and inequitable land-tenure systems that contribute to land degradation through unsustainable practices, declining soil fertility, poor land management and conservation, and the conversion of fragile natural habitats to agricultural and urban uses (UNEP, 2002a). Land use and degradation are priority issues for the region because of their cross-cutting impacts on other resources and human activities, particularly agriculture (UNEP, 2007a).

Land degradation is a loss of ecosystem function and services caused by disturbances from which the system cannot recover unaided. Land degradation, which includes soil erosion by wind or water, nutrient depletion, desertification, salinity caused by land-use and management, and chemical contamination and pollution, is broader than soil degradation, since land includes vegetation, water and microclimate (Bojo, 1996). Climate variability and unsustainable human activity are associated with land degradation (UNEP, 2007b). Approximately 65% of agricultural land, 35% of permanent pastures and 19% of forest and woodland in the region were estimated to be affected by some form of degradation in 1990 (Oldeman, 1994; WRI, 2005).

There is considerable variance among countries in SSA as to estimates of the costs of losses resulting from land degradation. In a 12-country study, the gross discounted cumulative loss (a metric which takes into account the cumulative nature of land degradation) varied from less than 1 to 44% of GDP with, for the most part, modest annual productivity losses (1-3%) (Bojo, 1996).

Desertification occurs when land degradation processes affect dry lands and is the most widespread form of land degradation in the region, affecting about 46% of Africa (Reich et al., 2001). A recent examination of existing available data however does not support the claim that the African Sahel is a desertification hotspot (Lepers et al., 2005), and in fact net greening has been observed following the droughts of the early 1980s. Possible reasons for this include changes in rainfall patterns, land use changes and improved land management (Olsson et al., 2005).

Insufficient nutrient replacement in agricultural systems on land with poor to moderate potential results in soil degradation. Whereas soil moisture stress inherently constrains land productivity on 85% of soils in Africa (Eswaran et al., 1997), soil fertility degradation now places an additional serious human-induced limitation on productivity (Figure 1-2).

Approximately 25% of soils in Africa are acidic, and therefore deficient in phosphorus, calcium and magnesium with often toxic levels of aluminum (McCann, 2005). Use of fertilizer in the region is the lowest in the world with average applications of less than 9 kg of nitrogen and 6 kg of phosphorus per ha, compared with typical crop requirements of 60 kg of nitrogen and 30 kg of phosphorus per ha. Recent research estimates that every country in SSA had a negative soil nutrient balance; the amount of nitrogen, phosphorus and potassium added as inputs was significantly less than the amount removed as harvest or lost by erosion and leaching (Swift and Shepherd, 2007). Although many farmers have developed soil management strategies to cope with the poor quality of their soil, low inputs of nutrients, including organic matter, contribute to poor crop growth and the depletion of soil nutrients.

1.2.1.2 Water
Freshwater resources are a critical input for agriculture, fisheries and livestock production as well as many other economic activities. SSA has significant surface and groundwater resources but they are unevenly distributed (FAO, 2002). The region is home to six of the world’s major river basins, namely the Congo, the Nile, the Niger, Lake Chad, Zambezi and Orange Rivers, and includes large water bodies such as Lakes Victoria, Tanganyika and Nyasa (UNEP, 2002b). Actual renewable freshwater resources average 6,322 m3 per capita, but this varies widely from only 509 m3 per capita in Burundi to about 218,000 m3 per capita in the Congo (D.R. Congo data not available) (WRI, 2005).

The agricultural sector is by far the biggest user of water resources; 88% of the total annual water withdrawals in SSA in 2000 were from agriculture, 4% by industry and 9% for domestic use (WRI, 2005). With growing demand for water resources from all sectors, it is projected that by 2025, 13 countries in SSA will experience water stress (less than 1,700 m3 per capita per year) and another ten countries will suffer from water scarcity (less than 1,000 m3 per capita per year) (UNEP, 2002b).

Furthermore, degradation of water resources including watersheds, wetlands and groundwater is occurring. For example, soil erosion leading to siltation of rivers and lakes adversely affects people’s health and access to clean water, and biodiversity, including fisheries, by changing the ecological conditions under which species live (MA, 2005a).

1.2.1.3 Biodiversity
Sub-Saharan Africa is rich in both a variety and abundance of biological diversity. The region closely corresponds to the Afrotropical biogeographical realm, which is the second most abundant realm in terms of numbers of species and endemic species (amphibians, birds, mammals and reptiles) after the Neotropical realm (Latin America and the Caribbean) (MA, 2005ab). Sub-Saharan Africa has a range of major habitat types or biomes, dominated by tropical and sub-tropical grasslands, savannas and shrub-lands. Other major habitat types include tropical and sub-tropical moist broadleaf forests, and deserts and xeric shrub-lands (MA, 2005c). These biomes have the highest levels of overall species richness (MA, 2005b). The region contains five internationally recognized “biodiversity hot spots” or areas of species richness and endemism which are under particular threat, namely the Western Indian Ocean islands, particularly Madagascar, the Cape Floristic Kingdom and the Succulent Karoo, both in southern Africa, the Guinea Forest in western Africa, and the Eastern Arc Mountain Forests of eastern Africa (UNEP, 2002a).

Plant and animal biodiversity are central to human wellbeing, most notably in food production but also as a source of fiber for clothing, wood for implements, shelter, and fuel, and for natural medicines and products, as well as having strong cultural and spiritual significance. Agricultural biodiversity encompasses domesticated crop plants and animals used for livestock or aquaculture, as well as wild food sources, their wild crop relatives, and “associated” biodiversity that supports agricultural production through nutrient recycling, pest control and pollination (Wood and Lenne, 1999). A number of important agricultural crops originated