  The indigenous oak species (Quercus spp.) of the Upper Rhine Valley have
migrated to their current distribution range in the area after the transition
to the Holocene interglacial. Since post-glacial recolonization, they have been
subjected to ecological changes and human impact. By using chloroplast
microsatellite markers (cpSSRs), we provide detailed phylogeographic
information and we address the contribution of natural and human-related
factors to the current pattern of chloroplast DNA (cpDNA) variation. 626
individual trees from 86 oak stands including all three indigenous oak species
of the region were sampled. In order to verify the refugial origin, reference
samples from refugial areas and DNA samples from previous studies with known
cpDNA haplotypes (chlorotypes) were used. Chlorotypes belonging to three
different maternal lineages, corresponding to the three main glacial refugia,
were found in the area. These were spatially structured and highly introgressed
among species, reflecting past hybridization which involved all three
indigenous oak species. Site condition heterogeneity was found among groups of
populations which differed in terms of cpDNA variation. This suggests that
different biogeographic subregions within the Upper Rhine Valley were colonized
during separate post-glacial migration waves. Genetic variation was higher in
Quercus robur than in Quercus petraea, which is probably due to more efficient
seed dispersal and the more pronounced pioneer character of the former species.
Finally, stands of Q. robur established in the last 70 years were significantly
more diverse, which can be explained by the improved transportation ability of
seeds and seedlings for artificial regeneration of stands during this period.
