In this study, 1) a model to estimate soil carbon dioxide (CO2) balance for forestry-drained peatlands was tested on site and countrywide levels in Finland. 2) A dataset of annual soil–atmosphere fluxes of CO2, methane (CH4) and nitrous oxide (N2O) from 68 sites was collected, and models fitted for their upscaling to a countrywide level. 3) The current greenhouse gas impact of the 68 study sites, including soil CO2, CH4 and N2O balances and the CO2 sink function of tree biomass increment, was estimated.
The soil CO2 balance estimation, as the difference between litter input to soil and CO2 efflux from soil, was straightforward to apply, but considerable uncertainty was caused by the inadequate level of knowledge on belowground plant–soil carbon fluxes. Soil–atmosphere gas fluxes could be upscaled to a countrywide level utilizing readily available forest inventory results and weather statistics. Soils in nutrient-rich study sites were sources of greenhouse gases while those in nutrient-poor study sites were sinks, on average. The current greenhouse gas impact, when no forest fellings occurred, was nevertheless climate cooling for both the nutrient-rich and poor sites due to the considerable CO2 sink formed by increasing tree biomass.