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Box 3.1. Direct Drivers: Example from Southern African Sub-global Assessment(SG-SAfMA) The direct drivers of biodiversity loss in southern Africa include the impacts of land use change, alien invasives, overgrazing, and overharvesting— all of which have already had a large impact on the region’s biodiversity, ecosystem services, and human well-being, and all of which are likely to spread in the absence of interventions. The dominant direct driver of ecosystem change in southern Africa is considered to be widespread land use change that in some cases has led to degradation. Forests and woodlands are being converted to croplands and pastures at a rate somewhat slower than in Southeast Asia and the Amazon during the 1990s, but nevertheless sufficiently fast to endanger ecosystem services at a local scale. Half of the region consists of drylands, where overgrazing is the main cause of desertification. In the first half of the twenty-first century, climate change is a real threat to water supplies, human health, and biodiversity in southern Africa. The threats arise partly because the projected warming may, over large areas, be accompanied by a drying trend, and partly because of the low state of human welfare and weak governance, which increases vulnerability of humans to climate change. Although some of these threats have slowed in some regions (afforestation with monocultures of alien species in South Africa has decreased, for example), some have accelerated elsewhere (afforestation with alien species in Mozambique has increased, for instance, due to favorable growing conditions and weak regulation). Thus, the region’s biodiversity remains vulnerable to land use change. In addition, the more subtle problem of land degradation is considered a bigger threat in the region. Several studies indicate that the biodiversity of southern Africa is at risk. There is now evidence, for example, that it is declining in the northern part of its range, but stable in the southern part, as predicted by the global change models. In addition, there is experimental evidence that the recorded expansion of woody invasions into grasslands and savannas may be driven by rising global CO2 concentrations. The ability of species to disperse and survive these pressures will be hampered by a fragmented landscape made inhospitable by human activities. The Assessments of Impacts and Adaptations to Climate Change in Multiple Regions and Sectors project is currently analyzing response options that may conserve biodiversity under future climate and land cover scenarios in southern Africa. Source:
Millennium Ecosystem Assessment |
