Designing weed containment strategies: An approach based on feasibilities of eradication and containment

Aim: To refine strategies for the containment of weed invasions. Location: World-wide, but primarily Australia and Galapagos Islands. Methods: By employing theoretical and semi-quantitative models, we estimated conditions under which barrier zones should be established and maintained around core infestations and when eradication of outliers should be attempted. Reference was made to published information on generic dispersal distances and the biological characteristics of a wide variety of weeds, including the targets of well-documented successful and failed eradication programmes. Results: When weeds generate fat-tailed dispersal distance distributions having relatively high median values, search efficiency will be compromised if barrier zones are employed. The theoretical model developed supports the non-use of barrier zones in management strategies targeting tree weeds that are predominantly wind dispersed, or any species that are dispersed by birds or larger wild mammals. Many weeds that have major impacts on natural ecosystems fall within these categories. Eradication of outliers generally should not be considered where weeds have short juvenile phases and long-lived seeds. Four containment substrategies are distinguished on the basis of whether barrier zones around core infestations are established and whether the eradication of outliers is attempted. The suitability of individual substrategies is indicated for weeds of a variety of growth forms, occurring in a range of land uses, and a decision tree is presented for categorical assignment. Main conclusions: A structured approach to the development of weed containment strategies will help to promote the efficient use of limited resources. Targeted species vary according to both the relative ease with which core populations can be contained and outlier populations eradicated - containment strategies should be designed accordingly. This study shows that semi-quantitative models can be powerful adjuncts to their theoretical counterparts in support of decision-making for the management of weed invasions.