Urban plant invasions: how to classify, prioritize and manage invasive alien plants; Cape Town as a case study

Afonso, Luca (2021-03)

Thesis (MSc)--Stellenbosch University, 2021.

Thesis

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.

AFRIKAANSE OPSOMMING: Stedelike gebiede word beskou as brandpunte vir plant indringing met menslike aktiwiteite as oorsaak en bron van bekendstelling en verspreiding van uitheemse indringer plant spesies. (UIPS) Dit maak natuurlike en semi-natuurlike areas binne stede en hulle omliggende areas besonder vatbaar vir indringing. Kaapstad is gelee in die Kaapse Floristiese Ryk, wat beskou word as n biodiverse brandpunt; verder, dit is aangewys as n Unesco wereld erfenis gebied. Hierdie biologiese diverse gebied, met van die beduidendste en unieke plantgemeenskappe in die wereld, is vatbaar vir indringing en word beskou as een van die mees bedreigde biodiverse brandpunte. UIPS hou n beduidende ekonomiese en ekologiese bedreiging in met n gevolglike impak op biodiversiteit en ekosisteemdienste.. Kaapstad se natuurlike gebiede ook gefragmenteer as gevolg van verstedeliking, met laagliggende gebiede dikwels meer ontwikkel en hoerliggende areas tersyde gestel vir bewaringsdoeleindes (soos in die geval van die Tafelberg Nasionale Park). Ek het die aard van stedelike indringing nagegaan en die bestuurstrategieë t.o.v. die impak van UIPS tans in gebruik geëvalueer. My doel was om te bepaal of UIPS werklik meer oorvloedig voorkom in natuurlike gebiede wat grens aan stedelike gebiede en om bestuurstrategieë te ontwikkel om ekologiese diversiviteit in stand te hou in die biologiese netwerk van natuurlike en semi-natuurlike gebiede in die stasd Kaapstad. Hiermee bied ek n klassifikasie protokol aan wat ontwikkel is uit n literatuuroorsig en gebaseer op die moontlikheid om UIPS uit te wis en die wydverspreide UIPS te groepeer asook om nuwe (opkomende) UIPS en potensiële uitwissingsteikens in verskillende bestuurstrategieë te kategoriseer. Daarbenewens het ek n model vir die prioritisering van opkomende UIPS (vroee opsporing en spoedige reaksie strategie) vir die Metropolitaanse gebiede van Kaapstad aangeneem en getoets. Vir hierdie navorsing het ek gefokus op die opkomende indringer Hypericum canariense en gebruik gemaak van lesse geleer uit die voorafgaande hoofstukke om die moontlikheid van uitwissing van hierdie spesie te bespreek. Ek het bevind dat UIPS se voorkoms (volopheid) die hoogste was by die stedelike wildland-koppelvlak (peri-stedelike sone). Ek het vasgestel dat versteuring in die natuurlike en semi-natuurlike gebiede by die peri-stedelike sone n beduidende rol speel in die indringing van UIPS na natuurlike areas. (In my klassifikasie protokol demonstreer ek dat die gebied van besmetting en die tempovan die UIPS se indringing kritiese aanwysers is t.o.v. die klassifikasie van UIPS as opkomend of wydverspreid, en vir die identifisering van potensiële uitwissingsdoelwitte (daaroplettend dat die drie hoof bestuurstrategieë vir UIPS versagting, uitwissing en beperking is). Verder, die hoof kriteriums gebruik in die prioritisering van opkomende spesies in die Metropool van Kaapstad is verspreiding, negatiewe impak,hoe maklik beperking geïmplimenteer sal kan word en indringingspotensiaal. Ek het gevind dat die opkomende indringer, H. canariense, geskik is vir uitwissing en dat dit ongeveer ZAR 57000 oor n tien jaar periode sal kos om die spesie uit te wis. Ek het tot die gevolgtrekking gekom dat stedelike gebiede ‘n noodsaaklike rol speel in effektiewe UIPS beheer en nie onderskat moet word t.o.v. hulle aandeel in die verspreiding van UIPS na omliggende natuurlike gebiede nie. Die peri-stedelike sone behoort die fokus te wees vir effektiewe bestuurspraktyke om toekomstige gesonde biologiese netwerke te verseker. Natuurbewaarders en land bestuurders moet spesies klassifiseer en prioritiseer vir effektiewe bestuurstrategieë, eerder as om n spesies na willekeur aan te pak, terwyl fondse beperk is. Nuwe, opkomende spesies moet ondersoek en geëvalueer word t.o.v. die moontlikheid van hulle effektiewe uitwissing voordat potensiële duur en uitgerekte uitwissing programme geïmplimenteer word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/110057
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