Investigating the role of restoration plantings in introducing disease — a case study using Phytophthora

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.