Modelling alien vegetation invasions and clearing strategies

[摘要] ENGLISH ABSTRACT: The burgeoning problem of alien plant invasions in South Africa necessitates effectivedecision-making based on an understanding of the complex processes that govern theseinvasions. Due to the spatial nature of the problem, this study explored the use of GeographicInformation Systems and spatial models for predicting the spread of alien vegetation andassessing the effectiveness of clearing strategies. The Spatially Explicit Individual BasedSimulation (SEIBS) model was identified as a potentially useful tool for alien plantmanagement. This thesis documents the further investigation and development that wasnecessary 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 andoutput of spatial data, making it possible to simulate invasions in different areas. An ArcViewextension was developed in order to facilitate the pre- and post-processing of the spatial datarequired 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 Clearmodel to spatial resolution, initial spatial fragmentation and heterogeneity. These testsrevealed that the model was sensitive to changes in resolution and needed to bereparameterised when using different resolutions. The initial level of fragmentation wasshown to have a major influence on the invasion rate. Although greater levels of spatialheterogeneity with respect to vegetation age did not significantly affect the spread rate, it didincrease the effectiveness of clearing strategies based on clearing juvenile or sparsevegetation.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 Clearmodel was shown to be a useful tool for evaluating clearing strategies and for investigatinginvasion rates. It is recommended that the model be introduced to a wider audience, in orderto obtain user feedback and further improve the accessibility of the model.

[发布机构] Stellenbosch University