CHAPTER 7: BIODIVERSITY

Lead Authors: Robert J. Scholes, Wolfgang Kuper, Reinette Biggs
Contributing Authors: Evans Mwangi, Jeanny Raharimampionona, Peter Lowry, ElHadji Sene, Peter Ashton, Stephen Blake, Christopher O. Justice

REGIONAL SYNTHESIS

Biodiversity offers multiple opportunities for development and improving human well-being. It is the basis for essential environmental services upon which life on Earth depends. Thus, its conservation and sustainable use are of critical importance.

The opportunities and challenges associated with biodiversity typically apply over large geographical extents, although one or two issues may be more important at any given location. To avoid repetition, particular issues are highlighted in the sub-regional sections, not because they are restricted to those areas, but because they are best illustrated there. Deforestation is discussed under Central Africa, while relations between protected areas and adjacent populations are dealt with under Eastern Africa. Riparian biodiversity is discussed in Northern Africa, climate change and invasive alien species (IAS) in Southern Africa, desertification in Western Africa, and endemism in the Western Indian Ocean (WIO) islands. Habitat degradation and resource overexploitation are discussed in this regional synthesis, because they are overwhelmingly important as drivers of biodiversity loss throughout Africa.

INVENTORY OF RESOURCES

Africa is well endowed with both variety and abundance of living things, together referred to as biological diversity, or biodiversity. That biodiversity, with some exceptions, is currently in a better condition than in many parts of the world. Biodiversity can be considered at three major levels:

  • The genetic variation within populations;
  • The number, relative abundance and uniqueness of species; and
  • The variety, extent and condition of ecosystems.

Broad geographical patterns

Ecosystems are broadly arranged in a latitudinal pattern (White 1983), with increasing species richness towards the equator (Mutke and Barthlott 2005). However, plant species richness is also high in the winter-rainfall Mediterranean climate regions of Northern Africa and the southern Cape (Cowling and others 1996). In between are the subtropical deserts, which are generally a zone of lower diversity: for example, a vast part of the Sahara, the Ténéré, is home to only 20 plant species in an area of about 200 000 km². Overlaid on these latitudinal patterns are pockets of rich biodiversity with small distribution ranges, particularly in tropical montane areas (Rahbek 1995). From Ethiopia to the Cape, mountains contain several centres of endemism for birds, mammals, and plants (Fjeldsa and Lovett 1997, de Klerk and others 2002). One of the most globally important centres of endemism is the coastal mountain range in the eastern part of Madagascar (Goodman and Benstead 2003).

Figure 1: The distribution of biodiversity The increasing richness of plants and vertebrates toward the equator is related primarily to climatic factors, such as water availability (Mutke and others 2001), however the diversity of land variations, such as topographic, is also important. There are exceptions to this: some areas with harsh climates including, the Namib Desert and the Karoo in the west of South Africa have an estimated 4 500 plant species, a third to one-half of which are endemic (Davis and others 1994).

Spatial patterns of diversity vary for different species, and the diversity and abundance of different species influence each other. For example, the Cape is a centre of plant diversity of global importance, but not a centre of diversity for mammals, birds, snakes and amphibians (Figure 1). The Central Zambezian Miombo woodlands located in Zambia, the Democratic Republic of the Congo (DRC) and Tanzania is a centre of bird diversity, but not of plant diversity.

Species richness and endemism

About 1 000 vertebrate species occur in just 4 of the 119 eco-regions (covering about 8 per cent of Africa’s total area): Northern Acacia-Commiphora bushlands and thickets, Northern Congolian forest-savannah mosaic, Albertine Rift montane forests and Central Zambezian Miombo woodlands (Burgess and others 2004).

A quarter (1 229 species) of the world’s approximately 4 700 mammal species occur in Africa (Brooks and others 2001), including about 960 species in sub-Saharan Africa (SSA) and 137 species in Madagascar. The eastern and southern savannahs host large populations of mammals, including at least 79 species of antelope (Klopper and others 2002).

More than 2 000 bird species occur, constituting more than a fifth of the approximately 10 000 bird species in the world, (Burgess and others 2004, BirdLife International undated). About 1 600 bird species are endemic to SSA (Jetz and Rahbek 2001). Bird species richness is highest in Eastern Africa around the Albertine Rift montane forests, the Victoria basin forest-savannah mosaic, East African montane forests, Northern Congolian forest-savannah mosaic, and then into the Acacia-Commiphora bushlands and thickets and the Central Zambezian Miombo woodlands. The large size of these eco-regions, their high level of habitat heterogeneity, and their presence on a migratory flyway explain this pattern. The next highest band of species richness is found across the remainder of the tropical belt, with the exception of the western portion of the Upper Guinea forests and the centre of the Congo basin. The eco-regions of Madagascar and other offshore islands all have much lower bird species richness than the continental mainland (Burgess and others 2004).

