Tree vitality predicts plant-pathogenic fungal communities in beech forest canopies

Forest canopies host diverse fungal communities that are crucial for tree vitality—defined as the physiological and structural traits influencing growth and resilience—and, consequently, for ecosystem functions. The canopy mycobiome has been shown to be closely associated with its tree hosts, especially in the case of pathogenic taxa. To better understand and predict how the canopy mycobiome will respond to changing environmental conditions, we used tree vitality-related variables to predict patterns in the beech canopy fungal plant-pathogens in two temperate forests— Bavarian Forest National Park, Germany and the Veluwe forest area, the Netherlands. Canopy water content, chlorophyll content, and crown diameter emerged as robust predictors of the canopy fungal plant-pathogen communities. We showed that these tree vitality-related variables predicted the unweighted relative abundance of plant-pathogenic fungi in the total fungal communities and the diversity of the fungal plant pathogen subgroup, but not the weighted relative abundance of plant-pathogenic fungi in the total fungal communities. Our model offers a powerful tool for monitoring this previously neglected biome in temperate beech forests in Europe. • Host trees and their canopy mycobiome are closely associated. • Canopy water, chlorophyll, and crown diameter are key predictors. • Fungal plant pathogens relative abundance and diversity were predicted.