Persistence of tree taxa in Europe and Quaternary climate changes

The possibility that some populations of tree species may have survived multiple Quaternary glacial–interglacial cycles in central Europe is discussed. The alternation of forest and non-forest phases observed in long pollen records shows a substantial correspondence with the variations in global ice volume and indicates that the last glacial has been one of the most unfavourable periods for tree survival in Europe. Therefore the species that have survived the last glacial period in central Europe may have reasonably persisted also during less severe glacial periods and ultimately since the beginning of the Quaternary. The history of Picea and Corylus exemplifies the possibility of a continuous presence of trees in Europe. Recognizing the persistence of tree populations is necessary to assess the timing of their genetic diversification. The importance of extending the observation of the species behaviour to the time scale of the whole Quaternary is highlighted, in order to explain the modern distribution of populations and species and to reach a better understanding of evolutionary processes.