Abstract
The multidisciplinary ‘Phyto-threats’ project was initiated in 2016 to address the increasing risks to UK forest and woodland ecosystems from trade-disseminated Phytophthora. A major component of this project was to examine the risk of Phytophthora spread through nursery and trade practices. Close to 4000 water and root samples were collected from plant nurseries located across the UK over a three-year period. Approximately half of the samples tested positive for Phytophthora DNA using a metabarcoding approach with 63 Phytophthora species identified across nurseries, including quarantine-regulated pathogens and species not previously reported in the UK. Phytophthora diversity within nurseries was linked to high-risk management practices such as use of open rather than closed water sources. Analyses of global Phytophthora risks identified biological traits and trade pathways that explained global spread and host range, and which may be of value for horizon-scanning. Phytophthoras having a higher oospore wall index and faster growth rates had wider host ranges, whereas cold-tolerant species had broader geographic and latitudinal ranges. Annual workshops revealed how stakeholder and sector ‘appetite’ for nursery accreditation increased over three years, although an exploratory cost-benefit analysis indicated that the predicted benefits of introducing best practice expected by nurseries outweigh their costs only when a wider range of pests and diseases (for example, Xylella) is considered. However, scenario analyses demonstrated the significant potential carbon costs to society from the introduction and spread of a new tree-infecting Phytophthora: Thus, the overall net benefit to society from nurseries adopting best practice could be substantial.
Highlights
The UK has a woodland resource of around 3.2 million hectares, which equates to13% of the total land area of the country
The incidence and diversity of Phytophthora species in water and plant samples collected from nurseries located in England, Wales and Scotland was examined over a threeyear period
The Phyto-threats project involved a consortium of scientists in disciplines ranging from plant pathology, ecological modelling, evolutionary genetics, economics, and social science as well as a range of consumer, practitioner, and policy stakeholders
Summary
13% of the total land area of the country. this figure is low compared with the European country average of 37% woodland cover, the UK’s woodlands are highly valued for a range of services including timber production, associated biodiversity, water and air quality improvement and numerous health and aesthetic benefits for society [1]. In 2019–2020, 13,700 Ha of new woodland was created in the UK [3] and there are plans for future, large-scale woodland planting schemes aimed at flood mitigation and offsetting CO2 emissions, for example the new ‘northern forest’ scheme led by the UK’s Woodland Trust which will involve the planting of 50 million native trees over 25 years Despite these recognised values and ambitions to increase and enhance the UK’s woodland resource, at the same time the country’s trees have never before been under such pressure from the threat of new pests and diseases introduced through the ever-burgeoning plant trade and other human-mediated pathways [4].
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