High pollen immigration but no gene flow via-seed into a Genetic Conservation Unit of the endangered Picea omorika after disturbance

•Disturbance promotes natural regeneration and pollen, but not seed, immigration.•Post-disturbance pollen immigration helps maintaining neutral genetic diversity.•Contrasting spatial genetic patterns are present in cohorts of adults and juveniles.•Gene flow monitoring is crucial to develop conservation plans, in particular in GCUs.•Skewed reproductive success might impact the adaptive potential of forest remnants.