Pests and diseases pose a growing threat to woodlands from both endemic sources, and increasingly, from interregional transmission. Strong comparative analyses of this threat are needed in order to develop preventative measures. Such analyses should include estimates of the potential worst-case loss from all relevant pest and disease (P&D) threats to key tree species. Existing approaches tend to focus on individual assessments of the risk from a single pest or disease, or assessments of overall trends. Effective risk management requires more comprehensive quantified assessments of the overall threat to woodland that includes comparisons of the threat to individual tree species and identification of the potentially most damaging P&Ds. Such assessments support important policy and management decisions including species selection; preventative action; and the size of buffers against losses from forest carbon projects. Here we present a new approach that supports a systematic, risk-based assessment of the future threat to a given woodland from all known individual P&Ds, and to constituent individual tree species, based on a risk management approach taken from the finance sector, but hitherto not applied in an ecological context. Unknown or unidentified pests and diseases can systematically be added in future as identified. We demonstrate the method through a case study evaluating the threat to projects certified under the UK's Woodland Carbon Code. The approach can be adapted to any woodland resource worldwide. Its novelty lies in the simplification of complex threats, from numerous pests and diseases, to measures that can be used by a range of forest stakeholders.

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