Eddy covariance observations of CO2, CH4 and N2O fluxes of a drained boreal peatland forest after clear-cutting

Clear-cutting of drained peatland forests, as a part of the conventional even-aged rotation forestry, significantly disturbs peat soil biogeochemistry due to changes in soil physical characteristics and microbial activity. Achieving spatially representative estimates of GHG emissions from such a complex area is a challenging task. Accurate estimates of GHG fluxes following clear-cutting are sorely needed for national greenhouse gas reporting and devising more climate-friendly forestry practices for these production ecosystems, abundant in the Nordic countries.

In December 2021 we initiated continuous eddy covariance (EC) measurements of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes on a nutrient-rich drained boreal peatland forest (ca. 6.1 ha) in southern Finland. The mature tree stand dominated by Norway spruce (Picea abies) was clear cut in March 2021. The measurements are part of a larger research effort aimed at understanding climatic impacts of forest management practices on drained peatlands. Here we focus on interpreting the spatiotemporal variability of GHG fluxes from the clear-cut site using the EC measurements.

The clear-cut area was emitting N₂O to the atmosphere throughout the measurement period, including the winter period. The emissions increased after snow melt and peaked during late July 2022. Despite CO₂ uptake offsetting approximately one third of ecosystem respiration, the clear-cut area was a strong source of CO₂ to the atmosphere during the year 2022 (2.0 kg(CO₂) m^-2 yr^-1). CH₄ emissions were small, yet clearly positive. The observed GHG fluxes showed clear wind-direction dependency indicative of spatial variability of GHG fluxes within the clear-cut. The spatial variability will be analysed based on detailed mapping of the clear-cut surface and footprint (i.e. source area) modelling, in combination with further scrutiny of the EC fluxes. Overall, these results provide the much-needed information on the GHG fluxes from such ecosystems and serve as a baseline for this site in the future.