Dissertations / Theses on the topic 'Theses – Botany'

“Tell me and I forget, show me and I remember, involve me and I understand.” - Chinese Proverb. Involvement in learning implies possessing skills and attitudes that permit students to seek resolutions to questions and issues while constructing new knowledge. Low enrollment in Plant Biology and Diversity and upper level plant science courses has been noticed at Western Kentucky University. In addition, graduating students performed below the national average on the senior assessment examination in the area of botany content knowledge offered by WKU’s Biology Department. This may be due to the fact that observation-based botany has been taught in a traditional way for biology majors at our university for many years. Traditional teaching methods include viewing prepared slides of plant sections, viewing live and herbarium specimens, and memorization of botanical terminology and illustrations. The goal of this study is to convert these existing traditional laboratories to investigative inquiry exercises without compromising the material covered by bringing observation-based labs into the twenty-first century. Various teaching strategies including inquiry, problem-based, case-based, and hands-on learning methods were implemented. Each exercise was reshaped around a central question or theme. These changes were expected to increase student learning and retention levels. Traditional teaching methods were used with the control group, while contemporary teaching strategies were used with the experimental set of students. Traditional assessments and anonymous surveys were statistically analyzed. The results of my analyses suggest that the experimental students were more challenged, interested, intellectually stimulated and less overwhelmed with contemporary teaching strategies and overall had higher learning retention demonstrated by their performance on assessments. Moreover, I predicted that an investigative approach will encourage larger numbers of students to take this restricted elective sophomore-level course for biology majors and further their study in plant biology.

Calcutta Botanic Garden was founded in 1786 to acclimatise economic plants, but it quickly became the main institutional base for scientific botany in colonial India. However, it had to make a new start in 1833 after the Garden superintendent, Nathaniel Wallich, distributed its herbarium to botanists in Europe. The thesis shows how the revival of the scientific project to investigate and catalogue the south Asian flora was the main priority for Wallich’s successors, but depended on successful negotiation with the government. The central theme of the thesis is the tension between scientists, intent on their research, and sponsors, who need to demonstrate practical outcomes. It breaks new ground by focussing on how these issues were debated and resolved within a particular colonial scientific institution. It argues that the Garden was able to attract the resources it needed for its scientific work by responding appropriately to government pressures: although its achievements in economic botany were limited, it successfully highlighted them, regularly citing the introduction of tea and cinchona; it reinforced its case by managing its site in ways that reassured the government. The thesis also adds to our understanding of centre-periphery relationships. It argues that the Garden’s role as an important nodal point in the global botanic network was key to achieving its objectives. It shows how the Garden was strengthened by its mutually supportive relationship with Kew Gardens, based on the close bonds that botanists formed with each other. The thesis concludes by showing how, despite the Garden’s achievements, the government gradually lost faith in the ability of botany to contribute to economic progress in India; in the twentieth century it increasingly turned to more specialist disciplines and institutions. The thesis therefore suggests that further studies of scientific institutions would enhance our understanding of how science continued to support and validate imperial rule.

Helianthus eggertii (Asteraceae) is a federally threatened sunflower species that typically grows between open woods and barrens. This species has both sexual and asexual modes of reproduction, which can influence the amount of genetic diversity present within and among populations. Maintaining genetic diversity is one of the primary objectives in managing threatened species or populations. Fire and population size may influence genetic diversity. Two Inter-Simple Sequence Repeat Markers (873 and MAO) were used to characterize many important genetic parameters of 17 populations in 2003 and four populations in 2004. This information was used to assess the effectiveness of different conservation management strategies. The main objectives of this project were to determine whether: 1) larger populations of Helianthus eggertii have a higher genetic diversity within populations than smaller populations 2) fire or other management strategies influence genetic diversity of populations 3) sexually derived progeny of H. eggertii have greater genetic diversity than mixed reproduction in parent populations assuming some degree of clonal reproduction. This study found that there is higher mean genetic diversity in larger populations, though not significant. Genetic diversity showed no difference in populations that are frequently burned than in populations that are not burned. However, there tends to be an increase in genetic diversity in some populations immediately after a fire event. The seed population studied had a higher genetic diversity. Genetic diversity is high at both Mammoth Cave National Park (.5246) and Arnold Engineering and Development Center(.4555). The high genetic diversity observed suggests that while clones may exist in a population, seedling establishment is actively putting new genetically diverse individuals in a population. These results show that the current management strategies being used are suitable for protecting this species.

Thesis (DPhil)--Stellenbosch University, 2002.
ENGLISH ABSTRACT: A biosytematic revision of the seven minor genera of the Hyacinthaceae, including twenty-two species, was undertaken. Muller-Doblies & Muller-Doblies (1997) considered these seven genera (Amphisiphon Barker, Androsiphon Schltr., Daubenya Lindl., Massonia Thunb. ex Houtt., Neobakeria SChItL, Polyxena Kunth and Whiteheadia Harv.) together with the genus Eucomis L'Herit. to form the subtribe Massoniinae of the tribe Massonieae. Previous revisions of the group were based only on morphological characters (Jessop 1976; Muller-Doblies & Muller-Doblies 1997). The subtribe Massoniinae is characterised by the large variety of floral forms exhibited by the different species in the group. In the past this has led to the establishment of many monotypic genera for species thought to have unique floral structures. Morphological, leaf anatomical, palynological, geographical and molecular data were studied in order to delimit the taxa and determine the phylogenetic relationships within the group. This showed that most of the unique floral structures are probably only adaptations to pollination strategies and all except one of the monotypic genera are now placed in the genus Daubenya. In the genus Massonia there is a great deal of variation in leaf morphology and this resulted in the establishment of many invalid species, now mostly reduced to synonymy. A new species was described, several name changes made and several species were reduced to synonymy.
AFRIKAANSE OPSOMMING: 'n Biosistematiese hersiening van die sewe kleiner genera van die Hyacinthaceae, insluitende twee-en-twintig spesies, is onderneem. Muller-Doblies & Muller-Doblies (1997) sluit hierdie sewe genera (Amphisphon Barker, Androsiphon Schltr., Daubenya Lindl., Massonia Thunb. ex Houtt., Neobakeria Schltr., Polyxena Kunth and Whiteheadia Harv.) saam met die genus Eucomis L'Herit. in die subtribus Massoniinae van die tribus Massonieae in. Vorige hersienings van die groep was meestal net op morfologiese kenmerke gebaseer (Jessop 1976; Muller-Doblies & Muller-Doblies 1997). Die subtribus Massoniinae word gekenmerk deur die groot variasie in blomstrukture wat by die verskillende spesies in die groep voorkom. In die verlede het dit gelei tot die beskrywing van verskeie monotipiese genera gegrond op wat geblyk het, unieke blomstrukture te wees. Morfologiese, blaar anatomiese, palinologiese, geografiese en molekulere data is bestudeer om die verskillende taksons af te baken en terselfdertyd die filogenetiese verwantskappe binne die groep te bepaal. Dit het aangetoon dat die unieke blomkenmerke eerder aanpassings aan bestuiwings-strategiee is en dat al hierdie monotipiese genera, behalwe een tot die genus Daubenya behoort. In die genus Massonia is daar baie variasie in blaarmorfologie en dit het veroorsaak dat 'n groot aantal spesies beskryf is, waarvan baie nou as sinonieme beskou word. Een nuwe spesies is beskryf, verskeie naarnsveranderinge is gemaak, en 'n aantal van die spesies is tot sinonieme verander.

Thesis (MSc)--Stellenbosch University, 2003.
ENGLISH ABSTRACT: Oxalis L. has two centres of diversity, one in South-Central America and the other in southern Africa. Previous palynological studies of southern Africa Oxalis revealed four main pollen types, namely rugulate-reticulate, micro-rugulate-spinate, reticulate and supra-areolate (Dreyer 1996). The reticulate pollen type is further divided into 15 subtypes, out of which five have a monotypic status. The supra-areolate pollen type is divided into four subtypes based on exine structure. The reticulate pollen type is the most common pollen type within the South African members of Oxalis. The three remaining main pollen types display more complex exine structures and are therefore considered more derived than the reticulate pollen type. The present study assessed the pollen of 50 American Oxalis species with three main objectives: 1. To observe pollen type variations among American members of Oxalis, 2. To compare pollen types from the two centres of diversity, and 3. To assess which centre of diversity house the palynologically more advanced species of Oxalis. Two main pollen types are recorded from the present study, namely reticulate and verrucate pollen types. The reticulate pollen type could be further divided into 11 subtypes. Out of the 11 subtypes observed, nine also occur among South African members of Oxalis, while two types are only observed in the American members of Oxalis. The verrucate pollen type is found in a single American taxon and displays a more complex exine structure than the reticulate pollen type. In this study the reticulate pollen type proved to be the most common pollen type among the American members of Oxalis. The South African members of Oxalis display more complex pollen types than the American members of the genus.
AFRIKAANSE OPSOMMING: Oxalis L. het twee diversiteitsentrums, een in Suid-Sentraal Amerika en die ander in suidelike Afrika. Palinologiese studies van suidelike Afrika Oxalis-taksa toon vier hoofstuifmeeltipes, naamlik gerimpel-netvormig, fyn-gerimpel-stekelrig, netvormig en supra-areolêr (Dreyer 1996). Die netvormige stuifmeeltipe word verder verdeel in 15 subtipes. Vyfvan hierdie tipes het 'n monotipiese status. Die supra-areolêre stuifmeeltipe word verdeel in vier subtipes gebaseer op eksienstruktuur. Die netvormige stuifmeeltipe is die mees algemene stuifmeeltipe aanwesig in die Suid Afrikaanse Oxalis-taksa. Die drie oorblywende hoofstuifmeeltipes toon 'n meer komplekse eksienstruktuur en word as meer gevorderd as die netvormig stuilmeeltipe beskou. In die huidige studie is stuifmeelkorrels van 50 Amerikaanse Oxalis spesies bestudeer met drie doelstellings in gedagte: 1. Om die variasie in die stuifmeeltipes van die Amerikaanse spesies van Oxalis te bestudeer, 2. Om die stuifmeeltipes van die twee diversiteitsentrurns te vergelyk, en 3. Om vas te stel watter diversiteitsentrum het palinologies die meer gevorderde spesies van die genus Oxalis. In die huidige studie is twee hoofstuifmeeltipes onderskei, naamlik netvormige en verrukate stuifmeeltipes. Die netvormige stuifmeeltipe is verder verdeel in 11 subtipes. Van die 11 subtipes wat onderskei is, kom nege tipes ook in die Suid Afrikaanse taksa van Oxalis voor, terwyl twee stuifmeeltipes slegs by die Amerikaanse soorte van Oxalis voorkom. Die verrukate stuifmeeltipe is slegs in 'n enkele Amerikaanse spesie gevind. Hierdie tipe toon 'n meer komplekse eksienstruktuur as die netvormige stuifmeeltipe. In die huidige studie het die netvormige stuifmeeltipe gebleik die mees algemene stuifmeeltipe in die Amerikaanse Oxalis-spesies te wees. Die Suid Afrikaanse taksa van Oxalis toon meer komplekse stuifmeeltipes as die Amerikaanse taksa.

Thesis (MSc (Botany and Zoology))--University of Stellenbosch, 2005.
The main substrate use during shoot establishment from the lateral bud of sugarcane setts and enzymes involved in sucrose metabolism were investigated in the shoots and the internodes acting as source of carbohydrates. Radiolabelling studies were conducted to investigate the metabolism of sucrose and glucose during shoot establishment. The internode’s total dry mass over the 21-day of shoot establishment period was reduced by 25% and 30% in plants incubated in dark/light and total darkness, respectively.

A Review of manuscripts written by European explorers and colonists affords the opportunity to develop a clearer understanding both of types of plants employed and their significance in religion and medicine during the 16th to 19th centuries. This paper is a distillation of accounts by thirteen European explorers, written between 1545 until 1861, about Laos and the Lao people in Siam. All of the references to plants and plant use have been extracted for an analysis of which plants European explorers viewed being used traditionally in Laos during this time period and information on how these plants were used and collected. Many of the plants described in the texts were medicinal in nature and some have been examined for modern pharmaceutical use. These pharmaceutical studies have substantiated the effectiveness of historical medicinal plant use. The texts also describe plants that were used in religious ceremonies and that continue to play an important role in Lao culture. Future comparative analysis of these early records with modern day observations of plant use should prove productive in formulating assessments of Traditional Environmental Knowledge loss and the impact of this loss on daily life. Understanding the plants that are important to native Lao in the past can lead to better methods of conservation in the future.

The potential for plantations to catalyze forest regeneration on highly degraded land and the need to research management methods to increase biodiversity within plantations have been widely recognized. Our study investigated the effects of creating artificial canopy gaps by girdling exotic timber trees in plantations on the germination, growth, and survival of native tree species that may be important food plants for the Puerto Rican parrot. We found that seedling growth increased significantly in gaps; there were no differences in survival or germination between gap and closed plots. Percentage cover of grasses, shrubs, and vines increased but did not prevent tree seedlings from growing significantly more in gaps. Leaf litter removal had no effect on germination, growth, or survival. Both local and landscape level diversity is predicted to increase in gaps if large saplings present in the understory replace the girdled timber trees, but plantations will still be dominated by exotics and timber species. Our results suggest that restoration of native forest diversity in plantations will require continued management to remove exotic species and promote growth of tree species with high wildlife habitat value.

