How to account for habitat suitability in weed management programmes?

Designing efficient management strategies for already established invasive alien species is challenging. Here, we ask whether environmental suitability, as predicted by species distribution models, is a useful basis of cost-effective spatial prioritization in large-scale surveillance and eradication programmes. We do so by means of spatially and temporarily explicit simulations of the spread of a case study species (Ambrosia artemisiifolia L.) in Austria and southern Germany under different management regimes. We ran these simulations on a contiguous grid of the study area with each grid cell (similar to 35 kmA(2)) characterized by a habitat suitability value derived from the predictions of a species distribution model. The management regimes differed in terms of (a) a minimum habitat suitability rank p (suitability threshold) used to separate cells for surveillance from those which are not controlled; and (b) the strategy for selecting cells for annual campaigns from the pool defined by p. According to the results (i.e., number of cells infested in 2050 as well as infested on average per year) the most efficient way to base surveillance on suitability is to define the temporal sequence of management according to the grid cells' suitability ranks. Management success declines sharply when the suitability threshold is set too high, but only moderately when it is set too low. We conclude that accounting for environmental suitability is important for large-scale management programmes of invasive alien species and that species distribution models are hence useful tools for designing such programmes.