Comparison of the ecosystem carbon balance of two contrasting drained peatland forests in boreal Sweden

Northern peatlands act as an important global reservoir of carbon. Extensive areas of natural peatlands have been drained during the past century to increase timber production, which has largely affected the ecosystem biogeochemistry and the associated climate impacts. However, the ecosystem carbon balance of drained peatlands are still not well understood, especially the difference between low- and high-productive drained peatland forests in the boreal region. In this study, we estimated the carbon balance from a nutrient-poor and a nutrient-rich drained peatland forest in boreal Sweden based on eddy covariance measurements over four years (2021–2024) and one year and a half (2023–2024), respectively. We found that the annual net ecosystem CO2 exchange (NEE) of the lower productive drained peatland forest showed a high interannual variability which varied from a carbon sink to carbon neutral over the 4 years (-82 to 0.18 g C m^-2 y^-1). In 2024, the high-productive drained peatland forest showed the tendency to serve as a carbon sink (-72 g C m^-2 y^-1) whereas the lower productive drained peatland forest was carbon neutral (0.18 g C m^-2 y^-1). Compared with the low drained peatland forest, the nutrient-rich drained peatland forest featured higher gross primary productivity (GPP) as well as higher ecosystem respiration (ER). Our study suggests the different carbon sink capacities of low- and high-productive drained peatland forests as well as their potential of distinct responses to future climate change.