Thesis (PhD)--Stellenbosch University, 1975. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: A study was made of certain relations operating within a South West African woodland savanna ecosystem which was characterised by simplification within most of its basic components. . Main attention was given to the relatively unexplored field of spatial and structural organisation of the primary producer component in relation to its quantified intra-seasonal functional changes including its phenology. Simple mathematical model descriptions of seasonal mass change of the herbaceous parts of the primary producer component were derived. Various parts of the primary producer component were also evaluated in terms of some of the main climatic driving forces of the ecosystem, decomposition relations in the form of disappearance rates, soil-vegetation mineral relations and consumer (mainly insect) relations. Gross effects of manipulation of the ecosystem type by fire and management is included.

No description available.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. August 2015. / iii ABSTRACT Global changes are likely to have negative impacts on many ecosystems including savannas. Semi-arid environments are notable for the wide range of seasonal patterns of leaf display in the tree communities. The environmental cues of leaf out and leaf drop are not consistent across species, and are not always directly linked to water availability, indicating that some species might be particularly sensitive to changes in climate. Strategies employed by trees which leaf early or drop their leaves late are likely to impact other aspects of their life-history and functioning so I expect particular plant functional types to be associated with particular vegetation functional traits. I assessed how variable savanna leafing strategies are among 28 species at a semi-arid savanna site at Nylsvley, and used this information to group species into plant functional types (PFTs). These PFTs were then assessed in terms of key vegetative traits to explore the life history consequences of different leafing strategies. Leaf phenology was monitored throughout one growing season and quantified using 8 key phenological metrics. The timing of leaf display tracks the timing of seasonal rainfall but with wide variation, with some species retaining their leaves throughout dry season. Other species loss some leaves throughout the growing season, some species only flushed their leaves after the first rains, and other flush before the first rains. I identified 4 clear PFTs using the MClust clustering integrated with subjective procedure. Four vegetative traits were measured: specific leaf area, leaf nitrogen, maximum stomatal conductance and wood density. I identified some clear trade-offs between vegetative traits and phenological strategies. There was also a positive relationship between degree of rain stimulated flushing metric and wood density. Using objective clustering methods to determine plant functional types has some clear advantages over more subjective methods but depends on good input data. Identifying plant functional types at Nylsvley has led to some insights into functioning of these savannas, but as there appear to be strong links between plant traits and particular leafing strategies it might be more appropriate to explore syndromes of vegetation functional traits when modelling responses to global change.

A dissertation submitted in fulfilment of the academic requirements for the degree of Masters of Environmental Science, School of Animal Plant and Environmental Sciences. University of the Witwatersrand. October 2016. / Fire and grazing are important drivers of grassland composition and function in savanna ecosystems. Fire alters the forage quality and vegetation structure, so changing fire regimes also changes grazer utilisation of the landscape. This study aimed to investigate how different fire regimes, specifically changes in fire size and season of burn, influence grazer attraction as well as grazing intensity and duration in the short-term, and further to determine how long-term fire-grazing interactions may influence the development of grazing lawns. In the short-term experiment, fires of three different sizes were applied in both the early dry season (EDS) and late dry season (LDS), and periodic collection of grass height and dung count data was conducted over a full year. Results showed that grazers were immediately attracted to the burned areas after the fires, and that fire and grazing together can maintain a short grazed patch for a full season. The greatest grazer visitation and grazing pressure (shortest grass) was observed on the intermediately sized burns (5ha). Furthermore, EDS treatments exhibited less initial grazer visitation but grass was kept in a short state for longer than on LDS burns. LDS burns had more intense grazing but over a much shorter time. For the long-term experiment, a long-standing fire experiment (Experimental Burn Plots, Kruger National Park, South Africa) was used to investigate change in grass community composition as influenced by firegrazing interactions over a 60 year period. Historical data were used, and grass composition data were also collected on three treatments that allowed for comparison of communities that experienced grazing and fires repeated at different fire frequencies and different seasons (April biennial and August annual burns), as well as a natural fire regime (control). By investigating the change in abundance in a few key grass species, grass ecological status classes, and grass functional guilds, results found that grasses associated with grazing lawns (stoloniferous, ‘disturbed’) increased in abundance, while grasses of bunch grass communities decreased, and that this change was more pronounced on April biennial burns. The results of this study show that small fires can act as a catalyst for grass community compositional and structural change by attracting grazers. Key words: Grazing lawns, fire size, fire season, pyric-herbivory, savanna. / TG2016

Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. Includes abstract and vita. Title from title screen (viewed May 9, 2006). Includes bibliographical references (leaves 167-174). Online version of the print original.

The detection of hierarchically nested structure in a semi-arid savanna as predicted by complex systems theory requires a method that detects context specific multi-scaled pattern in a proxy that represents the net effect of system processes. Statistical assumptions preclude the use of many traditional methods in the detection of hierarchical structure in heterogeneous landscapes so to circumvent statistical barriers to inference I developed a linear scale-space based application to represent multi-scaled woody vegetation structure in a spatially explicit manner. Analysis of a scale-space representation of woody cover across multiple scales explicitly recognizes landscape context and emergent pattern due to the causality principle inherent linear scale-space generation. As a proxy for process in scale and space I utilize the merge events of woody canopy cover, which should theoretically be considered the point at which processes shift domain. Scale-space representations were analyzed using a spatially explicit discontinuity analysis that compares the distribution of structure across the dimension of scale to that of a neutral model specific to the landscape in question. The application was tested for rigor and ability to detect multi-scaled, context dependent pattern in test datasets. The effects of fire and herbivory on the multi-scaled structure of a semi-arid savanna landscape were compared using the merge events from scale-spaces generated from a 33 year herbivore browser exclosure. No more hierarchical structure is present in real world savannas than can be expected from random. Hypotheses put forward to explain the results include: procedural and philosophical bias, errors in the application, or that the landscapes are not hierarchically nested. Each hypothesis is discussed in the light of the evidence and after synthesis I discuss that savanna landscapes may have more randomness within the pattern and process than previously acknowledged

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science, Johannesburg, South Africa 2017. / Fuelwood is still heavily relied upon by rural communities as a source of energy. The current levels of wood harvesting have been deemed unsustainable, with models predicting the local exhaustion of wood resources in most cases. However, wood depletion has generally not happened to the level of severity predicted by the models. This may partially due to under-accounting for coppice regeneration. Many savanna species that are harvested for fuelwood demonstrate strong coppicing ability, which allows for regrowth after a disturbance. This ability to regrow or coppice is a key functional trait which allows species to persist and survive in frequently disturbed environments. There is surprisingly limited knowledge about coppice dynamics in savanna trees and how managerial actions might influence the coppice response and production of savanna species. To address this problem, this study investigated the influence of four post-harvest treatments on various aspects of the coppice response of Terminalia sericea and Dichrostachys cinerea – two important savanna fuelwood species – in a field experiment. A total of 108 felled trees per species were exposed to one of four treatments, which were applied monthly for 12 months. The treatments were (1) Control – no coppice shoots were removed for 12 months, (2) Harvest – all coppice shots were removed monthly, (3) Single prune – the coppice shoot with the widest diameter was left on the stump, and (4) Usable – coppice shoots that reached a diameter of 2 cm were removed. The effect that these treatments had on the average diameter, length and cumulative number of coppice shoots produced per stump was compared. The measurements of diameter and length were used in developing allometric equations for the prediction of coppice shoot biomass. The predicted biomass produced through the study was compared across treatments to gain an understanding of how productivity could be influenced by management of coppice shoots. The mean shoot diameter, length, as well as cumulative number of coppice shoots produced per stump was higher in the single prune treatment for both species while the harvest treatment resulted in high numbers of coppice shoots but with low average diameter and length. Applying the growth rates of coppice shoots found in this study it can be assumed that unmanaged coppice shoots will take approximately 5.5 years to reach a preferred harvestable diameter of 4 cm, while single prune coppice shoots would take 3.3 years to reach the preferred harvestable diameter. Diameter had more of an influence on the predicted coppice biomass production of T. sericea while D. cinerea biomass prediction was more influenced by shoot length. However, only diameter was used to compare the prediction of coppice biomass with previously developed equations as these equations did not consider length for predicting biomass of different components of trees. From the derived models, the calculated biomass at the end of the study period as well as the calculated biomass produced through the year was greatest for the control treatment. The predicted dry shoot stem biomass at the harvestable diameter of 4 cm was 114.60 g for T. sericea and 95.88 g for D. cinerea. From the findings of this study it is clear that post-harvest management can be utilised to manipulate coppice response and biomass production. Keywords: Fuelwood; Coppice shoot; Post-harvest treatment; Diameter; Length; Biomass / LG2018