Carolina Bays are unique elliptical depressional wetlands that are abundant in the Atlantic Coastal Plain, particularly in North Carolina. A large percentage of these bays have been ditched, drained, logged, or otherwise disturbed by humans in the past 200 years. Currently, Carolina Bay restoration provides a means for mitigating wetlands lost to development. The purpose of this study was to characterize compositional variation of vegetation relative to gradients of environmental conditions in three Carolina Bays in order to provide reference data for restoring impacted bays. Within three unaltered Carolina Bays, soil sampling, water table monitoring, and vegetation assessments were conducted. Four community types were identified: pond pine woodland, non-riverine swamp forest, high pocosin, and bay forest. Distributions of these community types were strongly correlated to depth of organic material and associated soil properties and hydrologic regimes. Pond pine woodland dominated mineral soils; both pond pine woodland and nonriverine swamp forest were found on histic and shallow organic soils; both high pocosin and bay forest were found on deep organic soils. Examination of the data included simple averaging, single factor analyses of variance, Fisher?s protected least significant differences, chi-square tests of independence, cluster analyses, and ordination procedures. The application of this material was intended for a North Carolina Department of Transportation Carolina Bay mitigation project and future Carolina Bay restoration projects in this region.

Wounding stress is a continuous threat to the survival of all organisms, and, in crop plants it leads to a dramatic reduction in crop yield. The signaling pathways that allow plants to respond to wounding stress are known to be complex. Many plant hormones such as jasmonic acid (JA), salicylic acid (SA), and ethylene have been identified as critical factors for the induction of wound-responsive genes in a number of plant species. However, the specific roles of each hormone in vivo, and how different hormones interact in the wound-stress response are largely unknown. Elucidation of the specific interactions of these plant hormones in response to wound stress is a major focus of wound research. The major goal of this research is to utilize Arabidopsis JA, SA, and ethylene biosynthetic and signaling mutants to analyze the role of each hormone separately and together in wound-responsive gene induction. Arabidopsis wild type, ein2, npr1, jar1, npr1/ein2, and npr1/jar1 plants were wounded and sampled at different times, after which RNA was extracted, subjected to electophoresis, transferred to filters and probed for several putative wound-regulated transcripts, which included PDF1.2, PR1, WAK1, and, LOX2. The constitutive levels of transcript expression as well as patterns of accumulation of these transcripts in response to the wounding stimulus varied in the different mutants.

Modulation of cytosolic calcium levels in both plants and animals is achieved by a system of Ca2+ -transport and storage pathways that include Ca2+ buffering proteins in the lumen of intracellular compartments. We used a transgenic approach to modulate calcium stores in the lumen of the endoplasmic reticulum in plants. We were able to use the low affinity, high capacity Ca2+ binding characteristics of the C-domain of calreticulin (CRT) to selectively increase Ca2+ storage in the endoplasmic reticulum, and to determine if those alterations affected plant physiological responses to stress. I fused the CRT C-domain to the C-terminal portion of the green fluorescent protein (GFP) and obtained transgenic plants that expressed high levels of the GFP-CRT C-domain fusion protein in the ER. I showed that this fusion protein was able to bind Ca2+ in vitro. These plants had increased Ca2+ stores in the ER and the ER calcium stores were used by the plant in times of calcium stress. The transformed seedlings also showed delayed loss of chlorophyll after transfer to high salt medium. The data suggest that expression of this calcium binding protein not only has the ability to increase bioavailable calcium stores but that the ER Ca2+ stores are important for plants to relieve the effect of salt stress. In the process of developing the transgenic plants, I also developed an array of other tools for subcellular localization, and targeting of the C-domain to various subcellular organelles. With two other colleagues, we also developed a GFP imaging system using the onion epidermal cells for visualizing subcellular localization of GFP and GFP fusion proteins.

Higher temperatures under climate change are likely to result in greater evaporation and increased soil moisture deficits. Increased drought will likely cause a shift in the vegetation distribution. This study focused on woody plants of the Southeastern United States mixed forest. Although water is not a primary limiting factor in this forest, species distribution suggests that water availability exerts a strong control on the success of woody plants. I used a comparative approach to understand environmental factors and corresponding species traits that determine species composition across a gradient of water availability. I compared hydraulic architecture, vulnerability to cavitation, and the ability of xeric and mesic species to germinate, grow and survive under varying levels of water stress. Congeneric pairs composed of one xeric and one mesic species were used. Seeds were subjected to polyethylene glycol solutions of different water potentials to compare the effects of water availability on germination of xeric and mesic species. I used understory saplings to compare the difference in the xylem hydraulic properties between xeric and mesic species and the air-injection method was used to determine differences in their xylem vulnerability to cavitation. I performed a dry-down experiment to compare the ability of the xeric and mesic species to survive extreme drought by evaluating survival after re-watering subsequent to drought exposure. Growth performance was evaluated by measuring electron transport rate (ETR), stomatal conductance (gs), shoot and root biomass of seedlings that were exposed to different levels of water (well-watered, dry, and flooded) and nutrients (high and low). Results indicate that the ability to germinate under drought did not differ consistently between xeric and mesic species, but, germination ability under drought was associated with the ability to maintain turgor. Stems of xeric species were less vulnerable to wilting than mesic species under drought stress. I found greater resistance to xylem cavitation in xeric species than mesic species. It appears that cavitation resistance was independent of specific conductivity and wood density since I did not find any trade-off between specific conductivity and vulnerability to cavitation among the woody plants examined. In the growth performance study, xeric species tend to have lower whole plant biomass, higher Root:Shoot (R/S) ratio, higher coarse root mass ratio (CRMR) and less reduction in gs under drought stress than mesic species. The higher stomatal conductance and lower photorespiration rates among the mesic species may have influenced their increased photosynthetic rates, thereby producing a greater total plant biomass than xeric species. Species distribution along water availability gradients appears to be better explained by the ability of seedlings to resist cavitation, to tolerate and survive water stress, and by their biomass allocation patterns, rather than by their ability to germinate under drought.

The ecological significance of montane non-alluvial wetlands in the southern Blue Ridge region of North Carolina is well known. However, there is relatively little quantitative documentation of these community types. In particular, our understanding of montane, peat-forming wetlands is based primarily on qualitative data, and there has been no previous comprehensive classification and description of these community types. In this study, species composition and vegetation-environment relationships are described for the geographically-isolated, non-alluvial wetlands of the southern Blue Ridge region of North Carolina. A hierarchical classification is presented for 12 community types within 2 broad vegetation classes based on 136 vegetation plots spanning the range of the southern Blue Ridge region of North Carolina. Hierarchical cluster analysis was used to delimit community types, and non-metric multidimensional scaling was subsequently used to help differentiate the community types identified by the cluster analysis. Although some of these community types fit well within currently recognized community concepts, others fit poorly within existing concepts, pointing to a need for definition of new types and/or significant refinement of types currently recognized. The 2 broad vegetation classes and 12 community types are discussed, each with a description of composition, related community concepts, and environmental context. Compositional variation among the types is most strongly associated with elevation, soil pH, soil nutrient availability, and soil cation exchange capacity.

The goal of this research was to build upon present understanding of the eutrophication process in the Neuse Estuary ecosystem by evaluating linkages among land use practices, nutrient concentrations and ratios, and phytoplankton assemblage composition. First, geographic Information Systems (GIS) analysis was used to characterize 26 sub-basins throughout the Neuse watershed for changes in land use over the past decade. GIS was also used in concert with multivariate statistics to synthesize and integrate ten years of land cover and water quality data into a conceptual model. Second, a continuous, decadal record of the phytoplankton in the mesohaline Neuse Estuary, in conjunction with synoptic measurement of environmental variables, provided a unique opportunity to evaluate responses of the phytoplankton assemblages to changing environmental conditions. Ordination techniques were used to investigate potential environmental predictors of phytoplankton community patterns through the process of eutrophication. Analyses indicated that over the past 10 years, total phosphorus concentrations were significantly higher during summer months in sub-watersheds with high densities of wastewater treatment plants (WWTPs) and confined swine feed operations. Nitrate concentrations were significantly higher during winter in sub-watersheds with high WWTP densities, and both inorganic and organic forms of nitrogen were significantly higher in sub-watersheds with greater agricultural land use. Ammonium concentrations were significantly higher after high-precipitation periods, but were not significantly correlated with the land-use parameters included in this study. In the Neuse Estuary, among several important findings, abundance of the potentially toxic, bloom-forming dinoflagellate Prorocentrum minimum was positively related to low water temperatures (winter/spring) and organic nitrogen and suspended solids concentrations. In addition, abundance of other potentially toxic flagellated algae such as the raphidophyte, Heterosigma akashiwo, has increased over the past decade, and H. akashiwo was found to be an ?indicator species? for high ammonium concentrations (> 50 μg/L). Overall, the data indicate that wastewater discharges in the upper Neuse basin and intensive swine agriculture in the lower basin have been the highest contributors of nitrogen and phosphorus to receiving surface waters. In the estuary, increased nutrients, especially ammonium, are promoting increased abundance of several potentially toxic, bloom-forming phytoplankton species.

Barrier islands include some of the most endangered and fragmented ecosystems on the Atlantic coast, providing critical habitat for many species, including some that are threatened and endangered. As the vast majority of these islands have been developed for human usage study and protection of the few remaining undeveloped and undisturbed islands is critical. This study was undertaken in order to characterize the vascular plant communities on Bird Island, an uninhabited, undeveloped barrier island on the border of North and South Carolina, with the objectives of a thorough survey of flora, vegetation, and environment, classification of plant communities, and multivariate analysis of vegetation and environmental data. A floristic inventory of the island and its associated marshes was conducted during the growing season (May-November) of 2002 and 2003. One hundred four 100m² plots were inventoried for vegetation and environment using protocols developed by the Carolina Vegetation Survey. Plant communities were identified according to the National Vegetation Classification, the Classification of the Natural Communities of North Carolina, and the Carolina Vegetation Survey. Interpretation of vegetation patterns was based on multivariate analysis of vegetation and environmental data. Ninety-one vascular plant species in 35 families, including 4 exotic species, were distributed across 12 communities. Communities on Bird Island appear to be distinctive when compared to those described for other barrier islands in the region. Additionally, the vegetation survey on Bird Island revealed suitable habitat for the federally listed Seabeach amaranth (Amaranthus pumilus); an important dune-building annual of the North American Atlantic coast. Surveys of the late 1980s and early 1990s documented small populations of Seabeach amaranth on Bird Island, but our work found no indication of a population in either 2002 or 2003. Seabeach amaranth?s existence range-wide is threatened by habitat loss and fragmentation, herbivory, and anthropogenic disturbances such as beach driving, hardening, and raking. Published work on this species has been limited, but observations of natural, experimental, and restored populations have indicated relationships between distance from the ocean and both survivorship and reproduction. To quantify this relationship, 314 plants were transplanted at varying distances from the ocean. Plants were monitored monthly from June until December 2003. We found that distance from the ocean had a significant effect on survivorship, size, and reproduction; however, presence of webworms and ghost crabs did not have significant effects on size or reproduction. Distance from the ocean combined with complex factors such as over wash and soil salinity appear to be important indicators of success for both natural and restored populations of this species, and landscape position should be incorporated into future conservation and restoration efforts for A. pumilus in the Carolinas and elsewhere. Overall, we found that the vegetation of Bird Island is mostly intact, with few exotic, invasive species present. Bird Island?s protected status and limited presence of invasive species make it suitable habitat for continued protection and further restoration of rare, threatened, or endangered species, such as Seabeach amaranth. Atlantic barrier islands in general provide distinct community types combined with a small species pool, a combination that may provide a model for examination of larger ecological questions.

A method of rapid field assessment and predictive modeling was developed to characterize vegetation communities of the Gorges State Park and Gamelands and to create predictive community maps for the area. This method placed an emphasis on locating rare communities using expert information, existing databases, aerial photography, and random encounters in efforts to provide information to researchers and park personnel about community locations. Approaches for classifying these communities were examined to identify which would provide suitable units for modeling community types. I sampled 102 field locations and assigned their vegetation to 16 different community types. Predictive community maps were generated using discriminant functions incorporating digital terrain data, including elevation, slope, relative slope position, terrain shape index, and weighted landform index. Three sets of discriminant functions were created to meet the different needs of persons interested in using these maps. Photo-interpreted cover classes were also including in the modeling process as filters. Map accuracies ranged from 65% to 75%, with those using only discriminant functions (without filtering) yielding higher accuracies.

