Rivalry for nutrient resources : is there competition below ground between leguminous trees and grasses in a mesic and arid savanna in the Kruger National Park?

As described in the resource-based co-existence theory, trees and grasses are able to co-occur due to partitioning of the edaphic environment in savannas. This study describes the fine root-distribution of dominant leguminous C₃ trees and C₄ grasses relative to soil nitrogen, phosphorus and water profiles using stable carbon and nitrogen isotope ratios (of the fine roots). The study occurs on a mesic savanna (737 mm MAP) site on sandy-loam soils and an arid savanna (547 mm MAP) site on clay-rich soils in the Kruger National Park, South Africa. We show that most tree and grass roots are located in the upper layers of the soil and both are present to the bottom of the profile. Root biomass is positively correlated to soil nitrogen and phosphorus and negatively to soil moisture and there were significant differences between sites, but very few of the results were significantly different down the soil profile. Therefore, the niche-separation hypothesis was not supported. The Scheiter & Higgins (2007) model illustrates that even though rooting niche separation is not an essential precondition for grass-tree coexistence, competition in the rooting zone can shape patterns of tree dominance in savannas, which may help in dealing with the problem of bush encroachment in savannas

Top-down or bottom-up?: Impacts of giraffe browse and water abstraction on two keystone tree species of the Kgalagadi Transfrontier Park

In this thesis I determine how an emphasis on tourism may have both a top-down and bottom-up affect on the two most dominant tree species in the southern Kalahari Desert of central southern Africa. Both tree species are considered as keystone species especially along ephemeral rivers. My focus is on the impact of the introduction of an extralimital megaherbivore, Giraffa camelopardalis, (top-down) and anthropogenic water abstraction (bottom-up) on the reproductive output and vegetation structure of Acacia erioloba and Acacia haematoxylon in the Kgalagadi Transfrontier Park. I determine the impact of giraffe on canopy structure and reproductive potential of the two tree species by comparing three zones of giraffe density (high, medium and low) along the Auob River. I do this through a series of transects through the river to determine both giraffe and tree density and also photographed several trees to determine change in canopy width, percentage canopy death and change in the number of flowers and pods between the three zones and between species. My results show a significant negative impact of giraffe browse on canopy structure, specifically for A. haematoxylon. I did not however find any significant differences in recruitment between the different giraffe density zones. However, a noticeable decrease in numbers of flowers and pods in the giraffe browse height of trees (2 - 5 m) between zones suggest that giraffe will have a negative effect on the A. haematoxylon population but not the A. erioloba population in the future. I use stable hydrogen and oxygen isotope ratios to determine the water source for the two tree species. I do this relative to the stable isotope ratio of the water extracted from nearby boreholes. I also determine how close to physiological stress the trees are (using specific leaf area, leaf δ¹³C values, canopy death and midday xylem pressure potentials) both upstream and downstream of active boreholes used for two tourist camps. One camp, Nossob, in the Nossob River is abstracting at a high rate while the other camp, Urikaruus, in the Auob River is abstracting at a lower rate. My results for water isotope ratios show that both A. erioloba and A. haematoxylon are using deep groundwater. My results also show that in the dry season, A. erioloba in the Nossob are losing contact with groundwater and have to rely on some as yet unmeasured water source in the soil profile. This 'stress' is not reflected in canopy dieback as yet. The trees continue to transpire in the dry season suggesting that they are physiologically able to adapt to fluctuations in the water table of between 4.5 - 5.2 m between the wet and dry season by closing their stomata but are prone to drought-induced carbon starvation, specifically for trees in the Nossob. Overall, my results show that the impact of giraffe on vegetation structure is already evident for A. haematoxylon, indicative of future negative effects on reproduction. My research also shows that although current levels of water abstraction are as yet not affecting vegetation structure below the abstraction points, the trees are edging closer to thresholds of water stress that would be exacerbated with drought. These findings are discussed within the context of ecosystem health and management implications for the giraffe population and water use within the Park

An Exploration of the Relationship Between Mentoring of New Teachers and Student Performance

