Browsing by Author "Schonegevel, Lucille"

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    Modelling alien vegetation invasions and clearing strategies
    (Stellenbosch : Stellenbosch University, 2001-12) Schonegevel, Lucille; Van Niekerk, Adriaan; Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography & Environmental Studies.
    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.