Overwintering fires can occur in both peatlands and upland forests with varying ecological impacts

Climate warming is increasing the prevalence of overwintering 'zombie' fires, which are expected to occur primarily in peatlands, undermining carbon storage through deep burning of organic soils. We visited overwintering fires in Northwest Territories, Canada, and Interior Alaska, United States, and present field measurements of where overwintering fires are burning in the landscape and their impact on combustion severity and forest regeneration. Combustion severity hotspots did not generate overwintering, but peat and woody biomass smouldering both supported overwintering, leading to wintertime smouldering in both treed peatlands and upland forests. These findings create challenges for fire managers and uncertainty about carbon emissions, but forest regeneration was not compromised.