Genome-wide association and phenotypic analyses of drought resilience in European beech (Fagus sylvatica) trees in Switzerland
Forests across Europe are increasingly threatened by climate change-induced drought. European beech (Fagus sylvatica L.), a dominant forest tree species, has experienced extensive but heterogeneous crown damage since the 2018 and 2019 hot drought events. In this study, we assessed drought resilience in Swiss beech forests using a natural case-control design of paired healthy and damaged trees from long-term monitoring sites. We integrated genomic approaches including low- and high-coverage whole genome sequencing, pool-GWAS, and population structure analysis, with phenotypic assessments such as canopy transparency, foliar nutrient concentrations, xylem function, and leaf reflectance spectra. Our results reveal distinct population genetic structures and candidate loci associated with drought-induced damage, alongside spectral and physiological indicators of stress. This study provides new insights into the genetic and functional basis of drought resilience in temperate forest trees and contributes valuable data for ongoing forest monitoring and conservation efforts.