Box 1: Plant Diversity: Kupe-Bakossi

The area of Kupe-Bakossi, 100 km north of Cameroon’s second city of Douala, is a highly diverse region, with two extinct volcanoes (Mwanenguba and Edib), river valleys, grassland and some of the wettest forest in Africa. It is also the top centre for documented plant diversity in mainland tropical Africa, with a total of 2 440 species of which 82 are strictly endemic and 232 are threatened with extinction according to IUCN 2001 criteria. This richly diverse area has been under threat both from illegal logging and encroaching farmland. Among recently documented species is a new Cola species, an orchid species and genus not seen since it was discovered around 30 years ago on a tree that had just been felled in a logging operation, Ossiculum aurantiacum, a new mint specific to waterfalls, Plectranthus cataractarum, a new shrimp plant, Justicia leucoxiphus, as well as three new species of coffee.

Source: RBG 2005

Ossiculum aurantiacum is a highly attractive and critically endangered orchid, endemic to Cameroon.
Source: H. Beentje

Africa has about 950 amphibian species (GAA 2004); however numerous new species and even genera are described every year. The highest levels of amphibian species richness occur in the DRC (210), Cameroon (189) and Tanzania (157); these countries are also ranked among the 20 countries with the highest level of diversity and endemism (GAA 2004). The fauna of Madagascar are particularly undersampled: from 1990 to 1999 discoveries of new amphibian and reptile species increased the number of known species by 25 per cent and 18 per cent, respectively (Goodman 2004). The Congo basin is also under-represented due to inadequate surveys (GAA 2004).

Overall plant richness at species, genus and family level is lower than that of other tropical areas. The African mainland has between 40 000 and 60 000 plant species (Beentje and others 1994, Beentje 1996), of which approximately 35 000 are endemic. South America, by comparison, has about 90 000 plant species (Frodin 2001) in an area 40 per cent smaller. Parts of the Congo basin have moderate levels of plant species richness, comparable to many parts of Central Europe (Barthlott and others 2005). This is a consequence of major extinction events due to historic climate variations (Hamilton and Taylor 1991, Davis and others 1994) and fewer major tectonic events, which are thought to having triggered the evolution of many species in the South American Andes (Burgess and others 2004). Five of the 20 global centres of plant diversity are located in Africa. More than 3 000 plant species per 10 000 km² occur in the Cameroon-Guinea centre, the Capensis centre, the Maputaland-Pondoland centre, the Albertine Rift centre and the Madagascar centre (Barthlott and others 2005).

At least a sixth of the world’s estimated 270 000 plant species (Groombridge and Jenkins 2002) are endemic to Africa. The Cape Floral Kingdom, a global centre of plant endemism (Barthlott and others 2005) has about 9 000 vascular plant species occurring in an area of 90 000 km² (Goldblatt and Manning 2000) of which about 69 per cent are endemic. More than 12 000 plant species occur in Madagascar, at least 81 per cent of which are endemic (Davis and others 1994), which is an exceptionally high proportion by global standards. More recent studies suggest that these figures for species richness and endemism in Madagascar may be underestimates (Goodman 2004).

Southern Africa has a rich and varied insect and arachnid fauna, with at least 580 families and about 100 000 species recorded (Barnard 1998).There is a high diversity of butterflies in the rainforests of the upper Guinea, the Albertine Rift, and the Congo basin, as well as in the Central Zambezian Miombo woodlands (Burgess and others 2004). Namibia is thought to be one of the global centres of arachnid richness (Barnard 1998) and about one-third of the Southern African insect species are believed to occur in Namibia, although less than a quarter of these species are described.

Figure 2: Global diversity of amphibians Africa has several global centres of freshwater biodiversity (Groombridge and Jenkins 2002) and many of these are also centres of intensive fishing activity. Centres of species richness and endemism for freshwater fish, molluscs and crustacea are located in the upper Guinea river region (mainly Guinea and Liberia), Cabinda (DRC), and the eastern part of Madagascar. It is conservatively estimated that Africa has at least 2 000 fish species, which is thought to be the highest species richness in the world (Klopper and others 2002). The explosive diversification of certain types of fish, such as the Cichlidae in the Great Lakes, has contributed to this richness. Fish species richness in the Congo basin is second only to that of the Amazon basin. Data on endemism is inadequate (Groombridge and Jenkins 2002). Fish diversity at the family level is somewhat lower than in southern America and Southeast Asia.