Dinoflagellates represent a diverse group of both auxotrophic and heterotrophic protists. Most heterotrophic dinoflagellates are raptorial feeders that encounter prey using ?temporal-gradient sensing? chemotaxis wherein cells move along a chemical gradient in a directed manner toward the highest concentration. Using short-term ?memory? to determine the orientation of the gradient, dinoflagellates swim in a ?run-and-tumble? pattern, alternating directed swimming with rapid changes in orientation. As the extracellular concentration of the attractant increases, a corresponding increase in the ratio of net-to-gross displacement results in overall movement toward the stimulus.The dinoflagellates Pfiesteria piscicida and P. shumwayae are heterotrophic estuarine species with complex life cycles that include amoeboid, flagellated, and cyst stages, that have been implicated as causative agents in numerous major fish kills in the southeastern United States These organisms show documented ?ambush-predator? behavior toward live fish in culture, including rapid transformations among stages and directed swimming toward fish prey in a manner that suggests the presence of a strong signalling relationship between live fish and cells of Pfiesteria spp.Zoospores of the two species of Pfiesteria can be divided into three functional types: TOX-A designates actively toxic isolates fed on fish prey; TOX-B refers to temporarily non-toxic cultures that have recently (1 week to 6 months) been removed from fish prey (and fed alternative algal prey); and NON-IND refers to isolates without apparent ichthyotoxic ability (tested as unable to kill fish in the standardized fish bioassay process; or without access to fish for ca. 1.5 years). Several Pfiesteria-like dinoflagellates have been isolated from samples in which P. piscicida and P. shumwayae are also present, including several cryptoperidiniopsoid species that have repeatedly been tested as lacking ichthyotoxic capability under ecologically relevant conditions (cell densities that occur in estuaries).Microcapillary assay techniques were employed to determine the attraction of P. piscicida and P. shumwayae zoospores to sterile-filtered fish mucus and excreta. Differences in attraction were measured among functional types, and between these two species and several isolates of cryptoperidiniopsoids, in ten-minute trials in which zoospores entering tubes filled with test substances were observed and counted. TOX-A zoospores of both P. piscicida and P. shumwayae were strongly and comparably attracted to fish secreta/excreta, relative to their behavior toward microcapillary tubes that were filled with filtered seawater. TOX-B zoospores of both Pfiesteria species showed intermediate attraction toward fish materials that appeared to be inversely related to time isolated from fish prey. NON-IND zoospores exhibited low attraction to fish materials. Cryptoperidiniopsoid zoospores showed moderate attraction with no apparent influence of previous exposure to fish.In an additional experiment that examined the signal activity in fish materials over time after collection from fresh fish, unfiltered fish materials ceased to attract P. piscicida zoospores after approximately 48 hours and ultrafiltered materials maintained attractive ability over the duration of the experiment (72 hours). These data show that filtration of fish materials may be used to extend the useful life of the chemical signal, possibly by removing bacteria that consume or degrade it.In recent years, several researchers have identified fish kairomones (pheromones that benefit the recipient) present in fish mucus that induce life history and behavioral changes in a range of zooplankters. It is likely that one or more of these kairomones, or similar compounds, are responsible for the behavioral and developmental changes observed in Pfiesteria spp. in the presence of live fish. Data from these experiments support the current understanding that significant behavioral differences exist between functional types of Pfiesteria spp., and between these toxic dinoflagellate species and known lookalike dinoflagellates without ichthyotoxic activity under ecologically relevant conditions.

Thesis (PhD (Botany and Zoology))—-Stellenbosch University, 2008.
Streptocarpus Lindl. (Gesneriaceae DC.) is a genus of herbaceous plants containing approximately 160 species, of which the majority occur in Africa and Madagascar. They are largely restricted to shaded and moist habitats such as primary forest and rock outcrops. The genus contains considerable morphological variation, with subgenus Streptocarpella containing caulescent species and subgenus Streptocarpus mostly consisting of acaulescent growth forms, mainly the unifoliates, plurifoliates and rosulates. Preliminary molecular analyses conducted using nuclear ITS sequence data suggested that subgenus Streptocarpus evolved in tropical central Africa, before radiating in several independent waves into southern Africa. Streptocarpus has therefore only recently spread into South Africa. Amongst the South African species, 11 morphologically similar species were identified as being closely related, together forming the Cape primrose clade, based on the analysis of nuclear ITS sequence data. However, these analyses only contained a few South African species, and the ITS data did not provide enough resolution of relationships within this clade. In this study nuclear and chloroplast sequence data as well as nuclear microsatellite data were therefore employed to unravel the complex relationships amongst the South African Streptocarpus species. The analyses indicate that 16 rosulate, palynologically similar species (S. primulifolius, S. rexii, S. johannis, S. baudertii, S. modestus, S. formosus, S. gardenii, S. lilliputana, the S. cyaneus complex [S. cyaneus, S. parviflorus, S. fenestra-dei, S. kunhardtii and S. roseo-albus], S. floribundus, S. aylae and S. kentaniensis), the core Cape primrose species, are closely related, while five unifoliate/plurifoliate, palynologically more variable species (S. denticulatus, S. dunnii, S. pusillus, S. rimicola and S. bolusii) consistently emerged as more distantly related to the core Cape primrose species. However, the positions of a further ten species (S. meyeri, S. montigena, S. fanniniae, S. caeruleus, S. longiflorus, S. polyanthus, S. saundersii, S. porphyrostachys, S. grandis and S. vandeleurii) were more complex in the analyses, indicating that hybridization has played a role in their evolution. Five of these species (S. meyeri, S. montigena, S. fanniniae, S. caeruleus and S. longiflorus) are, however, palynologically homogenous and rosulates, and therefore are probably more closely related to the core Cape primrose species, while the other five (S. polyanthus, S. saundersii, S. porphyrostachys, S. grandis and S. vandeleurii) are unifoliates/plurifoliates that are palynologically more heterogenous, and are probably more distantly related to the core Cape primrose species. Amongst the core Cape primrose species, S. primulifolius emerged as being ancestral or having hybridized with many of the other species, while the S. cyaneus complex forms a geographically and genetically more isolated group. However, evolutionary relationships amongst these species were to a certain extent obscured by incomplete lineage sorting caused by limited interpopulation gene flow, frequent hybridization and rapid speciation. The analyses confirmed that the Pondoland Centre forests constitute important Pleistocene refugia, and revealed some of the historical migration routes along which the species had radiated.

Thesis (PhD) -- Stellenbosch University, 1991.
ENGLISH ABSTRACT: The effect of partial defoliation as canopy management practice on metabolism and grape composition of the grapevine, Vitis vinifera L cv. Cabernet Sauvignon, was investigated. The establishment of physiologically sound principles on how to overcome deleterious effects associated with vigorous and dense-canopy vines is emphasized. Experimental vines were defoliated 33 % and 66 % evenly over the whole canopy from different developmental stages in a field study. Effects on canopy microclimate, photosynthesis, photosynthate translocation, vegetative growth, reproductive growth, root development and distribution, as well as grape and wine quality, were determined. A method for the simultaneous extraction of sugars and organic acids from freeze-dried berries at different developmental stages is described. Partial defoliation of vines improved canopy microclimate and photosynthetic efficiency of remaining leaves. Normal translocation and distribution patterns of photosynthates were apparently unaffected by partial defoliation. Translocation to and accumulation of photosynthetic products in the leaves and bunches of partially defoliated vines were, however, improved. Remaining leaves of partially defoliated vines were in comparison photosynthetically more active. Apart from a less favourable canopy microclimate, it seemed that the sink capacity of non-defoliated vines did not comply to the source capacity, inducing a reduced rate of photosynthesis. Normal sigmoidal growth patterns of vines were not affected by partial defoliation as applied in this study. This is important for the longevity, healthiness and productivity of vines. Vegetative growth was differentially affected by partial defoliation. No compensatory leaf growth occurred in reaction to partial defoliation from different developmental stages. Main shoot length, however, decreased slightly. Lateral shoot length and number of laterals increased, whereas cane mass decreased when vines were partially defoliated, particularly the earlier and more severe the defoliation. Reproductive growth in terms of yield was deleteriously affected by 33 % defoliation prior to pea size and 66 % defoliation prior to veraison. Budding percentage was, however, improved by 33 % and 66 % defoliation, whereas bud fertility was only improved by 33 % defoliation. Partial defoliation changed the canopy microclimate to conditions favourable for pest and disease control and higher grape quality. Subterranean growth was favourably affected by partial defoliation, particularly when applied from pea size stage. These changes included higher root densities, development of higher numbers of fine and medium diameter roots and occurrence of higher total root numbers in all soil layers. Generally, defoliations from pea size and veraison were more efficient regarding root development than defoliations from just after bud break and from berry set. Partially defoliated vines reacted by forming new roots, creating a more efficient nutrient absorption capacity and utilization of soil and available water and that, together with higher photosynthetic activities of leaves, provided an efficient mechanism for continued high performance. Grape quality was not affected markedly by partial defoliation. Total soluble solids in berries of defoliated vines were comparable to and even significantly higher than those of non-defoliated vines in some cases, in spite of much lower leaf areas. Generally, total titratable acidity of musts was also slightly higher for partially defoliated vines. Glucose and fructose concentrations in berries were unaffected by partial defoliation, while tartaric acid concentrations were slightly increased and malic acid concentrations slightly decreased. Partial defoliation generally increased the anthocyanin concentration of berry skins. These changes in grape composition suggest higher grape quality and seemed to result from improved light conditions in the canopy interior. Berry volume decreased with partial defoliation, which lowered the pulp:skin ratio. These berries are more desirable for quality wines. Regardless of severity or the developmental stage defoliation was commenced, wine cultivar character and overall wine quality were significantly improved. Partial defoliation changed the general metabolism of vines, mainly in terms of more favourable source:sink ratios, resulting in more efficient photosynthesis, subterranean performance and canopy microclimate. In general, the results suggest that an even removal of 33 % of leaves opposite and below bunches during the period from flowering or berry set to pea size stage may be applied. lt is further suggested that existing vigorous and dense-canopy vines be 33 % defoliated evenly on the lower half of the shoot (canopy) from pea size or veraison. This hypothesis proved effective in improving canopy microclimate, photosynthetic activity and yield, while vegetative growth was inhibited. Grape and wine quality were higher. On the whole, partial defoliation as applied in this study, is recommended as canopy management practice in order to facilitate the abolishment of deleterious effects of excessive vegetative growth and canopy density on balanced metabolic activity, fruit and wine quantity and quality, as well as longevity and healthiness of grapevines.
AFRIKAANSE OPSOMMING: Die invloed van blaarverwydering as loofbestuurspraktyk op die metabolisme en druifsamestelling van die wingerdstok, Vitis vinifera L cv. Cabernet Sauvignon, is ondersoek. Die vestiging van fisiologies-betroubare beginsels oor hoe nadelige effekte geassosieerd met geil en lower-verdigte wingerde uitgeskakel kan word, word beklemtoon. Proefstokke is in 'n veldondersoek 33 % en 66 % eweredig oor die hele lower vanaf verskillende ontwikkelingstadiums ontblaar. Effekte op lowermikroklimaat, fotosintese, translokasie van fotosintetiese produkte, vegetatiewe groei, reproduktiewe groei, wortelontwikkeling en verspreiding asook druif- en wynkwaliteit is bepaal. 'n Metode vir die gelyktydige ekstraksie van suikers en organiese sure uit gevriesdroogde korrels op verskillende groeistadiums is ontwikkel. Blaarverwydering het lowermikroklimaat verbeter en fotosintetiese doeltreffendheid van oorblywende blare op die stok verhoog. Normale translokasie en verspreidingspatrone van produkte van fotosintese is skynbaar nie deur blaarverwydering befiwloed nie. Translokasie na, en akkumulering van fotosintetiese produkte in die blare en druiwe van gedeeltelik ontblaarde stokke, is egter verbeter. Oorblywende blare van gedeeltelik ontblaarde stokke was fotosinteties meer aktief. Afgesien van 'n ongunstiger lowermikroklimaat, het die sinkkapasiteit van nie-ontblaarde stokke skynbaar ook nie teen die bronkapasiteit opgeweeg nie en is 'n verlaagde tempo van fotosintese verkry. Normale sigmofdale groeipatrone van die stokke is nie deur blaarverwydering befrivloed nie. Dit is belangrik vir langlewendheid, gesondheid en produktiwiteit van stokke. Vegetatiewe groei is differensieel deur blaarverwydering befrivloed. Geen kompenserende blaargroei het in reaksie op blaarverwydering vanaf verskillende ontwikkelingstadiums voorgekom nie. Hooflootlengte was egter effens korter. Sylootlengte en aantal sylote het toegeneem, terwyl lootmassa afgeneem het met blaarverwydering, veral hoe vroeer en strawwer dit toegepas is. Reproduktiewe groei in terme van opbrengs is nadelig befrivloed deur 33 % ontblaring voor ertjiekorrelstadium en 66 % ontblaring voor die deurslaanstadium. Botpersentasie is egter deur blaarverwydering verbeter, terwyl oogvrugbaarheid slegs deur 33 % ontblaring verbeter is. Blaarverwydering het 'n gunstige lowermikroklimaat vir die beheer van plae en siektes en hoer druifkwaliteit geskep. Ondergrondse groei is gunstig deur blaarverwydering befrivloed, veral wanneer toegepas vanaf ertjiekorrelstadium. Hierdie veranderinge het ingesluit hoer worteldigtheid, ontwikkeling van groter hoeveelhede wortels met 'n fyn en medium deursnit en die voorkoms van 'n groter aantal totale wortels in alle grondlae. Blaarverwydering vanaf ertjiekorrel- en deurslaanstadia was in die algemeen meer doeltreffend ten opsigte van wortelontwikkeling as blaarverwydering vanaf net na bot en vanaf korrelset. Gedeeltelik ontblaarde stokke het gereageer deur nuwe wortels te vorm, waardeur 'n meer doeltreffende vermoe tot voedingstofopname en benutting van grand an beskikbare water verkry is. Tesame met hoer fotosintetiese aktiwiteite van die blare is 'n doeltreffende meganisme vir aanhoudende hoe prestasie verkry. Druifkwaliteit is nie aanmerklik deur blaarverwydering beirwloed nie. Totale oplosbare stowwe in druiwe van gedeeltelik ontblaarde stokke was vergelykbaar en selfs betekenisvol hoer as die van nie-ontblaarde stokke in sekere gevalle, ten spyte van die baie laer blaaroppervlakte. In die algemeen was die totale titreerbare suur in die mos van gedeeltelik ontblaarde stokke oak effens hoer. Glukose- en fruktosekonsentrasies in die druiwe is nie deur blaarverwydering beinvloed nie. Die konsentrasie wynsteensuur is egter effens verhoog en die appelsuurkonsentrasie effens verlaag. Antosianienkonsentrasie van korreldoppe is in die algemeen deur blaarverwydering verhoog. Hierdie veranderinge in druifsamestelling dui op hoer druifkwaliteit en is skynbaar die resultaat van verbeterde ligtoestande in die binnekant van die lower. Korrelvolume het afgeneem met blaarverwydering. Dit het die pulp:dop verhouding verlaag. Sulke korrels is meer gewens vir bereiding van kwaliteitswyne. Wyn cultivarkarakter en totale wynkwaliteit is betekenisvol deur blaarverwydering verhoog, onafhanklik van die strafheid of ontwikkelingstadium waarvandaan blare verwyder is. Blaarverwydering het die algemene metabolisme van die wingerdstok verander, hoofsaaklik ten opsigte van meer gunstige bron:sink-verhoudings en derhalwe meer doeltreffende fotosintese, ondergrondse groei en lowermikroklimaat. Die resultate dui in die algemeen daarop dat 'n eweredige blaarverwydering van 33 % regoor en onderkant die trosse tydens blomvorming of korrelset tot ertjiekorrelstadium toegepas kan word. Die resultate dui verder daarop dat 33 %van bestaande geil en lower-verdigte stokke se blare eweredig verwyder kan word op die onderste helfte van die loot (lower) vanaf ertjiekorrel- of deurslaanstadium. Hierdie hipotese was suksesvol in die verbetering van lowermikroklimaat, fotosintetiese aktiwiteit en oesmassa. Vegetatiewe groei is gestrem. Druif- en wynkwaliteit was hoer. In die geheel kan blaarverwydering soos toegepas in hierdie ondersoek aanbeveel word as loofbestuurspraktyk ten einde die uitskakeling van nadelige effekte van oormatige vegetatiewe groei en lowerdigtheid op gebalanseerde metaboliese aktiwiteit, druif- en wynkwantiteit en kwaliteit, asook langlewendheid en gesondheid van wingerdstokke te bevorder.

