Thesis (doctoral)--Swedish University of Agricultural Sciences, 2007. / Thesis documentation sheet inserted. Includes appendix of five papers and manuscripts, three co-authored with others. Includes bibliographical references. Also issued electronically via World Wide Web in PDF format; online version lacks appendix.

Thesis (Ph.D.)--University of Melbourne, School of Resource Management and Amenity Horticulture, 2002. / Typescript (photocopy). Includes bibliographical references (leaves 373-392).

Thesis (M. Sc.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (leaves 109-118). Also available via the World Wide Web.

Thesis (doctoral)--University of Tartu, 2004. / Includes bibliographical references.

Thesis (Ph. D.)--Colorado State University, 2004. / Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1999. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.Sc.)(Botany)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Nitrogen deposition to adjacent grassland and forested areas in the vicinity of Sabie, Mpumalanga, South Africa was studied. Total deposition amounts to the forested area are calculated to be 7l.2 kg N ha-1 yr1 and to the grassland area, 25 kg N ha· 1 yr1. The average deposition amounts are similar to or at least approach nitrogen mineralisation amounts at nearby sites of 50-70 kg N ha-1 yr1. The deposition amounts are made up of 21.4 kg N ha-1 yr1 dry deposition, 7.8 kg N ha-1 yr1 wet deposition and 42 kg N ha-1 yr1 cloud droplet deposition for the forest. For the grassland, the amounts are 7 kg N ha-1 yr1 dry deposition, 7.8 kg N ha-1 yr1 wet deposition and 10.5 kg N ha-1 yr1 cloud droplet. deposition. For both wet and cloud droplet deposition, the amount attributable to nitrate was greater than that attributable to ammonium. For wet deposition, nitrate contributed 4.1 kg N ha-1 yr1 and ammonium contributed 3.7 kg N ha-1 yr1 to both forests and grasslands. For cloud droplet deposition to forests, the amounts were 28 kg N ha-1 yr1 attributable to nitrate and 14 kg N ha-1 yr1 attributable to ammonium. For grasslands the amounts were 7 and 3.5 kg N ha-1 yr1. In both forests and grasslands, the component of dry deposition contributing the most to deposition was ammonia gas, the amounts being 14.2 and 4.3 kg N ha-1 yr1 respectively. Nitric acid contributes 3.7 and 1.9 kg N ha-1 yr1 respectively and is followed by the nitrogen dioxide component that contributes 1.6 and 0.5 kg N ha- I yr1. Ammonium and nitrate particles contribute the least to deposition. For the forests the amounts are 1 and 0.9 kg N ha-1 yr1 and for the grasslands they are 0.2 and 0.1 kg N ha-1 yr1. A strong seasonal variance in deposition amounts is apparent with maximum deposition amounts occurring in Summer and minimum amounts in Winter. Intermediate amounts are deposited in Autumn and Spring, with the latter season having slightly larger deposition amounts. The seasonal variance is strongly linked to the seasonal rainfall and cloud droplet deposition patterns. Biomass burning is indicated as a possible important factor in influencing the chemical composition of rainfall during Spring. Of the deposition amounts obtained in this study, the deposition from cloud droplets is high compared to other studies and is probably overestimated. Further research into this area is needed.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the academic requirements for the degree of Doctor of Philosophy. May 2016 Johannesburg / This thesis reveals previously unknown facts concerning the invasion, ecology and management of the perennial alien forb Campuloclinium macrocephalum (Less.) DC. (Asteraceae, pompom weed) in the grassland biome of South Africa. All these areas of research are of critical importance to identify the causes of invasion and prescribe best management practises aimed at reducing the density and spread of the weed and restoring these ancient grasslands. Grassland biomes throughout the world are receiving international attention because of their vulnerability to transformation, a history of ignorance regarding their evolution and prejudice as evidenced by their exploitation. There are many theories as to why alien plants become invasive outside of their native range but most are controversial, except those that support the absence of natural enemies as the primary reason for invasiveness. Few studies have attempted to empirically measure environmental and ecological factors that facilitate invasion, not to dispute the Absence of Predators Hypothesis (APH); APH regulates