Genetic make-up and diversity of regenerated Betula maximowicziana Regel. sapling populations in scarified patches as revealed by microsatellite analysis

In June 2002, the genetic make-up and diversity of regenerated populations of Betula maximowicziana Regel. saplings in two scarified patches were investigated by microsatellite analysis. The scarified patches, SP-1 (0.63 ha) and SP-2 (0.20 ha), were established in 1988 around single seed-trees of B. maximowicziana in the Tokyo University Forest in Hokkaido, located in central of Hokkaido district in Japan. Comparing genotypic data of the adult population around the two patches with the sapling populations, the genetic contribution of the seed-trees to SP-1 and SP-2 was evaluated by three methods of parentage analysis: simple exclusion, categorical allocation and fractional allocation. Although the scarified patches were established close to the seed-trees, the genetic contributions of the seed-trees to SP-1 and SP-2 were surprisingly low: 4.25% and 2.35%, respectively, according to simple exclusion, 2.08% and 0.00% according to categorical allocation and 2.39% and 1.95% according to fractional allocation. The areas covered by SP-1 and SP-2 were small compared to that of the adult population, but their genetic diversity was similar to that of the adult population: the expected heterozygosity (HE) of SP-1, SP-2 and the adult population was 0.365, 0.341 and 0.371, respectively. The genetic differentiation between pairs of populations was low; pairwise FST values ranged from 0.003 to 0.016. Genetic diversity may be maintained in the regenerated sapling populations in scarified patches by temporal gene flow from the old to the new populations, and by extensive spatial gene flow, promoted by the species’ small winged seeds and long-distance pollen flow.