Restoration of forestry-drained oligotrophic peatlands can bring climate change mitigation within a few decades

Teemu Tahvanainen 

Introduction: Assessment of climate mitigation of peatland restoration is urgently needed, but data on greenhouse gas (GHG) fluxes from restored forestry-drained peatlands (FDP) is sparse. Using surrogate values from pristine peatlands, some studies have indicated long-lasting warming effect of restoration especially of nutrient-poor FDPs, while studies considering realized conditions and data from restored sites are missing. Objectives: This study aims at estimation of climate mitigation potential of restoration of FDPs based on post-restoration development of vegetation and hydrology. Methods: Dynamic trajectories of GHG-fluxes were calculated with process-based models informed by published studies of FDPs and restored peatlands. The model was applied to a sample of 12 restoration sites in Finland with data of carbon sequestration and water-table depth trends. The impact of restoration on global climate forcing was modelled against reference scenario of continued drainage. Results: Hypothetical restoration scenarios resulted in initial warming effect, but a hummock-level scenario (deep WTD) shifted to a climate cooling effect already after 15 years of restoration. In contrast, a flark-level scenario (shallow WTD) showed increasing warming over the 100-year assessment period. In the empirical data, climate cooling impact was predicted in half of cases already after 10 years, and in most cases within 100 years. Restoration resulted in an average reduction of cumulative absolute global forcing by -1.78 (SD 1.74) t CO2-equivalent ha-1 yr-1 over 100 years. Incorporating historical inference from peat inventories and forest management in the drainage scenario indicated even higher mitigation potential for restoration. Conclusions: The results predict considerably better climate mitigation potential for restoration of oligotrophic FDPs than suggested by previous modelling studies. Implications for Practice: Climate mitigation by restoration of nutrient-poor FDPs can be improved with temporarily high CO2 sequestration and potential dampening of CH4 emissions by optimizing growth of new Sphagnum moss layer. Oligotrophic FDPs have higher mitigation potential than mesotrophic FDPs due to higher moss growth above water level. Drainage scenarios should be considered with alternative management options for climate impact assessment of restoration.