Genetic diversity and differentiation of introduced red oak (Quercus rubra) in Germany in comparison with reference native North American populations.

Abstract

Northern red oak (Quercus rubra) was introduced to Europe in the late 17th century and is today the most important deciduous foreign tree species in Germany. Despite its importance little is known about the origin of local red oak stands and patterns of genetic variation in German red oak stands. To be able to make recommendations regarding the adaptive potential of red oak and the selection of provenances with respect to climate change, a better understanding of the genetic diversity and structure of German red oak stands is needed. Therefore, individuals from 62 stands in Germany and North America were genotyped at five chloroplast microsatellite loci to characterize chloroplast haplotype diversity and geographical structure. Compared to reference stands from the natural distribution range, German stands demonstrated a relatively low genetic differentiation among populations and represented only a fraction of the haplotype diversity found in North America. For several stands located in the south of Germany a considerably higher haplotype diversity was found. Therefore, we conclude that German stands originated from a limited geographic range within the natural distribution, which was possibly located in the northern part of the native distribution range. While most German stands showed signatures of founder effects due to originating from a small number of individuals within a limited range, particularly stands in the south of Germany could have benefited from admixture and multiple introductions of different North American provenances.