Pressures on terrestrial ecosystems: # 1

Population growth, income disparity, population mobility, international demand, and policy, result in increased demand for resources, and generation of wastes and other by-products. Increased demand for resources is manifest as a pressure to exploit natural resources, to convert land from natural to man made systems, and to increase productivity of these agricultural, silvicultural (plantation forestry), and industrial systems, to meet this demand. Increased productivity is often associated with generation of wastes and pollutants, which compromise the environment's ability to function normally. Pollution has also resulted in noticeable changes to the global climate. Side effects of increased population mobility and trade include invasions of alien organisms.

Exploitation of Natural Resources:  

Figure 2.1 Satellite images showing deforestation (left side of image), compared to natural vegetation. Source: Agricultural Research Commission.

Exploitation of natural woodlands and forests to meet energy and construction needs has led to the depletion of resources, and degradation of these systems. The effects of deforestation on ecosystem function have been poorly studied, but there are indications, for example, that the removal of dead wood could have a negative effect on the diversity of mammals, birds and insects by removing cover and nesting material. Other impacts include bush encroachment and an increase in alien invader plants. Bush encroachment reduces grass cover and therefore carrying capacity for grazing and browsing animals. Disturbance and land use history, rather than environmental or primary factors, appear the most important determinants of the extent and rate of bush encroachment (Hoffman et al. 1999). The impacts of deforestation are compounded by subsistence agriculture, especially in the communal areas where the density of human and livestock populations is high. Eberhard (1990) has estimated that the natural woodlands of communal areas will be completely denuded by 2020. An example of deforestation impacts is given in the satellite images above, comparing a communal area with an area of a national park. Images were taken four years apart and clearly indicate increases in bare soil where the vegetation has been removed.

Ironically this situation is less serious where alien trees have invaded, such as in areas of the Eastern Cape, where many people depend on the invasive trees to satisfy fuelwood needs, and often market woodstocks.

Figure 2.2 Market demand for medicinal plants

Income disparities and economic incentives have, and will continue to pressurize biological resources. The legal and illegal trade in wildlife products both nationally and internationally demonstrates this. The medicinal and horticultural trades are major users of South Africa's plant diversity. Approximately 10% of southern African plants (roughly 3000 species) are used medicinally, and 10% of this proportion (about 350 species) are commonly and widely used (van Wyk et al. 1997). The medicinal plant trade is a multimillion rand "hidden economy", with over 400 indigenous plant species sold for this purpose in KwaZulu-Natal alone (Cunningham & Davis 1997). A huge market demand in urbanized areas, especially of the eastern half of the country (Figure 2.2), drives the sale of more than 3000 Stangeria eriopus cycads per month in the Durban markets alone. The illegal collecting of plants in the wild, for private horticultural collections, targets rare and endemic species specifically (Hilton-Taylor & Le Roux 1989), and has the potential to reduce local populations below the minimum viable size, and even to extinguish species entirely.

Stangeria eriopsis

In contrast to this, the formal European horticultural and cut-flower trade, a multi-billion dollar industry, has been a major boost to the South African economy. In 1980, European traders spent about R3 million on fresh fynbos material, of which approximately 60% was protea flowers (van Wilgen & Lamb 1986). Controlled exploitation of plant genetic resources and cut flowers (which now comprise about 20% of the industry), can boost biodiversity levels through the preservation of natural veld, and controlled harvesting rates (intensive harvesting rates can deplete of the population by removing plants before they are able to drop seeds in the area), in addition to generating income.

Game farming and wildlife tourism are further examples of resource exploitation with beneficial outcomes. Commercial game ranching, for meat, hunting, and tourism, can increase the number and range of species in the area, by restoring or maintaining natural habitat conditions. These conditions attract small mammals, birds, insects, and provide germination grounds for seeds, in addition to the species that are stocked intentionally. Game animals are much better adapted to the arid and semi-arid environments in South Africa, and are less damaging to the vegetation and soil, as they trim the vegetation rather than pulling at the roots, and many species have smaller, more delicate hooves than domestic cattle. Parsons et al. (1997) found that game farming produces a herbaceous community structure and functional composition regarded as more desirable than domestic cattle ranching, even though stocking densities on game farms were much higher than would occur naturally.

Exploitation of non-living (mineral) resources uses vast quantities of water, energy, and timber, as well as being a significant contributor to waste and pollution generation in South Africa.

>     Terrestrial Ecosystems: Pressures #2

There is also information about Terrestrial Ecosystems in the following reports:
Metropolitan reports:
	Cape Metropolitan Council (1998 edition)		Durban Pilot Study
	Greater Johannesburg Metropolitan Council (1999 edition)		Greater Pretoria Metropolitan Council (1999 edition)