STRATEGIES FOR CONTROLLING WEEDS IN NATURAL ECOSYSTEMS: A DYNAMIC OPTIMISATION APPROACH

Scotch Broom is a serious environmental weed in Barrington Tops National Park and the surrounding areas. It poses a significant threat of reducing the diversity of flora in invaded ecosystems and generating a false understorey. It also harbours feral pigs, which perpetuate the cycle of disturbance. To address problems caused by Scotch Broom in the 10000 hectares already invaded and the threat of further invasion, it is vital to understand why this species is able to invade and persist in Australian ecosystems. Such understanding will be the key to developing effective management strategies, both to prevent further invasions and to suppress dominance of Scotch Broom. The budget available for weed control, pests control, and other activities in the Park, is limited and so managers must identify control strategies that are efficient and sustainable. A deterministic dynamic programming model is developed for this purpose in this paper. A simulation model, which captures Broom population dynamics, was developed first and takes account of two state variables, which are then incorporated in the dynamic program. The dynamic programming model contains these two state variables and five control variables. The state variables are the area occupied by Scotch Broom and the seed bank. The control variables are excluding tourists, manual pulling, herbicide application, feral pig control and biological control. We acknowledge the help of the NSW National Parks and Wildlife Service for providing us with the information required by the models. The National Parks and Wildlife Service already has an effective containment strategy for Broom. In the present paper, we attempt to develop a management strategy that covers the park area and surrounding agricultural areas. Preliminary results are presented and further information requirements are discussed.