are threatened by the rapid urbanization of the Cape Metropolitan Area.
|Table 2b.9 threatened species in Southern Africa 2000|
|Source: IUCN 2000a a|