Ranked current and anticipated threats to Scotland from global Phytophthora species

To develop a ranked list of threats to Scotland from Phytophthora species we joined predictions from new models of probability of arrival into the UK through trade (Barwell et al. 2025), and current climate suitability for establishment in 342 pixels (approximately 15x15 km grid) in Scotland (Green et al. 2024). These were integrated with information on Phytophthora distributions, host associations and interceptions extracted from a global database of Phytophthora records. Potential impacts on Scotland's priority plants and habitats were assessed through scoring the number of susceptible host genera on Scotland's Biodiversity List, and within NVC habitats and National Forest Estate Subcompartments in Scotland. Each risk metric was scored from 0 (low risk) to 3 (high risk) and these scores were summed to produce an overall risk score for each Phytophthora species. Some species are missing scores for climate suitability in Scotland (n=37) or UK arrival risk (n=89) due to the absence of data on source regions or thermal tolerance traits to inform the underlying models.

The final report (L. J. Barwell, G. Amankwaa, F. Asaaga, K. Turvey, D. E. L. Cooke, R. Mitchell, & B. V. Purse (2025). Improved preparedness for Phytophthora prevention in Scotland: Project Final Report. PHC2023/02. Scotland's Centre of Expertise for Plant Health (PHC). https://www.planthealthcentre.scot/projects/improved-preparedness-Phytophthora-prevention-scotland) was peer-reviewed by Scotland’s Plant Health Centre. Underlying models of pathogen-specific climate suitability have been evaluated against independent detection data in the UK and Europe where available. Arrival risk models integrating trade flows from source regions and pathogen traits explained up to 78% (61.8, 84.6) of variance in the probability of a new detections since 2005 across Phytophthora species globally. Interceptions and host associations were derived from a global cross-sectoral database compiling information from multiple data providers and sectors to capture the broadest picture possible of Phytophthora host use and prevalence. Where possible, pathologists validated the records and rankings against their knowledge of pathogen behaviour.

However, users of the list should be mindful that not all Phytophthora species are included in the ranking presented here due to lack of knowledge on their distributions and hosts, and that a considerable proportion of global Phytophthora diversity may be unknown to science. Some of the most impactful Phytophthora species were only described after their emergence in regions that were likely outside of their native range and with unknown source regions. Moreover, quantitative metrics capturing the severity of interactions (e.g. pathogenicity) between Phytophthora species and their hosts are only available for a fraction of the host-pathogen interactions captured in our data and are not considered within the qualitative ranking presented here.

Related datasets

Spatial risk analysis for Phytophthora x alni infection of alder fragments in Scotland

Spatial risk analysis for Phytophthora pinifolia infection of Caledonian Pinewood Inventory fragments in Scotland

Spatial risk analysis for Phytophthora pluvialis infection of Douglas fir and western hemlock in Scotland

Spatial risk analysis for Phytophthora ramorum infection in Larch fragments in Scotland

Spatial risk analysis for Phytophthora ramorum infection in heathland fragments in Scotland