Genetic diversity and population structure of pedunculate oaks (Quercus robur) in Wytham Woods

Societal Impact StatementGenetic diversity underpins forest resilience and adaptation, yet centuries of human activity have reshaped woodland ecosystems worldwide. We studied the population genetics of pedunculate oaks (Quercus robur) in Wytham Woods, UK, across stands with different ages and management histories. We found high within‐stand diversity, low genetic differentiation among stands and signs of inbreeding in the youngest plantation. These findings suggest oak's adaptation and resilience to genetic erosion but highlight the result of intense management. Our results inform forest management, conservation policy and long‐term ecological research by providing critical baseline data for monitoring keystone tree species across human‐modified landscapes.Summary Genetic diversity is fundamental for adaptation to changing environments. It is particularly important in forest trees because of their significant role in nature's contribution to people. However, forests have been significantly changed by human activities in the past centuries with potential effects on genetic diversity. This paper presents a population genetic study on the keystone producer, pedunculate oaks (Quercus robur) in Wytham Woods, UK, one of the most researched woodlands on Earth. We genotyped 210 trees and quantified levels of genetic diversity across stands with different histories and management regimes. We detected a weak population structure with the 218,567 SNPs, such that most genetic variation occurred within but not among stands, which included semi‐natural woodland areas and plantations aged between 200 and 50 years ago. We also observed little difference in observed and expected heterozygosity among stand types, but detected signs of inbreeding in the youngest plantation. We discovered 161 genes (0.42%) that were under putative balancing selection (Tajima's D > 2), enriched in defence‐related functions. We suggest that the life history traits of oak contribute to its resistance against genetic erosion. Preference for oaks as a timber tree and the tendency to use local seed sources might have resulted in the homogeneous population structure. However, tree‐to‐tree differences may still harbour variation in putatively adaptive loci. Our study contributes crucial baseline information on the conservation and management of human‐modified woodlands, in addition to supporting long‐term ecological studies on many other species, which depend on this keystone oak species.