FIRE, GLOBAL WARMING, AND THE CARBON BALANCE OF BOREAL FORESTS

Fire strongly influences carbon cycling and storage in boreal forests. In the near-term, if global warming occurs, the frequency and intensi ty of fires in boreal forests are likely to increase significantly. A sensitivity analysis on the relationship between fire and carbon stora ge in the living-biomass and ground-layer compartments of boreal fores ts was performed to determine how the carbon stocks would be expected to change as a result of global warming. A model was developed to stud y this sensitivity. The model shows if the annual area burned in borea l forests increases by 50%, as predicted by some studies, then the amo unt of carbon stored in the ground layer would decrease between 3.5 an d 5.6 kg/m(2), and the amount of carbon stored in the living biomass w ould increase by 1.2 kg/m(2). There would be a net loss of carbon in b oreal forests between 2.3 and 4.4 kg/m(2), or 27.1-51.9 Pg on a global scale. Because the carbon in the ground layer is lost more quickly th an 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 min eral soil in the ground layer (which is presently not well-understood) and the increase in fire frequency caused by global warming.