Introduction
Terrestrial ecosystems provide human beings with food and raw materials, space for our housing and recreation, and control the air, water, and soil quality. The land on which we live, its condition, and how we use and manage it, are therefore vital components of our existence.
South Africa is characterized by a wide diversity of plant and animal life and is ranked as the third most biologically diverse country in the world (mainly due to the richness of the plant life). Over 18 000 species of vascular plants occur in South Africa, of which over 80% occur nowhere else. Estimates of total species numbers in the country vary from 250 000 to 1 000 000 and it is estimated that South Africa has 5.8% of the world's mammal species, 8% of the world's bird species, 4.6% of the world's reptile species, 16% of marine fish species and 5.5% of the world's recorded insect species (DEAT 1997). Over 10 000 species of the coastal animals and plants (almost 15% of the world's total coastal species) are found along South Africa's coast, with about 12% of these occurring nowhere else. In terms of the number of endemic species of mammals, birds, reptiles and amphibians, South Africa ranks as the 5th richest country in Africa and the 24th richest in the world (DEAT 1997). This diversity is caused by variation in climate, geology, soils and landscape form.
However, South Africa also has the highest concentration of threatened plant groups in the world (Cowling & Hilton-Taylor 1994). Approximately 3 435 of South Africa's plant groups are considered to be globally threatened with extinction (Hilton-Taylor 1996). A further 204 groups are estimated to be threatened at a local level.
South Africa's terrestrial systems are fragile, however, and must be managed carefully. Nearly 91% of the country falls within the United Nations definition of "affected drylands" (UNCCD 1994). These are extraordinarily dry areas where the rainfall is low, and potential evaporation is high. Dryland systems are often very sensitive to change, and therefore need to be managed carefully. For example, crops grown in these areas are usually not irrigated, and depend on rainfall. Drought-induced crop failure can result in direct food shortages at the local level, usually affecting subsistence agriculturalists the hardest. Removal of vegetation (ground cover) from dryland areas can increase the risk of soil erosion, making the soil less fertile, and less able to support vegetation (natural or cultivated crops) in future.
The maintenance of biodiversity is a prerequisite for ecosystem sustainability; once extinct, species cannot be brought back. The local extinction of species constitutes transformation of an ecosystem. The knock-on effects of this contribute to further transformation of the ecosystem. For example large browsers like elephants select certain types of plants from the vegetation, and therefore control the structure of the vegetation, and the species which can survive there (Owen-Smith & Danckwerts 1997). Local extinction of elephants from, for example, a savanna system, would lead to transformation of the vegetation composition and structure, by increasing the woody component in relation to the grass component. This has further consequences for animals that use both woody and grassy species for food and shelter. Unfortunately, very little is known about the knock-on effects of local extinctions, and the time scale over which these occur. Good environmental management therefore requires that we apply the "Precautionary Principle" and try to minimise the risk of extinctions, until we are sure that the impacts will not be detrimental to ecosystem functioning or to human quality of life. One way of ensuring this is to manage populations of plants and animals within an area, and make sure they do not fall below a minimum viable size ( Minimum Viable Population or MVP; Gilpin & Soulé 1986, Soulé 1987). This is the smallest number of individuals which can reproduce and function normally, even under stressful conditions such as drought.
The surface area of South Africa is 122 million hectares of which 86% is classified as agricultural, although most of this is grazing land, rather than crop cultivation. The land ownership reform process which has taken place since 1994, allowing all South Africans fair access to land and natural resources, has resulted in more than 6 million hectares of previously state-owned land now being more intensively cultivated (GCIS Document, 1999). This already significant demand on the land, combined with a growing population, and hence growing demand for food, space and other resources, make it essential that the land and its resources are used wisely and sustainably. Plantation forests occur on about 1.5 million hectares of land in South Africa. These forests support industries important in the economy of South Africa. Although the area of these forests is relatively small (a little more than 1% of total land area), the forests place high demands on the environment, (e.g. in terms of water use) compared to both the area occupied, and compared to the natural vegetation which they replace. There is therefore special concern about the role of forestry in national sustainable development.
Many international conventions and commissions have been brought about by the global recognition of the need to manage terrestrial ecosystems and resources on a sustainable basis, and South Africa is party to many of them (see Conventions and Agreements). The Intergovernmental Forum on Forests of the United Nations Commission for Sustainable Development (UNCSD), for example, recognises the economic benefits and the social and environmental costs of plantation forests as important policy issues. The Convention on Biological Diversity aims to promote the sustainable use of living natural resources worldwide. It also aims to bring about the sharing of the benefits arising from the utilisation of natural resources. The Convention to Combat Desertification is a global initiative aimed at combatting the economic, social and political impacts of desertification in those countries experiencing serious drought and/or desertification, particularly in Africa.
Special attention needs to be paid to effective land-use planning and minimizing the effects of loss of habitat and of prime agricultural land , as well as pollution and land degradation in its broadest sense. This chapter explains what is causing changes in terrestrial ecosystems, describes the current state of terrestrial systems, and lists what can, and is being done, to reduce the pressures causing degradation.
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There is also information about Terrestrial Ecosystems in the following reports:
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Metropolitan reports:
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Affairs and Tourism. All Rights Reserved.
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Last update: October 1999
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