|François Suchel/Still Pictures|
Biological diversity or 'biodiversity' means the variety of plant and animal life at the ecosystem, community or species level, and even at the genetic level. Biodiversity is most commonly measured and reported at species level with characteristics such as species richness (number of species), species diversity (types of species), and endemism (uniqueness of species to a certain area) being the most useful elements for comparison.
Only a fraction of the species inhabiting the earth have been identified and studied to date and the roles they play in influencing the environment are still often poorly understood. Studies have tended to concentrate on higher plants and mammals and such species have also been the focus of most conservation efforts. This can give a misleading impression of the importance of 'lower organisms' such as bacteria, insects, and fungi which play vital ecological roles-for example, in nutrient cycling, and regulation of water, soil and air quality. Lack of understanding of the role of such organisms can lead to their being 'sidelined' when conservation efforts or commercial utilization are being considered. It is worth noting that around 1 million of the 1.75 million species described so far are insects and myriapods, and that the total number of such species is estimated to be around 8 million. In other words, only one-eighth of insect and myriapod species have been identified and recorded to date. It is also estimated that there are 1.5 million species of fungi, of which 72 000 have been described, and 1 million species of bacteria, of which a mere 4 000 have been described (WCMC 2000).
Figure 2b.1: map of Africa showing biodiversity hotspots and potential hotspots
Source: Conservation International
Africa has rich and varied biological resources forming the region's natural wealth on which its social and economic systems are based. These resources also have global importance, for the world's climate and for the development of agriculture or industrial activities such as pharmaceutics, tourism or construction, to name but a few of the most important areas.
Africa is also a continent of extremes, both in terms of physical features and climatic conditions, and therefore in terms of the life it supports. The humid tropical forests of equatorial Africa are among the most productive ecosystems in the world with Net Primary Productivity (NPP)-the net flux of carbon from the atmosphere into green plants-greater than 800 gCarbon/m2/yr). They also support an estimated 1.5 million species. By contrast, Africa's arid areas are among the harshest environments in the world. The Sahara and Namib deserts and the Sahel, for example, have NPP of just 100 gCarbon/m2/yr (WCMC 2000). But even under these conditions many plant and animal species manage to thrive.
The designation of some areas as 'biodiversity hotspots' is a useful concept developed in recent years as a means of prioritizing habitats for conservation Myers 1990). Hotspots are areas where species diversity and endemism are particularly high and where there is an extraordinary threat of loss of species or habitat. There are 25 internationally recognized hotspots, six of them are in Africa (Mittermeier, Myers, Gil & Mittermeier 2000). These are shown in Figure 2b.1 and are described below:
Africa also has several areas where both species richness and degree of threat are high but endemism is lower. These 'potential hotspots' include the highlands of Ethiopia; the forests of the Albertine Rift in eastern Congo, Rwanda, Burundi and adjacent parts of Uganda and Kenya; the western escarpment of Angola; and the Miombo Woodlands of interior Southern Africa (Mittermeier and others 2000).
Africa also has a range of aquatic habitats with very high levels of biodiversity. Marine ecosystems tend to be more diverse than terrestrial ones and reach even higher levels of diversity in warmer tropical waters than in cooler seas. The coasts of many African countries have rich ecosystems such as coral reefs, seagrass meadows, mangrove forests, estuaries and floodplain swamps (Martens 1995). Rivers, lakes (freshwater and soda) and riverine edge swamps, valley swamps, seasonal floodplains, ponds and high altitude peatforming wetlands all contribute to a wide variety of aquatic ecosystems in Africa that support an extensive range of resident as well as migratory species (Harper & Mavuti 1996).
The national and sub-regional boundaries that characterize present day Africa are the result of geographical and human activities often determined by political or economic factors, they therefore seldom reflect the boundaries of ecological systems. This difference between political and ecological units is significant-when the boundaries of ecosystems extend beyond territorial boundaries, the protection of the natural resources within those ecosystems requires management strategies that are coordinated jointly between nations or sub-regions (Westing 1993). The disparities between political and ecological boundaries also imply some overlap in discussion of biological systems in the sub-regions referred to in this report. For example, Tanzania forms part of the Southern African sub-region but shares major ecological systems with Kenya and Uganda. It is therefore discussed in both the Southern Africa and Eastern Africa analyses.