The Balkans: a genetic hotspot but not a universal colonization source for trees

In the context of Europe, the southern peninsulas including the Balkans are considered hotspots of diversity. They preserved substantial parts of tree species and genera occurring in Europe during the Tertiary, as the effects of the Quaternary glaciations on species richness were not as severe here as in more northerly regions. The Balkans also harboured glacial refugia of most European trees, and this was probably the reason for a premature suggestion that this region was the main source for the Holocene recolonization of Central and Eastern Europe. However, studies based on a combination of paleobotanical and genetic evidence showed that this was an exception rather than a rule. In most tree species, the Balkan refugia have not effectively contributed to current gene pools. In spite of this, empirical studies have documented that genetic diversity in the Balkan region is generally higher than elsewhere in Europe, which can be attributed to a high number of refugia in this area harbouring differentiated genetic lineages, and high environmental heterogeneity. This makes the Balkans an important source of genetic material for forestry, especially in the light of the ongoing climate change.