The growth and recovery of trees from disturbances such as fire and browsing is driven by the intensity of the disturbances and the availability of resources. In savannas, resprouting has become recognized as a key functional trait in plant ecology over the past decade. Although this may indeed be the case, there is still limited information about the physiology and growth strategies of resprouting trees. Available information about the influence of disturbance comes from ecosystems that are in many ways different from tropical and sub-tropical savannas. Therefore it is important to know and understand post-disturbance tree responses and limitations so as to establish sustainable use and management practices. This thesis reports the findings of a study, conducted in the Mpumalanga province of South Africa, aimed at achieving a better understanding of the influences of resource availability (water and nutrients) and disturbances (herbivory and repeated cutting) on the coppicing of a widely distributed savanna tree species that is both ecologically and economically important; Terminalia sericea. To investigate the effects of resource availability, cut trees were exposed to different levels of water and nutrient (nitrogen and phosphorus) supplementation over a period of two years in a factorial experimental design. A number of coppice regrowth variables (e.g. shoot production, resprout shoot diameter and shoot length) were measured monthly, while the phenological responses (e.g. timing of leaf discolouration and fruit presence) were monitored every two weeks. The effects of disturbances were investigated in two separate experiments, in which cut trees were exposed to a five month browsing period and different cutting frequencies, respectively. Coppice regrowth variables were monitored for 12 months in trees exposed to browsing and for five months in trees exposed to different cutting frequencies. The effect of multiple cutting cycles on total non-structural carbohydrates and leaf chemistry (carbon, nitrogen and phosphorus) was measured. There was evidence of self-thinning of coppice shoots within cut trees in all experiments in the second year of growth, with supplemented trees also recording lower shoot numbers. With shoot production higher in trees that received no resource addition, water and nutrients interacted synergistically, doubling shoot diameter and shoot length for supplemented trees after 12-months of addition. The majority of the phenophases monitored peaked in the wet growing season. Supplemented trees changed colour from the typical green to senescent yellow later in the growing season than unsupplemented trees. Fruit presence occurred in the second year after cutting for supplemented trees. Shoot length and shoot diameter for unbrowsed trees were twice those for browsed trees, with leaf nitrogen and phosphorus content significantly higher for browsed trees compared to unbrowsed trees. Trees subjected to multiple cutting cycles recorded half the TNC levels, and half the resprout shoot diameter and shoot length of trees cut only once. Results from this study demonstrate that self-thinning (i.e., negative change in shoot number) is not primarily under resource control. By contrast, the findings suggest that shoot growth characteristics, the timing and duration of phenological stages in coppicing trees are resource-limited in savannas. Browsing induces an initial compensatory response through higher shoot production in browsed trees and should be kept minimal because, in the long run, browsed cut trees would take longer to recover lost biomass compared to unbrowsed cut trees. Repeated cutting significantly depleted non-structural carbohydrate reserves in stems, implying that repeatedly cut trees rely heavily on non-structural carbohydrate reserves for regrowth. The significantly lower shoot diameter and shoot length in repeatedly cut trees imply that the coppicing ability of a tree reduces as the cutting frequencies increase. Such information can be vital in establishing the competitive growth ability of T. sericea in a multiple-species ecosystem affected by changes in resource availability as well as natural disturbances. With reference to multiple cut trees, a form of cutting or harvesting strategy should be in place that allows for sustainable regeneration of the study species. A threshold in terms of number of cutting cycles a tree can tolerate based on either maximum or minimum levels of reserve carbohydrates should also be established, as this has a direct effect on the coppice growth and survival.

Thesis (Ph.D.)--University of the Witwatersrand, Faculty of Science, School of Animal, Plant and Environmental Sciences, 2004

Ph.D., Faculty of Science, University of the Witwatersrand, 1987

A thesis submitted to the Faculty of Science University of the Witwatersrand, Johannesburg for the Degree or Doctor or Philosophy October 1987 / A t h r e e - y e a r study was un dertaken in the semi-arid (500mm p a . ) n o rth -eastern lowland area of South Afric a. All the woody plants were removed from one -hectare savanna plots on three d i f f e r e n t soil types , and key hydrological and biological changes were monitored relative to adjacent controls. Runoff increased initially, but decreased once the grass cover increased. Deep drainage and lateral subsurface flow increased on the sandiest site. Evaporation from the soil surface increased on the heavier t e x t u r e d soils. The duration of plant - available water in the soil increased on all cleared p l o t s . & The p re - c l e a r in g woody plant abo veground biomass was in the range of of which 0 . 6 6 to 0 . 8 0 t ha was 5.6 to 11.2 t ha -1 leaf biomass. The annual herbaceous production was stron gly rainfal' dep endent, averaging 1 to 1.5 t ha -1 , and increased by 0 . 4 - 0 6 t .ha -1 except on the most f erti le site ( 0 . 6 - 2 0 t ha ) . Total available forage increased with c l e a ring, but so did its variability The observed changes in herbaceous layer palatability could not be a t trib u t e d to clearing. Woody plants and grasses wore shown to have w a te r- u s e niche separation in both rooting depth and time of water use. Simulation over forty years of wetting patterns indicated 75 to 85 % niche overlap, w t h separation on the depth axis more important in sandy sites, and on the time axis in clayey sites. Competition between woody plants and grasses was strongly asymmetrical in favour of woody plants. w >

