Assessing weed spread in Australia using pathway risk analysis

While considerable effort has been made to establish how weeds and potential weeds enter Australia, no comprehensive studies had previously ascertained the ways that weeds spread once present within Australia, or assessed the relative threats or risks (likelihood and potential magnitude) of different weed 'sources' and 'pathways' due to species, quantity of propagules, distance and sensitivity of the invaded environment. Using a pathway risk analysis approach, this research sought to identify: which weed sources and pathways account for the majority of weed ingress; which pathways pose the greatest risk; ways in which these risks are changing (e.g. due to changing climate, economic or demographic patterns); and how pathway management strategies might be improved. These questions were addressed through a review of literature and a survey of Australian experts working in weed science, extension, and with relevant government agencies. Twenty-four 'sources' and seventeen natural and human-assisted 'pathways' were identified and assessed. The survey found the most significant weed sources were transport sites, land in transition, pastures and rangelands, ornamental horticulture, private gardens and arable/cropping land. When prevalence, risk and related weed sources were taken into account, the most significant spread pathways in Australia were trade in ornamental plants and machinery and vehicles - a finding that is supported in the literature. Nearly all pathways will be equally or more important in the future due to variable climate and changing economic and demographic patterns. Experts thought all pathways were inadequately managed and, while improvements will need to be pathway-specific, a general strategy of 'negative' regulation, 'positive' management, and more Australian-focussed research was suggested.