Data from: Fungal disease incidence along tree diversity gradients depends on latitude in European forests

European forests host a diversity of tree species that are increasingly
threatened by fungal pathogens, which may have cascading consequences for
forest ecosystems and their functioning. Previous experimental studies
suggest that foliar and root pathogen abundance and disease severity
decrease with increasing tree species diversity, but evidences from
natural forests are rare. Here, we tested whether foliar fungal disease
incidence was negatively affected by tree species diversity in different
forest types across Europe. We measured the foliar fungal disease
incidence on 16 different tree species in 209 plots in six European
countries, representing a forest-type gradient from the Mediterranean to
boreal forests. Forest plots of single species (monoculture plots) and
those with different combinations of two to five tree species (mixed
species plots) were compared. Specifically, we analyzed the influence of
tree species richness, functional type (conifer vs. broadleaved) and
phylogenetic diversity on overall fungal disease incidence. The effect of
tree species richness on disease incidence varied with latitude and
functional type. Disease incidence tended to increase with tree diversity,
in particular in northern latitudes. Disease incidence decreased with tree
species richness in conifers, but not in broadleaved trees. However, for
specific damage symptoms, no tree species richness effects were observed.
Although the patterns were weak, susceptibility of forests to disease
appears to depend on the forest site and tree type.