Translocating plants to natural habitats is a long-standing conservation practice but is growing in magnitude to deliver international targets to mitigate climate change and reverse biodiversity loss. Concurrently, outbreaks of novel plant pests and pathogens are multiplying with increased global trade network connectivity and larger volumes of imported plants, raising concerns that restoration plantings may act as introductory disease pathways. We used UK common juniper, subject since ~1995 to conservation plantings and now experiencing significant mortality from the non-native pathogen Phytophthora austrocedri Gresl. & E. M. Hansen, as an example species to explore the availability of monitoring data that could be used to assess disease risks posed by planting. We compiled spatial records of juniper planting including qualitative data on sources of planting material, propagation settings and organization types that managed planting projects. We found that juniper planting activity expanded every decade since 1990 across the UK and while not all planting resulted in outbreaks, 19% of P. austrocedri detections were found within 2 km of a known planting. We highlight the scale and diversity of organizations raising and planting juniper, as well as the lack of source material traceability, and suggest that cross-sector collaboration and changes in practice are required to reduce the risks of pathogen introduction posed by restoration planting.

Increased imports of plants and timber through global trade networks provide frequent opportunities for the introduction of novel plant pathogens that can cross‐over from commercial to natural environments, threatening native species and ecosystem functioning. Prevention or management of such outbreaks relies on a diversity of cross‐sectoral stakeholders acting along the invasion pathway. Yet, guidelines are often only produced for a small number of stakeholders, missing opportunities to consider ways to control outbreaks in other parts of the pathway. We used the infection of common juniper with the invasive pathogen Phytophthora austrocedri as a case study to explore the utility of decision tools for managing outbreaks of plant pathogens in the wider environment. We invited stakeholders who manage or monitor juniper populations or supply plants or management advice to participate in a survey exploring their awareness of, and ability to use, an existing decision tree produced by a coalition of statutory agencies augmented with new distribution maps designed by the authors. Awareness of the decision tree was low across all stakeholder groups including those planting juniper for restoration purposes. Stakeholders requested that decision tools contain greater detail about environmental conditions that increase host vulnerability to the pathogen, and clearer examples of when management practices implicated in pathogen introduction or spread should not be adopted. The results demonstrate the need to set clear objectives for the purpose of decision tools and to frame and co‐produce them with many different stakeholders, including overlooked groups, such as growers and advisory agents, to improve management of pathogens in the wider environment.

The oomycete plant pathogen, Phytophthora austrocedri , is an aggressive killer of cypress trees causing severe mortality of Chilean cedar ( Austrocedrus chilensis ) in Argentina since the 1940s and now common juniper ( Juniperus communis s.l.) in the UK. Rapid mortality of key UK juniper populations was first observed in the early 2000s; the causal agent of mortality was confirmed as P. austrocedri in 2012 and the pathogen has now been widely detected - but is not ubiquitous - in juniper populations across Scotland and England. Although juniper has a broad distribution across the northern hemisphere, the UK incidence of P. austrocedri remains the only confirmed infection of juniper populations globally. Juniper is an important species for biodiversity, so it is imperative to understand the abiotic and biotic drivers of emergent P. austrocedri infection to inform detection, containment and conservation strategies to manage juniper populations across the full extent of its range. As management of UK juniper populations is primarily conducted at a local level, we investigated field scale drivers of disease – in three, geographically separate populations with different infection histories. Variation in the proportion of juniper showing symptoms - discoloured or dead foliage – was measured using stratified sampling across along key environmental gradients within each 100-hectare population, including juniper density identified from aerial imagery. Potential predictors of infection included altitude, slope, distance to nearest watercourse, soil moisture (mean percentage volumetric water content), area of red deer browsing damage and area of commonly associated vascular plant species. We assessed support in the data for alternative models explaining the spatial distribution of P. austrocedri symptoms using full subset covariate selection and Deviance Information Criteria (DIC). Despite differences in environmental gradients and infection histories between populations, area of juniper symptomatic for P. austrocedri increased with waterlogging, increasing with soil moisture in sites where soils had higher peat or clay contents, and decreasing with proximity to watercourses where sites had shallower, sandier soils. These results are consistent with key drivers identified at both local and landscape scale in Chilean cedar. Our approach enables identification of site-specific disease management strategies including prioritisation of inspections in microsites with high soil moisture and promoting conservation measures such as creation of sites for natural regeneration in drier microsites to minimise pathogen spread and maximise the resilience of existing juniper populations.