Transmission of Genetic Variation from the Adult Generation to Naturally Established Seedlings of Fagus orientalis in the Hyrcanian Forest

Oriental beech (Fagus orientalis) is distributed from Turkey to northern Iran. It is one of the most economically important tree species in this natural distribution range and has been exploited for a long time in the Hyrcanian forest. This study compared genetic variation between adult individuals and recent cohorts of 1–3-year-old seedlings using 14 SSR primers in four pure stands of F. orientalis with over 90% canopy cover. The results showed that the expected heterozygosity (He) varied from 0.83 to 0.92 (mean value 0.88), and a significant difference was detected between the expected and observed heterozygosity. In total, 75 private alleles were detected; of these, 56 were rare and had a frequency below 0.05. Pairwise Fst values indicated that seedlings were more similar to each other than to mature trees in the same population. It was found that the populations in each pair (mature trees-seedlings) differed (global average D = 0.35). The average percentage of migrants in the population was 8.83% and varied from 6.64% to 13.41%. The genetic differentiation within the same stands, the genetic differences between adults and seedlings were also significant in some populations, and contemporary gene flow drastically decreased in the next generation. Therefore, the transfer of genetic variation between tree generations is currently strongly affected by anthropogenic influence, at least in the studied beech populations, leading to the high vulnerability of Oriental beech populations to future climate changes.