The coastal and marine ecosystems along Africa’s 40 000 km coastline contain a high marine biodiversity, with overlapping centres of endemism of, for example, fish, corals, snails and lobsters at the coast of eastern South Africa and in the Red Sea (Roberts and others 2002). See also Chapter 5: Coastal and Marine Environments.

Centres of biodiversity

Biodiversity information is patchy for many organisms. Centres of biodiversity are located in the following eco-regions: Mt Cameroon and Bioko montane forests, overlapping with the Cross-Sanaga-Bioko coastal forests; the Cameroon highlands’ forests; the Eastern Arc forests and the northern Zanzibar-Inhambane coastal forest mosaic; the Guinea montane forests and the western Guinea forests; the Drakensberg montane grasslands and forests; the Albertine Rift montane forests and the upper Guinea lowland rain forests.

Figure 3: Plant and vertebrate diversity Nearly two-thirds (62 per cent) of SSA species of plants and vertebrates can be represented (though not necessarily adequately protected) in approximately 1 per cent of its land area, as shown in Figure 3. This 1 per cent area includes key taxon-specific centres of diversity (such as the Cape for plants) and a few multi-taxon centres of biodiversity such as, for example, Mt Cameroon, East Usambaras, Mt Nimba, Western Ruwenzori, Mt Elgon and parts of the upper Guinea lowland forests. Many of the represented species are endemic to these areas. To include all vertebrate and plant species occurring in SSA in protected areas, about a third of its total area would need to be included into conservation strategies. Hence, identifying locations of high biodiversity in several major groups, so that a high proportion of biodiversity can be protected in a comparatively small area, is an important research goal.

Ecosystem change and conservation

In comparison with most other parts of the world, such as eastern Europe, North America and Southeast Asia, Africa’s biodiversity is still in good condition (Hoekstra and others 2005, Scholes and Biggs 2005). Contemporary biodiversity patterns are strongly influenced by land-use patterns of mammalian herbivores and people. However:

  • Approximately half of Africa’s terrestrial eco-regions have lost more than 50 per cent of their area to cultivation, degradation or urbanization (Burgess and others 2005).
  • Eco-regions that have gone through more than a 95 per cent transformation include the Mandara Plateau mosaic, Cross-Niger transition forests, Jos Plateau forest-grassland mosaic, and Nigerian lowland forests.
  • Nine other eco-regions have lost more than 80 per cent of their habitat, including the species-rich lowland Fynbos and Renosterveld and the forests and grasslands of the Ethiopian Highlands.
  • The Mediterranean woodlands and forests have lost more than 75 per cent of their original habitat, and the few remaining blocks of habitat are highly fragmented (Burgess and others 2005).

The challenges and opportunities associated with human activities are also considered in relation to specific themes in the other chapters of this section.

Africa has over
2 million km²
of protected areas.

IUCN-WCPA undated

Africa has over 2 million km² of protected areas (an area four times the size of Spain) (IUCN-WCPA undated). The eco-regions under the best protection tend to be the savannah habitats, particularly those of Eastern and Southern Africa (Burgess and others 2005). Charismatic animals, such as large mammals, are much better covered by the current network of protected areas (de Klerk and others 2004, Fjeldsa and others 2004) than, for example, plants (Burgess and others 2005). Many range-restricted species are not adequately included in these areas (Rodrigues and others 2004).

The least protected areas are found in Northern Africa, Madagascar, the drier parts of South Africa, and in the most heavily deforested parts of Western and Eastern Africa (Tables 1-6). Of the 119 ecoregions, 89 have less than the 10 per cent of their area officially protected, which is the guideline suggested by the 2010 biodiversity targets of the Convention on Biological Diversity (CBD). Some of the least well-protected eco-regions are also those with high biodiversity values, including Mt Cameroon and the Bioko area, the Eastern Arc forests, the Succulent Karoo, the Ethiopian montane forests, the lowland Fynbos and Renosterveld, the western Guinean lowland forests, the east African montane forests, the Albertine Rift montane forests, and the Northern Zanzibar- Inhambane coastal forest mosaic.