No description available.

No description available.

No description available.

Zugl.: Marburg, University, Diss., 1999.

Thesis (MSc)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

En una condición de secano semiárido de Chile central (33º28’ LS - 70º50’ LO) se evaluó, sobre la base de algunas propiedades químicas del suelo, el comportamiento de un sistema agroforestal sustentado por un sistema de cosecha de agua. Luego de siete años de establecido el sistema los resultados muestran significancia en variables de fertilidad. La concentración de aguas provenientes de las lluvias en determinadas áreas influyó en el crecimiento de plantas (Acacia saligna) y análogamente en las propiedades químicas del suelo (materia orgánica del suelo y contenidos totales de nitrógeno y potasio). Respecto de la evaluación previa realizada el año 2000, los contenidos de materia orgánica del suelo aumentaron en un 55% en el tratamiento Agroforestería-Escurrimiento (a la profundidad de 30-40 cm). Los tratamientos Agroforestería-Labranza-Escurrimiento y Agroforestería-Escurrimiento, tuvieron incrementos en los niveles de nitrógeno total (a la profundidad de 10-20 cm) de 27 y 44%, respectivamente. Por otro lado, se advirtió que los niveles de potasio total disminuyeron en los primeros 30 cm de profundidad en el tratamiento Agroforestería-Escurrimiento. Las funciones de respuesta de A. saligna mostraron que sólo los contenidos totales de potasio (en el rango de 10-30 cm de profundidad) fueron determinantes en su crecimiento. Al respecto, el incremento en biomasa aérea de A. saligna implica, en condiciones de secano, un uso más eficiente del agua donde el potasio tendría un rol crítico en la economía de este recurso.

Thesis (Ph.D.) - University of Queensland, 2006. / Includes bibliography.

The impacts of invasive species on the environment, human health, and the economy continue to gain interest from public and private agencies, scientists, and the media. This study aimed to investigate the utility of SPOT 5 imagery and Artificial Neural Networks, in the identification and mapping of Acacia mearnsii within environments of varying complexity. Results showed that it is possible to identify and map Acacia mearnsii using SPOT 5 imagery, depending on the classification algorithm used. It was established that the neural network algorithms performed with greater success when compared to the performance of traditional classifiers, confirming other similar studies. The utility of the various classification algorithms was also investigated in terms of their applicability to environments of varying complexity. The neural networks once again, proved to be more successful and performed well in both the complex and relatively simple environments, indicating the robustness of the neural network algorithm. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

The influence of herbivory, grass competition and grazing system on emergence, growth and survival of Acacia seedlings in burnt and unburnt areas was investigated in their first growing season, from September 1997 to May 1998. The study was aimed at determining possible reasons for the increase in woody plant density in semi-arid savannas, specifically the effect of excluding small-mouthed herbivores from domestic and livestock systems, and switching from continuous grazing to rotational grazing systems. The effect of fire intensity and maximum fire temperature on seed viability, germination and mortality, specifically with regard to back versus head fires and seed size , were investigated. Variability among species in the number of seedlings emerging generally resembled differences in viability. Emergence of Acacia karroo and Acacia tortilis was poorer than that of Acacia nilotica under grass competition. Emergence was lower in burnt and open areas, the latter depending on Acacia species. Herbivory did not affect seedling emergence, in both domestic and wildlife systems. Seedling survival and growth was adversely affected by small-mouthed herbivores in both domestic and livestock systems, whilst large-mouthed herbivores exerted no direct effects on woody seedlings, except to a small degree by trampling. Seedlings showed better growth and survival under low grass competition, which also resulted in greater leaf-to-height ratios , indicating that grass interference with irradiance affects woody seedlings. This effect appeared to be greater for cattle and rotational grazing, and for burning, in domestic and wildlife systems respectively. Woody seedling establishment was also better in burnt areas. Whilst seedling growth was better under rotational than continuous grazing, survival was not significantly different. Grass competition influenced seedling establishment to a greater extent than herbivory, whilst burning made a greater impact than grass competition. Seed mortality in response to maximum fire temperature was inversely related to seed size, and trends in seed germination and mortality, although very variable, appeared to be influenced by threshold fire intensities and maximum temperatures. Back fires had hotter maximum temperatures and fire intensities at ground level than head fires, which result in greater seed mortality following fire. Based on the current study it is likely that the removal of grass competition, burning, and a change from continuous to rotational grazing systems, and small-mouthed to large-mouthed herbivores, will result in an increase in woody seedling establishment. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

Thesis (PhD)--Stellenbosch University, 2013. / Australian Acacia species are an important group of invaders and are known to form dense monospecific cultures in invaded habitats. Despite the ecological and economic importance of invasive acacias, little is known about their invasive biology both from an ecological and evolutionary perspective. Molecular genetic methods have increasingly become important in identifying source populations for invasive species and determining the population genetic structure of these populations. This thesis applied molecular tools to understand the invasion ecology of Acacia pycnantha and its rhizobial symbionts as a model system of Australian Acacia introductions. Specific objectives were to: reconstruct the molecular phylogeny of invasive and native populations of populations of Acacia pycnantha and identify the native provenance of A. pycnantha; identify microsatellite markers for Acacia pycnantha and other invasive Australian acacias based on transferring microsatellite markers developed for A. mangium, A. saligna, Paraserianthes lophantha and universal chloroplast microsatellites developed from tobacco; assess the introduction dynamics of Acacia pycnantha in South Africa and identify the source populations in the species’ native range ; and determine which nitrogen fixing symbionts nodulate A. pycnantha and determine whether A. pycnantha brought its symbionts along from its native range or acquired them in the invasive range. Nuclear and chloroplast DNA sequence data were used to reconstruct phylogeographic relationships between native and invasive A. pycnantha populations. The chloroplast phylogeny showed that Australian populations of A. pycnantha are geographically structured into two previously informally recognized lineages (representing wetland and dry land forms). Habitat fragmentation is probably the result of cycles of aridity and abundant rainfall during the Pleistocene0. The invasive population in Portugal was found to be the wetland form while South African populations were found to be predominantly wetland form although some dryland forms were identified. Thirty microsatellites out of the forty nine tested microsatellites successfully amplified across all species tested (A. implexa, A. longifolia, A. melanoxylon, A. pycnantha and A. podalyriifolia). High Transfer rates varied between 85% for microsatellites developed for A. mangium to 50% for those developed in A. saligna. Although transfer rates were high only twelve microsatellites (24%) out of the fifty tested were polymorphic while the chloroplast microsatellites showed no polymorphism. The low level of polymorphic loci calls for development of more microsatellites in this genus especially for species that have high commodity value. Nuclear microsatellites revealed three genetic groupings with substantial admixture in the native range (1. wetland Victoria and South Australia populations; 2. dryland Victoria and Flinders Range population; and 3. New South Wales). Admixture in the native range may have occurred as a result of reforestation exercises. Acacia pycnantha has been widely used in rea forestation projects in Australia because of its fast growth rate and ease of germination. Admixed populations were most - likely introduced to South Africa thus establishment of A. pycnantha may have been facilitated by already admixed propagules in the invasive range. Extensive admixture in the native range made it difficult to identify source populations of invasive A. pycnantha found in South Africa. The rhizobial symbionts of A. pycnantha were identified, showing that this species utilizes a wider suite of symbionts in its invasive range than its native range and there is support for both the co-introduction and host jumping hypotheses. This creates substantial opportunities for horizontal gene transfer between previously allopatric bacterial lineages, with as yet unknown consequences for plant and bacterial invasions.