invasiveness but the external factors affecting habitat vulnerability to invasion remain unchanged. Based on the assessments of 80 invaded grasslands in Gauteng Province prior to the release of any host-specific biocontrol agents, it was concluded that C. macrocephalum favours disturbed grasslands. Numerous agencies of disturbance were identified; the most important being heavy grazing, abandonment (e.g. old lands) and modification (e.g. draining of wetlands). Herbivory by generalist insects was insignificant. The main drivers of native species composition in the invaded study sites were rainfall, topography and soil texture. The weed was most problematic in grasslands with a basal cover of <19% and in poor condition from a pastoral perspective. Other alien and native invasive species were also found in grasslands with C. macrocephalum. High fire frequency also appeared to exacerbate weed density. The Novel Weapons Hypothesis postulates that some invasive species transform vegetation for establishment, densification and expansion because they are allelopathic. Stems and leaves of C. macrocephalum have both rigid multicellular hairs and glandular trichomes that exude an unidentified substance. It has been speculated that allelopathy may be an important trait aiding its rapid expansion in invaded grasslands. The importance of allelopathy and competition was investigated under controlled conditions using Eragrostis curvula (perennial grass), E. tef, (annual grass) and Lactuca sativa (lettuce) as test species. Petri-dish studies proved that root and shoot extracts of adult C. macrocephalum plants had zero inhibitory effect on the seed germination in all three test species. Stunting of radicles was evident in treatments comprising leaf extracts at 10 and 25% w/v; with E. tef displaying a higher tolerance than E. curvula. Eragrostis curvula, because it was the most sensitive of the test species, was used in a pot study together with C. macrocephalum to evaluate allelopathy and interference. The biomass and growth of E. curvula was not affected by C. macrocephalum at densities of one or five plants per pot. The weed on the other hand incurred density-dependant trade-offs in size, biomass and mortality. In a separate pot study, the incorporation of weed residues into the potting medium had no impact on the growth of E. curvula. The process went one step further by analysing the association between E. curvula and C. macrocephalum from the 80 grassland assessments. Eragrostis curvula had a narrower ecological niche and was only found in disturbed grasslands on well drained soils. Campuloclinium macrocephalum invaded a broad gradient of soil types including poorly drained wetland soils not amenable for E. curvula. Competitive exclusion between the two species was not apparent. Pot studies and field observations support a degree of tolerance between C. macrocephalum and E. curvula that lends support to coexistence at a range of weed densities. The conclusions from this study were (a) C. macrocephalum is not allelopathic and allelo-chemistry cannot be inferred as a causal mechanism for the weed’s invasiveness, and (b) C. macrocephalum and E. curvula have different limiting resource requirements that enables coexistence in areas where the latter can grow. In 2006 C. macrocephalum infestations in Gauteng Province were severely damaged by Puccinia eupatorii Dietel (Pucciniaceae), a biotrophic rust identical to the P. eupatorii strain in quarantine that was imported into South Africa from Argentina as a potential biocontrol agent. An investigation of the rust’s impact on C. macrocephalum was carried out in the 80 rangeland infestations previously assessed and how pathogen pressure affected the weed’s realised niche. The rust caused premature senescence of the stems in late summer with compensatory regrowth in autumn. In contrast disease-free plants senesced in late autumn; the rootstocks remained dormant throughout winter and did not produce compensatory regrowth. No significant changes in weed density were detected and C. macrocephalum retained its realised niche. The weed remains adapted to the rust despite a 40-year separation from the pathogen. Registered herbicides should provide 80% control of the targeted plants, providing label directions concerning concentration, mixing, application and environmental considerations are adhered to. Herbicide trials were conducted at two contrasting sites in Gauteng, a wetland and a rocky grassland, to test the efficacy of picloram and