Department of Botany and Zoology

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Browsing Department of Botany and Zoology by Author "Afonso, Luca"

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    Urban plant invasions: how to classify, prioritize and manage invasive alien plants; Cape Town as a case study
    (Stellenbosch : Stellenbosch University, 2021-04) Afonso, Luca; Esler, Karen J.; Gaertner, Mirijam; Sjirk, Geerts; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Urban areas are considered hotspots for invasions, with human activity being a major source of introduction and causing the dispersal of invasive alien plant species (IAPs). This makes natural and semi natural areas within and surrounding cities particularly susceptible to invasion. Cape Town is located within the Cape Floristic Region (CFR) which is considered a biodiversity hotspot; furthermore, this region has been identified as a UNESCO world heritage site. This biologically diverse area – which has some of the most recognizable and unique plant communities in the world – is therefore susceptible to invasion and is considered one of the most threatened biodiversity hotspots. IAPs pose a significant ecological and economic threat, impacting biodiversity and ecosystem services. Cape Town’s natural areas are also fragmented due to urbanization, where low lying areas are often developed and areas at higher altitudes are set aside for conservation purposes (such at the Table Mountain National Park). I reviewed the nature of urban invasions and the management strategies currently being employed to mitigate the impacts of IAPs within urban areas. I aimed to determine whether IAP richness and abundance is highest within natural areas within (or adjacent to) urban areas compared to peri-urban areas and rural areas and present management strategies to maintain ecological diversity throughout the city of Cape Town’s biological network of natural and semi-natural areas. I present a classification protocol developed from a literature review based on the feasibility of IAP eradication and grouped widespread IAPs, emerging IAPs and potential eradication targets into different management categories. In addition to this I adopted and tested a model for prioritization of emerging IAPs (known as early detection and rapid response [EDRR]) in the City of Cape Town (CCT) Metropolitan area. Finally, I focused on the emerging invader Hypericum canariense, and use lessons from earlier chapters to discuss feasibility of eradication of this species. I found that IAP species abundance was highest at the urban wildland interface (the peri-urban zone) between urban areas and rural areas. I discovered that disturbance in the natural and semi natural areas at the urban wildland interface plays a significant role in the invasion of IAPs into natural areas. In my classification protocol I identified that the area of infestation and the IAP species rate of spread are key indicators in classifying IAPs as widespread or emerging IAPs and for identifying potential eradication targets, noting that the three main management strategies for IAPS were mitigation, containment and eradication. Furthermore, the main criteria used in prioritizing emerging species in the Cape Town metropolitan area are “spread, negative impacts, ease of control and invasive potential”. I discovered that the emerging invader, H. canariense is feasible for eradication and that it would cost approximately ZAR57000 over a 10 year period to eradicate this species. I conclude that urban areas are important for effective IAP management and must not be disregarded or underestimate the role they play in the dissemination of IAPs into surrounding natural areas. The Peri-urban zone should be the focus of future management to ensure healthy biological networks. Conservationists and land managers should classify and prioritize species for management efforts instead of tackling species arbitrarily when funding is limited. Emerging species should be investigated in terms of their feasibility of eradication before undertaking potentially lengthy and costly eradication program.