Are we defending the indefensible? Reflecting on policy and practice around ‘the border’ in plant biosecurity for tree health

The challenges to forest health from climate change, globalization, contemporary trade practices and new recreational patterns require effective biosecurity. We asked: How is the biosecurity border for tree health understood and enacted by state and non-state actors? What are the consequences for tree health? Semi-structured interviews (N = 10) were conducted with scientists and other relevant actors (N = 21). The border was understood variously as: a biophysical boundary, often the coast; a geopolitical boundary, usually of the European Union; the points of main inspection focus; dispersed nodes of inspection; a ‘pre-border’ outside of UK; or by the location of detection activities. A wide range of state, non-state and hybrid groups are engaged in border practices. These practices have been altered due to trade and climate changes, are subject to cost and resource priorities and reflect particular knowledge flows and the biological nature of the agents. We suggest that there is an ‘everyone’ as well as ‘everywhere’ border that demands clarification of risks, roles and responsibilities, and we offer practical recommendations. We conclude that tree health border challenges are a manifestation of wider sustainability issues that enable us to explore human–nature relationships, democratic engagement and the pursuit of more sustainable futures.