Genetic diversity of the shrub birch Betula humilis Schrk. at the south-western margin of its range

Abstract

In Europe, 21% of vascular plant species are threatened. One of the endangered taxa is the shrub birch (Betula humilis Schrk.) The main reason for its disappearance is the development of brushwood and forest canopy as a consequence of the human management of the environment. The aim of our study was to estimate genetic resources in six Polish populations of B. humilis using nuclear microsatellites. The results obtained should have implications for the conservation of this species in Poland. In general, genetic diversity in B. humilis populations seems to be quite substantial, and comparable to other outcrossing trees and shrubs. This phenomenon could be explained by either too short time that has elapsed for genetic variation to be reduced following a decrease in population sizes and isolation, or the outcrossing breeding system. Distinct population structure and isolation by distance were not observed within the studied area. However, pairwise comparison of F ST between localities revealed low to moderate, and in most cases statistically significant, genetic differentiation. The latter result may suggest that limited gene flow is occurring. Reduced gene flow and genetic drift in the most isolated populations of B. humilis can trigger a loss of genetic variation in the future.