The Threat of Alien Vegetation
Invasive alien plants now infest 20 million hectares of South Africa – an area twice as large as previously estimated. The shock finding comes from an Agricultural Research Council (ARC) report commissioned by Water Affairs, published in 2010. If these 20m hectares could be condensed into a single area, it would form a dense, impenetrable thicket about twice the size of the Kruger National Park.
These aliens, including various species of wattle, pine, poplar, weeping willow, gum trees, hakea and prickly pear, pose a serious threat to South Africa’s water supply, as well as to the country’s agricultural potential and biodiversity.
Australian plant species were introduced to the Western Cape for practical purposes like providing a source for fuel and to stabilise dunes. Ornamentals were imported from all over the world to beautify outdoor spaces.
Because these plants have no natural enemies such as the insects, animals and diseases that would have controlled them as in their own countries, they rapidly spread, taking over riverine, fynbos and forest fringes. Invading alien plants use much more water than indigenous trees and plants. They prevent rainwater from reaching rivers and deprive people and ecosystems of much needed water. Many springs and streams have already dried up because of invading alien trees. Some alien species inhibit germination of native plant seeds, with the result that biodiversity in certain regions is threatened.
Fires in invading alien vegetation are more intense than those in natural vegetation, resulting in damage to the soil. With the first rains the soil is then washed into rivers causing the rivers and dams to fill up with sand.
What can we as gardeners do?
• Look for invading alien trees and plants in your area and cut them out
• Ask your neighbours to do the same
• Report alien infestations to the Municipality
• Plant indigenous trees and plants in the garden
See Sana’s list of invasive plants: www.sana.co.za/alien-invasive-plants