Evaluation of long-term carbon dynamics in afforested drained peatlands: Insights from using the ForSAFE-Peat Model

Abstract. Afforested drained peatlands have significant implications for greenhouse gas (GHG) budgets, with contrasting views on their effects on climate. This study utilized the dynamic ecosystem model ForSAFE-Peat to simulate biogeochemical dynamics over two full forest rotations (1951–2088) in a nutrient-rich drained peatland afforested with Norway spruce (Picea abies) in southwest Sweden. Model simulations aligned well with observed groundwater levels (R² = 0.71) and soil temperatures (R² ≥ 0.78), and captured seasonal and annual net ecosystem production patterns, although daily variability was not always well represented. Model outputs were analysed under different system boundaries (soil, ecosystem, and ecosystem plus the fate of harvested wood products named ecosystem+HWP) to assess carbon exchanges using the net carbon balance (NCB) and the integrated carbon storage (ICS) metrics. Results indicated negative NCB and ICS across all system boundaries, except for a positive NCB calculated by the end of the simulation at the ecosystem+HWP level. The soil exhibited persistent carbon losses primarily driven by peat decomposition. At the ecosystem level, net carbon losses were reduced as forest growth partially offset soil losses until harvesting. NCB was positive (1015 g_C m^-2_soil) at the ecosystem+HWP level due to the slow decay of harvested wood products, but a negative ICS (-7.0×10⁵ g_C yr m^-2_soil) due to initial carbon losses. This study highlights the importance of system boundary selection and temporal dynamics in assessing the carbon balance of afforested drained peatlands.