Optimal control of a stochastic biological invasion

Although there have been numerous studies on the economics of weed control, relatively few of these studies have focused on natural ecosystems. The aims of this papers are: A) to identify the combination of control options that is optimal for blackberry (Rubus anglocandicans) in Australian natural ecosystems, B) to assess whether an integrated control strategy is superior to chemical-only strategies, C) to evaluate the economic net benefits of specific biologically oriented control methods (a rust and grazing by goats), D) to determine how changes in model parameters affect the optimal control strategy. To address these aims, a stochastic dynamic simulation model and a stochastic dynamic programming model are developed. The results indicate that, while an integrated strategy combining chemical and non-chemical control methods may be optimal in certain circumstances, it is not necessarily superior to a chemical-dominant strategy in all cases. Results show that in most cases a combination of herbicides and one physical control method (mowing) is optimal in the base-case scenario. However, if chemical efficacy is greater than in the base-case, the optimal strategy involves chemicals only. The results indicate that grazing goats for control of blackberry can be optimal despite its stochastic effectiveness and relatively low efficacy.