Soils linked to climate change

Carbon has been stored in the organic layers of boreal-forest soils for hundreds of years. An analysis reveals that this carbon might be released into the atmosphere as global warming increases the frequency of wildfires.

In this article authored by Cornelia Rumpel, from the CNRS, Institute of Ecology and Environmental Sciences in France, she writes that the cause of this shift is due to the impact of more-frequent fires on legacy carbon — the organic carbon that has escaped earlier fires and has accumulated at the surface of boreal- forest soils. A boreal forest will act as a carbon sink if a fire removes less soil carbon than the amount that accumulated after the previous fire — or, to put it another way, if the soil carbon removed by a fire is younger than the community of trees affected by the fire.

In a paper in Nature, Walker et al. show that the increase in fire frequency might turn boreal forests from carbon sinks into carbon sources. Walker and colleagues’ results suggest that certain boreal forests are about to reach a tipping point in their resilience to fire, beyond which the carbon-storage function of this ecosystem will change. This is a major concern, not only because it will increase the rate at which carbon dioxide is released to the atmosphere, but also because these forests provide multiple benefits.

Boreal forests constitute the largest terrestrial biome, with some of the world’s largest intact areas of untouched forest, and they harbour unique biodiversity. Moreover, they are sources of timber products and contribute greatly to global air quality and climate regulation. Carbon loss and removal of organic soils by fire will transform this ecosystem, with unknown consequences.