Dealing with 'new' alien plants: risk assessment and risk management.
Decisions on how to deal with newly detected alien plant incursions need to be made against a background of uncertainty, initially with respect to the weed risk posed. Then, should a high risk be indicated there will be further uncertainty regarding how best to manage it. If a coordinated management strategy (e.g. eradication) is favoured, its feasibility and likelihood of success will depend inter alia upon the allocation of sufficient resources, but what constitutes 'sufficient' is difficult to estimate. Weed risk assessment (WRA) is challenging, in part owing to an incomplete understanding of the mechanisms of invasiveness and, especially, impact. Desktop post-border WRA procedures are available, but there appears to have been little attempt to estimate the invasiveness or potential impact of new incursions based on real-time field observations. I discuss how such observations, in conjunction with weed history (where available), could be used to determine appropriate incursion responses. A recent categorisation of species in relation to biological impedance to eradication is recommended as a qualitative aid to estimating the resources required for eradication. Implications for the assessment of containment feasibility are also considered.