Diversity, Structure And Dynamics Of An Acacia Erioloba Woodland In The Windhoek Area: Insights For The Management Of Urban Habitats

ABSTRACT 

Acacia erioloba, a tree species of great ecological and economic importance is threatened by urban expansion and a lack of sustainable management in the Windhoek area. The overall objective of this study was to determine the diversity and structure of an Acacia erioloba woodland and the influence of herbivory, wood harvesting, fire and physical soil properties on vegetation structure. Forty quadrats 625m2 in size were demarcated in pairs on alternative sides of a transect line to sample trees at 50m intervals. Shrubs were sampled in 100m2 quadrats nested in the tree quadrats and herbaceous plant cover was estimated in 1m2 quadrats within the shrub quadrats. Mean Shannon-Wiener diversity (H') index was 1.929, and could be interpreted as reflecting moderate to low species diversity, indicative of a disturbed community. Height structure and density differed significantly between the woodland community and A. erioloba population. A. erioloba population height patterns showed an ageing population with most plants in the largest (>5m) height class. Density patterns supported this trend with higher shrub densities in the community than in the A. erioloba population. The HCA and DCA of plant species composition showed no a clear separation of  quadrats into groupings. DCA axis 1 explained 46% of the variation in species composition while CCA showed environmental variables explained 19% of the observed variation in species composition. The overall test of all canonical axes was significant (F= 1.82, p < 0.05) with the explanatory variables fire (F= 1.82 p< 0.05), pH (F= 1.54 p< 0.05) and woodharvesting (F=1.46 p< 0.05) significantly influencing species composition. This illustrates that these factors are important in determining woodland structure. However, management could be facilitated by further research on more determinants of woodland structure and simulation modelling of woodland dynamics.