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.

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, 2017 / Plant phenology, the study of the timing of biological events such as leaf flush, has been identified as a key tool in monitoring and understanding the impacts that changing climates may have on the world. Unfortunately there is a noticeable lack of phenological research in Africa’s savannas in comparison to other global ecosystems, such as temperate forests. Savannas are known for their complexity in structure and composition and the phenology of their flora is no exception to this. Owing to the highly seasonal climates in this system, plants have had to evolve a range of phenological strategies to cope with the limited window of suitable growth conditions during the periodic wet season in the austral summer. One of these phenological strategies is that of early-greening; where deciduous trees will produce new flush prior to the onset of seasonal rainfall when the environmental conditions are at their driest. There is likely no other ecosystem in the world where the early-greening phenomenon occurs, however, it has been recorded in savannas from Africa, Australia, Asia and South America. The global prevalence of this strategy suggests that early-greening trees must gain some benefit from utilising this seemingly risky leaf flushing strategy. The main aim of this study was to investigate two of the hypothesised benefits of an earlygreening strategy for semi-arid savanna trees. The first hypothesis suggested that earlygreeners are extending their growing season beyond that of grasses and late-greeners – whose leaf flush is limited by the availability of water through the onset of seasonal rainfall. The second hypothesis is that early-greeners produce new leaves ahead of the emergence of invertebrate herbivores with the onset of the first rains, therefore decreasing the risk of damage to the vulnerable tissues and allowing the defence mechanisms within/upon the leaf to develop. This study took place in the Nylsvley Nature Reserve (NNR) over three consecutive austral growing seasons (August 2012 to April 2015) and was conducted on the two dominant deciduous broad-leaved trees: Burkea africana and Terminalia sericea. Burkea africana is known to flush prior to the onset of seasonal rainfall and was considered the earlygreening species in this study. Terminalia sericea has been recorded as flushing leaves prior to the onset of rainfall, but is more often a facultative-greener – rapidly producing new leaves with the onset of seasonal rainfall. This study experienced high seasonal variability between years with early-greening only occurring during the final (2014-2015) season. Nevertheless, I was able to assess the weekly green-up phenology of both species during the first three months of green-up and found that the green-up of the trees was largely disconnected from the main system driver – water – while grass green-up was closely linked to the onset of rainfall. This complements the theory of temporal niche separation; however, when assessing the functionality of the new leaves produced, carbon gain only occurred after the first two weeks post bud-break. In a system such as the NNR where rainfall onset variability is high, trees will only gain the advantage of an extended growing season if the onset of rainfall is more than two weeks after the start of flush. Using historical rainfall records (1980-2014), I estimated that 46% of years could have potentially experienced early-greening with rainfall commencing after the 15th October – the earliest date of green-up prior to rainfall onset in the NNR during this study. One of the benefits tested relating to early-greening in this study was that early-greeners avoid invertebrate herbivore damage on vulnerable new leaves. This study provided evidence for the use of a phenological defence strategy to cope with invertebrate herbivory pressure. Leaves which emerged before the rains had lower rates of herbivore damage than those which emerged after. Moreover, it was demonstrated that the constant turnover of leaves with high photosynthetic rates (T. sericea) is a reasonable mechanism for dealing with high leaf herbivory, and can result in equivalent end of season leaf area (and carbon gain) to species which invest in defence and have slower turnover rates (B. africana). Using the ground-based phenological measures in conjunction with remotely sensed NDVI imagery, the frequency of early-greening across seven comparable broad-leaved woodland sites in southern Africa from 2002 to 2014 was quantified. Of the environmental variables considered, the predictability of early-season rain (rather than total rainfall amount) was best correlated with early-greening. In savannas where rainfall onset and annual amounts were highly variable (such as the NNR), early-greening was less frequent (20% of the years) while in savannas closer to the equator where rainfall amounts were consistently >900 mm per annum and the onset dates began within a two week window each season, early-greening occurred in 80-90% of all years. The decrease in the proportion of early-greening events in the NNR from the 1980s to the past decade could be driven by the changing rainfall regimes over South Africa – with a predicted decrease in the number of precipitation events, but an increase in the storm intensity and rainfall amounts in each of these events. Fewer precipitation events may increase the risks associated with the early-greening strategy and this may be driving the NNR trees to use this strategy less frequently. This study has highlighted the need for a long-term phenological monitoring network within southern Africa’s savannas and has illustrated how early-greening species can benefit over other flora when environmental conditions are suitable for them to commence early leaf flush. This thesis has shown that early-greening broad-leaved savannas trees in South African savannas are more likely to avoid invertebrate herbivory than extend their growing seasons. / XL2017

