Alien Plant Species And Noxious Weeds

South Africa has the third richest biodiversity in the world, which is under considerable pressure and threat. The remarkable richness of South Africa’s biodiversity is a result of the mixture of tropical, subtropical and temperate climates and habitats, which gives rise to extraordinary plant variety.

Human activity has changed ecosystems in South Africa. Ecosystems have been degraded and ecological processes impaired. One of the reasons for this is the increasing growth of urbanisation and industrialisation. The South African Red Data Book reports that the following percentages of species can be considered threatened:

• Plants: 15%
• Amphibians: 18%
• Reptiles: 24%
• Birds: 14%
• Mammals: 37%
• Butterflies: 22%

Alien plant species is another factor that threatens biodiversity and indigenous plant species.

Identification Of Alien Plant Species

Alien Plants - Alien or invasive plants refer to plants that do not originate in South Africa. They cause problems by using 10% of South Africa’s annual rainfall, killing indigenous plants, causing fires and soil erosion, and endangering many animals.

Alien plants came to South Africa as garden plants, in horse feed, and with forestry plantations. Alien plant species grow well in South Africa because they have no natural enemies such as insects, animals and disease that would control them in their original countries.

Some alien plants spread less aggressively than others. The Department of Water Affairs has identified and categorised 198 invader or alien plants in South Africa. These alien plants have detrimental effects on farming areas, indigenous bush, water supply, cause fires, and increase soil erosion. For more information refer to www.dwaf.gov.za for a detailed list.

Alien plant species grow in different regions in South Africa. For the purpose of the classification, South Africa has been divided into three sections, namely:

Subtropical Region: K-Zulu Natal, Mpumalanga, Limpopo, North-West Province, Gauteng

Fynbos Region: Western and Eastern Cape

Arid Region: Northern Cape, Eastern Cape, Free-State

Click here to view and download a table that contains, the alien plants that are found most commonly in the different regions are listed together with its control measures.

Clearing Alien Plant Species

In the tables in the previous section, the control measures for the various alien species are stated. The following method is used for removing alien plants:

• Identify the area and extent of coverage of invader plants and weeds.
• Identify the invasive species present.
• Segment the area into manageable units.
• Remove invader plants from the first segmented area by using the measure suited for the specific plant and the growth stage and size of the plant.
• Make sure that personnel handling chemicals and equipment are trained to apply any chemical and understand the precautionary measures.
• Be careful not to remove all vegetation. Remove the invaders but retain the indigenous plants and prevent weeds from taking over.
• Once the first segment is cleared, move on to the next area.
• Remove secondary growth of the invader in the cleared area using the relevant methods
• Maintain area to ensure re-growth and seedling emergence is minimised.
• Continue with the process until no regrowth or new seedlings emerge.
• Removed plant material can be used as compost or mulch or in the case of larger trees, like charcoal or firewood.

Remember

Alien, or invasive, plants are plant species that are not indigenous and were brought to South Africa as garden plants, in horse feed or when plantations were established.

Alien plants proliferate in South Africa because they do not have any natural enemies in their environment.

Alien plants are categorised into three categories, from plants that should be removed and destroyed wherever they are found, to plants that may not be planted, but that may be allowed to continue growing where they already are.

Alien plants are controlled by means of sawing, hand pulling, bio-control or herbicides.