The imperative to improve human well-being can place multiple and often competing demands on ecosystems. Difficult trade-offs may have to be made, for instance between the protection of habitat for biodiversity, and the transformation of ecosystems for human needs. Some ecosystem transformation is inevitable if the Millennium Development Goals (MDGs) are to be met, but the impact on biodiversity will depend on how development activities are carried out. Significant opportunities exist to generate wealth through activities that draw on environmental goods-and-services, and at the same time promote the conservation of these resources. These activities include a range of moderate intensity extractive uses, such as livestock or wildlife ranching, wild plant harvesting, lowimpact logging, and sustainable fisheries, as well as nonextractive uses, such as nature-based tourism and the exploitation of genetic resources.

The major current
cause of biodiversity
loss in Africa is
habitat loss and that
is likely to remain true
for the first third of
the 21st century.

Sala and others 2000

As already discussed, despite significant environmental change, Africa still has a significant store of biodiversity. The key challenge in promoting sustainable natural resource use is to ensure that the rate of extraction (including the incidental damage caused during the harvest process) remains within the limits of sustainability. Strategies to ensure sustainability may rely on a combination of protection strategies including protected areas and conservation measures within “used-and-lived-in” spaces. Important challenges are how to:

  • Determine the sustainable extraction rate and practices; and
  • Establish and maintain institutions that are able to regulate natural resource use within the limits without placing undue constraints on their legitimate use.

Habitat degradation and loss

Habitat refers to the range of resources that a species needs to maintain a viable population including sufficient territory, necessary food and water, and required physical features such as tree cover, rocky hills or deep pools, as well as the organisms and ecosystem disturbances that must be present for it to complete its life cycle. The major current cause of biodiversity loss in Africa is habitat loss and that is likely to remain true for the first third of the 21st century (Sala and others 2000).

Habitat is lost when land cover (or its aquatic equivalent) is changed, usually as a result of changing use by humans. Common examples are the conversion of near-natural vegetation to temporary or permanent croplands; the replacement of forest by pastures; the expansion of human settlements; and the alteration of river habitats by dams, pollution and removal of water for human use. Forests and woodland cover is declining at a rate more or less equivalent to the increase in cropland (Scholes and Biggs 2005). The terrestrial ecosystem type where the greatest degree of habitat loss has occurred is grasslands, which have been converted to cereal agriculture (Scholes and Biggs 2005).

Habitat fragmentation – the division of continuous patches into smaller pieces which are partly or fully disconnected from one another by infrastructure, agricultural fields or human settlements – can have similar outcomes for biodiversity as outright habitat losses. First, the “edge effect” disrupts biodiversity for a considerable distance into the remnant patches. Second, the number of species that can be supported in the long term depends on habitat size.

Overexploitation of resources

If renewable resources are harvested at a rate greater than their regeneration rate, the long-term flow of benefits is reduced, and they are said to be overharvested. When natural capital is drawn down too far, fundamental ecosystem changes can occur which make ecosystem recovery to full service delivery potential very slow or impossible, and degradation is said to have occurred. Degraded ecosystems support half or less of the biodiversity of non-degraded used ecosystems (Scholes and Biggs 2005).

Much overharvesting is the unintended side effect of activities aimed at harvesting just one or a few components of the ecosystem. The discarded “bycatch” in fisheries and the habitat destruction caused by logging are examples of this. Regulatory policies that pay no heed to anything other than the target species encourage this kind of damage.

Overharvesting is a problem in many localities. For example, about 9 per cent of rangelands south of the equator are grazed by domestic livestock at unsustainable rates (Scholes and Biggs 2004). The fish stocks in the Great Lakes (Lake Victoria in particular) show classic symptoms of overfishing, and marine fish stocks in Western and Eastern Africa are at risk of overfishing.