Thesis (MSc)--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: The changes in carbon allocation to sucrose, hexoses, fibre, starch and respiration were investigated in developing internodes of sugarcane. Radiolabelling studies were conducted on internode 3, 6 and 9 tissue, representing three stages of increasing maturity. It was apparent that a high rate of cycling between triose-phosphate and hexose-phosphate occurred. A maximum of 50% of carbon entering triose-phosphates was returned to hexose-phosphate in internode 3 tissue, and this flux decreased with tissue maturity to 30%. Carbon partitioning into sucrose increased from 34% of total 14C uptake in internode 3, to 61% in internodes 6 and 9. In immature tissue, the protein and fibre components were the dominant competing sinks with sucrose for incoming carbon, to which 14 and 16% of carbon were allocated respectively. Increased carbon allocation to sucrose with tissue maturity, coincided with a decrease in partitioning to fibre. This indicated that previous studies had underestimated total carbon allocation to respiration, since the protein component was not considered. In contrast with earlier work, the respiratory pathway was the strongest competitor with sucrose for incoming carbon, even in mature tissue. Between internodes 3 and 6, carbon allocation to total respiration did not change significantly, but decreased 50% in mature tissue. Starch was a weak competitor with sucrose, for incoming carbon, to which a maximum of 2% of 14Cwas allocated in immature tissue. In cane harvested in early spring, radiolabelled maltose was recovered in internode 3 tissue of ripening cane, indicating that concomitant starch synthesis and degradation occurred. The. redistribution of C-1 and C-6 in starch glucose was analysed following feeding of tissue with [1_14C]_and [6_14C]_glucose. Randomization of label in starch indicated that the pathway for carbon movement into sugarcane plastids for starch synthesis is primarily through the triose-phosphate translocator. Finally, this study indicated that radiolabelling of tissue discs is a suitable experimental system to determine carbon flux in sugarcane. During the 3 h labelling period the rate of 14C02 release became linear, indicating that the system approached isotopic steady state between the external and internal glucose pool; and the respiratory processes involved in CO2 release.
AFRIKAANSE OPSOMMING: Die veranderinge in koolstoftoedeling na sukrose, heksoses, vesel, stysel en respirasie is in ontwikkelende internodes van suikerriet ondersoek. Die koolhidraatmetabolisme in internodes 3, 6 en 9, wat drie stadiums van toenemende rypheid verteenwoordig, is met behulp van 14Cmerkingstudies ondersoek. Dit is duidelik dat daar 'n hoë mate van koolstofsirkulering tussen die heksose- en triose-fosfaat poele voorkom. In internode 3 word tot 50% van die koolstofwat in triose-fosfate geïnkorporeer is, weer na heksosefosfaat omgeskakel. Selfs in volwasse weefsel vind daar nog soveel as 30% koolstofsirkukering plaas tussen die twee poele plaas. Koolstoftoedeling vanaf glukose na sukrose het van 34% in internode 3, tot 61% in internodes 6 en 9 toegeneem. Proteïn en selwandkomponente was die belangrikste swelgpunte vir koolstof in onvolwasse weefsel gewees. Namate die weefsel meer volwasse word, word sukrose 'n belangriker swelgpunt. Die koolstoftoedeling aan sukrose is veral ten koste van toedeling aan die selwandkomponente. Die bevinding dat die proteïenpoel 'n sterk swelgpunt is dui aan dat vorige studies die belang van respiratoriese koolstofvloei onderskat het. In teenstelling met vorige aansprake is dit duidelik dat selfs in volwasse weefsel respirasie die grootste swelpunt vir die inkomende organiese koolstof in die internode vorm. Koolstoftoedeling aan respirasie het nie noemenswaardig tussen internodes 3 en 6 verskil nie, maar het met 50% in volwasse weefsel afgeneem. Stysel is deurgaans 'n swak swelgpunt vir koolstof met die hoogste toedeling aan die poel (2%) in die jong weefsel (internode 3) . Na toediening van [U- 14C]-glukose is radioaktief gemerkte maltose gevind in suikerriet wat vroeg in die lente geoes is. Dit dui aan dat gelyktydige afbraak en sintese van stysel plaasgevind het. Die herverdeling van C-l en C-6 in glukose afkomstig van stysel is na toediening van [1_14C]_ en [6-14C]-glukose ontleed. Die ewekansige verspreiding van radioaktiwiteit tussen koolstof 1 en 6 van die glukose in stysel dui aan dat dit hoofsaaklik die triose-fosfaat translokeerder is wat in die plastied verantwoordelik is. Hierdie studie het ook aangetoon dat radioaktiewe merking van weefselsnitte 'n geskikte eksperimentele sisteem is om koolstoftoedeling in suikerriet te ondersoek. Die patroon van 14C02 vrystelling dui daarop dat die weefsel na 'n 3 h inkuberingsperiode isotopiese ewewig tussen die eksterne en interne glukose poele en die respiratoriese prosesse begin bereik het.

Thesis (MSc)--University of Stellenbosch, 2005.
ENGLISH ABSTRACT: The aim of this study was to elucidate the control of flowering in Protea spp. The main factor that makes studying flowering in this diverse genus so challenging is the fact that most Protea spp. and their commercial hybrids have very dissimilar flowering times. The carbon input into floral organ formation and support is expensive as flowers from Protea spp are arranged in a very large ‘flowerhead’ (50 mm by 130 mm for ‘Carnival’) that can take up to two months to develop fully. Therefore the carbon needed for structural formation, metabolic respiration and the sugar-rich nectar production make these structures extremely expensive to form and maintain. Protea is a sclerophyllous, woody perennial shrub with a seasonal flush growth habit. The leathery leaves (source tissue) produce most of the carbon needed for support and growth of the new leaves, roots and flowers (sink tissue). In the case of expensive structures, such as the inflorescences, remobilization from stored reserves, probably from underground storage systems, can be observed for structural development and maintenance. At all times the flush subtending the apical meristem or florally developing bud provides the largest proportion of carbon for support of the heterotrophic structures. Protea apical meristems stay dormant during the winter months, but BA (benzyl adenine, 6-benzylaminopurine) application to the apical meristem of the Protea hybrid ‘Carnival’ has shown to be effective in the release of dormancy and subsequently shift flowering two months earlier than the natural harvesting time. BA is thought to shift source/sink relationships by stimulating the remobilization of carbon to the resting meristem. Although no direct evidence was found for this in our assay, possible reasons for a weak assay are discussed. This study combined physiological research with the use of molecular tools. An homologue of the Arabidopsis thaliana meristem identity gene, LEAFY, was identified in Proteaceae. PROFL (PROTEA FLORICAULA LEAFY) is expressed in both vegetative and reproductive meristems as well as leaves. PROFL expression in leaves may have an inhibitory effect on vegetative growth, as the expression was high at the same time as the expression in the apical meristem increased marking the transition to reproductive growth. In perennial species such as Protea, the availability of carbon is thought to be the main factor controlling floral development. Possible mechanisms of control may be through the direct control of meristem identity genes such as PROFL through sugar signaling. BA did not have a direct effect on PROFL expression although the expression pattern was one month in advance when compared to the natural system. PROFL expression seems to be consistent with that found for other woody perennial species and would therefore be a convenient marker for floral transition.
AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die inisiëring van blomvorming in Protea spp. te ondersoek. Die verskil in blomtyd tussen Protea spp. en hul kommersieel ontwikkelde hibriede maak die studie van hierdie genus ‘n groot uitdaging. Die groot hoeveelheid koolstof wat benodig word vir blomvorming in Protea is hoofsaaklik as gevolg van die grootte (50 mm by 130 mm vir ‘Carnival’) van die blomkop waarin individuele blomme geranskik is. Hierdie blomkoppe kan tot 2 maande neem om volwassenheid te bereik. Die koolstof benodig vir strukturele ontwikkeling, metaboliese respirasie en produksie van suiker-ryke nektar maak die vorming van hierdie structure ongelooflik duur. Protea is ‘n bladhoudende, houtagtige bos met ‘n seisoenale groeipatroon. Die leeragtige blare voorsien die grootste hoeveelheid koolstof vir die ontwikkelende blare, wortels en blomme. Koolstof vir die ontwikkeling en ondersteuning van die groot stukture soos die blomkoppe word gedeeltelik deur die huidige fotosinfaat voorsien en bewyse vir die remobilisasie van gestoorde koolstof, heel waarskynlik vanaf ondergrondse stukture, is gevind. Die blare van die stemsegment wat die apikale meristeem of ontwikkelende blom dra, voorsien altyd die grootse hoeveelheid koolhidrate aan die ontwikkelende struktuur. Die apikale meristeme van Protea bly dormant gedurende die winter maande, maar applikasie van BA (bensieladenien, 6-bensielaminopurien) aan die apikale meristeme van die Protea hibried ‘Carnival’ verbreek dormansie en die blomtyd van hierdie gemanipuleerde plante is daarom twee maande vroeër as die natuurlike oestyd. Daar word gespekuleer dat BA applikasie aan die apikale meristeem die hoeveelheid koolstof wat na die dormante meristeem gestuur word verhoog wat dan die dormansie verbreek. Hierdie studie beproef ongelukkig hierdie hipotese swak en redes hiervoor word bespreek. In hierdie studie word fisiologiese analises met molekulêre studies gekombineer. ‘n Meristeem identiteits gene wat homologie wys met LEAFY (LFY) in Arabidopsis thaliana (Arabidopsis), PROFL (PROTEA FLORICAULA LEAFY), is in Proteaceae geïdentifiseer. PROFL word uitgedruk in reproduktiewe meristeme so wel as die vegetatiewe meristeme en blare. PROFL uitdrukking in blare mag dalk ‘n inhiberende effek hê op die vorming van nuwe blare, omdat die uitdrukking hoog was op die selfde tyd as wat blominisiëring plaasgevind het in die apikale meristeem. Die transisie tot reproduktiewe groei word gekenmerk deur ‘n verhoging in PROFL uitdrukking in die apikale meristeem. In meerjarige plante soos Protea spp word daar verwag dat die teenwoordigheid van voldoende koolstof die oorskakeling na reproduktiewe groei inisieer. Dit mag wees deur die direkte aksie van suikers met gene soos PROFL wat die finale skakel na reproduktiewe groei beheer. Alhoewel BA applikasie geen direkte effek gehad het op PROFL uitdrukking nie, was die blomtyd met twee maande vervroeg. PROFL uitdrukking was vergelykbaar met die uitdrukking van LFY homoloë in ander houtagtige, meerjarige plante en kan gebruik word as ‘n merker vir blominisiëring in Protea spp.

