LONG-TERM TREE POPULATIONS IN NORTHWEST GREECE THROUGH MULTIPLE QUATERNARY CLIMATIC CYCLES

THE emergent view of Quaternary cold stage European landscapes dominated by open vegetation communities has led to the concept that tree populations occurred only in restricted sites (refugia) in southern Europe1-5, although there is still considerable uncertainty over the precise location and extent of such populations. Trees respond to Quaternary climatic change by spreading from refugia during interglacials, but at the end of an interglacial period there is no reverse migratory movement in the direction of refugia, as most northern populations degrade in situ. It has thus been proposed that survival of European trees through Quaternary climatic cycles is dependent on populations persisting continuously in southern Europe6. According to this model, it is these southern populations that furnish European interglacial forests with essentially the same components during the Quaternary and, moreover, it is failure to survive in these 'long-term refugia' that brings about a tree species' ultimate disappearance from Europe6. I present here a 430,000-year record of vegetational and climatic change from northwest Greece comparable to that of other long sequences, but exceptional in documenting the continuous presence of temperate tree pollen throughout the sequence. The levels and consistency of representation suggest the local occurrence of tree populations at fluctuating densities and distributions according to prevailing climatic regimes.