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.
Highlights
Every country needs up-to-date lists of introduced species to ensure that management actions are directed appropriately to deal with taxa at all stages of the introductionnaturalisation-invasion continuum (Latombe et al 2017, McGeoch et al 2012, Regan et al 2002)
We found evidence that 141 Australian Acacia species have been introduced to South Africa (Table 1)
In terms of Blackburn et al.’s (2011) Unified Framework for Biological Invasions, 13 of these species are in category E, two are in category D2
Summary
Every country needs up-to-date lists of introduced species to ensure that management actions are directed appropriately to deal with taxa at all stages of the introductionnaturalisation-invasion continuum (Latombe et al 2017, McGeoch et al 2012, Regan et al 2002). Wattles have been introduced to many parts of the world for many purposes (Le Maitre et al 2002, Kull and Tassin 2012) and they have played a major role in improving the livelihoods of communities (Kull et al 2011, van Wilgen et al 2011) and in economic growth (Griffin et al 2011, Richardson et al 2011). Despite these benefits, some wattle species have become widespread invaders, threatening biodiversity by transforming ecosystems (Le Maitre et al 2000, 2011)
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