Genetic diversity Scandinavian spruce trees higher – as some survived ice age

Science man [probably native Scandinavian subspecies] standing atop a nunatak – looking across a still ice-covered Scandinavian mountain landscape. Could trees have survived in such refugia, even during the bitter cold of the Pleistocene ice ages? Image credit: Nicolaj K. Larsen, Department of Geoscience, Aarhus University

As the Pleistocene ice sheets across Northwest Europe originated in the Scandinavian mountains, it was assumed that during the ice ages the Nordic countries too were entirely covered in a thick, lifeless desert of ice.

An international team of researchers led [‘in equal contribution’ – you folks know you can actually overdo this democratic spirit?] by Uppsala University, the University of Copenhagen and the Norwegian Forest and Landscape Institute have however found evidence that this image somehow needs revising.

In their Science publication they write that some Scandinavian spruce trees contain unique DNA, which cannot be found in spruce trees in South and East Europe, regions which were not covered in ice. It was thought that when the ice retreated at the onset of the Holocene coniferous trees, like pine and spruce, slowly moved north from these ice-free regions and colonised Scandinavia, where they now constitute the European part of the taiga or boreal forests.

This hypothesis is still supported by genetic similarities between different spruce populations, but at least two seem to be uniquely Scandinavian – and must therefore have survived the harsh conditions within the glacier heartland.

Gardening trend: conifer refugia

The researchers think that somewhere along the Norwegian coast small pockets of land or rock must have somehow remained ice free – and acted as refugia for the coniferous trees.

One candidate in mountainous area are the so-called nunataks, mountain peaks or ridges that are high and steep enough to shed themselves of the snow and stick above ice accumulations in the valleys. Similar sites in present-day Greenland do however not harbour any trees.

Another spruce refugia candidate is formed by small isolated Norwegian islands which protrude in the Atlantic Ocean. There was no Gulf Stream during the ice ages and the northern regions of the ocean were a lot colder – but open water still, so on average above freezing. One of such ice-free pockets was Andøya Island in Northwest Norway and the researchers have indeed found spruce pollen with the uniquely Scandinavian DNA at the site, dating back 17,700 to 22,000 years – so that’s at the height of the last ice age and glaciation.

The Swedish Norwegian spruce

The story got us to remind another scientific report about old Scandinavian trees. In 2008 researchers of Umean University proudly announced that they thought the world’s oldest living tree grows at a high and remote spot in the Swedish mountains, bordering Norway. It is actually a Norwegian spruce and – as these are able to clone themselves [like this Mediterranean seagrass we reported on in our previous story] – is thought to have continuously tapped and grown from the same living root system at the exact same location for 9,000 years.

That is sort of the dawn of the Holocene, when the spring sun finally managed to burn through the snow at the south slopes. It was thought the oldest theoretically possible.

Get to know a tree

But now that we know of the Pleistocene refugia can’t these researchers take a better look when walking around Andøya? With a bit of luck perhaps there you could find one that is just a thousand years older than the Swedish spruce – and be able to officially shake hands with an ice age tree, alive and standing up to this very day. Wouldn’t that be cool.

You would have to hurry up though. These extremely old boreal trees are ill-fated. The reason they survived the millennia is because up in the High North even in the early Holocene it has been cold throughout, which means plant life moved at a very slow pace. Under the recent climate warming tiny tundra trees have all begun a growth spurt, which also speeds up the ageing process.

Unfortunately you will not be the only one in search of the last tree standing. The foresting industry has shown special interest in the new study. ‘These spruce with ice age genes must be really sturdy. That should make for high quality furniture!’