Alien Vegetation Removal Program

Plants are indigenous to the region in which they originated and evolved. An indigenous (native) plant species is one that has occurred in that region for thousands of years, and was not brought there by direct or indirect human action. A plant species in its region of origin (native range) usually has a large variety of natural enemies (predators, parasites and diseases) that have co-evolved (developed) with it and that keep its population numbers in check without eradicating it. Since all indigenous plants in an area have their own natural enemies, none of them has a competitive advantage over the others, and therefore they all live in a state of equilibrium with each other.

The boundaries of the native range of a plant species need not coincide with the borders of a country. Other, more specialised species are indigenous to a particular region, ecosystem or habitat. The Cape Floral Kingdom (popularly known as Fynbos) consists of a distinctive combination of plant species that is limited to parts of the Western and Eastern Cape Provinces in South Africa, and includes numerous species that are restricted to much smaller areas. Such an indigenous species that has a very limited distribution is said to be endemic to that area.

If a plant occurs in a region where it is not indigenous, it is referred to as an alien (exotic, foreign, introduced, non-native, non-indigenous) plant. Any plant that occurs artificially outside its known historical natural range, no matter how long ago it was introduced, is regarded as an alien. A plant that was taken by people from one part of a country in which it is indigenous to another part of the same country can even be considered to be an alien plant there.

Most alien plants can survive in their adopted country only if they are cared for, especially if the conditions in the adopted country differ much from those they are adapted to. However, a certain proportion of alien plants manage to thrive in the new country, to reproduce and to maintain populations without human help, and are then called naturalised plants. If such naturalised plants are also able to spread over considerable distances into new, undisturbed, natural areas and replace the indigenous vegetation, they are regarded as invasive alien plants, or invaders for short.

The majority of alien plants were introduced intentionally, with some useful purpose in mind, e.g. as crops, forestry species, dune binders, ornamentals or simply as curiosities. Many alien plants also arrived inadvertently, e.g. as contaminants of grain or fodder or adhering to animals, humans or vehicles. In an effort to control the invaders at Abo Shamani, projects are being undertaken to remove invaders such as Black Wattle, Bluegum, Lantana, Scottich Thistle, Jointed Cactus and others to allow for rehabilitation of indigenous bush and grasslands.

There are four basic methods of controlling invasive alien plants:

• Mechanical control

  This involves removing the invasive plants or damaging them severely by physical actions such as uprooting, clear-felling, slashing, mowing, ring-barking or bark-stripping or by hauling aquatic weeds out of the water. Felled trees often coppice, and the soil disturbance caused during the control action often stimulates the seeds of the invasive plant to germinate after clearing. Therefore, follow-up actions are very important.

• Chemical control

  This involves the application of registered herbicides to the invasive plants or to the soil surrounding them, with the aim of killing or suppressing the plants. The choice of herbicides, the correct application method, dosage, time of application and follow-up actions are very important.

• Biological control

  This consists in the use of host-specific natural enemies to reduce the populations of the invasive plant to an acceptable level.

• Indirect control

  This refers to methods that are not primarily aimed at killing invasive plants, but that can contribute towards their control, e.g. ploughing, the use of fire, the utilisation of parts of the plant, or the oversowing of and area with beneficial plant species.