Cold winters, warm summers, no dry season: greenhouse gas emissions from forest organic soils in the Köppen–Geiger Dfb climate zone

Abstract. Greenhouse gas (GHG) emissions from organic soils are a key component of land-use-related emissions, particularly in countries with large areas of organic soils. Temperate-zone forest soils remain less studied in GHG research than boreal soils. However, recent work has expanded coverage in the northeastern temperate region, which, under the Köppen–Geiger climate classification, shares key climatic characteristics with the southern boreal region (Dfb). This study synthesised updated GHG flux data to evaluate carbon balance and emissions from forest organic soils in the Dfb zone, stratified by drainage status, nutrient availability, and dominant tree species. Such stratification revealed CO₂ source-sink patterns, which encourage the ecological relevance of using these categories for data aggregation. The dominant tree species reflected nutrient status: drained coniferous and deciduous stands have been reported as CO₂ sources, emitting 0.03 ± 0.55 and 0.47 ± 0.29 t CO₂‑C ha⁻¹ year⁻¹, respectively, though soils tended to shift toward CO₂ sinks in stands older than 25 years. In contrast, undrained soils have generally been observed to function as CO₂ sinks, although not necessarily in all sites. However, this stratification was less informative for CH₄ and N₂O. CH₄ fluxes were primarily determined by water table level rather than by other site variables, whereas N₂O showed a tendency toward elevated emissions in deciduous stands, irrespective of drainage status.