Genetic diversity and fine-scale spatial genetic structure of unmanaged old-growth versus managed second-growth populations of Scots pine (Pinus sylvestris L.) in Lithuania

Abstract

We tested the hypothesis that old-growth unmanaged (OGU) forests have higher genetic diversity than second-growth man aged (SGM) forests and systematic forest tending markedly reduces genetic diversity and alters the fne-scale spatial genetic structure (SGS) of contemporary generation in natural populations, employing Scots pine (Pinus sylvestris L.). We examined genetic diversity, diferentiation and SGS of three OGU and three post-tending natural SGM populations of Scots pine on similar ecosites in diferent parts of Lithuania by genotyping 890 mature trees at 11 nuclear microsatellite loci. The genetic diferentiation between OGU and SGM population groups was not signifcant. Although OGU populations had higher allelic diversity, efective population size (Ne) and higher inbreeding coefcient than SGM populations, the diferences between OGU and SGM populations were not signifcant for these parameters. However, we found a signifcant loss of OGU-specifc private rare alleles, copies of rare alleles and genotypic diversity in the SGM populations. OGU populations had signifcantly stronger SGS and larger neighborhood size than SGM populations. We infer that systematic tending in natural Scots pine forests does not cause a signifcant reduction in common genetic diversity parameters and reduces SGS by disrupting clusters of relatives. However, it does cause signifcant loss of rare alleles and genotypic diversity and some genetic diferentiation from OGU. We suggest genetic monitoring for genetic diversity conservation and Ne maintenance, and developing forest management and gene conservation guidelines for better conservation of rare alleles and genotypic diversity.