Thesis (M.S.)--Missouri State University, 2008. / "May 2008." Includes bibliographical references (leaves 39-42). Also available online.

Thesis (Ph.D.)--University of Washington, 1994. / Vita. Includes bibliographical references.

Thesis (PhD)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Lisa J. Rew. Includes bibliographical references (leaves 198-217).

Thesis (MScConEcol)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of California, Santa Cruz, 2003. / Typescript. Includes bibliographical references (leaves 177-180).

Dissertation (Ph. D.)--University of South Alabama, 2007. / Vita. Includes bibliographical references (leaves 108-122).

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010. / Full text also available online. Scroll down for electronic link.

Thesis (M.Sc.(Agricultural and Applied))--University of Pretoria, 2009. / Summary in English. Includes bibliographical references.

Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The burgeoning problem of alien plant invasions in South Africa necessitates effective decision-making based on an understanding of the complex processes that govern these invasions. Due to the spatial nature of the problem, this study explored the use of Geographic Information Systems and spatial models for predicting the spread of alien vegetation and assessing the effectiveness of clearing strategies. The Spatially Explicit Individual Based Simulation (SEIBS) model was identified as a potentially useful tool for alien plant management. This thesis documents the further investigation and development that was necessary before recommendations could be made regarding the future use of the model. The landscape version of the SEIBS model was adapted to allow for the convenient input and output of spatial data, making it possible to simulate invasions in different areas. An ArcView extension was developed in order to facilitate the pre- and post-processing of the spatial data required and created by the model. Changes were also made to the fire routine of the model. The new version of the model was called Clear. A series of model tests for Pinus pinaster were conducted to assess the sensitivity of the Clear model to spatial resolution, initial spatial fragmentation and heterogeneity. These tests revealed that the model was sensitive to changes in resolution and needed to be reparameterised when using different resolutions. The initial level of fragmentation was shown to have a major influence on the invasion rate. Although greater levels of spatial heterogeneity with respect to vegetation age did not significantly affect the spread rate, it did increase the effectiveness of clearing strategies based on clearing juvenile or sparse vegetation. Based on these tests, it is concluded that the model can be readily applied to different areas, provided the influence of spatial characteristics is understood and accommodated. The Clear model was shown to be a useful tool for evaluating clearing strategies and for investigating invasion rates. It is recommended that the model be introduced to a wider audience, in order to obtain user feedback and further improve the accessibility of the model. / AFRIKAANSE OPSOMMING: Die toenemende probleem van uitheemse indringerplante in Suid Afrika, noodsaak effektiewe besluitneming wat gebaseer is op 'n begrip van die ingewikkelde prosesse wat indringing beheer. As gevolg van die ruimtelike geaardheid van die probleem, is die gebruik van Geografiese Inligtingstelsels en ruimtelike modelle vir die voorspelling van die verspreiding van indringerplante en die evaluasie van die effektiwiteit van opruimingstrategieë in hierdie studie ondersoek. Die Spatially Explicit Individual Based Simulation (SEIBS) model is as 'n moontlike geskikte hulpmiddel vir die bestuur van uitheemse indringerplante geïdentifiseer, alhoewel verdere ondersoeke en ontwikkeling nodig was voordat aanbevelings vir die gebruik van die model gemaak kon word. Vir hierdie studie is die landskapweergawe van die SEIBS model aangepas om die maklike toevoer en afvoer van ruimtelike data te fasiliteer. 'n ArcView uitbreiding is ontwikkel om met die voor- en naprosessering van ruimtelike data, wat deur die model gebruik en geskep is, te fasiliteer. Veranderinge is ook aan die vuur sub-roetine van die module gemaak. Die nuwe weergawe van die model word Clear genoem. 'n Reeks toetse is vir Pinus pinaster gedoen om die sensitiwiteit van die Clear model te toets teenoor ruimtelike resolusie, aanvanklike vlak van versnippering en vlak van heterogeniteit. Vanuit die toetse het dit geblyk dat die model sensitief was ten opsigte van verandering in resolusie en dat die model se parameters verstel moes word wanneer verskillende resolusies gebruik word. Daar is ook gewys dat die die vlak van aanvanklike versnippering 'n groot impak op die verspreidingstempo het. Alhoewel hoër vlakke van ruimtelike heterogeniteit teenoor plantegroei nie 'n merkbare impak op die verspreidingstempo gehad het nie, het dit wel die effektiwiteit van opruiming-strategieë, gebaseer op die opruiming van jong of yl verspreide plante, verbeter. Die gevolgtrekking wat uit die toetse gemaak kan word is dat die model geredelik op verskillende areas toegepas kan word, op die voorwaarde dat die invloed van ruimtelike eienskappe in ag geneem word en in berekening gebring word. Dit word aanbeveel dat die model wyer bekendgestel word om sodoende gebruikersterugvoer te bekom.

>Magister Scientiae - MSc / Invasive alien plants (IAPs) are often reported to use more water than indigenous plants. Inaddition, IAPs have an ability to adapt to harsh environmental conditions and they tend to spread at rapid rates, thereby threatening the country’s water resources, agricultural land, and biodiversity. Much of South Africa is expected to get drier in future due to climate change and the new climatic conditions are also predicted to accelerate the rate at which alien plants will spread. Approximately 10 million hectares are currently estimated to have been invaded by alien plants in South Africa, with an estimated average annual rate of spread of more than 5%. The first objective of this study was to compare the water use by deep rooted tree species which include invasive alien Prosopis (sp) trees and the co-occurring indigenous A. karroo. These trees are growing in a flood plain of a groundwater dependent catchment in the Northern Cape Province. Both species are dependent on groundwater and thus compete with local communities for this resource. The second objective was to determine the sources of water that the trees were using in order to understand the impacts of each species on groundwater resources. Transpiration was measured using the heat ratio method of the heat pulse velocity sap flow technique while the volumetric soil water content was monitored at several depths down the soil profile using automated capacitance soil water content probes. Weather data was collected using an automatic weather station. Stable isotopes of oxygen and hydrogen from plant, soil and groundwater samples were analysed to determine the sources of water used by the trees. Average tree density was approximately 613 stems per hectare for Prosopis compared to about 100 stems per hectare for A. karroo. Comparative measurements of water use shows that the annual stand level transpiration from Prosopis invasions was approximately 353 mm/year while that from A. karroo was only about 137 mm/year. Differences in stand transpiration were a result of the higher plant density for Prosopis than A. karroo. There were no significant differences in the transpiration rates of the two species for trees with a similar transpiring leaf area. Application of a two compartment linear mixing model for the oxygen isotope ratio during the peak transpiration period in summer showedthat Prosopis derived 23% of its water from the unsaturated zone and 77% from the saturated zone. A. karroo on the other hand derived 53% of its water from the unsaturated zone and47% from the saturated zone. Diurnal fluctuations in groundwater levels were strongly related to the transpiration dynamics of both species. This supports the observation that these deep rooted trees have substantial impacts on groundwater at the study site. Root sap flow patterns of Prosopis showed evidence of hydraulic redistribution wherein the groundwater abstracted by the tap roots was deposited in the shallow soil layers by lateral roots. However, the root sap flow patterns of A. karroo growing adjacent to the Prosopis did not show this phenomenon.