A high-resolution pollen record from western Greece shows that the amplitude of millennial-scale oscillations in tree abundance during the last glacial period was subdued, with temperate tree populations surviving throughout the interval. This provides evidence for the existence of an area of relative ecological stability, reflecting the influence of continued moisture availability and varied topography. Long-term buffering of populations from climatic extremes, together with genetic isolation at such refugial sites, may have allowed lineage divergence to proceed through the Quaternary. Such ecologically stable areas may be critical not only for the long-term survival of species, but also for the emergence of new ones.
Here, we examine the evidence for tree refugia in northern Europe during the Late Pleniglacial (LPG) interval of maximum tree-range contraction. Our review highlights the often equivocal nature of genetic data and a tendency to overestimate potential tree distributions due to warm climate-model bias, and also reveals a convergence of macrofossil and pollen evidence. What emerges is the absence of temperate trees north of 45°N and a west-east (W-E) asymmetry in boreal tree distribution, with a treeless Western Europe north of 46°N, while restricted boreal populations persisted in Eastern Europe up to 49°N, and higher latitudes east of the Fennoscandian ice-sheet. These results have implications for current thinking on European genetic diversity patterns, species migration capacity, and conservation strategies.
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