Effect of stand management on genetic diversity of Fagus sylvatica L. natural regeneration

The most common method of beech stands management are polycyclic harvesting systems with use of shelterwood cuttings, which ensure proper conditions for beech regeneration development. However, there is little information about the impact of this management method on the genetic structure of the young generation of the stand. We aimed to figure out whether the use of this management method significantly modify the natural course of processes related to the reproduction of beech stands. We compared the genetic parameters of two subsequent generations of beech stands managed with irregular shelterwood system with old-growth forests. The study was conducted in three different regions of southern Poland (Beskid & Zdot;ywiecki, Beskid S & aogon;decki, Bieszczady). In each region, in the immediate vicinity, two beech stands with different management history were selected: stand managed with irregular shelterwood system (IV d), in renewal class and forest of the primeval character protected as a nature reserve. In each stand 50 mature trees and 100 saplings were genotyped at 4 highly polymorphic nuclear microsatellite loci, then population genetic parameters were calculated, separately for parental and progeny generation of each stand. The comparison of genetic diversity parameters between managed and unmanaged stands did not reveal significant differences. High genetic similarity between adults and seedlings was likewise found in all studied populations, indicating the effective gene flow between mature stand and its progeny from self-seeding. However, we found slightly larger genetic differences between generations in the reserves. Significant differences in allele frequency distribution between adults and seedlings occurred more often in reserves than in managed stands. Differences in total num- ber of alleles and number of rare alleles between generations were bigger in reserves as well. Furthermore, in all three locations, genetic distance and genetic differentiation between adults and seedlings were higher in old-growth forest than in managed stand. These results indicate that gene pool of parental and progeny generation differed more in reserves, what can be related to a different vertical and horizontal structure of managed stands and old-growth forest. Our results confirm that management with irregular shelterwood system is an effective way of managing beech stands in the context of preserving forest genetic resources. It seems that the impact of forest management on the genetic diversity of forest trees population should be measured in terms of change in stand density and structure.