Thesis (MSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: This thesis explores how human dictated methods of introduction and species-specific traits interact to define spatial patterns in invasive plant populations using Acacia elata as a model species. I initially asked whether the relatively small invasive extent (when compared to congeners introduced for forestry or dune stabilization) of a species used widely for ornamental purposes (A. elata) is due to low rates of reproduction in South Africa. Results indicate that A. elata has similar traits to other invasive Australia Acacia species: annual seed input into the leaf litter was high (up to 5000 seeds m-2); large seedbanks develop (>20 000 seeds m-2) in established stands; seed germinability is very high (>90%); seeds accumulate mostly in the top soil layers but can infiltrate to depths of 40cm; and seed germination appears to be stimulated by fire. I argue that the current limited distribution of invasive A. elata populations is not attributable to species-specific reproductive traits. Following on from this I addressed the relative importance of species traits, the recipient environment, and introduction dynamics using species distribution models and spread models defined using a range of parameters representative of invasive Australian acacia species. Results indicate that in the early stages of simulated invasions, the number of trees introduced was the most important parameter influencing abundance and extent, while the placement of introduction foci in urban areas associated with ornamental introductions limited the extent and abundance of invasive populations. I suggest that conditions relating to human-mediated introduction events initially mask the influence of intrinsic species traits and help to explain the failure and success of species associated with specific human-shaped pathways. Third, I used scale-area curves to determine how these human-dictated introduction conditions influenced the spatial structure of populations. The fractal dimension (Dij) of A. elata populations indicates plot scale (2.5-25m) spread with high densities that are increasing. Artefacts of introduction history were observed at the regional scale (2.5-25km) - populations are contiguous around introduction foci such as towns and roads. Moreover, fragmentation of A. elata populations at local to landscape scales (0.25-2.5km) is due to a combination of the haphazard regional placement and limited secondary dispersal vectors, both of which can be linked to their introduction history. In summary, this study used a combination of field-based data, modelling techniques and broad-scale sampling methods to assess how intrinsic species traits and introduction conditions mediate invasive spread. I conclude that introduction history can have a long-lasting (100+ years) influence on the spatial structure and distribution of invasive plants, which can mask the influence of individual species traits.
AFRIKAANSE OPSOMMING: Alhoewel menigte plant spesies deur mense ingevoer word, word slegs 'n klein hoeveelheid van plante indringers. Die beperkte aantal spesies wat in nuwe habitatte vestig en versprei, kan grotendeels toegeskryf word aan die omgewing en mensgemaakte hindernisse ten opsigte van oorlewing, voortplanting en verspreiding. In hierdie tesis gebruik ek Acacia elata as ʼn model spesie om te ondersoek hoe die invoeringsproses sowel as spesie spesifieke eienskappe die ruimtelike struktuur van indringende populasies bepaal. Aanvanklik was my vraag of die relatiewe klein indringingsarea van ʼn spesie wat ingevoer is vir ornamentele doeleindes (Acacia elata), teenoor die groot indringingsareas van Australiese Acacia-spesies wat ingevoer is vir bosbou of duin stabilisering, die gevolg is van lae voortplantings tempo in Suid-Afrika. Resultate dui daarop dat A. elata soortgelyke eienskappe as ander indringende Australië akasia spesies het: jaarlikse saad produksie is hoog (tot 5000 sade m - 2); groot ontwikkelde saadbanke (> 20 000 sade m - 2); hoë saad ontkieming (> 90 %); saad versamel in die boonste grondlae, alhoewel dit kan infiltreer tot 'n diepte van 40 cm; laastens, ontkieming word deur vuur gestimuleer. Hierdie resultate stel voor dat die huidige beperkte verspreiding van indringende A. elata populasies nie die gevolg is van spesie spesifieke voortplantings eienskappe nie. Gevolglik het ek 11 indringende Australiese akasia-spesies ondersoek om die relatiewe belangrikheid van spesie eienskappe, die area waar hul geplant is, asook invoerings aspekte te ondersoek. Resultate wys dat die aantal bome wat ingevoer is, die belangrikste eienskap was ten opsigte van digtheid en verspreiding van ʼn indringende spesie, terwyl invoering naby fokuspunte in stedelike gebiede weer spesie digtheid en verspreiding beperk. Hierdie resultate toon dat spesies eienskappe aanvanklik nie ʼn groot invloed het op hul sukses nie, maar dat hul sukses eerder afhang van waar hul geplant word. Derdens, gebruik ek skaal - area kurwes om te bepaal hoe die invoering van A. elata die ruimtelike struktuur van populasies beïnvloed het. Die fraktale dimensie (Dij) van A. elata bevolkings dui op verspreiding by die plaaslike vlak (2,5 - 25m), wat voorstel dat verspreiding nie op hierdie skaal beperk is nie. Eienskappe van die rede/metode van invoering was wel waargeneem op die groter skaal (2.5 - 25km) waar populasies digter was naby dorpe en paaie. Die intermediêre skaal (0,25 - 2.5km) dui daarop dat A. elata populasies huidiglik beperk word deur 'n kombinasie van lukrake plasing en beperkte sekondêre verspreiding, albei wat gekoppel kan word aan hul invoer geskiedenis. Hierdie studie maak dus gebruik van 'n kombinasie van veld gebaseerde data, modellerings tegnieke en breë skaal steekproefmetodes om te evalueer hoe algemene spesies eienskappe en invoer toestande verspreiding bepaal. Sodoende verskaf ek ʼn raamwerk om die invloed van invoer toestande op die ruimtelike struktuur en verspreiding van ornamentele plant indringers te verstaan.

Thesis (PhD (Botany and Zoology))—University of Stellenbosch, 2009.
The genus Oxalis forms a major part of the flora of southern Africa, in particular the Cape Floristic Region (CFR) at the southwestern tip of the continent, but the current taxonomy is outdated and ecological knowledge of the lineage is sadly incomplete. In this thesis I set out to address several aspects of Oxalis systematics that urgently require attention. Firstly, the current macro-morphological taxonomy requires phylogenetic testing, as it is acknowledged to be incomplete and artificial. I address this need by providing a DNA sequence-based phylogeny of three markers, using three different inference methods, for nearly three quarters of the indigenous species. This phylogeny confirmed both the monophyly of the southern African taxa, and the artificiality of the current classification system. It is congruent with previous sequence-based reconstructions of smaller groups of southern African Oxalis species, and with the palynological classification proposed for the genus. Secondly, previous phylogenetic work on the southern African members could not resolve basal relationships within the southern African clade. I attempt to address this problem by sequencing three extra chloroplast markers for a select group of taxa, followed by separate and combined (total evidence) molecular phylogenetic analyses. This approach did increase resolution at the base of the southern African lineage, but many clades still showed poor resolution and support despite the use of more than 7 000 bases of sequence data. Resolving these clades within the southern African Oxalis phylogeny remains a challenge, and should prove a fertile field for future research. Thirdly, the ages (and thus duration of presence) of many Cape plant lineages within the CFR are of major interest, given that the CFR represents a global biodiversity hotspot. The age of the genus in the Cape is estimated by analyzing combined sequence data for all sampled taxa under both a Bayesian Relaxed Clock and a semiparametric Penalised Likelihood method, using calibration points inferred from Relaxed Clock analyses of the entire order Oxalidales, for which fossil data are available. In an attempt to account for known problems with divergence time estimation, I explored the potential bias introduced by method used, marker genome source and different calibrations on the root. The results indicate substantial variation in the age of crown southern African Oxalis over a nearly twenty million year period, varying according to source data, calibration estimate and methodology employed in the reconstruction. Despite this major variability, all average estimates are older than iv 18 million years, which agrees with a growing body of evidence that there has been a gradual accumulation of floristic diversity in the CFR, rather than a rapid, recent burst of speciation. Fourthly, as the produced phylogenies conclusively show the artificial nature of the current taxonomy, I propose a new, almost completely different classification for southern African Oxalis taxa. Although a significant improvement, this classification is considered informal due to the complete disagreement between the old and proposed new taxonomies, poor resolution in some of the proposed lineages, and a need to confirm proposed groups (clades) with the identification of morphological synapomorphies. Potential synapomorphies for various clades are proposed and discussed, which should guide future research. Fifthly, the presence of bulbs in this genus is of great interest as a potential preadaptation for seasonally arid climates. The evolution of the bulbous habit in Oxalis is here explored for the first time. I address the sequence of major morphological character state changes leading to the suite of characters corresponding to the bulbous habit. The homology of basal leaf petioles, fleshy leaf scales and tunics is discussed, and it is shown that many bulb characters present in the southern African lineage are also found in the close relatives of this lineage, and are thus older than this lineage. The ecological and evolutionary implications of bulb geophytism in the CFR Oxalis are also discussed. Finally, I address certain taxonomic issues that arose during the course of this study. Co-authors and I describe the new species O. saltusbelli and O. ericifolia. We also clarify issues surrounding the tremendously variable group species O. flava and propose some nomenclatural changes and synonyms for related taxa. We also address the taxonomic position of the rare species O. purpurata, which was located too late in the course of this study to include in the main analyses.

Thesis (MSc (Botany and Zoology))--Stellenbosch University, 2008.
Sequence data from the Internal Transcribed Spacer (ITS) of the nuclear ribosomal DNA were used to study the phylogenetic relationships in the genus Ursinia Gaertn. (Asteraceae, Anthemideae) in the southern African region. Closely related genera, i.e. Cotula L., Osteospermum L. and Agoseris Raf., were used as outgroups. The study also included maximum parsimony and principal component analyses. The taxa within the genus Ursinia had previously been classified into two subgenera, Ursinia and Sphenogyne R.Br., mainly on the basis of distinct cypsela characters. The maximum parsimony, principal component and the phylogenetic analyses revealed two subgenera, corresponding to the existing subgeneric classification. Principal component analysis shows that the pappus, the number of pappus bristles and the colour of the cypsela are the most informative characters. However, the low number of phylogenetically informative characters of the ITS sequences, the poor resolution in the consensus tree, and low branch support values indicate that the ITS data contain weak phylogenetic signals. The low bootstrap values for many nodes suggest that one should be cautious in using the ITS region alone to make final conclusions about the origin and evolution of taxa. In maximum parsimony analysis, the RI, CI and bootstrap values are low; principal component analysis values are also low. Furthermore, there is a lack of resolution in subgenus Sphenogyne. In the literature, Ursinia is divided into seven series but they were not retrieved as monophyletic in this study, probably because of short branch lengths in the phylogeny. Further molecular data are therefore required to be able to support or reject the present classification. Maximum parsimony, principal component and molecular analyses show that U. trifida f. calva Prassler and U. trifida (Thunb.) N.E.Br. f. trifida are not sister taxa, supporting the recognition of these two taxa as separate species. The Ursinia taxa from the summer-rainfall region are not monophyletic and are sister to a clade of Cape species. This supports a hypothesis that Ursinia migrated from the Cape into the Drakensberg which has been shown for a number of other Cape groups that have Drakensberg relatives.

