DNA-based tracking of historical introductions of forest trees: the case of European beech (Fagus sylvatica L.) in Lithuania.
Is it possible to untangle the historical mosaic of human interference with the origin of forest plantations in Europe? This topic is relevant at the northern frontier of species expansion such as western Lithuania, where European beech was introduced by German foresters in the eighteenth century. Our aim was to identify the origin and assess the genetic diversity of the introduced European beech populations in Lithuania with the aid of DNA markers. We used 10 nuclear microsatellite loci to genotype 1260 European beech trees from the introduced populations in Lithuania and 18 natural reference populations from Germany, Sweden and Poland as the most likely sources of the introduction. We calculated common genetic diversity indexes and used several clustering approaches to investigate the genetic associations. There was a significant differentiation among the populations at all the loci (Dest = 0.07 to 0.24). The Bayesian clustering returned high likelihood for the Lithuanian European beech stands to originate from three distinct sources: (a) the Bavarian Alps, (b) north-eastern Poland, and (c) south-eastern Poland and the Carpathian Mountains. Despite the high allelic diversity, the Lithuanian European beech populations possessed a markedly lower observed heterozygosity than the natural populations. We assume that the seeds for the Lithuanian stands were collected over a geographically wide range (resulting in high allelic diversity), but at each spot, a few adjacent and likely related trees were sampled. A DNA-based tracking system could efficiently reveal historic transfers of forest reproduce material Europe and help to improve the adaptability of future forests.