Thesis (M.S.)--Wisconsin. / Includes bibliographical references (leaves 74-78).

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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 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

Thesis (M.Sc.)--York University, 2004. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 115-122). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url%5Fver=Z39.88-2004&res%5Fdat=xri:pqdiss&rft%5Fval%5Ffmt=info:ofi/fmt:kev:mtx:dissertation&rft%5Fdat=xri:pqdiss:MQ99304

Thesis (M. Sc.)--York University, 2002. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 186-198). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ71626.

The goals of this research are to identify the major constraints to plant succession in degraded cerrado vegetation. The area selected for this research, is located on the right bank of the Araguaia River in Goias State (Brazil). Floristic composition survey, seed rain and soil seed bank assessments were conducted in four forest fragments and in a degraded area. Planted seedlings, Soil translocation, Seed translocation and Artificial perches were also investigated. Floristic composition survey showed a richness of 145 species for the whole area and absolute density of 623.89 individuals.ha-1 for the degraded area and a range from 1333.72 to 2247.27 individuals.ha-1 for forest fragments. Seed rain survey resulted in 87 species identified, and annual seed arrival was 2.36 seeds.m-2 for the degraded area and 103.75 seeds.m-2 to 236.25 seed.m-2 to forest fragments. Soil seedbank analysis found a richness of 33 species and 87% of germinated seeds were from non-woody plants. The mean seed density of woody plants was 0 for the degraded area and ranged from 25 seeds.m-2 to 257.50 seed.m2 for forest fragments. Introducing seedlings showed a seedling survival rate of 38% after 24 months observation. Enterolobium sp and Inga spp showed higher rates of growth and positive interaction with fertilizer. The application of Tanglefoot, showed no significant results in any treatment. Treatments with fertilizer had less herbivory registered. Luehea candicans showed higher rate of herbivory. Seedling mortality was lower in fenced blocks and indicated Inga spp with lowest rate. Amongst nucleation strategies Seed translocation recruited more individuals after two years, followed by perches and soil seed bank translocation, but perches recruited more different species and had the same rate for seedling survival when compared to seed rain translocation. The results from this study show that succession in degraded Cerrado may be constrained by biotic and abiotic barriers.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, for the degree of Master of Science. Johannesburg 1993. / The prediction that savanna communities with similar conditions of plant available moisture (PAM) and available nutrients (AN) have similar structural and functional features was tested for a range of southern African savanna types. This prediction forms the basis of an hypothesis that savannas can be classified functionally on the basis of PAM and AN. Nineteen South African savanna types were sampled over a rainfall gradient of 369 to 690 rnm pa and on different geological parent materials. Ecologically meaningful indices of PAM and AN were derived using climate and soil physical and chemical data. The floristic structural and functional characteristics of the woody plant and herbaceous components of the savanna communities were ordinated and classified in relation to the PAM and AN gradients. The functional classifications were assessed in the plane of PAM and AN. Plant available moisture was indexed as the mean number of growth days per annum derived form a water balance modelling approach. This index reflected the duration of the growing season in days and was suitably detailed for use at the community level. The AN indices ranged in complexity from a measure of the availability of individual nutrients in the soil to an index based on the results of a bioassay experiment. The usefulness of the AN indices was assessed on a number of criteria and the soil A horizon total nitrogen content in mg/kg was chosen as a suitable AN index. The species composition of the woody plant and graminoid communities was primarily related to the PAM gradient with AN having a significant but secondary effect. There was overall a high degree of similarity between woody plant and graminoid floristic types. The distribution of members of the woody plant families, Mimosoideae, Caesalpinoideae and Combretaceae were primarily related to the AN gradient. The higher taxonomic classifications of the graminoid communities, based on subfamilies and tribes, were primarily related to PAM. Structural trends of the woody plant and herbaceous communities were related to the PAM gradient but not to soil fertility. There were a range of structural types for similar conditions of PAM and AN. The functional trends of the woody plants were primarily related to the AN gradient with PAM having a secondary but significant effect while the graminoid community functional trends were primarily related to PAM with AN having a secondary but significant effect. The woody plant and graminoid communities were notgrouped into functional types in the same way. It was evident from this study that these South African savanna types were related floristically, structurally and functionally to either or both of PAM and AN, which are hypothesised to be the primary determinants of savanna structure and function. Although communities with similar conditions of PAM and AN were not consistently functionally similar, the functional classifications of both the woody plant ami graminoid communities mapped well onto the PAM-AN plane. This indicated that the PAM-AN plane does have potential foruse as an overall framework for the classification of savannas on a functional. basis. / AC2017