A dissertation presented to the Faculty of Science in fulfilment of the requirements for the Master of Environmental Sciences degree University of the Witwatersrand, School of Animal, Plant and Environmental Sciences. South Africa, Johannesburg. March, 2016 / Understanding how trees limit light will advance theories of bush encroachment and tree-grass coexistence in savannas and it will enable us to explore how we can best conserve fire maintained, fire-dependent vegetation systems in South Africa and how our biome boundaries may shift. In order to understand how fire maintains the boundary between closed canopies and open grassy environments, the aim of this research was to test the hypothesis that; tree traits affect light that passes through the canopies of trees to the ground, by in uencing the threshold tree density at which grass stops growing under trees. Using the Point-Centered-Quarter method I estimated tree density using a proxy, mean PCQ distance, to refl ect changes in inter-tree distance across the gradient of tree density. At the same plots I used dry-weight ranking to record changes in grass cover, species composition and abundance, a balance scale to weigh wet and dry grass biomass, in tandem with densiometer measurements and hemispherical images to obtain canopy cover and the amount of sunlight received by the ground, in addition to the tree density data. To elucidate the interaction between tree traits and sunlight (correlation, boxplots, ANOVA, post-hoc test, MRD, quartile-regression analyses and linear modelling) as well as response of grass species to light (regression analysis, boxplots, ANOVA and GAMs), respective passable analyses were employed using R. The results show that biomass declines with changes in grass species composition and abundance, that are in turn driven by decline in light transmittance; when horizontal and compound leafed trees, especially on short, umbrella shaped trees with horizontal spheroids prevail. Consequently reducing light loving grass species with characteristics that lead to high fire frequency and intensity; high cover, height and biomass, that prevail when tall trees with vertically angled leaves and spheroids dominate, leading to higher light transmittance. This succinct understanding highlights variation in the tree-grass relationship across savanna ecosystems, suggesting site-specific interventions and recommendations to bush encroachment. Findings reveal value in monitoring tree canopy cover across savanna ecosystems; using it as an early warning proxy for changes in primary production and fire regimes. Conclusions challenge assumptions about the minimum light tolerance of grass, and provide important clues to help disantangle mechanisms by which grasses may persist at low light levels. Key words: Savanna, South Africa, light transmittance, trees, grass, bush encroachment / LG2017