Browsing by Author "McLean, Phil"

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    Patterns and processes of alien plant invasions in small urban areas in South Africa : the Berg River catchment as a case study
    (Stellenbosch : Stellenbosch University, 2018-03) McLean, Phil; Richardson, D. M.; Wilson, J. R. U.; Gaertner, Mirijam; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Many studies in invasion biology focus on the negative consequences of invasive alien plant species in natural areas. In South Africa, national legislation relating to invasive species focusses mainly on the management of such species in areas that provide strategic water and/or biodiversity resources. However, urban centres are host to many alien plant species, specifically those associated with the very popular activities of gardening and the pet trade. Urban environments can facilitate plant invasions because alien plants are cultivated in large numbers and are nurtured, and there are often sites of regular disturbance that provide favourable conditions for colonisation which allow some species to become naturalized and invasive. Small urban centres are more numerous than large cities and are often more deeply embedded in the landscape. This, combined with their higher proportional perimeter-to-area ratio, means they could be launching invasions into their surrounding areas. I investigated one such small town in detail to determine the patterns of spread of alien plant species. I then surveyed, in less detail, an additional 11 towns within the Berg River Catchment. Lastly, I compared the type and abundance of alien plant species found in towns to data on invasive alien plant species found specifically outside urban areas in the same catchment. I found a large number of alien plant species within small urban areas, with a high proportion of listed invasives. Most of the total alien plant diversity resides in gardens, but the most abundant alien plant species in all land-use types are either listed as invasive in national legislation, or are noted as problematic species in the regional literature. The extremely high species heterogeneity between gardens means that detailed, time-consuming surveys and high levels of taxonomic expertise are needed to ensure accurate results. However, reasonable assessments of a town’s invasive plant species component can be made by surveying gardens and roadsides in low-income areas and in town centres (with the exception of the Main road, as commercial activity often render these areas hostile to plants). All urban areas surveyed were equally capable of hosting a high proportion of invasive plant species, irrespective of their location within the catchment. By comparing abundant alien plants to regional lists of invasive plant species, I was able to determine the suite urban species which have naturalization records in this catchment and have thus ‘jumped the garden fence’ to become invasive in the surrounding natural areas. Most species in this group were introduced for ornamental horticulture, highlighting the risks associated with this pathway. Small urban areas are difficult to survey comprehensively due to extreme context speceficity, but contain a high diversity of alien plant species. The most abundant species are typically also naturalized, if not invasive, in the region, highlighting that small towns are important for launching plant invasions into surrounding natural areas.