South Africa is a semi-arid country, and drought and desertification are real threats to food security. Terrestrial ecosystems are very complex, and research has only been able to cover a few aspects. For more background information about terrestrial ecosystems, read this section . These processes impact terrestrial ecosystems, through degradation, alteration of processes, or transformation. In some cases these species have become invasive, i.e. they have dominated the natural vegetation, and place an additional burden on already scarce resources, such as water.
Government policies cause changes to terrestrial ecosystems, in both positive and negative ways.
For example, nature conservation laws have contributed to protection of species and habitats, preserving populations of species, the wilderness experience, enhancing quality of life, and slowing the rate of extinctions. On the other hand, government policies which encouraged monoculture and intensive use of agrochemicals have resulted in over-use of the land, and degradation of vegetation and soils. International demand for resources such as timber, and for biological resources such as wild animals, certain types of plants, and products such as elephant ivory and rhino horn, also cause changes to terrestrial ecosystems. For more information about the drivers of terrestrial ecosystem change, read this section . This places pressure on the environment in terms of suitable waste disposal sites, pollution, and changes to the atmospheric composition, with knock-on effects for climate stability.