Estimating the value of a nation's terrestrial border biosecurity system

Estimating the economic damages of invasive species and the value of their management is critical for informing policymakers and developing effective biosecurity strategies. However, traditional assessments often double-count damages and fail to account for ecological complexity. Here, we introduce a new asset-based modelling approach, the Value of Biosecurity Model, which simultaneously models the invasion of multiple co-occurring focal species to deliver more accurate predictions. This model offers a holistic framework for assessing the damages of invasive species and enables the value of a biosecurity system to be conceptualised and estimated in terms of the damages that it avoids or mitigates. Using Australia's terrestrial border biosecurity system as a case study, we demonstrate the Value of Biosecurity Model's application at the national level by simulating the establishment, spread, and damage of 40 high-risk invasive species for up to a 50-year period on a 2.5 km national grid impacting 16 asset layers, and highlight the model's flexibility to generate results for specific regions or timeframes as well as specific threats and assets/industries. Results indicate that, with the terrestrial border biosecurity system in place (at a cost of AUD$10.45 billion), Australia can avoid approximately AUD$314 billion in present value damages over 50 years, reflecting a significant return on investment. In addition, the model can contextualise the economic damage caused by individual invasive species within a species-co-occurring framework, providing estimates of economic damages for specific species across different time steps. Given the advantages of the Value of Biosecurity Model, we recommend integrating it into biosecurity risk management to inform future investment decisions and support more effective resource allocation.