metsulfuron-methyl on the control of C. macrocephalum. Both sites had dense infestations of C. macrocephalum at the beginning of the study in 2005. Herbicides were applied in either February (summer) or April (autumn) annually for three consecutive years. Monitoring continued for an additional three years after spraying was terminated. Puccinia eupatorii established at both study sites from the second year of study. Both sites also experienced wildfires and drought. As these uncontrolled factors were not anticipated in the design their individual effects could not be factored out. Mean mortality however was <80% expected of registered herbicides which can only be attributed to uncontrolled factors acting as natural constraints. The efficacy of picloram was not significantly different (P<0.05) to that of metsulfuron methyl within a season. Autumn applications are not recommended because rust damage on the leaves is too advanced to ensure adequate herbicide uptake and translocation. Herbicide persistence in the topsoil was not detected by gas chromatography. Three applications of herbicide were inadequate to bring C. macrocephalum under control in plots. It is estimated that five to seven years of herbicide application are needed to reduce the weed density to <1 plant per plot (25 m2). This effectively renders chemical control in medium to dense infestations uneconomic. Chemical control of C. macrocephalum will only be effective if there is a commitment to follow-ups and remedial vegetation management practices. The herbicide trials also looked at the impact of picloram, metsulfuron methyl and hoeing on native species and other alien species that occurred in plots. Three plant functional groups were analysed, namely native grasses, native forbs and alien broadleaf species. The herbicides were applied as broadcast sprays over three years and therefore their effect on all broadleaf species was non-selective. Hoeing twice a year for three years only targeted C. macrocephalum. High forb richness coupled with low abundance and patchy distribution meant there was a high turnover between replicate plots across the study sites. Herbicides had a significant impact on the native forb functional group compared to hoeing which had a superficial effect. Hoeing did not suppress C. macrocephalum. The parasitic forb Thesium utile was killed in all treatments except the untreated control. The target-specific hoe treatment also eliminated T. utile, suggesting a new association might exist between parasite and C. macrocephalum. Hoeing also facilitated the establishment of alien annual weeds. In South Africa the grassland biome is under considerable threat from mining, afforestation, agriculture and urban development. Although alien plants pose a minor threat in contrast to these land-transforming activities they remain the greatest threat to grasslands that are not threatened by exploitation. Campuloclinium macrocephalum is not a pioneer species, but rather a long-lived perennial herb with evolutionary adaptations to fire, herbivory and disease. These characteristics have enabled it to establish and spread in grasslands that have been maintained in a variety of disturbed states by a range of agencies that reduce grass basal cover and exacerbate soil erosion. Addressing poor land use practises that foster C. macrocephalum invasion and spread are as important as the remedial activities necessary to control the species. Grassland restoration/rehabilitation practises have not been investigated in the context of C. macrocephalum management and is of critical importance to the integrated control of the weed. Although comprehensive literature about C. macrocephalum have recently been published gaps in our understanding of its biology, ecology and control still exist that prevent the development of best management practices. These areas for new research make ideal projects for post-graduate students. Future research should focus on (a) rust–herbicide interactions, (b) fire and seedbank dynamics, (c) integrated weed management incorporating biological control, fire, selective herbicide application techniques (e.g. spot-spraying) and ecosystem restoration practises. Grazing strategies promoting grass species adapted to frequent non-selective defoliation restrict pompom weed better than degraded underutilised rangelands, as evidenced by low levels of C. macrocephalum in communal areas, and warrants further investigation, including fence-line contrasts in invaded and un-invaded road reserves.

