Chloroplast DNA variation of oaks in France and the influence of forest fragmentation on genetic diversity. Forest Ecol

Chloroplast DNA variation was studied in a total of 878 French oak populations from four different species. Three main cpDNA lineages were found, which have well-demarcated distributions in the country. The study of the distribution of haplotypes in each species supports the view that the four species were restricted to different refugia during the last ice-age. This is evident despite the fact that extensive cpDNA introgression occurred during and after postglacial recolonisation. Nevertheless, the individual species have different ecological requirements and also differ in their ability to hybridise, resulting in heterogeneous levels of partitioning of cpDNA diversity and incomplete cpDNA introgression. The first analysis of the effect of the landscape structure on genetic diversity in these oak species is presented here. The only discernible effect of landscape structure on cpDNA diversity was found in Quercus robur, and is very weak and rather counterintuitive. The biology and abundance of these oak species may make them particularly resistant to fragmentation; in addition, artificial seed flow may complicate the picture, and will require more direct investigations. # 2002 Elsevier Science B.V. All rights reserved