Optimal eradication: when to stop looking for an invasive plant

Area of Science:

• Ecology
• Conservation Biology
• Environmental Economics

Background:

• Invasive species eradication efforts often face challenges due to imperfect detection methods and persistent seed banks.
• Current practices for declaring eradication rely on ad hoc decisions, seed bank longevity estimations, or arbitrary confidence thresholds.
• These methods may not be scientifically or economically optimal for determining successful eradication.

Purpose of the Study:

• To develop and evaluate an economic framework for determining the optimal stopping time for invasive species surveys.
• To minimize the net expected cost of eradication programs by balancing survey costs against potential damage costs.

Main Methods:

• Development of a theoretical model using stochastic dynamic programming to determine the optimal number of years of absent surveys.
• Formulation of an economic approach that compares the expected costs of continued surveying with the expected benefits of confirmed eradication.
• Application of the model to a case study of *Helenium amarum* eradication.

Main Results:

• The optimal stopping time represents a trade-off between ongoing survey expenses and the risks associated with premature eradication declaration.
• A simple rule of thumb demonstrated comparable results to the exact optimal solution derived from stochastic dynamic programming.
• Analysis of the *Helenium amarum* eradication program indicated that the stopping time was precautionary, considering the parameter ranges.

Conclusions:

• An economic approach provides a more robust method for determining eradication stopping times than arbitrary confidence levels.
• The optimal stopping time balances the costs of continued monitoring against the potential economic and ecological impacts of species resurgence.
• The developed framework offers a valuable tool for optimizing resource allocation in invasive species management programs.