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This thesis explores techniques which ultimately strive to optimize production systems in rangeland areas of southern Africa. By linking spatially significant, satellite derived data to practical measurements of vegetation structure, valuable insight has been derived on processes of ecosystem function, in the Sabi Sand Game Reserve. A broad ecosystem response mechanism has been established from a conventional Normalized Differentiation Vegetation Index (NDVI). By responding to increases in production, which are driven by disturbance, this index has allowed quantitative systems theory in savanna to be tested and refined. Methods of biomass and production estimation which are specifically designed to reduce the cost and time involved with the more conventional method of destructive harvesting have been tested in the savanna at the Sabi Sand Game Reserve. Results from these estimates relate well with data derived through destructive harvesting in structurally similar savanna. Moreover, by relating the above-ground woody production estimates to remere sensing indices, it was possible to demonstrate that the problem of extrapolation, universal to most biomass and production studies can be overcome. Since remote sensing encompasses an array of tools fundamental to rangeland inventory, monitoring and management, valuable spatially significant information pertaining to ecosystem structure and function has been provided for managers in the Sabi Sand Game Reserve.

A crucial question in the debate about reintroducing elephant culling is whether the long-term effects of elephants and mesobrowsers on woodlands are similar. Sufficiently high biomass-densities of mesobrowsers may, following reduction or removal of elephants, continue to heavily impact earlier life-history stages of a similar suite of woody plants that elephant impacted, preventing these species from maturing. Thus a similar end-point for woodland structure and composition is achieved. No study exists in the literature where woody plant and habitat utilisation of the savanna browser guild has been determined in the same locality over the same period. A review of 49 years of literature implied that the two groups impact the same core woody-species in the same habitats. Dietary and habitat utilisation of guild members was determined in Hluhluwe-iMfolozi Park, South Africa. A small suite (n = 8) of woody species formed the core diet of all guild members. Herbivores’ densities were determined using a novel GIS approach; all members of the guild showed extensive overlap in habitat use. GPS collars and a GIS were then used to detect zones of different density of impala in the landscape, thus defining, for the first time, a natural fine-grain browsing gradient. Densities of woody seedlings were significantly less (average 48% reduction) in areas of high versus low impala density. A simple browse-browser model, incorporating, in a novel approach, functional groups of plant species, was parameterised from these results and an extensive review of the literature. Outputs suggest that over the long-term (100 years), impala will have a similar impact on woodland structure as elephant. An apparently strong synergistic effect between impala and elephant impact, suggests that reduction or removal of either impala or elephant will radically reduce long-term destruction of woodlands. In smaller or medium sized reserves, where control of mesobrowser populations is practical, profitable and more acceptable than elephant culling, these findings imply a re-direction of management efforts. Management should consider the biomass-density of both groups, rather than just focus on the system’s perceived ‘keystone’ species. Such principles may also apply to temperate and other systems.

D.Phil. / What underlies species distribution and species coexistence has long been of key interest in community ecology. Several methods and theories have been used to address this question. However, it still remains a controversial debate. The recent development of plant DNA barcodes with possibility of merging phylogeny with ecology brings high expectation in uncovering the processes underlying community assemblages. Previous works that used molecular approach in community ecology focused mainly on rainforests. Using a phylogenetic approach, this study brings novel understandings about savanna ecology, especially regarding how megaherbivores impact plant community composition. The Kruger National Park (KNP) is one of the world’s largest reserves, but less studied from a phylogenetic perspective. A DNA database of 445 DNA sequences (plant DNA barcodes, rbcLa + matK) was generated for the woody plants of the KNP. This database proves reliable in reconstructing the phylogeny of Angiosperms of the park. Based on this phylogeny, the present study characterised plant community composition, and investigated how megaherbivores influence this composition. Results indicate that plant communities in the KNP are not neutral, i.e. they are more clustered than expected under various null models. This suggests that ecological forces, most likely habitat filtering may be playing key role in dictating community structure in the KNP. The KNP is well-known for its richness in megaherbivores. The contribution of these animals to the current shape of plant community structures was therefore further investigated. Where megaherbivores have been excluded, plant diversity decreases, but shifts in plant community structure are contingent upon the initial community composition, suggesting that herbivory might be important filter that drives the clustering pattern observed.

