Eddy covariance fluxes of CO₂, CH₄ and N₂O on a drained peatland forest after clearcutting

Abstract. Even-aged forestry based on clearcut harvesting, planting, and one to three thinnings is currently the dominant management approach in Fennoscandia. However, our understanding of the greenhouse gas (GHG) emissions following clearcutting remains limited, particularly on drained peatland forests. In this study, we report eddy covariance-based (EC) net emissions of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from a boreal fertile drained peatland forest one year after the harvest. Our results show that on annual scale, the site was a net CO₂ source. The CO₂ emissions dominate the total annual GHG balance (23.3 t CO₂-eq ha^-1 a^-1, 82.5 % of the total), while the role of N₂O emissions (4.8 t CO₂-eq ha^-1 a^-1, 17.1 %) was also significant. The site was a weak CH₄ source (0.1 t CO₂-eq ha^-1 a^-1, 0.4 %). A statistical model was developed to estimate surface-type-specific CH₄ and N₂O emissions. The model was based on air temperature and fraction of specific surface-types within the EC flux footprint. The surface-types were classified using unmanned aerial vehicle (UAV) spectral imaging and machine learning. Based on the statistical models, the highest surface-type specific CH₄ emissions occurred from plant-covered ditches and exposed peat, while the surfaces dominated by living trees, dead wood, and litter along with plant-covered ditches were the main contributors to N₂O emissions. Our study provides new insights into how CH₄ and N₂O fluxes are affected by surface-type variation across clearcutting areas in boreal forested peatlands. Our findings highlight the need for integrating surface-type-specific flux modelling, EC-based data, and chamber-based flux measurements to comprehend the GHG emissions following clearcutting. Results strengthen the accumulated evidence that recently clearcut peatland forests are significant GHG sources.