Fire, Global Warming, and the Carbon Balance of Boreal Forests

Abstract

Fire strongly influences carbon cycling and storage in boreal forests. In the near‐term, if global warming occurs, the frequency and intensity of fires in boreal forests are likely to increase significantly. A sensitivity analysis on the relationship between fire and carbon storage in the living‐biomass and ground‐layer compartments of boreal forests was performed to determine how the carbon stocks would be expected to change as a result of global warming. A model was developed to study this sensitivity. The model shows if the annual area burned in boreal forests increases by 50%, as predicted by some studies, then the amount of carbon stored in the ground layer would decrease between 3.5 and 5.6 kg/m2, and the amount of carbon stored in the living biomass would increase by 1.2 kg/m2. There would be a net loss of carbon in boreal forests between 2.3 and 4.4 kg/m2, or 27.1‐51.9 Pg on a global scale. Because the carbon in the ground layer is lost more quickly than carbon is accumulated in living biomass, this could lead to a short‐term release of carbon over the next 50‐100 yr at a rate of 0.33‐0.8 Pg/yr, dependent on the distribution of carbon between organic and mineral soil in the ground layer (which is presently not well‐understood) and the increase in fire frequency caused by global warming.