The UK’s trees, woodlands and forests are a vital national asset providing multiple economic, social and environmental benefits. However, in recent years there have been an increasing number of pest and pathogen incursions and outbreaks on trees. Increased global plant trade (more volume, from more countries and of more exotic plant species), the effects of climate change and changes in nursery practices (e.g. public demand for large semi-mature trees) are believed to be contributory factors in the increase in incidents. Threat from pests and pathogens increases the risk of incurring severe economic, social and environmental losses, not only through the loss of trees but also potentially through losses of other native flora which may be susceptible to the same pests and pathogens. Early identification of these pests and pathogens increases the chance of successful eradication, containment or control.

In the face of the potentially large geographical scale of pest and disease spread across trees, woods and forests, both in commercial forestry settings, but also the wider environment, the government has limited institutional capacity to provide for effective tree health surveillance on its own. Part of the solution to this challenge is to have effective support from a wide range of stakeholders including the public.

Citizen Science (CS) provides opportunities for engaging people and is seen as a powerful research tool for undertaking environmental monitoring and scientific research. It involves the collection and analysis of scientific data by volunteers (members of the public) and encompasses a broad range of projects. One advantage of CS is that volunteers can make observations over large geographical scales that can be too large for teams of professional scientists to study alone. The discovery in 2012 of Chalara fraxinea (now called Hymenoscyphus fraxineus) on ash in the UK significantly raised the public and political profile of tree heath. The confirmation of Chalara generated extensive media comment, followed by a range of government initiatives and interventions by citizens and other concerned stakeholders. During this time, several CS projects were set up to mobilize and involve the general public in spotting infected trees in their local areas.

Recognising that CS represents a key dimension of a collaborative approach to safeguard the health of the nation's trees and forests, and given that the current tree health CS landscape is still fairly nascent, now is an appropriate time for a stock-take of the portfolio of projects and the data they are producing. In order to do so, Defra commissioned the research presented in this report to develop an understanding of the current and potential contribution of citizen science to tree health by reviewing CS projects on tree health in the UK and by exploring different stakeholder views.

This research presents a comprehensive analysis of the current landscape of tree/plant health citizen science (CS) projects in the UK. It has brought together the views of many of the relevant stakeholders involved in tree health and CS and who are likely to shape the future application of tree health citizen science. Their opinions are therefore highly valuable and timely to inform the planning and delivery of future CS initiatives related to tree health. Most of the research done on CS in the past has explored the views and experiences of the volunteers alone. Research reported in this report adopted a unique approach of exploring the opinions and experiences of professionals working within projects as well as volunteers. The rationale being that their continued involvement and motivation is key to the design, delivery and implementation of successful CS projects in the future. This report reveals behavioural and motivational aspects of both professionals and volunteers. It also highlights the importance of adopting a CS approach and provides the basis for setting out some key policy recommendations and strategies aimed at improving the future design and delivery of citizen science in tree health.

THCS in the UK Defra Report (September 2019)