Thesis (MSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Alien invasive species are a global concern not only threating biodiversity, but also negatively impacting regional economies. Consequently research aimed at understanding the invasion process is crucial for management of invasive alien species to reduce these impacts. Identifying accurate natal ranges is the key first step for efficient alien plant management, especially biological control. Such knowledge may assist in selecting host-specific biological control agents and help prevent non-target impact on native species. A case in point is the genus Cardiospermum of which species have been extensively moved around the globe with two species now being possible widespread invaders (C. grandiflorum and C. halicacabum), and a third species (C. corindum) having significant invasion potential. However, in some regions the native statuses of these species are not clear, hampering management. In order to minimize potential non-target impacts it is prudent to determine the relationships between Cardiospermum taxa in unknown native ranges prior to the release of biological control agents. With this thesis I aim to review available literature on the genus Cardiospermum, determine potential spread to suitable habitats globally for selected taxa, resolve unknown native ranges in southern Africa, and investigate rapid speciation of an endemic Namib Desert species of balloon vine. Through exhaustive searches for available literature on the genus Cardiospermum I report on the biology and ecology of selected species within the genus, with special focus on the most widespread species. Specifically, using species distribution modelling I investigate the potential spread of C. halicacabum, C. corindum and C. grandiflorum globally and assess the accuracy with which this can be determined using known native ranges to predict current alien ranges. Results indicate that these species have significant potential to spread, though highlighting that species distribution modelling over-fit predicted suitable ranges when using native range data alone. To resolve uncertain native ranges of selected species within the genus I reconstructed a dated multi-gene phylogeny and chloroplast haplotype network to investigate relationships within and among Cardiospermum species. I conclude that C. halicacabum is non-native in southern Africa due to polyphyletic relationships among accessions, while C. corindum is native due to natural long distance dispersal as indicated by a single monophyletic southern African clade. The close relationship observed between C. corindum and the African species, C. pechuelii, lead to a population-level genetic investigation of these two taxa. For this, I constructed a multi-gene phylogeny, chloroplast haplotype network and conducted population genetic diversity analyses which all indicated that the African arid adapted taxa, C. pechuelii, endemic to the Namib Desert of Namibia, evolved from C. corindum following long distance dispersal from South America. This study firstly provides insights into the ecology and biology of Cardiospermum, warning against further introduction due to potential spread. Secondly I resolved the unknown native statutes of Cardiospermum species in southern Africa and, lastly, illustrated the origin of African C. pechuelii. My research findings have major implications for on-going biological research against C. grandiflorum in South Africa and cautions strongly against the release of already-identified biological control agents due to their potential non-target impacts.
AFRIKAANSE OPSOMMING: Indringerspesies is 'n wêreldwye probleem as gevolg van hul direkte bedreiging van biodiversiteit asook hul negatiewe impakte op streeksekonomieë. Gevolglik is navorsing aangaande die indringingsproses van uiterste belang om doeltreffende beheer van indringerspesies te verseker. Die bepaling van die inheemse herkoms van indringerpopulasies is die eerste belangrike stap tot doeltreffende beheer, veral biologiese beheer. Hierdie informasie kan help met die identifisering van gasheer-spesifieke biologiese agente en om potensiële nie-teiken impakte op inheemse plant spesies verhoed. ‘n Voorbeeld is ballon rankplante in die genus Cardiospermum, waarvan verskeie spesies wêreldwyd verspreid is, met die gevolg dat minstens twee spesies (C. halicacabum en C. grandiflorum) nou moontlike wydverspreide indringers is en ‘n derde spesie (C. corindum) ook potensiaal toon as ‘n indringerspesie. In sommige streke is die in- of uitheemse statusse van hierdie spesies onbekend en belemmer gevolglik hul doeltreffende beheer. Met hierdie tesis streef ek om die genus Cardiospermum te hersien en potensiële verspreiding van geselekteerde spesies na geskikte habitatte te bepaal, om onbekende inheemse streke binne Suider-Afrika op te los en laastens, om die herkoms van ‘n ware Afrika spesie (C. pechuelii) te ondersoek. Na deeglike ondersoek van beskikbare literatuur doen ek verslag omtrent die biologie en ekologie van spesies binne Cardiospermum, met spesiale fokus op die mees wydverspreidste spesies. Deur gebruik te maak van spesies verspreidings modelle bestudeer ek die potensiaal van verdere verspreiding wêreldwyd vir C. halicacabum, C. corindum en C. grandiflorum en rapporteer ook omtrent die akkuraatheid van hierdie tegniek. Resultate toon dat alle spesies aansienlike potensiaal toon om verder te versprei, maar beklemtoon ook dat hierdie metode inheemse streek data “oor-aanpas”. Om enige onsekerhede aangaande inheemse streke op te los, het ek ‘n gedateerde multi-geen filogenie en ‘n chloroplas haplotipe netwerk opgetrek om die verhoudings binne en tussen geselekteerde Cardiospermum spesies te bepaal. Ek kom tot gevolgtrekking dat C. halicacabum nie inheems in Suider-Afrika is nie, as gevolg van polifiletiese verhoudings, en dat C. corindum inheems is en moontlik ook ‘n voorbeeld van natuurlike langafstand verspreiding, soos aangedui deur ‘n enkele monofiletiese groep. Die naverwante filogetiese verhouding tussen C. corindum en C. pechuelii het daartoe gelei dat ek die herkoms van C. pechuelii in Afrika ondersoek het. ‘n Multi-geen filogenie, chloroplas haplotipe netwerk en populasie genetiese diversiteit analises het aangedui dat C. pechuelii endemies is tot die Namib Woestyn van Namibië, en die produk is van lang afstand verspreiding van C. corindum vanaf Suid-Amerika. Hierdie studie gee eerstens insig tot die ekologie en biologie van Cardiospermum en waarsku teen verdere verspreiding. Tweedens dui my studie ook die opgeloste inheemse streke in Suider-Afrika aan van sekere Cardiospermum spesies, en laastens, illustreer ek die herkoms van C. pehuelii. My navorsing het baie belangrike gevolge vir die huidige biologiese beheer program teen C. grandiflorum in Suid-Afrika en waarsku teen die vrystelling van reeds geïndentifiseerde biologiese beheer agente weens potensiële nie-teiken impakte op inheemse spesies.

Thesis (MSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: The generally low concentrations of P and N in the soil, causes most plants to experience nutrient deficiency during their life cycle. Lupins can rely on both cluster roots and nodules for P acquisition and biological nitrogen fixation (BNF) respectively. The legume Lupinus albus is able to survive under low nutrient conditions, because it has two specialized belowground organs for the acquisition of N and P. In this regard, cluster roots increase P uptake and root nodules acquire atmospheric N2 via biological nitrogen fixation (BNF). Although these organs normally tolerates low P conditions, very little is known about their physiological and metabolic flexibility during variations in P supply. Furthermore, the resource allocation (C, N and P) between cluster roots and nodules has also been largely understudied. The aim of this investigation was therefore to determine the resource allocation, physiological and metabolic flexibility of these organs during variations in P supply. Although variation on P supply had no effect on the total biomass, there were significant differences in specialised below-ground organ allocation to cluster roots and nodule formation. Cluster root formation and the associated C-costs increased during low P supply. In contrast to the cluster root decline at high P supply, there was an increase in nodule growth allocation and corresponding C-costs. Since cluster roots were able to increase P acquisition under low P conditions, this below-ground investment may also have benefited the P nutrition of nodules. These findings provide evidence that when lupins acquire N via BNF in their nodules, there may be a trade-off in resource allocation between cluster roots and nodules. The short-term elevated P supply, caused an increased allocation of C and respiratory costs to nodules, at the expense of cluster roots. This alteration was also reflected in the increase in nodule enzyme activities related to organic acid synthesis, such as Phosphoenol-pyruvate Carboxylase (PEPC), Pyruvate Kinase (PK), Malate Dehydrogenase (NADH-MDH) and Malic Enzyme (ME). In cluster roots, the elevated P conditions, caused a decline in these organic acid synthesizing enzymes. This suggests that during short-term elevated P supply, there is a great degree of physiological and metabolic flexibility in the lupin nutrient acquiring structures.
AFRIKAANSE OPSOMMING: Die algemeen lae konsentrasies van fosfaat en stikstof in die grond , veroorsaak dat die meeste plante voedingstekorte ervaar tydens hul lewensiklus. Lupiene kan staatmaak op beide groep-wortels en wortel-knoppies vir P verkryging en biologiese stikstofbinding onderskeidelik. Die peulplant Lupinus albus is in staat om te oorleef onder lae voedings toestande , as gevolg van die twee gespesialiseerde ondergrondse organe vir die verkryging van stikstof en fosfaat. In hierdie verband verhoog groep-wortels fosfaat opname en wortel-knoppies verkry atmosferiese stikstof via biologiese stikstofbinding. Alhoewel hierdie organe normaalweg lae fosfaat toestande verdra , is baie min bekend oor hul fisiologiese en metaboliese buigsaamheid tydens variasies in fosfaat aanwending. Daar is verder ‘n tekort aan die studie van hulpbron toekenning tussen groep-wortels en wortel-knoppies. Die doel van hierdie ondersoek was dus om die toekenning van hulpbronne , fisiologiese en metaboliese buigsaamheid van hierdie organe tydens variasies in fosfaat aanwending te bepaal. Variesie in fosfaat verskaffing het geen invloed op die totale plant biomassa gehad nie, maar daar was wel ‘n beduidende verskil in gespesialiseerde ondergrondse toekenning tussen groep- wortels en wortel-knoppies. Groep-wortel vorming en die gepaardgaande koolstof koste het toegeneem met lae fosfaat verskaffing. In teenstelling met die groep-wortel daling met hoë fosfaat verskaffing, was daar 'n toename in groei van wortel-knoppies en die ooreenstemmende koolstof koste daarvan. Aangesien groep-wortels in staat was om fosfaat verkryging te verhoog onder lae fosfaat toestande, mag hierdie ondergrondse belegging bygedra het tot die voeding van wortel-knoppies . Hierdie bevindings bewys dat lupiene afhanklik van wortel-knoppies ‘n wisselwerking in toekenning van hulpbronne, tussen groep-wrotels en wortel-knoppies handaaf. Kort termyn verhoogde fosfaat aanwending veroorsaak 'n verhoogde toekenning van koolstof en respiratoriese energie na wortel-knoppiess, ten koste van groep-wortels . Hierdie verandering is ook weerspieël in die toename in wortel-knoppie ensiem aktiwiteit in verband met organiese suur sintese (PEPC PK,MDH,ME) . In groep-wortels, het die verhoogde P toestande verder 'n afname in die organiese suur produserende ensieme veroorsaak. Dit dui aan dat tydens kort termyn verhoogde P aanwending, daar 'n groot mate van fisiologiese en metaboliese buigsaamheid in die lupiene voedingstowwe verkryging strukture plaasvind.

The levels of sulfur present in xylem tissue of Quercus alba (white oak) show a statistically significant increase from 1970 to 1983. This increase was found in trees from three different sites in Kentucky and Tennessee. The levels of sulfur present in Tsuga canadensis (hemlock) show a statistically significant increase from 1955 to 1970. Sensitivity, growth response to the tree's environment, decreased in oaks from 1933 to 1968 but increased slightly in hemlocks during the same time period. The data tend to support a direct relationship between increasing sulfur levels and a reduction in growth. Physiological and ecological studies of the impact of sulfur on trees should be continued to investigate all aspects of sulfur dioxide damage.

Thesis (MSc)--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: The effects of regulated deficit irrigation on the production and fruit quality of peaches were investigated. A field trial was carried out in a twelve-year-old Neethling peach orchard at Robertson Experiment Farm. Treatments consisted of five different soil water depletion levels applied during five different growth stages. Irrigation was applied at the five soil water depletion levels of which T1 was regarded as relatively wet (irrigation was applied when the average soil matric potential reached ca. -50 kPa). T2 was regarded as normal (irrigation applied at ca. -100 kPa) and three different deficit irrigation regimes T3, T4 and T5, irrigated at soil matric potentials of ca. -200, -400 and -800 kPa respectively. The five growth stages were Stage 1 (cell growth), Stage 2 (slow fruit growth), Stage 3 (rapid fruit growth), Stage 4 (ripening) and Stage 5 (post-harvest). The soil water content was monitored and irrigation was scheduled by means of a neutron probe. Vegetative and fruit growth, fruit mass and production were measured. Fruit were examined for bruises and firmness. Fruit size, fruit mass, fruit quality, as well as production, were not sensitive to water deficits during the different growth stages with a normal crop load. However, a tendency to reduced shoot growth with decreasing soil matric potentials was observed during the slow fruit growth, rapid fruit growth as well as the ripening stages. The application of deficit irrigation during the slow fruit growth or post-harvest stages can save substantial amounts of water with a normal crop load, provided that normal irrigation is applied during the other growth stages. A combination of water deficits during the ripening stage and high crop load resulted in smaller fruit and lower production. Fruit size, fruit mass, fruit quality, as well as production, were not sensitive to water deficits during either the cell growth, slow fruit growth or post harvest growth stages, provided that normal irrigation is applied in the other growth stages. Irrespective of crop load, soil matric potentials up to -200 kPa can be applied during anyone of the growth stages without seriously affecting the final fruit size, fruit mass, fruit quality or production. However, this soil water deficit may then only be applied in one of the growth stages and normal irrigation must be applied in the other four stages. Although deficit irrigation reduced seasonal water consumption, it could not be justified as water saving with a heavy crop load.
AFRIKAANSE OPSOMMING: Die effekte van gereguleerde tekort besproeiing op die produksie en vrugkwaliteit van perskes is ondersoek. 'n Veldproef is in 'n twaalf-jaar-oue Neethling perskeboord te Robertson Proefplaas uitgevoer. Die behandelings het bestaan uit vyf grondwater-ontrekkingspeile wat gedurende vyf verskillende groeistadiums toegepas is. Besproeing is toegedien by vyf verskillende grondwaterontrekkingsvlakke waar T1 beskou is as redelik nat (besproeiing is toegedien wanneer gemiddelde grondmatrikspotensiale ca. -50 kPa bereik het). Behandeling T2 is as normaal beskou (besproeiing toegedien by ca. -100 kPa en drie verskillende regimes van tekort besproeiing naamlik T3, T4 en T5 wat onderskeidelik by ca. -200, -400 en -800 kPa besproei is. Die vyf groeistadiums was onderskeidelik Stadium 1 (selgroei), Stadium 2 (stadige vruggroei), Stadium 3 (vinnige vruggroei), Stadium 4 (rypwording) en Stadium 5 (na-oes). Die grondwaterinhoud is gemonitor en die besproeiing is met behulp van 'n neutronpeiler geskeduleer. Vegetatiewe groei, vruggroei, vrugmassa en produksie is gemonitor. Vrugte is ook ondersoek vir kneusbaarheid en fermheid. Geen negatiewe effek as gevolg van watertekorte is ten opsigte van vruggrootte, -massa, -kwaliteit sowel as produksie waargeneem gedurende die verskillende groeistadiums waar 'n normale vruglading gehandhaaf is nie. 'n Afnemende tendens in lootgroei met afnames in grondwatermatrikspotensiale is egter gedurende die stadige- en vinnige vruggroei-stadiums, asook in die vrugrypwordingstadium, waargeneem. 'n Aansienlike hoeveelheid water kan bespaar word deur gereguleerde tekort besproeiing gedurende die stadige vruggroei- of na-oes-stadiums toe te pas, mits 'n normale vruglading gehandhaaf word en normale besproeiing in die ander groeifases toegedien word. 'n Kombinasie van watertekorte en 'n hoë vruglading gedurende die rypwordingstadium het tot kleiner vrugte en laer produksies gelei. Vruggrootte, -massa, -kwaliteit en produksie is egter nie gevoelig vir watertekorte gedurende die selgroei-, stadige vruggroei- en na-oes-stadiums nie. Tekort besproeiing by 'n grondwatermatrikspotensiaal van tot -200 kPa kan egter met 'n normale en hoë vruglading in enige van die fases toegepas word, sonder om die finale vruggrootte, -massa, - kwaliteit of produksie nadelig te beïnvloed. Hierdie tekort besproeiingsregime mag egter slegs in een van die groeistadiums toegedien word en normale besproeiings moet in die ander groeistadiums toegedien word. Alhoewel tekort besproeiing die seisoenale waterverbruik verminder het, kan dit nie geregverdig word as 'n waterbesparende praktyk indien 'n hoë vruglading gehandhaaf word nie.

