Polocies for the Management of Weeds in Natural Ecosystems: A Dynamic Programming Approach

Environmental weeds are plants that invade natural ecosystems and are considered to be a serious threat to nature conservation. Environmental weeds have been implicated in the extinction of several indigenous plant species, and they also threaten ecosystem stability and functional complexity. Historically, emphasis has been placed on chemical control, manual pulling of small plants, excluding tourists and feral pig control measures. Recently, biological control has been introduced to control weed infestations. These methods of control have been applied alternatively, with little consideration of the long- term effectiveness. As the threat from environmental weeds is becoming more fully recognised, an integrated, strategic, ecological and economical approach to weed management is needed. A deterministic dynamic programming model is developed for this purpose in this paper. A case study for the environmental weed scotch broom is presented, to assess the ways in which this approach can address the policy issues that face the community in the management of an environmental weed. The model takes account of the weed population dynamics and thirty-two combinations of control developed from the five basic control measures. The dynamic programming model is developed for three different cases, first with weed density as the state variable, second, with weed density and seed bank as state variables and third, with weed density and seed bank as state variables and with a budget constraint for the control variables. Results are