In order to understand how bunchgrasses achieve dominance over other plant growth forms and how they achieve dominance over one another in different environments, it is first necessary to develop a detailed understanding of how their growth strategy interacts with the resource limits of their environment. Two properties which have been studied separately in limited detail are architecture and disproportionate resource allocation. Architecture is the structural layout of organs and objects at different hierarchical levels. Disproportionate resource allocation is the manner in which resources are allocated across objects at each level of hierarchy. Clonal architecture and disproportionate resource allocation may interact significantly to determine the growth ability of clonal plants. These interactions have not been researched in bunchgrasses. This thesis employs a novel simulation technique, functional-structural plant modelling, to investigate how bunchgrasses interact with the resource constraints imposed in humid grasslands. An appropriate functional-structural plant model, the TILLERTREE model, is developed that integrates the architectural growth of bunchgrasses with environmental resource capture and disproportionate resource allocation. Simulations are conducted using a chosen model species Themeda triandra, and the environment is parameterised using characteristics of the Southern Tall Grassveld, a humid grassland type found in South Africa. Behaviour is considered at two levels, namely growth of single ramets and growth of multiple ramets on single bunchgrass clones. In environments with distinct growing and non-growing seasons, bunchgrasses are subjected to severe light depletion during regrowth at the start of each growing season because of the accumulation of dead material in canopy caused by the upright, densely packed manner in which they grow. Simulations conducted here indicate that bunchgrass tillers overcome this resource bottleneck through structural adaptations (etiolation, nonlinear blade mass accretion, residual live photosynthetic surface) and disproportionate resource allocation between roots and shoots of individual ramets that together increase the temporal resource efficiency of ramets by directing more resources to shoot growth and promoting extension of new leaves through the overlying dead canopy. The architectural arrangement of bunchgrasses as collections of tillers and ramets directly leads to consideration of a critical property of clonal bunchgrasses: tiller recruitment. Tiller recruitment is a fundamental discrete process limiting the vegetative growth of bunchgrass clones. Tiller recruitment occurs when lateral buds on parent tillers are activated to grow. The mechanism that controls bud outgrowth has not been elucidated. Based on a literature review, it is here proposed that lateral bud outgrowth requires suitable signals for both carbohydrate and nitrogen sufficiency. Subsequent simulations with the model provide corroborative evidence, in that greatest clonal productivity is achieved when both signals are present. Resource allocation between live structures on clones may be distributed proportionately in response to sink demand or disproportionately in response to relative photosynthetic productivity. Model simulations indicate that there is a trade-off between total clonal growth and individual tiller growth as the level of disproportionate allocation between ramets on ramet groups and between tillers on ramets increases, because disproportionate allocation reduces tiller population size and clonal biomass, but increases individual tiller performance. Consequently it is proposed that different life strategies employed by bunchgrasses, especially annual versus perennial life strategies, may follow more proportionate and less proportionate allocation strategies respectively, because the former favours maximal resource capture and seed production while the latter favours individual competitive ability. Structural disintegration of clones into smaller physiologically integrated units (here termed ramet groups) that compete with one another for resources is a documented property of bunchgrasses. Model simulations in which complete clonal integration is enforced are unable to survive for long periods because resource bottlenecks compromise all structures equally, preventing them from effectively overcoming resource deficits during periods when light is restrictive to growth. Productivity during the period of survival is also reduced on bunchgrass clones with full integration relative to clones that disintegrate because of the inefficient allocation of resources that arises from clonal integration. This evidence indicates that clonal disintegration allows bunchgrass clones both to increase growth efficiency and pre-empt potential death, by promoting the survival of larger ramet groups and removing smaller ramet groups from the system. The discrete nature of growth in bunchgrasses and the complex population dynamics that arise from the architectural growth and the temporal resource dynamics of the environment, may explain why different bunchgrass species dominate under different environments. In the final section this idea is explored by manipulating two species tiller traits that have been shown to be associated with species distributions across non-selective in defoliation regimes, namely leaf organ growth rate and tiller size (mass or height). Simulations with these properties indicate that organ growth rate affects daily nutrient demands and therefore the rate at which tillers are terminated, but had only a small effect on seasonal resource capture. Tiller mass size affects the size of the live tiller population where smaller tiller clones maintain greater numbers of live tillers, which allows them to them to sustain greater biomass over winter and therefore to store more reserves for spring regrowth, suggesting that size may affect seasonal nitrogen capture. The greatest differences in clonal behaviour are caused by tiller height, where clones with shorter tillers accumulate substantially more resources than clones with taller tillers. This provides strong evidence there is trade-off for bunchgrasses between the ability to compete for light and the ability to compete for nitrogen, which arises from their growth architecture. Using this evidence it is proposed that bunchgrass species will be distributed across environments in response to the nitrogen productivity. Shorter species will dominate at low nitrogen productivity, while taller species dominate at high nitrogen productivity. Empirical evidence is provided in support of this proposal. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.