Abstract
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.
Highlights
The rise of global trade and long-distance transportation has resulted in an exponential increase in the number of invasive alien species globally (Lockwood et al, 2013)
Trees were only acknowledged as major invasive species during the early 1980s, but there has been a rapid increase in the number of invasive alien trees, the extent of invasions, and the magnitude and types of impacts in recent decades (Richardson and Rejmánek, 2011; Richardson et al, 2014)
We categorized all data points following the criteria proposed by Pyšek et al (2004) and Richardson et al (2011) as follows: “native”; “introduced”; “naturalized”; “widely invasive”
Summary
The rise of global trade and long-distance transportation has resulted in an exponential increase in the number of invasive alien species globally (Lockwood et al, 2013). Woody plant species are very well represented in national and regional lists of invasive plant species in South Africa, and species in the genera Acacia, Hakea, Eucalyptus, Pinus and Prosopis are the dominant invasive plant species in many parts of the country (Richardson et al, 1997) Most of these species have long residence times (N 100 years) and have been widely planted in the country (Wilson et al, 2007). Many other alien tree species, some of them with long residence times, have not yet become widespread invaders Some of these will probably never become important invaders, but others are likely in the lag phase between introduction and rapid spread that characterizes many invasions. Limited resources mean that control efforts need to be carefully prioritized (Nel et al, 2004; Van Wilgen et al, 2011, 2012)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