Thesis (MSc)--Stellenbosch University, 2011.
ENGLISH ABSTRACT: Species’ seasonal behaviour is of paramount importance in understanding community functioning and dynamics. Recently, plant phenology has further gained significance as a reliable indicator of climate change impacts. Despite the importance of understanding plant dynamics, there are relatively few plant phenological records for the sub-Antarctic region, and where records exist they are often not extensive. Sub-Antarctic Marion Island, typical of Southern Ocean Islands, offers a useful setting for addressing these knowledge gaps. This study documented the vegetative and reproductive phenologies (or aggregate phenological patterns) of twelve indigenous and three alien vascular plant species on the island. The phenological differences among the species and distinct seasonal groupings (e.g. early, intermediate and late species) were examined. I also investigated the phenological differences among the indigenous and alien plant species. Furthermore, the onset of selected reproductive phenophases from the current records was compared with historical records for determining the extent of climate change-related alterations in phenology. Phenological data were collected fortnightly on five, 5 m x 5 m permanent plots per species (except for a few species) for a full growing season. Thus the sample size is n = 5 for all plant species except for Crassula moschata (n = 4), Juncus effusus (n=4) and Rumex acetosella (n=1). Sites of the same species were separated by at least 500 m except for the alien plant, Juncus effusus, where all four known populations were selected despite two of these populations being < 500 m apart. This study indicated that Marion Island plants grow throughout the year with no major peaks except in Azorella selago and Acaena magellanica which showed winter dormancy. However, reproduction in most plant species predominately occurred in spring and summer months. Pringlea antiscorbutica and Poa cookii were the first two species to set flower buds in September while most species dispersed their seeds in summer except for Agrostis magellanica and Crassula moschata which dispersed in early autumn. Distinct from most temperate systems, the reproductive seasonality displayed by Marion Island plant species is explained more by daylength than by temperature, perhaps due to the region’s typical thermal aseasonality. Interestingly, many cooccurring species and/or clades across the Falkland, Kerguelen, Macquarie and South Georgia Islands also showed similar flowering onset date to the Marion Island plants, further confirming their daylength sensitivity. However, other external factors seem to come into play at later events of reproduction. Consequently, fruit maturation time of similar species across the sub-Antarctic islands varied substantially despite the plants having flowered in the same month. Although plant species showed similar reproductive seasonality, there were significant differences among species phenologies i.e. phenophase timing, duration and peak occurrence dates. However, using 95% confidence intervals of Generalized Linear Models weighted means, and/or one-way ANOVA (Tukey post hoc test), three homogenous sets of species (early, late, or intermediate onsets) were identified based on flower bud, flowering and seed dispersal phenophase onset dates. The homogenous species groupings observed for flower buds also remained unchanged during flowering onset except for Cotula plumosa and Callitriche antarctica which switched groups. As for the seed dispersal timing, the pattern was not consistent with that of the flower bud and flowering onset homogenous groupings, except for Acaena magellanica and Agrostis magellanica which remained in the early and late groups, respectively. Conversely, in the case of the timing of other phenophases (pollen release, fruit set and fruit ripening), entire phenophase durations, and peak occurrence dates, species overlapped greatly, resulting in an unbroken progression or continuum of phenology among species. Similarly, the three alien plant species investigated here (Cerastium fontanum, Juncus effusus and Rumex acetosella) showed no consistent phenological differences from the rest of the species. However, a widespread alien plant species on Marion Island, C. fontanum, reproduced for most of the year, although its reproduction peak was in summer months as was the case for the rest of the species. This study also indicated that indigenous plant species have altered their reproductive phenologies since 1965. Although the response was species-specific, the majority of plant species significantly delayed the onset of reproductive activities in 2007 by comparison with 1965. However, it is not clear if the observed species response was caused by the now drier and warmer Marion Island climate or by discrepancies in reporting in the earlier studies and/or sampling differences between the recent and historical records. Therefore, these results should be taken with caution. In conclusion, this research provided a detailed phenological dynamics record for vascular plant species on the island. Over time these records may be used as a basis for monitoring and modelling the impact of climate on plant phenology on the island.
AFRIKAANSE OPSOMMING: Spesies se seisoenale gedrag is van die allergrootste belang in die begrip van gemeenskapsfunksionering en dinamika. Meer onlangs het plant fenologie verdere betekenis verwerf as ‘n betroubare indikator vir die impakte van klimaatsverandering. Ondanks die belangrikheid om plant dinamika te verstaan, is daar relatief min plant fenologiese rekords vir die sub-Antarktiese streek en waar rekords wel bestaan is dit dikwels nie omvangryk nie. Sub- Antarktiese Marion Eiland, tipies van Suidelike Oseaan Eilande, bied ‘n nuttige ligging om hierdie kennis gapings aan te spreek. Hierdie studie het die vegetatiewe en voorplantingsfenologieë (of gesamentlike fenologiese patrone) van elf inheemse en drie uitheemse vaatplantspesies op die eiland gedokumenteer. Die fenologiese verskille tussen die spesies en duidelike seisoenale groeperings (bv. vroeë, intermediêre en laat spesies) is ondersoek. Ek het ook die betekenisvolle fenologiese verskille tussen die inheemse en uitheemse plantspesies ondersoek. Voorts, die aanvang van gekose voortplanting feno-fases van huidige rekords is vergelyk met historiese rekords om die mate van klimaatsverandering verbandhoudende veranderings in die fenologie te bepaal. Fenologiese data is twee weekliks ingesamel op vyf, 5 m x 5 m permanente plotte per spesie (behalwe vir ‘n paar spesies) vir ‘n volle groei seisoen. Dus, die insamelings grootte is n = 5 vir al die plantspesies behalwe vir C. moschata (n = 4), Juncus effusus (n=4) en Rumex acetosella (n=1). Persele vir dieselfde spesies is geskei deur ten minste 500 m, behalwe vir die uitheemse plant, Juncus effusus, waar al vier populasies wat bekend is gekies is, ten spyte daarvan dat twee van hierdie populasies < 500 m uitmekaar is. Hierdie studie het aangedui dat Marion Eiland plante regdeur die jaar groei, met geen belangrike spitstye nie, behalwe in Azorella selago en Acaena magellanica wat ‘n winter rusperiode wys. Hoe ookal, voortplanting in meeste van die plantspesies het hoofsaaklik voorgekom tussen die lente en somermaande. Pringlea antiscorbutica en Poa cookii was die eerste twee spesies om blomknoppe uit te stoot in September, terwyl die meeste spesies hulle sade versprei het gedurende die somer, behalwe vir Agrostis magellanica en Crassula moschata wat versprei het in vroeg herfs. Duidelik van meeste gematigde sisteme, word die voortplanting seisoenaliteit, getoon deur die Marion Eiland plantspesies, verduidelik meer deur daglengte as deur temperatuur, moontlik weens die streek se tipiese termiese a-seisoenaliteit. Interessant, baie spesies en/of afstameling-groeperings wat saam aangtref word dwarsoor die Falkland, Kerguelen, Macquarie en Suid Georgia Eilande wys ook soortgelyke bloei aanvangsdatums as die Marion Eiland plante, nog meer bevestigend van hulle dag-lengte sensitieweteit. Hoe ookal, ander eksterne faktore blyk betrokke te raak by latere gebeure van voortplanting. Gevolglik het vrug rypwordingstyd van dieselfde spesies oor die sub-Antarktiek noemenswaardig verskil, ten spyte daarvan dat die plante in dieselfde maand geblom het. Alhoewel plantspesies dieselfde voortplanting seisoenaliteit gewys het, was daar ‘n noemenswaardige veskil tussen spesie fenologieë, m. a. w. feno-fase tydsberekenning, tydsduur en spits voorkomsdatums. Hoe ookal, deur gebruik te maak van 95% betroubaarheid intervalle van Algemene Lineêre Modelle gewigte gemiddelde en/of een rigting ANOVA (Turkey post hoc toets), is drie homogene stelle van spesies (vroeë, laat en intermediêre aanvang) geïdentifiseer gebasseer op blomknop, bloei en saad verspreiding feno-fase aanvangsdatums. Die homogene spesie groeperings waargeneem op blomknoppe het ook onveranderd gebly gedurende bloei aanvang behalwe vir Cotula plumosa en Crassula antarctica wat groepe geruil het. Vir die saadverspreiding tydsberekenning was die patroon nie konstant met die van die blomknop en bloei aanvang homogene groepe nie, behalwe vir Acaena magellanica en Agrostis magellanica wat in die vroeë en laat groepe respektiewelik gebly het. Omgekeerd, in die geval van tydsberekenning van ander feno-fases (stuifmeel vrysetelling, vrugwerp, vrugrypwording), volledige feno-fase tydsduur en spits voorkomsdatums het spesies grootliks oorvleuel, wat ‘n ongebroke vordering of deurlopendheid van fenologie tussen die spesies tot gevolg het. Ooreenkomstig het die drie uitheemse spesies wat hier ondersoek is (Cerastium fontanum, Juncus effusus en Rumex acetosella) geen bestendige fenologiese verskille van die res van die spesies gewys nie. Hoe ookal, ‘n wydverspreide uitheemse spesie op Marion Eiland, Cerastium fontanum, het deur die meeste van die jaar voortgeplant, hoewel met ‘n voorplanting spits in die somer maande soos die res van die spesies. Hierdie studie dui ook aan dat inheemse plantspesies hulle voortplanting fenologieë verander het sedert 1965. Alhoewel die reaksie spesiespesifiek was, het die meerderheid van die plantspesies hulle voortplanting aanvang aansienlik vertraag gedurende 2007 in vergelyking met 1965. Hoe ookal, dis nie duidelik of die waargeneemde spesie reaksie was as gevolg van die nou droër en warmer Marion Eiland klimaat of deur teenstrydighede in verslagewing gedurende die vroëre studies en/of insameling verskille tussen die onlangse en historiese rekords. Daarom moet hierdie resultate met versigtigheid hanteer word. In samevatting, hierdie navorsing voorsien ‘n gedetaileerde fenologiese dinamieka rekord vir vaatplantspesies op die eiland. Oor tyd kan hierdie rekords gebruik word as basis vir monitering en modellering van die impak van klimaat.

Thesis (MSc)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: Arbuscular mycorrhizal (AM) C-costs in grapevines were investigated. Since both dormant vines and AM colonisation rely on stored C for initial growth, AM colonisation costs would therefore compete with plant growth for available C reserves. The aims of this study were to assess the host C economy during AM development and the subsequent C-costs of N and P uptake, as well as the effects of C costs on host growth. This was evaluated in two separate experiments; one assessing the symbiotic influence on the C costs of fungal establishment and nutritional benefits, whilst the other one evaluated the effects of the symbiosis on host growth and nutrient productivities. This study has shown that AM acts as a C sink, competing with the host for available C. Past work on the AM sink effect has focused mainly on the movement of photosynthetic C below ground to support the AM fungus. This however, does not take into account the effect that stored C will have on the C economy of the plant and symbiosis. The role of stored C becomes even more crucial when working with deciduous plants that rely on stored C for new growth at start of a growing season. It has been reported that stored C in AM plants is remobilized at the start of a growing season and then the C reserves are refilled towards the end of the season, when the plants enter dormancy. The initial costs of AM fungal colonisation were borne by the above-ground C reserves, at the expense of new growth in host plants. These costs were offset once the plateau phase was reached, and the depleted reserves started to refill. Once established, the active symbiosis imposed a considerable below ground C sink on host reserves. In spite of these costs, the improved P nutrition of AM roots was achieved with a more efficient C-use. This concurs with other findings, that of the belowground C allocated to AM roots, a greater part is used by AM respiration and a smaller part for P uptake. The C costs of the AM fungal phase of rapid development can be seen as negative to root growth and shoot development. These negative effects may continue for a period of time, even during the plateau phase of fungal development. Once the AM symbiosis is fully established, the host growth and development is then improved to a greater extent than in non-AM plants. From this study it can be concluded that AM growth directly competes with host development, but the symbionts revert to a beneficial partnership once it is fully established.
AFRIKAANSE OPSOMMING: Die C koste van arbuskulêre mikorisa (AM) in wingerdstokke is ondersoek. Beide rustende wingerdstokke en AM koloniseering is afhanklik van gestoorde C vir aanvanklike groei. AM kolonisering sou dus met plantgroei kompeteer vir beskikbare C reserwes. Die doelstellings van hierdie ondersoek was eerstens om die C-ekonomie van die gasheer tydens AM ontwikkeling en die gevolglike Ckostes van N en P opname te bepaal en tweedens sowel as die invloed van C veranderings op gasheergroei vas te stel. Hierdie is in twee afsonderlike eksperimente ondersoek: een om die simbiotiese invloed op die C-kostes van swam-vestiging en voedingsvoordele te bepaal, terwyl die ander die uitwerking van simbiose op gasheergroei en voedings doeltreffenheid evalueer het. Die ondersoek het bewys dat AM, as ‘n C-sink, kompeteer met die gasheer vir beskikbare C. Vorige werk oor die AM sink-effek het hoofsaaklik gefokus op die afwaartse beweging van fotosintetiese C om die AM-swam ondergronds te ondersteun. Die werk neem egter nie in ag wat die effek van gestoorde C op die C-ekonomie van die plant en simbiose sou wees nie. Die rol van gestoorde C is selfs nog meer belangrik wanneer met bladwisselende plante gewerk word, omdat sulke plante op gestoorde-C vir nuwe groei aan die begin van die groeiseisoen staatmaak. Dit is op rekord dat gestoorde C in bladwisselende plante by aanvang van die groeiseisoen gemobiliseer word en dat die C-reserwes teen die einde van die seisoen wanneer die plante rustyd nader, weer hervul word. Die aanvanklike kostes van AM kolonisering is deur die bogronds C-reserwes, ten koste van nuwe groei van die gasheerplante, gedra. Hierdie kostes herstel sodra die plato-fase bereik is, waar die uitgeputte reserwes begin hervul het. As die aktiewe simbiose eers gevestig is, sal dit as ‘n onderg P-voeding van AM wortels verkry wordrondse C-sink vir gasheer optree.Hierdie C verbruik word egter as doeltreffend beskou aangesien verbeterde. Dit is bekend dat ‘n groter deel van die ondergrondse C geallokeer word aan AM-wortels, deur middel van AM respirasie en P-opname. Die C-kostes van die AM-fungus tydens die fase van vinnige ontwikkeling, kan ‘n negatiewe effek op wortel- en lootontwikkeling hê. Hierdie negatiewe uitwerking kan vir ‘n tydperk voortdeur, selfs gedurende die plato-fase van fungi-ontwikkeling. Sodra die AM-simbiose volledig gevestig is, word gasheergroei en ontwikkeling tot ‘n groter mate verbeter as in plante sonder AM-fungi. Hierdie ondersoek het bewys dat AM groei direk met gasheerontwikkeling kompeteer, maar dat die simbiose ‘n voordelige vennootskap vorm sodra dit volledig gevestig is.

