DOI: 10.5285/f6809e00-91cb-494d-babd-5d60d938ad97
title: Spatial risk analysis for Phytophthora ramorum infection in Larch fragments in Scotland

description: This dataset maps the risks of Phytophthora ramorum infection for 79062 larch fragments identified in Scotland, of which 79060 were assigned a risk score. Two fragments without climate and/or habitat suitability scores were excluded. Fragment risk scores integrate multiple risk factors. The primary risk factor is climate suitability for P. ramorum using pathogen-specific temperature-dependent growth curves and a relative humidity threshold. Other risk factors integrated are proximity to larch/infected larch within 500m or 5000m and other (non-Larch) wider environment infections within 1500m. Presence of alternative hosts are scored using habitat suitability within the fragment for sporulating hosts (Vaccinium myrtillus, V. vitis-idaea, Acrostaphylos uva-versi) and the reservoir host Rhododendron ponticum. Additionally, proximity to inspected premises with confirmed infections and the presence of water courses are also assessed. The maximum possible risk score for a larch fragment is 12. Fragments were also classified as low, medium or high risk. 
description: We employed an iterative and collaborative co-production process that brought together stakeholders with diverse expertise from across Scotland’s plant health sector, including forestry, conservation, horticulture, and government agencies to co-design the risk framework. Larch fragments in Scotland were compiled from the National Forest Estate Sub-compartments Scotland 2019, the Native Woodland Survey of Scotland, survey data, Statutory Plant Health Notices and larch layers from Scottish Forestry, and a Phytophthora database. Any areas felled since 2013 were identified and removed using the National Forest Inventory GB from 2013 to 2023 and completed Statutory Plant Health Notices. Key risk factors and their scoring were agreed with 15 cross-sectoral stakeholders through a self-completion survey and two workshops. The risk scoring has been adjusted to reduce the emphasis on proximity to inspected premises as a pathway of spread, reflecting stakeholder perspectives on improved biosecurity practices in trade.  The previous risk analysis for P. ramorum infection for Scotland’s larch fragments (https://doi.org/10.5285/29726cda-09f5-4661-8fd4-ddaa5555466a) has been updated to reflect the removal of larch since 2013 through Statutory Plant Health Notices and other clear-felling, to include new P. ramorum detection data in larch woodlands and inspected premises provided by Scottish Forestry and SASA. In addition, new climate suitability models of pathogen growth are used to score risk of establishment and new species distribution models have been used to score risks of transmission from alternative host species of P. ramorum. The scored fragment data were intersected with the boundaries of local authorities, Scottish Forestry Conservancies, and P. ramorum policy zones to summarise the distribution of risks across regions in Scotland.

The final report was peer reviewed by the Plant Health Centre. In addition, a knowledge integration and validation workshop (November 13, 2024) examined the adequacy of the outputs for horizon scanning and decision-making across sectors. Validation of the climate suitability models for P. ramorum has been attempted using independent UK and European detections for P. ramorum. This spatial risk framework cannot yet be fully validated until future detection data are available, because previous detections are used within the model and are not independent of the risk scores assigned. However, the previous risk framework for Larch has been cross-validated against subsequent, independent P. ramorum detections, as proof of concept.