Chloroplast DNA variation of white oak in the Baltic countries and Poland

In this study we were interested how recolonisation of oak in the Baltic region occurred after the last ice-age. To analyse the chloroplast DNA (cpDNA) variation for white oak species at the more northerly limit of their distribution, a total of 394 samples from 54 locations from Estonia, Latvia, Lithuania and Poland were assessed for previously characterised as well as newly found cpDNA variation. Of the oak samples taken, Quercus robur was most frequently found throughout the entire Baltic area. Quercus petraea was only found and characterised in Poland. A total of 13 different haplotypes were found within the Baltic area. Most frequent (75% of all samples) are members of lineage A (common in the Balkan refugial area) while 16% belong to oak from the Italian Pleistocene forest refuge and only a total of 9% originate in the Spanish refuge the majority of which is likely to be also allochtonous. Haplotype 7 of lineage A is found in 33% of the sample set in the entire Baltic region. Haplotype 6 is found at the more northern limit of the area. Haplotype 5 a more eastern member of the lineage is found at low frequency in the east of the region. Haplotype 4, rather sparse in Europe, is mainly scattered throughout Poland. Lineage C is represented by haplotypes 1 and 2 the former found close to the Baltic Sea while the latter, being an Eastern member of the lineage originating in Italy, is found at low frequency to the east of the region. Oak from refugial areas in Spain has limited impact on the area and is found exclusively in Poland. Such genotypes are found mainly close to the Baltic Sea in Poland and only 2% show up in uniform stands. Therefore members of lineage B could either have their most north-easterly limit of distribution in Poland or most likely they have been transferred there from possible German locations. In spite of the historical anthropogenic influences in the Baltic States as well as in Poland clear tracks of recolonisation could be identified.