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South Africa has a major problem with invasive plant species. Many species have long residence times, are well established, and have large invasive ranges, whereas others are still in the early stages of invasion. Predicting the full extent of invasions for species that have only recently started spreading is important for guiding management strategies. Ailanthus altissima is a widespread invasive species in many parts of the world. Although it has had a long residence time in South Africa, it is yet to replicate the extent of invasiveness and major impacts reported for the species in other parts of its adventive range. We mapped the countries in which A . altissima has been reported and evaluated the invasion status of the species in each (i.e. the position of the species on the introduction-naturalization-invasion continuum as conceptualized by Richardson and Pyšek, 2012). We then mapped the current distribution in more detail for South Africa. The species is known to be present in at least 51 countries and is invasive in 23 countries. Ailanthus altissima is present in all South African provinces except Limpopo and is most common and abundant in the Western Cape, Gauteng, Eastern Cape, and the Free State. We applied species distribution modelling using global distribution data to determine parts of the world, and in particular regions within South Africa, that are climatically suitable for the species. Large parts of Africa are potentially invasible by this species. Seven regions in South Africa were identified as high-risk areas for invasion by A . altissima . The species is already far too widespread in South Africa for eradication at the national scale to be feasible. A national strategy for managing the species should focus on: 1) early detection and rapid response in areas identified as climatically suitable and where the species is not already present; and 2) local and regional-scale initiatives based on objective prioritization in terms of feasibility of management success and asset protection. [ABSTRACT FROM AUTHOR]

Invasive alien plants pose a threat to biodiversity worldwide, and the costs of control are ever-escalating. Early detection and prediction of areas potentially at risk is crucial to minimise ecological and socio-economic costs. Maxent was used to predict the area within which Ageratina adenophora can potentially naturalise and spread in South Africa. The model was set up with 1020 occurrence records (10 replicates, 70% of records for calibration:30% for validation), and four climatic predictor variables. Background data were selected using Köppen–Geiger (vegetation-based) climate classification zones. All model replicates performed better than random in both binomial tests of omission and ROC analysis. The model was statistically significant and its mean AUC was 94%. The modeled prevalence was 0.21 and the sensitivity was 0.99. The Eastern Cape, KwaZulu-Natal, Mpumalanga and Gauteng provinces have climatic conditions indicative of a high potential for invasion by A. adenophora, followed by parts of the Western Cape, North West and Limpopo provinces. The model predicted areas beyond the current distribution, suggesting that A. adenophora has potential for further spread, and that searches for it need to be made beyond its currently known distribution. On the other hand it appears not to have spread into some climatically suitable areas near its current occupancy sites, such as throughout the KwaZulu-Natal mist belt, suggesting that unknown biotic (including human) or abiotic factors are also limiting its naturalization and require further study to be identified. [ABSTRACT FROM AUTHOR]