Short-term effects of harvesting alternatives on soil nitrous oxide fluxes in a boreal drained peatland forest

Abstract

Extensive areas of boreal peatland forests in the Nordic countries are approaching maturity and face harvesting, yet effects on soil nitrous oxide (N2O) fluxes remain unclear. This study examined short-term changes in soil N2O fluxes following two harvesting methods, clear-cutting (CC) and continuous-cover forestry via selection harvesting (CCF), compared to a non-harvested control (C) in a nutrient-rich, forestry-drained boreal peatland in southern Finland. Fluxes were measured using manual and automated chambers during pre-harvest (2020) and post-harvest (2021–2022) periods, alongside soil physical, chemical, and environmental properties to identify key controls of flux variability. N2O fluxes showed high temporal variation (−39 to 459 μg N2O m–2 h−1), primarily driven by temperature, precipitation, moisture, and water table dynamics, and pronounced spatial variation linked to soil nutrient concentrations (potassium, copper, phosphorus, and nitrogen), bulk density, and temperature. While emissions remained near neutral at the C site, harvesting increased emissions, although not significantly. In the first post-harvest year, annual emissions increased with harvesting intensity, yet no significant differences emerged between CCF and CC. Median [interquartile range] emissions were 0 [25], 163 [533], and 185 [194] mg N2O m−2 y–1 at the C, CCF and CC sites, respectively, with inherent spatial variability strongly influencing their spatial distribution. Limited water table rise at the CCF site and high spatial heterogeneity at the CC site likely constrained clearer treatment differences. Overall, our findings suggest that CCF may better mitigate emissions than CC in nutrient-rich, forestry-drained boreal peatlands, warranting further replicated and long-term research.