M.Sc. / Boreholes in the Kruger National Park (KNP) was at first developed to increase the number of animals that were at low densities because of poaching, diseases, fencing and low permanent water availability. This development of artificial waterholes without managerial measures or knowledge of possible consequence led to negative impacts on the environment. These included that the higher concentration of herbivores around artificial waterholes led to a change in vegetation; secondary vegetation growth did not support the feeding habits of water dependent species; the infiltration rate of water in the soil surrounding waterholes changed and animal distribution patterns also changed, in turn changing the predatory base. Due to the above the KNP developed a new water policy. The policy states that all artificial waterholes that are open should be part of natural ecosystem principles. This led to the closure of many artificial waterholes that did not conform to the requirements of the new water policy. This study aimed to determine the ecological implications of artificial waterholes and whether tourism will be affected by the closure of these artificial waterholes. The following two hypothesis were thus tested in this project: i) Artificial waterholes have ecological implications on the environment. ii) The closure of artificial waterholes will have a negative response from tourists and thus affect tourism to the KNP. The results from this project indicated that both these hypothesises can be accepted as the available literature clearly showed that artificial waterholes do have a negative impact on the environment and that the majority of the tourist questioned asked for the waterholes to be opened again. The latter reaction was mainly due to the tourist‟s concern that the animals will suffer and die without water. Furthermore the visitors are concerned they won‟t see animals anymore. This result can partly be due to the low awareness of the visitors on the subject. No effort was made to communicate these decisions, and the reasons it‟s based on, to the public. Although a certain number of artificial waterholes were closed according to the new KNP policy, it is still important to keep a number open due to fact that KNP is not a natural system. It is suggested however that the closure of the artificial waterholes take place differently, following a principle of rotational opening and closing of patches of waterholes to allow recovery of vegetation and facilitate migration between waterholes.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy The support of the Global Change and Sustainability Research Institute (GCSRI) towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at, are those of the author and are not necessarily to be attributed to the GCSRI. February 2017 in Johannesburg, South Africa / Global change, specifically land cover change and climate change, are recognised as the leading drivers of biodiversity loss worldwide. Habitat loss has resulted in a loss of biodiversity and led to significant declines in species populations. Climate change is altering species distributions, ecosystem composition and phenology. Conservation planning is required to offset these dynamic threats to species persistence into the future. Plants form the basis of trophic structure and functioning and may not be able to track changing environmental conditions as well as mobile species. They thus represent an essential starting point for understanding climate change and habitat loss impacts. The patterns and processes which generate and maintain floristic diversity must be explored before global change impacts on these communities can be assessed and planned for at a landscape scale. This thesis investigates the environmental variables structuring indigenous plant community composition, pattern and turnover in grassland and savanna systems in KwaZulu-Natal. The threats posed by land cover change and climate change are explored and a coarse-grained landscape connectivity map developed to impart maximum resilience in order to maintain floristic diversity in the era of anthropogenically induced global change. The environmental variables correlated to floristic pattern and turnover were temperature, soil fertility and precipitation variables. The orientation of the temperature gradient conflicts with the soil fertility gradient, hence species with particular soil requirements will be hampered in their efforts to track the temperature gradient. The gradients were non-linear with turnover highest on dystrophic soils in warm and drier summer regions. The major drivers of land cover change were cropped agriculture, timber plantations (agroforestry), rural and urban development, dams and mines. The drivers of change differed according to land tenure type. The average rate of habitat loss in the province over an 18 year period was 1.2% per annum, levels which are considered unsustainable. A target level of 50% of natural habitat remaining is recommended. Environmental domains were identified using the environmental correlates of plant community composition. These were used to investigate climate change impacts using a collection of downscaled climate models. Conditions suiting savanna species are set to increase at the expense of conditions suiting grassland species raising significant challenges for the conservation of grasslands. Indices of habitat intactness and climatic stability were used to develop a vulnerability framework to guide conservation actions to mitigate global change impacts on floristic diversity. Building on the insights gained from the study, a connectivity map linking protected areas was developed, that if implemented, will maximise the opportunity to maintain floristic diversity into the future. The spatial location of the corridors was prioritised based on broad scale climatic refugia, high turnover areas and important plant areas for endemic and threatened species. The corridors were aligned along the major climatic gradients driving floristic pattern. The corridors represent the most natural and cost-effective way for species to adapt to climate change and persist in the landscape. This thesis provides new insights into two global threats facing plant communities in KwaZulu-Natal and provides a suite of products that inform dynamic conservation planning and directs appropriate conservation action. The results may be used to inform policy and legislation. / MT2017