Browsing by Author "Magona, Nkoliso"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- ItemDetermining the invasive status of Australian Acacia species in South Africa, and the potential for eradicating species with limited distributions(Stellenbosch : Stellenbosch University, 2018-03) Magona, Nkoliso; Wilson, John R.; Richardson, David M.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: While widespread invasions of Australian acacia species (wattles) have been fairly well documented, very little is known about species that have no substantial commercial value or those that are not well-established invaders yet. South Africa has the highest number of invasive wattle species in the world. These have had negative impacts on the environment and socio-economy. However, the last detailed inventory of the group in South Africa was based on data collated forty years ago. In addition, there are several species with small naturalised populations that might pose a future risk. A recent study quantified different aspects of this “invasion debt” for wattles, both for South Africa and globally and found out that southern Africa has a large invasion debt. In Chapter 2 I aimed to determine how many Australian Acacia species are known to have been introduced to South Africa, which species are still present and what their status is. I visited herbaria, arboreta, botanical gardens and conducted field surveys in order to compile a list of introduced wattles, and used DNA barcoding to confirm the identity of these species. I found records for 114 wattle species introduced into South Africa, but I found the presence of only 50 species. Seventeen of these species are invasive (16 are in category E, one in category D2 in the Unified Framework for Biological Invasions); eight species have naturalised (category C3); and 25 species are present but are not known to produce seed in South Africa (category C1). Four of these occur in the Western Cape (three on the Cape Peninsula, A. piligera, A. retinodes and A. viscidula; 1 near Paarl, A. adunca) and two species, A. cultriformis, A. fimbriata in Grahamstown in the Eastern Cape. In Chapter 3, I focus on the potential to eradicate these six naturalised wattle species from South Africa. I carried out a systematic survey of populations and the surrounding areas. For each plant, I recorded plant canopy, height, stem basal diameter, presence or absence of reproductive structures and GPS coordinates. I then cut or pulled out the plants. I assessed the risk posed by these species using Australian weed risk protocol and lastly, I determined the current size of the seedbank for these species. Risk assessment showed that all of these species have high potential impact, hence, they should be considered as a threat. All of these species except A. retinodes can reach reproductive maturity within a year and three of these species have large seedbanks. If control efforts can continue to prevent reproduction, eradiation will be a matter of reducing the seed banks across the limited distributions for these species. I conclude that eradicating five of the species is feasible and annual clearing resurveys are recommended in order to prevent production of seeds. Acacia cultriformis was clearly at some point used in the ornamental plant trade and there are many isolated populations. This makes it difficult to find all plants and eradication is unfeasible. I conclude with Chapter 4, where I provided recommendations for listing and management.
- ItemEven well-studied groups of alien species might be poorly inventoried : Australian Acacia species in South Africa as a case study(Pensoft Publishers, 2018-06-26) Magona, Nkoliso; Richardson, David M.; Le Roux, Johannes J.; Kritzinger-Klopper, Suzaan; Wilson, John R. U.; Hufbauer, R.ENGLISH ABSTRACT: Understanding the status and extent of spread of alien plants is crucial for effective management. We explore this issue using Australian Acacia species (wattles) in South Africa (a global hotspot for wattle introductions and tree invasions). The last detailed inventory of wattles in South Africa was based on data collated forty years ago. This paper aimed to determine: 1) how many Australian Acacia species have been introduced to South Africa; 2) which species are still present; and 3) the status of naturalised taxa that might be viable targets for eradication. All herbaria in South Africa with specimens of introduced Australian Acacia species were visited and locality records were compared with records from literature sources, various databases, and expert knowledge. For taxa not already known to be widespread invaders, field surveys were conducted to determine whether plants are still present, and detailed surveys were undertaken of all naturalised populations. To confirm the putative identities of the naturalised taxa, we also sequenced one nuclear and one chloroplast gene. We found evidence that 141 Australian Acacia species have been introduced to South Africa (approximately double the estimate from previous work), but we could only confirm the current presence of 33 species. Fifteen wattle species are invasive (13 are in category E and two in category D2 in the Unified Framework for Biological Invasions); five have naturalised (C3); and 13 are present but there was no evidence that they had produced reproductive offspring (B2 or C1). DNA barcoding provided strong support for only 23 taxa (including two species not previously recorded from South Africa), the current name ascribed was not supported for three species and, for a further three species, there was no voucher specimen on GenBank against which their identity could be checked. Given the omissions and errors found during this systematic re-evaluation of historical records, it is clear that analyses of the type conducted here are crucial if the status of even well-studied groups of alien taxa is to be accurately determined.