Land degradation and desertification are major causes of biodiversity loss. Three factors contribute:
- A relatively dense and growing population with strong dependence on natural resources:
- Relatively easy access to resources; and
- Recurrent droughts.
These processes affect grasslands, steppes, savannahs and woodlands:
- They fragment forests and alter their structure and composition, especially when they are followed by recurrent forest and bush fires;
- They reduce surface water points and their associated plants;
- They strongly deplete animal populations and notably reduce a number of rare and vulnerable species through habitat degradation, sport hunting and especially through exploitation for bushmeat, which is exacerbated by drought-related food deficits.
Dust storms, forest fires, locust outbreaks and population displacement are all linked to the phenomenon of desertification, and have strongly negative consequences for people, in particular through the loss of livelihood and economic opportunities.
Land degradation is a persistent reduction in the capacity to support life and supply ecosystem services. It affects biological diversity directly and indirectly. It may affect the survival of species and alter processes that support their life, or it may trigger socioeconomic phenomena that impact on living species and their ecosystems. Land degradation phenomena directly affecting biodiversity include water and wind erosion. Along major river basins siltation processes accumulate debris and materials that engulf natural vegetation, such as the Acacia nilotica riparian forests. Trees may survive for years, but the diverse understorey may not. Soil erosion contributes to moving the seed capital of the ground, uprooting grassy as well as woody species, and in accumulation areas it smothers valuable species. This occurs in the sand dune areas of countries such as Mauritania, Mali, Niger, Nigeria and Senegal.
Indirect factors associated with land degradation that impact on biodiversity include the coping strategies people adopt to deal with environmental change. The movement of people south towards subhumid to humid tropical areas has resulted in depletion of natural resources: loss of primary forests and woodlands, repeated logging of the secondary vegetation, and depletion of a number of species. The influx of refugees from war-stricken areas also triggers severe land degradation in host regions and the overuse of wildlife resources. More diffuse degradation of land resources also occurs in the arid and sub-humid parts. These include the extraction of tree resources outside forests for charcoal making (about 150 million tonnes/year from the savannahs and woodland areas), and the use of high-value woods. Most affected are the Meliacaea family (Khaya species), Pterocarpus erinaceus, and Dalbergia melanoxylon.
The degradation and fragmentation of natural landscapes is caused by agricultural expansion. Agricultural expansion affects the survival and regeneration of animal populations, destroys the structure of wildlife habitat, and strongly contributes to reduction of wildlife populations. The number of species threatened continues to grow; these include lion, elephant, most of the greater antelopes, and waterdependent species such as manatees and crocodiles, which could form the basis of a tourism industry.