Thesis (MSc)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Understanding the processes that drive the invasion of non-native species is often essential for effective management. This thesis focuses on Casuarina spp. – an economically and ecologically important tree genus with taxa that have been widely disseminated by humans. I explore the effects certain taxa can have on community dynamics in recipient environments, investigate the factors that mediate invasion of Casuarina species, and from this aim to develop recommendations for managing the group. First, I assessed the global introduction history, invasion ecology and the evolution of management approaches of Casuarina. Ten of the 14 species in the genus have been introduced outside their native ranges to over 150 countries, but only three species are recorded as naturalized or invasive. As with other groups there is a correlation between native range size and invasiveness – the three invasive species also have the largest introduced ranges. Propagule pressure explains much more of the variance in observed invasiveness between Casuarina taxa than any known combination of life-history traits. Large-scale plantings of casuarinas in some climatically suitable areas have not yet resulted in large-scale invasions; there is a substantial global Casuarina invasion debt. Experiences in Florida and the Mascarene Islands highlight that casuarinas have the potential to transform ecosystems with significant control costs. Despite modest progress with managing invasions in some areas, substantial problems remain. As with most other invasive tree taxa, complex conflicts of interest are particularly challenging. Second, I looked at mechanisms underlying naturalization and assessed invasion risk at a regional scale. Here, I examined Casuarina cunninghamiana invasions in the south-western Cape of South Africa – the part of the country with the largest contiguous area climatically similar to the native range of the species. Propagule pressure is a key driver of naturalization of C. cunninghamiana populations in climatically suitable areas. The species also naturalizes in regions with suboptimal bioclimatic conditions, but then only very near (<10 m) planted trees. Risk models indicate that C. cunninghamiana is likely to spread across a greater region of the Western Cape than it currently occupies. Naturalized populations of C. cunninghamiana are young and expanding. The capacity of the species to resprout and attain reproductive maturity at an early age suggests that this species could become a widespread and damaging invader in South Africa. We conclude with some recommendations for management, and argue that if particular steps are taken (e.g. the immediate removal of all female plants from proximity to dams and water-courses; all future sales and plantings to be restricted to male plants) then it might be possible to safely utilise the species in future. Third, I examined the invasion dynamics of a single Casuarina species at the landscape scale. I explored how interactions between disturbance and invasion govern successional trajectories, using the remarkable invasion of C. equisetifolia on the volcanic island of Réunion. Invasive populations of C. equisetifolia have increased substantially in extent over 40 years. Lava flows have facilitated the spread of C. equisetifolia and invasion of this species has radically changed successional trajectories, increasing the rate of succession sevenfold. This case mirrors work done on Morella faya and Falcataria moluccana on Hawa'ii, which shows the extent to which invasive species can alter ecosystem function and benefit from natural disturbances generated by volcanic lava flows. The continued spread of C. equisetifolia poses a major threat to the small area of remaining native lowland rainforests on Réunion which cover < 2 % of their original extent. The studies in this thesis have uncovered patterns, processes and invasion risks for invasive trees that are not well represented in the literature. Some insights derived from well-studied tree genera, such as Acacia and Pinus, seem to apply fairly well to tree invasions in general. However, special ecological features of Casuarina species and the ways they are used by humans call for unique considerations when piecing together changing global distributions and creating effective strategies for management.
AFRIKAANSE OPSOMMING: ‘n Deeglike begrip van die prosesse wat die indringing van uitheemse spesies fasiliteer is noodsaaklik vir effektiewe besturing. Hierdie tesis fokus op Casuarine spp. – ‘n ekonomiese en ekologiese belangrike boom genus, met menigte spesies binne hierdie genus wyd verspreid deur mense. Ek ondersoek die effekte wat sekere taksa kan hê op die gemeenskap dinamika in die ontvanger omgewing, sowel as die faktore wat Casuarina indringing bemiddel, en deur hierdie doelwitte beoog ek om aanbevelings te maak aangaande die effektiewe bestuur van hierdie groep. Eerstens evalueer ek die invoerings geskiedenis van die genus wêreldwyd, die indringer ekologie en ook die evolusie van bestuurs benaderinge ten opsigte van Casuarina. Tien van die 14 spesies binne hierdie genus is ingevoer na meer as 150 verkillende lande buite hul inheemse streek, maar slegs drie van hierdie spesies word beskou as genaturaliseerd of indringers. Soos met ander groepe is daar ‘n korrelasie tussen inheemse streeks-grote en indringerheid – die drie indringer spesie het ook die grootste ingevoerde streke. Propaguul druk verduidelik die meerderheid van die variasie in die waargeneme indringer Casuarina taksa as enige ander kombinasie van lewens geskiendenis eienskappe. Groot skaalse plantasies van casaurina taksa in sommige klimaat geskikste areas het nog nie na groot skaalse indringing gelei nie; daar is wêreldwyd ‘n aansienlike Casuarina indringer skuld. Ervarings in Florida en die Mascarene Eilande beklemtoon dat casuarinas die potensiaal het om ekosisteme te transformeer met geweldige beheer omkostes. Ten spyte van redelike vordering aangaande die besturing van indringers in sekere areas, is daar steeds aansienlike probleme. Soos met meeste ander indringer boom taksa, is die botsing van belange veral uitdagend. Tweedens, het ek die meganismes van die naturalisasie bemiddel as ook indrigner risiko op die plaaslike skaal ondersoek. In hierdie deel het ek Casuarina cunninghamiana indringers in die Suid-Wes Kaap van Suid-Afrika ondersoek – die deel van die land met die grootste aangrensende area wat ‘n ooreenstemmend klimaat het met die inheemse areas van die spesie. Propaguul druk is ‘n belangrike drywer vir die naturalisasie van C. cunninghamiana populasies in areas met ‘n geskikte klimaat. Hierdie spesie het ook genaturaliseer in areas met suboptimale klimaats kondisies, maar slegs baie naby (<10m) aan plantasies. Risiko modelle dui aan dat C. cunninghamiana die potensiaal het om te versprei na ander dele van die Wes-Kaap waar dit huidiglik afwesig is. Natuurlike populasies van C. cunninghamiana is jonk en in die proses van uitbreiding. Die kapasiteit van die spesie om te hergrooi en voortplantings volwassenheid op n vroeë ouderdom te beriek stel voor dat hierdie spesie ‘n wyd verspreide en skadelike indringer kan word. Ons sluit af met aanbevelings vir effektiewe bestuur en stel voor dat indien sekere stappe geneem word (bv. ontmiddelike verwydering van die vroulike plante naby damme en water areas; alle verdere verkope beperk word tot manklike plante), dit moontlik sal wees om hierdie spesie op ‘n omgewings-veilige manier te gebruik. Derdens het ek die indringing dinamika van ‘n enkele Casuarina spesie on landskap skaal ondersoek. Ek het verken hoe interaksies tussen versteurings en indringing plantegroei prosesse dryf, deur gebruik te maak van die merkwaardige indringing van C. equisetifolia op die vulkaniese eiland van Reunion. Indringer populasies van C. equisetifolia het aansienlik vermeerder in die afgelope 40 jaar. Lava vloei het die verspreiding van C. equisetifolia gefasiliteer en indringing van hierdie spesie het plantegroei prosesse radikaal verander, deur die tempo van opvolging sewevoudig te verhoog. Hierdie studie weerspieël werk wat op Morella faya en Falcataria moluccana in Hawa’ii gedoen is en toon tot watter mate indringer spesies ekosisteem funksies kan verander en voordeel kan trek uit natuurlike versteurings wat gegenereer word deur vulkansiese lava vloei. Die voortgesette verspreiding van C. equisetifolia hou ‘n groot bedreiging in vir oorblywende inheemse laeveld reënwoude op Reunion wat tans < 2% van hul oorspronlike area dek. Die studies in hierdie tesis het patrone, prosesse en indringer risikos vir indringer bome ontdek wat nie goed in die literatuur verteenwoodig word nie. Sommige insigte wat deur goed bestudeerde boom genera, soos Acacia en Pinus, ontdek is, blyk om redelik goed van toepassing te wees op boom indringers in geheel. Alhoewel, sekere ekologiese funksies van Casuarina spesies en die manier wat hulle deur mense gebruik word, vra vir unieke oorwegings aangaande hul wêreldwye verspreiding en effektiewe beheer.

Members of the genus Ledebouria Roth (Hyacinthaceae), which occur in South Africa, are revised. This genus occurs throughout Africa, India and Madagascar. 33 Species are recognized and placed into nine provisional infrageneric groups. A multidisciplinary approach was used in an attempt to provide natural groupings. The following characters were analysed; morphology, micromorphology, palynology and caryology. Aspects of ovary structure and leaf micromorphology proved especially useful in the synthesis of infrageneric and specific concepts. Keys, descriptions, illustrations, distributional, ecological, medicinal and toxicological data are provided. This study is based on plants in their natural habitat, cultivated specimens and representative herbarium specimens from herbaria in South Africa and in Europe.
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1993.

This investigation confirmed that plant reaction to Al was directed through the disruption of intercellular co-ordination existing between the cell populations comprising the root meristem. The first detectable response to A1 in the root involved disruption of Golgi apparatus function in the cap periphery. Ultrastructural changes in the cap periphery coincided with the presence of A1 in these cells. Conspicuous physiological changes involving cell enlargement, cell metabolism and root elongation were identified in cells initially remote from the site(s) of A1 uptake. Communication between A1-damaged peripheral root cap cells and the cell populations of the cap and proximal meristems, quiescent centre and region of cell growth was therefore indicated. A decrease in amyloplast numbers in response to increasing AI concentration coincided with diminished Golgi apparatus activity in the peripheral cap. These changes preceded detectable reductions in mitotic activity, indicated by decreases in cap volume and root length, and it was consequently suggested that control of intercellular activities in the root meristem may be directed through polysaccharide metabolism. Low concentrations of A1 (≤ 1,25 mg dm ¯³) produced a positive growth response in the primary root. This coincided with an increase in mean cap volume and these events were interpreted as an A1-induced release of the proximal meristem from growth inhibition originating in the cap. Experiments which followed the effect of decapping on the morphology of quiescent centre cells in the presence and absence of A1 supported the existence of a Golgi apparatus-derived morphogen involved in the control of Golgi apparatus secretory activity and plastid differentiation. In contrast to the controls (0 ABA). treatment of decapped roots with 2 X 10[-4] and 5 X 10[-5] M abscisic acid inhibited the development of Golgi apparatus secretory activity and plastid differentiation. It is postulated therefore, that an early response to AI may involve inhibition of the basipetal movement of an endogenous growth inhibitor originating in the cap, which may be ABA. The presence of A1 in the nutrient solution caused an efflux of H[+] from the root. Some of the more adverse plant responses to AI were initiated at A1 concentrations where the molar ratio of charge between Ca[2+] and A1[3+] favoured A1. An hypothesis for an electrophysiological plant response to A1 involving membrane hyperpolarisation by Al ions is developed. Chemical analysis of plant fractions did not connect A1-induced nutrient disorders with the primary expression of A1 toxicity.
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.