Geographic differentiation of management objectives for invasive species: a case study of Hymenachne amplexicaulis in Australia.
Management of invasive species depends on local actions but these will be more effective and efficient when they are part of a broader scale strategic approach. We advocate geographic differentiation as a key element of broad-scale strategic plans for widespread weeds. We assert that different objectives and approaches are appropriate for different parts of a species' introduced range and areas that it might yet invade. Management zones should reflect the habitat preferences and dispersal mechanisms of the species being targeted and the spatial patterns of the invaded region. This approach is exemplified using the case of the invasive wetland grass Hymenachne amplexicaulis in Australia. Geographic differentiation is appropriate for this species because further spread is inevitable unless effective action is taken, there is substantial spatial variation in the risk of invasion and in its impacts and control options and values attributed to the species differ widely from region to region. We define four distinct objectives (prevention, eradication, containment and asset protection) and propose a continent-wide strategy based on 21 management zones that cover mainland Australia and relevant off-shore islands. One of the four objectives is assigned to each zone, commensurate with the status of the plant and the feasibility of achieving particular outcomes. This approach could be usefully applied to more effectively address the broad-scale management of other invasive species.