Trees constitute the foundation of our natural ecosystems and contribute considerable value to the economy. Emerging infectious diseases, such as the chalara fungus (Hymenoscyphus fraxineus) that infects ash (Fraxineus excelsior), are destroying tree populations, and novel and effective control strategies are urgently needed. Natural microbial communities of trees regulate health and pathogenic invasion, and present a unique opportunity to develop such strategies. Here we aim to identify microbial (bacterial and fungal) signatures of ash resistance to chalara.