Modelling integrated weed management of an invasive shrub in tropical Australia

1. Most invasive plant species are not well controlled and where biocontrol programs are in place only one third are fully successful. Integrated weed management (IWM) emphasises the use of several complementary control measures. Choosing which combinations will yield control and how biocontrol fits within the strategy requires detailed knowledge of the dynamics of the target and its ecosystem. 2. We used models of increasing complexity to determine which parameters affect site occupancy of an invasive shrub, Mimosa pigra L. in tropical Australia. Two introduced biocontrol agents have spatial effects on both plant fecundity and the probability of recolonisation after senescence. We incorporated biocontrol effects into IWM models with disturbance, mechanical control, herbicide and fire. The models were parameterised from experimental and field data. 3. Models indicate that the reduction in fecundity is not the most important impact of biocontrol; rather it is through defoliation at the edges of stands allowing grasses to out-compete M. pigra seedlings. We demonstrate that biocontrol alone is only successful at low disturbance and seedling survival and even then, current biocontrol agents would take decades to reduce a stand to