Abstract
Protected areas face mounting pressures, including invasion by alien plant species. Scientifically sound information is required to advise invasive species management strategies, where early detection and rapid response is particularly important. One approach to this is to determine: (i) the relative importance of pathways of invasion by which a species is introduced, (ii) the range of likely impacts associated with each species, and (iii) the relationship between pathways and impacts, to assess the relative threats posed by different pathways of alien species introductions. This assessment was performed on 139 alien plants that are invasive across the South African National Parks (19 national parks, covering ~39,000 km2), and based on available literature and expert opinion, known to have negative ecological impacts. For each species the likelihood of being introduced by each of eight pathways, and of having negative impacts in each of 13 identified impact categories, was assessed. The similarity of impact and pathway types between species was assessed using the Jaccard index and cladograms. Differences in the prevalence of impacts and pathways and relationships between these were assessed using a Chi-squared contingency and Generalised Linear Model. Nearly 80% of the species are ornamental plants and about 60% are also dispersed by rivers, highlighting the importance of managing ornamental species and surveillance along rivers in preventing future invasions. As to the impacts, ~95% of the species compete directly with native species and 70% change the physical structure of the environment. The majority of species exert multiple impacts, with 70% of species assessed having five or more impacts. There was a significant positive relationship between the number of pathways via which a species can be introduced into an area and the number of potential impacts they can have. This suggests that species using multiple pathways reach a wider range of suitable habitats, increasing the potential for different kinds of impacts over a wider area.
Highlights
Protected areas represent some of the last opportunities to retain intact or at least relatively naturally functioning ecosystems with a near full complement of biological diversity (e.g. Geldmann et al 2013)
We used a combined assessment of the impacts that an invasive species can have and the potential pathways of invasion, to develop an approach to determine species of highest concern and inform management strategies. To do this we assessed 139 alien plants across the South African National Parks estate that are considered to be transformer or potential transformer species and determined: (i) the relative importance of pathways of invasion by which a species is introduced, (ii) the range of likely impacts associated with each species, and (iii) the relationship between pathways and impacts, to assess the relative threats posed by different pathways of alien species introductions in different parks and biomes
We used South African National Parks (SANParks) as a model system as it has 752 alien plant species recorded across 19 national parks (Spear et al 2011, Foxcroft et al 2017)
Summary
Protected areas represent some of the last opportunities to retain intact or at least relatively naturally functioning ecosystems with a near full complement of biological diversity (e.g. Geldmann et al 2013). Geldmann et al 2013) They are increasingly becoming disconnected remnants of natural habitats embedded within a larger mosaic of varying land use types (DeFries et al 2005, Koh and Gardner 2010, Meiners and Pickett 2013). As such, these areas are threatened by a wide range of anthropogenic actions (Carey et al 2000). This necessitates careful prioritisation and allocation of funds to maximise long-term benefits (Leung et al 2002, Evans et al 2011, van Wilgen et al 2016)
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