The demography of Acacia stands on the Hluhluwe-Umfolozi Game Reserve

Bachelor Thesis


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University of Cape Town

Little is known about the demographics of the genus Acacia in Africa, despite its prominence and the economic and environmental importance of this group. The demographics and species composition of stands of four different Acacia species was investigated in the Hluhluwe-Umfolozi Game Reserve in northern Kwazulu-Natal in order to determine whether stands were self-replacing, or whether other Acacia species were invading them. Soil and stand density as well as the density and composition of the grass layer were investigated in order to determine whether any of these affected Acacia demography and species composition. In three out of four cases, the species whose large size class dominated the stand (known as the "stand species") was found to have a strongly bimodal size class distribution, skewed primarily towards the large size class and secondarily towards the small size class. Other Acacia species in the stands, with few or no large individuals present ("nonstand species") tended to have unimodal size class distributions, skewed primarily towards the small size class and secondarily towards the medium size class. Based on the proportion of small to large individuals, non-stand species are more likely to increase in overall numbers in future, suggesting that the species composition of the stands may be in a state of flux. Few relationships were found between stand density, grass density, grass composition and numbers of small and medium acacias. This could be as a result of differentiation between Acacia species, meaning that they cannot be analysed collectively. Furthermore, sample sizes of individual species may have been too small to analyse individually. Alternatively, it could mean that none of these factors have a significant effect on one another and that other explanations need to be found for the demographics of this genus.