Fire survival and life histories of Acacia and Dichrostachys species in a South African savanna

Includes bibliographical references.The tree-grass mix defines savannas, yet savannas can be defined as ecosystems that move between transition states of grass and bush, the dynamics of which are complex, being affected by a number of biotic and abiotic factors. Recently there has been renewed interest in fire and its role in shaping and maintaining savanna communities in Africa. Other than its ability to radically alter the savanna components, relatively little is known about the mechanistic effects of fire regimes on the structural and functional dynamics of the ecosystem. Furthermore, the biological basis of the observed response has been very poorly studied. An improved understanding of savanna tree biology and how they respond to disturbance is essential for more effective ecosystem management. This study investigates variation in response of savanna trees to fire, and the underlying causes, in the Hluhluwe-Umfolozi Park, KwaZulu Natal, South Africa. This variation is explored by means of clipping experiments and controlled bums, across species, tree height (seedlings to adults), a rainfall gradient, and intensity and season of injury. The four study species were Acacia karroo, A.nilotica, A.caffra and Dichrostachys cinerea. A total of 670 trees were subjected to different clipping treatments and their response monitored for two years. The response of 1512 trees was assessed following eight controlled burns of varying intensity and season. I investigated seasonal variation in root starch storage as a possible mechanisms underlying tree response