The genetic assessment of the natural regeneration capacities of black poplar populations in the modern river valley landscapes

•The level of genetic variation was high and comparable between populations.•The genetic structure of black poplar populations was homogenous.•All examined populations experienced the demographic bottleneck in the past.•Clear signals of introgression were detected in analyzed black poplar seedlings.•The results support the need to protect the genetic resources of P. nigra in Poland.