While much research has explored the positive correlation between mentoring programs and resulting reduction in teacher attrition, the relationship between mentoring activities and student learning remains equivocal. The purpose of this study was to investigate the possible relationship between frequency and depth of mentoring activities in which high school teachers in their first three years of teaching report engaging, on the 2011 Colorado TELL (Teaching, Empowering, Leading and Learning) Survey, and examining concurrent student achievement growth and shifts in growth gaps as measured by the Colorado Growth Model in those teachers\u27 schools. This mixed methods study also entailed open-ended interviews of five high school teachers in their first three years of teaching regarding their mentoring experiences. Responses were coded and themes were captured to add depth of understanding regarding the dynamics of mentoring of teachers and their students\u27 achievement. As 50% of teacher evaluation in Colorado will be anchored to student academic growth by 2014, the relationship between mentoring and student learning is especially salient for school districts implementing mentoring programs, as well as for teachers who are relying in part on mentoring to help them positively impact student learning

Diels-Alder Reactions in Multi-Ring Forming Processes

The Diels-Alder reaction is one of the most powerful reactions available to the synthetic organic chemist. Its greatest strength is its ability to generate the most prevalent cyclic system, namely the six-membered ring, in one synthetic operation from a versatile array of substrates. This thesis explores the application of the Diels-Alder reaction to multi-ring forming processes. Chapter 1 - By way of introduction, the first chapter provides a brief commentary on the pursuit of efficiency in synthetic organic chemistry and, as a matter of course, the power of the Diels-Alder reaction as a multi-bond forming process. As a preamble, it signposts these important themes, which have driven the investigations conducted in this thesis. Chapter 2 - The second chapter encapsulates two separate pieces of synthetic work. Firstly, the diene-transmissive twofold Diels-Alder reaction sequence of [3]dendralene with relatively un-activated cyclic dienophiles is developed. This methodology permits access to a diverse array of polycyclic structures, with twenty structurally distinct tetracyclic frameworks prepared. Secondly, Chapter 2 reports the application of this methodology to the concise enantioselective synthesis of the popular synthetic target and biologically-important marine natural product, (+)-xestoquinone. Notably, this work a) constitutes the first application of the parent [3]dendralene in total synthesis; and b) constructs three out of the four carbocyclic rings of the natural product via a Diels-Alder reaction, resulting in the shortest preparation of the molecule to date. This work is presented as a journal article draft for submission to Science. Chapter 3 - In the third chapter, the pentacyclic marine natural products, (+)-xestoquinone and (+)-halenaquinone are introduced in detail. Previous syntheses of these natural products as well as structurally similar compounds are comprehensively and systematically reviewed to place the preceding synthetic work (Chapter 2) in context. Chapter 4 - In Chapter Four, the diene-transmissive Diels-Alder reaction sequence of parent and substituted [3]dendralenes is developed to use enantiomerically pure, readily available, cyclic dienophiles for the first time. This methodology builds upon the key Diels-Alder reaction sequence reported in the synthesis of (+)-xestoquinone (Chapter 2) and enables the rapid synthesis of a range of chiral polycyclic frameworks in enantiopure form. Chapter 5 - Chapter Five reviews the development and application of the intramolecular Diels-Alder reaction to total synthesis and takes the form of an invited journal article drafted for publication in Angewandte Chemie. The application of the Diels-Alder reaction to multi- ring forming events is explored from a different perspective to that examined throughout the rest of this thesis

Stress and ill health associated with fungi, indoor environmental factors and personal factors in hospitals.

Doctoral Degree. University of KwaZulu-Natal, Durban.Abstract available in PDF

Environmentally sustainable food production and marketing : opportunity or hype?

Purpose: Identify and analyse the beliefs of value-chain intermediaries regarding the production and marketing of food products conforming to environmentally sustainable standards.Methodology: In-depth, semi-structured, face-to-face interviews with senior managers of food companies across the value chain.Findings: In Australia, the demand for foods that are produced under environmentally sustainable standards has been slow to take-off because (a) customers do not perceive these products as offering any special benefits (b) customers distrust the claims made by organisations (c) these products are much more expensive than traditional products, and (d) the implementation of environmental standards is expensive. Customers claim that the use of different terminologies such as organic, green and environmentally friendly in promotingfood products is confusing.Research Limitations: Findings are not generalisable because the study is based on a small sample.Practical Implications: Value-chain intermediaries are unlikely to voluntarily adopt environmental standards because of low demand for such foods and the high costs of adopting and monitoring environmentally sustainable production and marketing regimes

The Libertine

6 p. l., 85, [2] p. ; 23 cm