Driving forces
It is possible to list a number of forces that affect terrestrial ecosystems, and they are often interlinked. Furthermore, driving forces can combine to produce more severe impacts than each force would create separately. For example, the development of a settlement, together with a small forestry development, and establishment of an agricultural enterprise, all within one vegetation type, may in total transform a large area of natural habitat, or may result in fragmentation (and hence impaired functioning) of the natural habitat, or it may result in a combined demand for water which the system cannot sustain. The driving forces behind terrestrial system change include population growth, uneven distribution of wealth amongst the population, international demands, population mobility, policy and legislation, and climate change.
Population growth increases the demand for land transformation for settlements, agriculture, and recreation, as well as the demand for resources such as food, fuel, building and furniture materials, paper and board, minerals and water. Urbanization, industrialisation, infrastructure development, and pollution also result from an expanding population. The population of 40.58 million is currently increasing by approximately 2% per year (link to Chapter 5). If this growth rate remains constant, the population, and hence the demand for resources will double within the next 35 years (i.e. by 2035 the same amount of land will have to support about 80 million people, providing them with space, food, clothing, energy, infrastructure and other commodities). Consumption of resources is related to socio-economic development, as well as population growth. For example, paper is used for education, communication, hygiene, and packaging of food and export products. Per capita consumption of these products increases with economic and social development. Conversion of natural habitats to urban, industrial and agricultural uses is often permanent (in terms of human life span) and usually has wide-ranging effects such as urban sprawl, acid rain, pollution of rivers.
The uneven distribution of wealth in South Africa has been created partly due to the apartheid laws of the past. In rural or undeveloped areas, where incomes are very low, people are highly dependent on natural resources to meet nutritional, medicinal, housing, and energy needs. Collection (and often exploitation) of natural resources from these areas to meet demands from urbanised or more developed areas, is also used as a means of generating much needed income.(See social section of report).
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| Elephant tusks confiscated at Lanseria Airport. Photo: SAP |
Rare and endangered species and products such as rhino horn, hippo tusks, elephant ivory, animal skins, and succulent plants and cycads, are also traded in response to international demand .
However, international demand can also act as a positive driving force. For example, environmental concerns about natural forests, especially tropical hardwoods, and the productivity and efficiency advantages of plantation forests, have prompted a global trend in the last one or two decades towards production from plantations. South Africa has been able to capitalise on these trends and has become a major plantation country.
The recent acceleration of international human movements, and international trade has introduced many alien species into this country, both intentionally and unintentionally. Introduced species can rapidly dominate ecosystems, replacing natural vegetation and animals, or using large amounts of water. This reduces the functionality of the natural system and lowers its ability to support the natural life forms, including humans.
Policy and Legislation have the potential to be both positive and negative driving force on terrestrial ecosystems. For example, the Environmental Conservation Act and the National Parks Act encouraged biodiversity conservation. However, historical land and development policies (e.g. the Land Act of 1913) have led to distorted demography and settlement patterns. Crowding people into relatively small communal areas, ("homeland areas") and high levels of unemployment and poverty resulted in large numbers of animals being grazed on the land. (Grazing lands in these areas are stocked at about 1.85 times the rate of commercial areas (Hoffman & Todd, 1999)). This caused significant overgrazing, veld degradation and erosion (Turner & Ntshona 1999). The high demand for fuel in these areas also resulted in excessive collection of biomass, especially wood, for fuel. It is important to note that people settled in these former homelands were aware that their actions were degrading the land, but were unable to prevent it (Hoffman et al. 1999). Soil degradation is most strongly correlated with high desities of people, animals and settlements in rural areas where unemployment levels are high and poverty is prevalent. However, overstocking on commercial farms (e.g. in the Cape midlands and eastern karoo which were between 27% and 36% overstocked during the 1980's (Wilson 1991)), has also contributed to land degradation. Commercial areas have also suffered from excessive use of agrochemicals, and the decline in soil organic matter under monoculture cultivation has caused acidification and erosion of soils.
Government subsidies (such as reduced irrigation costs, and reduced costs of agrochemicals) also encouraged poor land-use practices such as cultivation of marginal areas, monoculture, and over-fertilisation.
Natural disturbances, including floods and droughts, winds, fires, quakes, and outbreaks of pests and diseases, occur from time to time and, although man has little or no control over these natural events, risk management to minimize their economic, social and environmental effects is important. Responsible management of terrestrial ecosystems which helps maintain their proper functioning, also increases the risk of the system being able to recover after natural disturbances. For example, drought may form a catalyst for desertification, but soils that are already degraded are more prone to drought. Degraded soils will also suffer more severe impacts of drought (Hoffman & Todd, 1999). Migratory pests such as the Brown Locust and Redbilled Quelea can devastate agriculture throughout southern Africa, by destroying both crops and other vegetation. Control measures, especially poisons, used against such pests cause environmental damage as they are not target-species specific, and have devastating effects on local populations of wildlife.
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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.
Site maintained by the Directorate Environmental Information and Reporting
Last update: October 1999
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