Carbon dioxide, methane and nitrous oxide fluxes from a fire chronosequence in subarctic boreal forests of Canada.

Forest fires are one of the most important natural disturbances in boreal forests, and their occurrence and severity are expected to increase as a result of climate warming. A combination of factors induced by fire leads to a thawing of the near-surface permafrost layer in subarctic boreal forest. Earlier studies reported that an increase in the active layer thickness results in higher carbon dioxide (CO2) and methane (CH4) emissions. We studied changes in CO2, CH4 and nitrous oxide (N2O) fluxes in this study, and the significance of several environmental factors that influence the greenhouse gas (GHG) fluxes at three forest sites that last had fires in 2012, 1990 and 1969, and we compared these to a control area that had no fire for at least 100years. The soils in our study acted as sources of CO2 and N2O and sinks for CH4. The elapsed time since the last forest fire was the only factor that significantly influenced all studied GHG fluxes. Soil temperature affected the uptake of CH4, and the N2O fluxes were significantly influenced by nitrogen and carbon content of the soil, and by the active layer depth. Results of our study confirm that the impacts of a forest fire on GHGs last for a rather long period of time in boreal forests, and are influenced by the fire induced changes in the ecosystem.