The Risks Associated with Weed Spread in Australia and Implications for Natural Areas

Abstract

Most recently naturalized weeds (invasive non-native plant species, or species growing outside their natural range) in Australia are still only locally distributed, so it is critical to identify the pathways by which these and more widespread species are most likely to spread and to identify the domestic sources from which they are most likely to emerge. Our research sought to identify which weed sources and pathways account for the majority of weed ingress, which pathways pose the greatest risk, how these risks are changing, and how pathway management strategies might be improved. These questions were addressed through a review of literature and a survey of Australian weed experts. Twenty-four sources and 17 natural and human-assisted pathways were identified and assessed. The most significant weed spread pathways in Australia appear to be the trade in ornamental plants and movement of machinery and vehicles, while other important pathways include fodder trade, aquarium plant trade, agricultural produce, and water. Economic and demographic trends, and changing climate, are likely to contribute to growing importance of a range of weed spread pathways in the future. Pathway risk assessment makes it possible to target scarce weed control resources, policy measures, and research efforts by highlighting the pathways that have the greatest potential (in terms of likelihood and potential magnitude) to spread weeds, now and in the future. Similarly, it informs natural area managers as they instigate control and management tools that address the highest risk means by which weeds might enter and spread through their area of responsibility.