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• Immediately after the fire, soil CO 2 effluxes increased compared to pre-fire conditions. • Through the post-fire growing season, fire had negative impact on soil CO 2 fluxes. • Unburned areas were sinks of CH 4 through the entire measurement period. • Shortly after the fire, the burned areas turned from CH 4 sink to source. • Shortly after the fire, there was a marked increase in post-fire soil C and N. Although forest fires are one of the main natural disturbance types in boreal forests, there is limited information regarding surface fires (dominant in Northern Europe), and how surface fires of different severities could affect post-fire soil greenhouse gas emissions. The results of our study show that fire severity, time since fire and post-fire changes in soil temperature were the main factors driving soil carbon dioxide (CO 2) flux (forest floor ecosystem respiration) from burned boreal forest soils. Approximately two hours after the fire, soil CO 2 emissions from burned areas were significantly higher compared to pre-fire conditions, and areas with high-severity fires had significantly higher soil CO 2 emissions compared to those with low-severity fires. Later (days, months) after the fire, the unburned control areas always had higher soil CO 2 emission values compared to burned areas. In the case of methane (CH 4), time since fire and post-fire changes in soil temperatures were the main factors driving soil CH 4 fluxes. Unburned study areas were sinks of CH 4 through the entire measurement period, while immediately after the fire, the burned areas turned from CH 4 sink to CH 4 source. For nitrous oxide (N 2 O) measurements, time since fire was the only factor that significantly affected soil N 2 O fluxes. Shortly after the fire, N 2 O emissions increased significantly from both low- and high-intensity study plots. Two days after the fire, post-fire soil C and N content decreased in the O-horizon and increased within the first 5 cm of the soil mineral layer, and the trend was visible both in low- and high-severity fire plots. Samples collected four months after the fire, showed similar total soil C and N content as there was before the fire. [ABSTRACT FROM AUTHOR]