Siberian larch forests are still polarized on ice age

Adaptation to climate change lags behind thousands of years

Despite climate change, the Siberian larch is widespread in Russia © ugraland / CC-by-sa 2.0
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Puzzles solved: Researchers have discovered why the flora in northern Russia seems to be barely reacting to climate change. Their study shows that even in the past, the vegetation in the permafrost regions often took several millennia to adapt to a new climate. The reason for the delayed reaction could be the insulating effect of larches. They protect the ice with their shallow roots - as a result, the frozen soil thaws more slowly.

The Siberian permafrost regions belong to those areas of the world that heat up very quickly in the course of climate change. Since the beginning of industrialization and the increasing emission of greenhouse gases, the Siberian winters have become significantly milder - a trend that is steadily increasing. According to forecasts, the frozen soil in these regions could thaw ever faster in the future.

Surprisingly, however, the vegetation hardly seems to respond to these drastic changes. Where pine and spruce forests have long since grown in terms of air temperature, Siberian larches still thrive. Scientists led by Ulrike Herzschuh from the Alfred Wegener Institute in Potsdam have now set out to find an explanation for this paradox - and discovered something astonishing.

Unusually long delay

For their search for clues, Herzschuh and her colleagues traced 2.1 to 3.5 million years back to the past: they examined pollen that they had taken from old sediment samples from Elgygytgyn Lake in eastern Russia. In this way they detailed the vegetation history of the region and then compared the development with reconstructed climate values ​​from this period.

The statistical analysis of the pollen data showed a clear pattern: in the past, the Siberian vegetation sometimes took up to several thousand years to adapt to climate change when changing from a cold to a warm period - the slow reaction is therefore not an isolated case. For the researchers, this is a completely new result: "Until now, we climate scientists only expected a delay of several decades or centuries - not millennia, " says Herzschuh. display

Insulating effect

A look into the past also revealed that the colder the previous ice age was, the longer it took the plants to adapt to the climate of the warm period. Even the youngest ice age 20, 000 years ago was a particularly cold one, according to the team: "As a result, the permafrost has spread generously, " the scientists write. Deep-rooted trees such as pines and spruces were displaced far to the south. The flat-rooted larches, which are tolerated by a summer soil layer of 20 to 30 centimeters, survived.

It could possibly be its protective effect, which delays the reaction to climatic change, the researchers believe: The larch forest with its flat, dense root carpet has an insulating effect on the ice out. It thaws permafrost more slowly than in non-wooded areas. Therefore, it could have lasted several millennia in the past, until after a particularly cold ice age, the permafrost had disappeared and pine and spruce had ousted the larches.

Woods as heat storage

The findings on the time-delayed adaptation of the vegetation now present the scientists with a new challenge: "As part of the ongoing warming of the Arctic, pine and spruce will migrate to the Siberian taiga with a time delay. This means that the forests are denser and therefore darker, which is why they will store more heat radiation than before, "says Herzschuh.

This in turn means that the temperature in Siberia will continue to rise into the distant future even if we humans succeed in stabilizing the carbon dioxide content in the atmosphere in the near future. The integration of these long-term vegetation processes into climate models is therefore urgently needed, concludes the team. (Nature Communications, 2016; doi: 10.1038 / ncomms11967)

(Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, 27.06.2016 - DAL)