Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Control of bush encroachment with fire in the arid savannas of Southeastern Africa.

Auteur : Trollope, Winston Smuts Watts.

Université de soutenance : University of KwaZulu-Natal

Grade : Doctor of Philosophy 1983

Résumé partiel
The arid savannas of southeastern Africa comprise the thornveld and valley bushveld areas of the Eastern Cape, Ciskei and Transkei that receive less than 650mm of rain per annum. Bush encroachment has become a serious problem in the thornveld areas where it has drastically reduced the grazing capacity of the veld. The encroachment has occurred from the valley bushveld of the dissecting river valleys and from the scrub forest that is marginal to the high forest of the Winterberg, Katberg and Amatole mountain ranges. The principal encroaching species is Acacia karroo but other important associated species are Scutia myrtina, May tenus heterophylla Rhus spp., Diospyros lycioides, Xeromphis rudis, Azima tetracantha and — -- ------  Zi ziphus mucronata. The two most important factors to be considered when formulating a program for controlling bush encroachment are the ecological and economic consequences of applying the control methods. Fire was chosen as a possible method of controlling bush encroachment because it is a non-capital intensive technique which makes it compatible with the inherent low economic potential of veld. From the ecoiogical point of view fire is recognized as being a natural factor of the environment in savanna areas of Africa and has been occurring since time immemorial. Consequently it was decided to conduct a research program on the use of fire in controlling bush encroachment. The initial key question that was investigated was the role fire can play in controlling bush encroachment in the arid savannas. A review of the literature and personal experience led to the postulation of an hypothesis that the role fire can play in controlling bush encroachment in these areas is to maintain bush at an available height and in an acceptable state for browsing animals. Generally the tree and shrub species of the savanna areas are very resistant to fire alone due to the presence of dormant buds at the base of the stem, from which coppicing occurs. In the arid savannas the rainfall is too low and erratic to support frequent enough fires under grazing conditions to prevent the regeneration of bush from coppice and seedling growth.

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