There have been many ice ages in the history of the Earth; but the last, which covered vast tracks of the Northern Hemisphere, came to an end some nine to ten thousand years ago – when the temperature (and sea level) rose.  It has always been assumed that no trees survived in the regions covered by the thick ice sheet, and that trees (like other plants) have returned to areas like Scandinavia by the gradual northern migration of species that had taken ‘sanctuary’ in warmer latitudes.

However, recently work has been undertaken by

• Professor Eske Willerslev, University of Copenhagen, Denmark
• Laura Parducci, University of Uppsala, Sweden, and
• Inger Greve Alsos, Tromsø University Museum, Norway.

Their studies focused on the DNA of present-day Scandinavian Spruce trees (and that of ancient samples / specimens found in lake sediments); and it is clear that there are two distinct populations of Scandinavian Spruce.

 
One population has relatively recent ancestors thought to be the descendants of those trees that moved in as the ice sheets retreated.  The other population are thought to be trees that are derived from the conifers that survived the ice age and the harsh, cold climate ‘in situ’. 

It is now thought that some trees of Spruce (and pine) survived in small ice free pockets amidst the extensive ice field, on the tops of mountains that stuck out above the ice (nunataks), or in coastal aras where the climate / environment was less extreme.  One such pocket or refuge was Andøya Island, in north-western Norway – which provided the researchers with material dated at circa 20,000 years ago.

As the two tree populations have very different histories, it is thought that they will have very different qualities / properties in terms of hardiness, growth pattern rate etc – which may be of value to commercial plantations and the like.