A dispersal-constrained habitat suitability model for predicting invasion of Australian alpine vegetation by Orange Hawkweed (Hieracium aurantiacum)

Developing tools to predict the location of new biological invasions is essential if exotic species are to be controlled before they become widespread. Currently, alpine areas in Australia are largely free of exotic plant species but face increasing pressure from invasive species due to global warming and intensified human use. To predict the potential spread of highly invasive Orange Hawkweed (Hieracium aurantiacum) from existing founder populations on the Bogong High Plains in southern Australia, we have developed a spatially-explicit dispersal-constrained habitat suitability model. The model combines a habitat suitability index, developed from disturbance, site wetness and vegetation community parameters, with a phenomenological dispersal kernel that uses wind direction and observed dispersal distances. After generating risk maps that defined the probability of invasion across the study area, we intensively searched several locations to validate the model. The highest probability of H. aurantiacum establishment was southeast from the initial infestations. Native tussock grasslands and disturbed areas had high probabilities of H. aurantiacum establishment. Extensive field searches failed to detect new populations however time-step validation, using 1998-2000 locations, accurately predicted the occurrence of all post-2003 populations in areas identified as having a high probability of occurrence. No H. aurantiacum was found in areas outside the predicted dispersal plume. This suggests our model has good predictive power and will improve the ability to detect populations and prioritize areas for on-going surveillance.