Genetic diversity of Quercus rubra populations in Baden-Württemberg

Forest managers in Germany are looking for alternative tree species to counteract forest decline due to climate change. Foreign species like the wind-pollinated American broadleaf Quercus rubra L. (northern red oak) may grow on sites where native species can no longer adapt and produce valuable timber. Even though northern red oak has grown in Germany for approximately 200 years, little is known about the origin and composition of seeds that were originally imported to Europe. Furthermore, populations are scattered over the landscape, some are small and presumably isolated from external pollen flow. This lack of insight into the genetic constitution of these stands poses a risk to the goal of intensifying silviculture with northern red oaks and collecting seeds for regeneration. In this thesis, we compared two continuous northern red oaks stands with two isolated stands using microsatellite analysis for genetic characterization. While adult populations exhibited low variation of genetic diversity, we observed a decline in the offspring generation, which was more pronounced in the two isolated stands. Our findings suggest that a lack of external pollen flow – and the resulting reduction in available mating partners – may drive the loss of genetic diversity in isolates stands. These results raise the question of whether a minimum population size sufficiently maintain genetic diversity for forest reproductive material from non-native tree species stands.