Carbon dioxide, methane and nitrous oxide fluxes from podzols of a fire chronosequence in the boreal forests in Värriö, Finnish Lapland

In boreal forests, wild fire is an important factor influencing the greenhouse gas (GHG) fluxes and emission rates. As the frequency and severity of forest fires are predicted to increase with a changing climate, the knowledge on the influence of GHG fluxes from fires and burned areas on the atmospheric warming will be of high importance. We studied the effect of forest fire and the time since the last fire on fluxes of three important long-lived GHGs from soil: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in northern boreal subarctic Scots pine forest stands with 5 to 155 years since the last forest fire. There was a seasonal pattern in all measured GHG fluxes: emissions of CO2 and N2O, and uptake of CH4 were increasing towards the end of the growing season throughout all fire chronosequence classes. Emission of CO2 was lowest in June, in area where the fire was 5 years ago (0.061 mg CO2 s− 1 m− 2) and highest in August in the area which burnt 155 years ago (0.120 mg CO2 s− 1 m− 2). We also found that the soil was a CH4 sink throughout the post-fire chronosequence in all stand ages. The uptake of methane was compensating the increase in radiative forcing resulting from the carbon dioxide emissions at the recently burned sites, but the compensating effect was very small. The influence and duration of the impact of forest fire were strongest on the carbon dioxide fluxes, but on the methane and nitrous oxide fluxes the effects were less evident.