A thesis submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the academic requirements for the degree of Doctor of Philosophy. August 2016, Johannesburg / Termites are widely distributed in tropical and subtropical savanna. They are recognised as major ecosystem engineers through their role in nutrient cycling, decomposition, hydrology and alteration of landscape topography with cascading effects manifesting in ecosystem heterogeneity and productivity up the food chains. In this thesis I addressed the effect of geology on termite species diversity, followed by questioning how the different geologies influence the size and spatial distribution of Macrotermes mounds. Furthermore, I explored the effect of termite mounds emanating from different geologies on herbaceous vegetation heterogeneity and finally the effect this heterogeneity has on grazing intensity. Although the diversity of termites has been explored across different environmental gradients such as rainfall, altitude and disturbance, little is known regarding variation in their diversity across landscapes of varying geology. In my quest to understand how varying geology influences the ecology of termites and their functional importance, I sampled granite and basalt for termite diversity using standard transects (100 m x 2 m). I predicted that termite diversity is higher on nutrient-rich geology following the productivity diversity hypothesis. However, both functional and taxonomic diversity were higher on nutrient-poor granite. Twelve species from three subfamilies representing two feeding groups were recorded on granite whereas on basalt only five species from two subfamilies consisting of one feeding group were recorded. Although the influence of Macrotermes mounds on ecosystem heterogeneity has been well studied, little is known on how the environment (geology) and other termite colonies influence size and distribution pattern, despite how these interactions could influence ecosystem functioning. Termite mounds were sampled in 1 km2 plots, four in each geology. Each mound location was recorded using a hand held GPS and structural variables (height and diameter) measured. The data were analysed for spatial distribution of termite mounds using the software Programita. The general distribution pattern of termite mounds (active and inactive mounds combined) was investigated using both the pair correlation function, g(r), and Ripley’s K(r) function. Termite mounds were larger and covered a significant proportion of the landscape on granite compared to basalt. Mounds were generally over-dispersed on granite and randomly distributed on basalt. Mounds covered ~ 6% of the landscape on granite compared with only ~ 0.4% on basalt. These results show that the significance of termites varies across geologies, being more important on nutrient-poor geologies because of their size and a more productive spatial pattern displayed here. The majority of studies testing mound effects on savanna vegetation spatial heterogeneity have been based on single site observations mostly comparing mounds and their paired savanna control plots. Furthermore studies did not consider the spatial effects of mounds with distance into the savanna matrix from mound edge, and this has rarely been tested across landscapes of varying geologies, as well as across mounds of different sizes. Therefore there was a need to explore this in order to broadly understand the functional importance of mounds. I sampled the herbaceous community on and off termite mounds and along distance transects from mounds on nutrient-rich and nutrient-poor geologies. Termite mounds as sources of spatial vegetation heterogeneity was more pronounced on nutrient-poor granite, with larger mounds having greater effect on vegetation composition and diversity than smaller ones. Mounds harboured compositionally different herbaceous plants compared with the savanna matrix on granite whereas there was no difference on basalt. In acknowledging the effect erosion from mounds may have on vegetation heterogeneity, termite mound effect on composition expressed at landscape level based on mound densities recorded in this study was estimated to be 19% of the landscape on granite whereas on basalt, the mounds influenced ~ 0.4% of the landscape. The choice of foraging sites by large herbivores in the landscape is influenced by food quantity, quality, inter and intra-specific competition and predation risk. Termite mounds harbour highly nutritious herbaceous plants compared to the savanna matrix, which makes them preferred foraging sites. Due to very small differences in soil nutrient content between mounds and savanna on basalt, mounds were expected to have little effect on grazing. In line with the set hypothesis termite mounds largely influenced grazing on the nutrient-poor granite and when viewed at landscape scale, based on mound densities and extent of erosion recorded, mounds influenced ~ 28% on granite and only ~ 0.8% on basalt. Overall my study has demonstrated that the significance of termites as ecosystem engineers varies across landscapes of varying geology, being more important on nutrient-poor compared with nutrient-rich geologies. / MT2017

The effects of artificially supplied perennial water on soil properties, vegetation dynamics and the distribution of large herbivores was investigated in southeastern Zimbabwe. Data collection took place between March 1997 and July 1998. Water points were situated primarily on three different soil types (clay-loam, sandy-clay-loam and sand), and in four different vegetation types (Hill communities, Colophospermum mopane veld, Acacia nigrescens woodland and Albizia petersiana woodland). One water point in C. mopane veld (Bandama) had been closed two years prior to data collection, while another, in the Hill community (Manyoka), had been introduced, two years prior to data collection. Changes in physical (infiltration) and chemical (organic carbon and nutrients) properties of soils around water points were largely restricted to within 100 m of water. Chemical enrichment of the soil occurred only at water points that had been in place for more than two years. Soil surface conditions were altered to distances beyond 100 m from water. Manyoka (the new water point) was an exception, with extreme changes limited to within 100 m of water. Herbaceous and woody species composition changed in response to distance from water with changes best described by asymptotic equations. Changes in species composition of the woody component appeared to be longer lasting than changes to the herbaceous component. Most perennial grass species declined close to water, but Urochloa mosambicensis increased close to water in areas outside of the Hills. Herbaceous species diversity was adversely affected by distance from water on sandy soils (Hill communities and A. petersiana woodland), but was largely unaffected on clay-loam (A. nigrescens woodland) and sandy-clay-loam soils (C. mopane veld). Woody species composition and density was altered out to 500 m from perennial water in Acacia nigrescens woodland on clay-loam soils. Results suggest that this vegetation type may be susceptible to bush encroachment close to water. Trends in woody canopy utilisation were generally similar to trends in woody species composition, and it is proposed that the former may be used to indicate future changes in the latter. Conversion of trees to shrubs was highest at Manyoka (the new water point) indicating that woody destruction by elephants is extreme during the initial years following water introduction. Large herbivore biomass was greatest close to water (< 1 km) during the dry season but not during the wet season. Herbivore species distributions appeared to be influenced by the position of perennial water, but since all range was within easy access of water, it is unlikely that animal distributions were constrained directly by the position of surface water. It is more likely that herbivores were spatially separated on the basis of habitat type. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1999.