Pattern and process of plant invasion in an African savanna ecosystem
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Biological invasions are a significant ecological and economic global crisis. Protected areas also suffer from the increased burden that invasions place on their resources and the impacts placed on the ecosystem. However, management requires an ecological foundation which can inform best practice and optimize its responses. I explored the patterns and processes of invasion in Kruger National Park (KNP), South Africa; a large national park situated in the Lowveld savanna ecosystem. I used spatially-explicit alien plant data at various scales from: a national database, the whole of KNP, a specific region, river system, and small scale plots in one invaded area of KNP. Using various statistical techniques, primarily classification and regression tree analysis, logistic regression, ANOVA, Nestedness and spatial pattern analysis, I assessed the relationship between the patterns observed at a specific spatial grain and extent, discussing the implications for invasion ecology and management. Using this knowledge and conceptual tools, I developed a new framework and model which contributes to invasion theory. Scale is a critical component in evaluating alien plant invasions. Without careful consideration of scale, studies from different scenarios cannot be compared and the science of invasion ecology will not advance. I provide a framework for assessing the risks of plant invasions in a watershed, using both an area- and species-approach, highlighting areas of current and future potential concern. I also explore the role of intentional introduction of ornamental plants and discuss management approaches for dealing with this. Evaluating a riparian system provides insights into how different patches in a landscape are differentially invaded, and how patch type characteristics need to be considered carefully for management and monitoring. I also describe how reconstructing the invasion history of a species, complemented by fine scale assessment, provides insights into species-specific spread models, and also how these types of studies can input into general theories, such as the role of propagule pressure. These components together provide insight into the dynamics of alien plant invasions in an African savanna and protected area system.