Genomic evidence of high gene flow and weak population structure in Siberian hazel (Corylus heterophylla)

Genetic diversity and connectivity strongly influence the capacity of forest tree species to persist under rapid environmental change. Corylus heterophylla Fisch. (Siberian hazel) is a widespread temperate shrub of ecological and economic importance in East Asia, yet genome-wide assessments of its population genetic patterns remain limited. We analyzed 4, 378 single-nucleotide polymorphisms generated from 161 individuals sampled across 20 populations in South Korea to quantify genetic diversity, population differentiation, gene flow, and demographic history. Levels of intrapopulation genetic variation were moderate and comparable to those reported for other long-lived, predominantly outcrossing tree species. Overall genetic differentiation was low (mean FST = 0.05), and isolation by distance was not detected, indicating extensive gene flow across the Korean Peninsula. Demographic reconstruction revealed two population declines during the Late Pleistocene, followed by rapid recovery and relatively stable effective population sizes toward the present. Given the limited natural dispersal capacity of the species, the observed high connectivity likely reflects long-term human-mediated movement associated with agroforestry practices. Together, these results suggest that C. heterophylla has maintained genetic diversity and connectivity despite historical climatic fluctuations and contemporary environmental pressures, highlighting its value as a genetic resource for conservation and breeding under ongoing climate change.