Background Preserving tree health is vital to human health and the natural environmental. It is also fundamental to combating climate change. However, trees in all situations are increasingly affected by health threats, with research showing across-the-board increases in damaging fungal infections. Around 11 million ha of EU forests (6%) are affected by forest damage, including many new pests and pathogens that have been introduced since 1900. A key source of threats to tree health is the importation of infected trees into new ecosystems. Movement of plants and plant products between countries is controlled by international protocols, and improvements to these systems are being made. In 2011, the UK agreed a Tree Health Action Plan (THAP) to address rising threats to its trees. Various actions have been taken to increase bio-security, including: strategic and applied research, extra plant inspectors at ports and airports, and practical actions to support pest and disease control. However, there are practical limitations to the capacity to find pests through inspection. Furthermore, there are limitations in terms of knowledge and understanding of the threats present on trees and the impact they might have in a new ecosystem. A particular challenge is that pests that co-evolved with their hosts in one country are unlikely to be damaging enough in that context to highlight their likely risks in another ecosystem. Objectives The LIFE ObservaTREE project aims to demonstrate an effective Tree Health Early Warning System (THEWS), based on public engagement. It seeks to mobilise the expertise and resources of landowners, industry, academia and governments to identify any significant impacts from new introductions of plants or trees. The system expects to enable early intervention to contain or eradicate identified pests, in a way that implies fewer environmental, landscape and economic costs. The project will create a cadre of engaged, knowledgeable Tree Health Champion volunteers, by training citizens - as well volunteers from within the forestry, horticultural and arboriculture sectors - to assist with the identification and verification of tree health incidents. In this way, the project aims to generate a tenfold increase in Tree Health Incident Reports, as well as a more general increase in bio-security awareness amongst citizens and civil society. LIFE ObservaTREE will work to ensure that all tree health information is readily available at national level through a central web portal that incorporates the latest research findings, and links with EU information. It will produce a single, transparent and unambiguous database of Tree Health Incident Reports, based on a bespoke online reporting and verification system. It will also create and maintain a prioritised list of tree health risks, acknowledging likely climate change impacts. To ensure the efficiency and effectiveness of the system, the project will employ dedicated NGO 'Engagement Co-ordinators' to filter all the expected incident reports on behalf of the public authorities. This will enable public sector diagnosticians to focus their attention and resources on the reports of greatest significance. The project thus targets the delivery of a coherent and integrated early warning system that avoids the proliferation of different approaches across the country, enabling cheaper and more successful UK eradication or containment efforts, and a greater exchange of knowledge across Europe. Expected results: Demonstrate a ‘best in Europe’ Tree Health Early Warning System (THEWS); Increase the capacity of citizens, civil society organisations, professionals and businesses to engage in tree health issues; At least 100 Tree Health Champions trained; A tenfold increase in Tree Health Incident Reports – from around 5 000 people; A central information portal containing a central database of 10 000 Incident Reports and an 'Information Library' of critical UK tree health risks; Identification of damaging tree pests and pathogens at an earlier stage; Practical multi-stakeholder and cross-border collaboration in England, Scotland, Wales and Northern Ireland; Improved cost-effectiveness – and reduced negative environmental impact - of public sector interventions to tackle threats; Intensified exchange of knowledge on tree health in Europe; Implementation of the new EU Plant Health Regime.