Potential key drivers of thicket expansion in savanna

Bachelor Thesis


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University of Cape Town

The invasion of grasslands by woody plants and their increase in savannas is a global phenomenon. There has been a lot of work on the ecology of savanna trees, but very little on the drivers of the increase of non-savanna (forest and thicket) vegetation within savannas. The swit9h from savanna to closed canopy thicket represents a biome switch for the system and is therefore of concern to land and conservation managers. Data on height growth, root suckering and fire damage were collected for two thicket forming species. A simulation model was developed to evaluate the effect of different biotic and abiotic factors on the spread of a thickerclump in savanna in the Hluhluwe Game Reserve, South Africa. The amount of damage from fire suffered by a thicket clump is increased by higher fire intensity and decreased by larger clump area or greater pre-burn mean clump height. A sensitivity analysis indicated that increased height and area growth rates and decreased fire frequency allows thicket expansion to occur and that data on these is essential for predicting the expansion of thicket clumps. Predictions from the model suggest that a thicket clump's situation within the landscape is important and that spatial modelling, incorporating fire spread and fire refugia such as river banks is necessary to further improve understanding of thicket expansion.