Determining optimal clearing treatments for the alien invasive shrub Acacia saligna in the southwestern Cape, South Africa

The results of a replicated field-scale trial of a range of control treatments for Acacia saligna were used to create a probabilistic model of the effects of repeated treatment applications. Using estimates of costs per plant treated for each treatment and for each of four size classes of plants, it was possible to compute the costs for every treatment combination. A Markov-chain model was created integrating all the transition probabilities and costing factors. A computerised system allows for the input of different initial densities and size-class distributions, different target population specifications, the variable use of fire during the control programme and different programme durations. The system allows for the a priori determination of optimal control treatment combinations and sequences and provides managers with forward estimates of budgetary requirements for control programmes. The approach developed can be applied to the control of other invader plants by modifying the transition probabilities and costing factors.