Effects of artificial selection on genetic structure of beech (Fagus orientalis Lipsky) populations

The impact of artificial selection as the critical practice in forest management, thinning and selection of seed trees, on genetic structure was examined in oriental beech (Fagus orientalis Lipsky). In ten beech (Fagus orientalis Lipsky) populations along Hyrcanian forests, genotype of trees compared with 10 selected mother trees and their seeds (each 7 seeds) as next generation, based on four highly polymorphic microsatellite loci. In two populations forked and monopodial trees and their seeds were also investigated to study phenotypically based tree selection in forest management. Significant differences were found for allelic richness (Na), effective number of alleles (Ne), number of rare alleles, either for observed (Ho) or expected heterozygosity (He) between trees and seed samples in each population. Because of an association between the occurrence of rare alleles and tree phenotypes, phenotypically based tree removals were associated with a shift in allelic frequency and number of rare alleles, which followed by decreasing future genetic potential. Because of the theoretical long-term evolutionary benefit of unique gene forms, the loss of rare alleles could diminish the potential of populations to adapt to and survive ongoing environmental change. The results indicated that intense selection or thinning might severely affect genetic structure of beech population in long term, confirming efficiency of sustainable stand management policies with emphasis on the close to nature silviculture system and the employment of un-even aged form methods. As beech populations seem not to be affected by single or partial thinning activities, the selection system (both, the single and the group selection system) is a suitable silvicultural system for the Caspian beech forests.