Tage der Biodiversität 2027

The white oak species complex (Quercus Section Quercus) comprises some of the most widespread and ecologically important tree species in Europe. These species are generally characterized by high genetic diversity due to large population sizes and extensive gene flow both within and among closely related species through hybridization. Nevertheless, knowledge of population-level genetic diversity, particularly adaptive genetic diversity, remains limited. This knowledge gap is especially pronounced in southeastern Europe and for endemic (sub-)species such as Q. frainetto and Q. pedunculiflora. This limits the development of informed forest conservation measures, including assisted gene flow or assisted migration which locally introduce genetic variation from progenies that are pre-adapted to future climates. Here, we present a comprehensive analysis of white oak genetic diversity based on population sampling spanning from Central Europe to the Caucasus. Our sampling includes widespread species such as Q. robur, Q. petraea and Q. pubescens, as well as geographically restricted (sub-)species. This unprecedented dataset comprises individual whole-genome data of 1,205 trees, complemented by high-throughput leaf morphology and population-level climatic data. We identify a longitudinal gradient in genetic diversity and investigate this pattern in light of the demographic history, past migration routes, and hybridization. Moreover, we use genotype-environment association approaches to uncover genomic hotspots of putatively adaptive variation associated with environmental drivers, for instance precipitation seasonality. Our results further suggest that some adaptive genetic variation has been transferred among species through hybridization and introgression. Overall, our work demonstrates how high-throughput genomic data can provide a detailed view of genetic diversity and the evolutionary processes shaping it. These insights expand the knowledge basis needed to preserve forest genetic diversity and improve climate-resilience strategies.