POPULATION-STRUCTURE AND POSTGLACIAL MIGRATION ROUTES OF QUERCUS-ROBUR AND QUERCUS-PETRAEA IN DENMARK, BASED ON CHLOROPLAST DNA ANALYSIS

Populations of Quercus robur L. and Quercus petraea [Matt.] Liebl. wer e shown previously to be fixed for the same chloroplast DNA marker in western Europe and for another form of this marker in eastern Europe. Application of this marker to 17 Danish populations of Q. robur showed significant population differentiation (G(ST) = 0.6). Restricted gene flow, low effective population size, restricted colonization ability of oak in dense forest and historical data might explain this. In addi tion, the genetic structure in eastern and western Denmark was quite d ifferent. In Jutland the populations were homogenous for the western m arker, in eastern Denmark, significant population differentiation and high diversity within populations were found. Post-glacial migration i s likely to explain the geographical structure. Oaks have immigrated t o Jutland from the west, whereas eastern Denmark was colonized from bo th east and west, forming a hybrid zone where immigrants met. Data fro m three populations of Q. petraea and from two hybrid populations also support this.