*2.2.2. Combating bush encroachment*

Clearing of woody species has been found to greatly increase grass and subsequently animal production [28, 30]. Mechanical, chemical and biological methods are employed in trying to control the spread of bush. Chemicals such as Tordon 225 and tebuthiuron have been successfully used, but the use of Tordon 225 is restricted by certain physiological and environmental conditions [30]. Concerns about tebuthiuron on the other hand pertain to the accumulation and persistence of the chemical in the soil thus posing potential threats to non-target species [36, 37]. Biological methods sometimes employed include the controlled use of herbivores (especially goats) and fire. Du Toit [29] observed in a study in the Eastern Cape that in comparison to continuous/rotational sheep grazing of a *V. karroo* stand, there was a higher mortality of trees and more efficient control of seedling regrowth under continuous goat grazing than rotational grazing. Goat grazing resulted in a marked improvement in the cover, composition and vigour of the grass sward [29].

Fire has also been extensively used in combating bush encroachment in savanna because it is known to maintain a balance of grass to trees and shrubs in the savanna areas [25]. Trollope [25] has observed that fire generally has different roles in controlling bush encroachment in the moist and arid savannas. In the moist savanna regions (>600 mm p.a.), bush encroachment may be controlled with fire alone because there is adequate grass material under grazing conditions to support frequent enough fires to burn down and control the bush. This is unlikely in the arid savanna regions (<600 mm p.a), which constitute the major portion of the South African savannas, because the rainfall is too low and erratic to support frequent enough fires under grazing conditions to prevent the regeneration of bush [25]. In grassland, Du Toit [34] made observations that the application of fire to combat *V. karroo* intrusion in the Eastern Cape sweetveld was not a practical approach. While fire was found to retard *V. karroo* seedling development, it could however not prevent the seedling establishment.

All in all, eradication of *V. karroo* is difficult once the thorn has invaded an area where it was previously absent, since a seed bank which did not previously exist is established. *V. karroo* trees can produce large amounts of seeds annually, and these have a high longevity. As a result, destruction of a stand of *V. karroo* is often times still followed by seedling establishment and considerable regeneration [34].
