Biogeography filters forest phytopathogen establishment

Forest phytopathogen invasions cause particularly extreme social and ecological harm1-7, but remain difficult to predict. Like plants and animals, phytopathogens are commonly introduced with imported goods and commodities. Global analyses have focused on trade volume8,9 and organismal compatibility with recipient climates10 and habitats to account for biological invasion pathways. Analyses also focused on invasive plants and animals, and rarely on host-dependent organisms11-16. Importantly, the role of biogeographic affinity with recipient environments, particularly plant communities, in successful establishment of forest phytopathogens has not been quantified, despite their dependence on compatible hosts to complete their life cycles17. We demonstrate quantitatively the importance of biogeography and non-native plant introductions in shaping global patterns of forest phytopathogen establishment and show how these important factors can lurk behind the results of studies that do not take them into account, by partitioning their collinearity with trade and climatic relationships. We explicitly integrate global spread of forest phytopathogens into the process-barrier invasion framework of introduction, establishment, and invasion18-20 adopted by IUCN by considering biogeographic relationships that facilitate establishment of phytopathogens. Biogeographic affinity, including floristic relatedness and introduced tree species, is an overlooked determinant of vulnerability of ecosystems to phytopathogen invasion and resulting loss of biodiversity and productivity.