Science - October 4, 2011

Shrubs obstruct permafrost thaw

Tundra shrubs can obstruct permafrost thaw caused by climate change, research by PhD candidate Daan Blok shows.

The shadow of the dwarf birch makes the permafrost thaw a few centimetres less deeply.
Blok drew this surprising conclusion in his thesis 'Shrubs in the cold', which he will defend at his PhD degree ceremony on Wednesday. He researched into how climate change has affected the vegetation and the permafrost in the tundra area in Siberia. A warmer climate has resulted in more plant growth. This extra greenery causes more solar energy to be absorbed at the earth's surface. Part of the energy which has been taken up is channelled into the soil. In theory, the soil would thaw to a greater depth in summer. This would be bad for the climate as permafrost thaw releases a lot of carbon dioxide and methane which can speed up the greenhouse effect.
However, this theory has to be readjusted based on Blok's research into the effect of the dwarf birch, the most common shrub on the Siberian tundra, at the thaw depth. He cleared small experimental tundra fields of dwarf birch trees. He then monitored the thaw depth throughout two summers and measured the various energy streams between the atmosphere and the soil.