Identifying hotspots of alien plant naturalisation in Australia: approaches and predictions

The early detection of newly naturalised alien species is vital to ensuring the greatest chance of their successful eradication. Understanding where species naturalise most frequently is the first stage in allocating surveillance effort. Using Australia’s Virtual Herbarium, we compiled the collection records for all plant species in Australia. We controlled for potential spatial biases in collection effort to identify areas that have an elevated rate of first records of alien species’ occurrence in Australia. Collection effort was highly variable across Australia, but the most intense collection effort occurred either close to herbaria (located in cities) or in remote natural environments. Significant clusters of first records of occurrence were identified around each state’s capital city, coinciding with higher collection effort. Using Poisson point process modelling, we were able to determine the relative influence of environmental and anthropogenic factors on the spatial variation in the risk of species naturalisation. Effort-corrected naturalisation risk appeared to be strongly related to land use, road and human population densities, as well as environmental factors such as average temperature and rainfall. Our paper illustrates how the risk of naturalisation at a location can be estimated quantitatively. Improved understanding of factors that contribute to naturalisation risk enhances allocation of surveillance effort, thereby detecting novel species sooner, and increasing the likelihood of their eventual eradication.