The boreal forest, also known as the taiga, is the northernmost and largest forest region on Earth, stretching from Alaska across Canada and Scandinavia to Siberia. Where these forests grow on continuous permafrost, they serve an important climate function: their canopies shade the surface and reduce thaw depth, helping preserve the vast carbon reserves contained in the frozen permafrost. A recent study published in the journal Nature Climate Change, in which the Alfred Wegener Institute was involved, has now, for the first time, quantified the amount of carbon that this ecosystem service conserves.
So far, the climate value of boreal forests has been judged mainly by the carbon held in their biomass. Their role in insulating permafrost soils and safeguarding a much larger underground carbon reservoir has received little attention. “One of the most important climate services provided by boreal forests lies beneath the trees. Their canopies keep permafrost cool and preserve carbon stocks that far exceed the carbon stored in the trees themselves. When the forest is lost, the ground loses this protection,” says Dr Simone Maria Stünzi, researcher at the Institute of Geography at Humboldt University of Berlin (HU) and a visiting researcher at the Alfred Wegener Institute (AWI) in Potsdam.
Together with colleagues from the Alfred Wegener Institute (Potsdam), the University of Oslo, and Vrije Universiteit Amsterdam, Stünzi investigated how strongly boreal forests insulate permafrost soil. For their analysis, the researchers combined several geospatial datasets and analysed them with models that simulate the thermal exchange between boreal forests and permafrost soils. For 16 bioclimatic regions in the continuous permafrost zone, the researchers compared the ground's heat budget with and without forest cover, drawing on satellite data and a meta-analysis of existing carbon-stock data.
Protecting Boreal Forests Is Essential for the Climate
In boreal forests within the continuous permafrost zone, the canopy keeps the ground markedly colder than in open terrain: the seasonal thaw depth is 50 to 62 percent shallower under forest cover, a difference of about one meter on average. For the first time, the study quantifies this protective effect across the entire continuous permafrost region: "59 petagrammes – that is, 59 gigatonnes – of carbon are currently stored in permafrost solely as a result of the cooling effect of tree canopies – a climate-relevant quantity on a global scale. This makes the protection of these forests a climate issue of the utmost importance", says Stünzi. Damaging or losing these forests, for instance through deforestation, wildfire, or other disturbances, would therefore have far-reaching consequences. Forest loss would affect not only the carbon stored in vegetation, Furthermore, once the insulating vegetation cover is gone, the ground thaws more deeply each summer, and up to 40 Pg of carbon stored in it can be broken down by microbes. On a far larger scale, carbon that has remained frozen for millennia could gradually be released to the atmosphere. What makes this especially critical is that much of this carbon accumulated since the last Ice Age over thousands of years and could not be restored on human timescales once lost.
Original publication
Stuenzi, S.M., Grosse, G., Miesner, F. et al. Canopy-mediated climate feedbacks in the boreal continuous permafrost zone. Nat. Clim. Chang. (2026). https://doi.org/10.1038/s41558-026-02692-z
