J. D. Sauerländer's Verlag, Bad Orb

Chloroplast DNA markers give valuable information about the geographic origin of oaks and other angiosperms due to their maternal inheritance and the absence of recombination, thus reflecting patterns of seed dispersal. Since the dispersal by seeds is restricted as compared to pollen dispersal, cpDNA markers show low variation within populations but strong differentiation among populations. Because differentiation patterns are strongly associated with the postglacial recolonization history of oaks, the identification of the chloroplast variants (haplotypes) gives valuable information about the geographic origin of populations. We identified chloroplast haplotypes in a total of 24 Quercus robur populations from four regions in North Rhine-Westphalia established between the early 18th to the middle of the 19th century before extensive seed trade with the expansion of railway connections started. Additionally, 63 very old trees (between 250 and 700 year old) from one region were analysed at the same cpDNA markers. A similar haplotype composition was found in the old solitary trees and in the old oak stands from the same region. H1 as the most frequent variant in western Germany is also the most frequent type in the present study (71.5%) followed by H12 (21.5%), H10 (4.9%), H11 (about 1%) with a centre of distribution in South Western and Western Europe (Petit et al., 2002b), and H7-26 (about 1%) as the most frequent type in South Eastern Germany. There was considerable genetic variation among populations (58.9%) and geographic regions generally allowing for the identification of stands that had been established with introduced non-indigenous plant material.

By analysing very old oak stands that had been established before extensive human seed transfer began, we can gain insights in the cpDNA haplotype composition in the past of that region. In combination with the knowledge on the haplotype distribution in more than 2600 populations in Europe we have very good reference data to distinguish between natural patterns of postglacial recolonization of the species and human interference due to long distance seed transfer.

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