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Peatland restoration is seen as a key nature‐based solution to tackle climate change and biodiversity loss. In Europe, nearly 50% of peatlands have been drained during the last decades, which have shifted their soils to carbon dioxide (CO2) sources. Soils of forestry‐drained peatlands are known to vary from CO2 sources to small sinks depending on their fertility and wetness. When peatlands are restored, it can be expected that rates of CO2 and methane exchange will vary depending on site fertility and wetness. We generated seven restoration pathways with different starting and end points and assessed the climate impacts of them. The GHG emission coefficients were compiled from literature, and radiative forcing was calculated for a 500‐year time period since restoration. All seven restoration pathways improved carbon sink capacity; however, the climate impact differed from cooling to warming. The highest cooling impact occurred in a pathway leading from nutrient‐rich drained peatlands toward tree‐covered spruce or pine mires. Warming impacts occurred in a pathway leading from nutrient‐poor drained peatlands toward open peatlands. The results of this study can be used to help identify peatland sites and restoration targets to maximize climate change mitigation from restoration. In practice, however, restoration has to fulfill other targets, such as biodiversity safeguarding, improvement of hydrological conditions, and socio‐economic aspects. Fulfilling all targets simultaneously requires compromises on all targets. [ABSTRACT FROM AUTHOR]

Peatland management practices, such as drainage and restoration, have a strong effect on boreal peatland methane (CH4) fluxes. Furthermore, CH4 fluxes are strongly controlled by local environmental conditions, such as soil hydrology, temperature and vegetation, which are all experiencing considerable changes due to climate change. Both management practices and climate change are expected to influence peatland CH4 fluxes during this century but the magnitude and net impact of these changes is still insufficiently understood. In this study, we simulated the impacts of two forest management practices, rotational forestry and continuous cover forestry, as well as peatland restoration on hypothetical forestry-drained peatlands across Finland using the land surface model JSBACH coupled with the soil carbon model YASSO and peatland methane model HIMMELI. We further simulated the impacts of climatic warming using two RCP (Representative Concentration Pathway) emission scenarios, RCP 2.6 and RCP 4.5. We investigated the response of CH4 fluxes, soil water-table level (WTL), soil temperatures, and soil carbon dynamics to changes in management practices and climate. Our results show that management practices have a strong impact on peatland WTLs and CH4 emissions continuing for several decades, with emissions increasing after restoration and clearcutting. Towards the end of the century, WTLs increase slightly likely due to increasing precipitation. CH4 fluxes have opposing trends in restored and drained peatlands. In restored peatlands, CH4 emissions decrease towards the end of the century following the decomposition harvest residue in the top peat layers, while in drained peatland forests sinks get weaker and occasional emissions become more common, likely due to rising WTL and soil temperatures. The strength of these trends vary across the country, with CH4 emissions from restored peatlands decreasing more strongly in southern Finland and forest soil CH4 sinks weakening most in northern Finland. [ABSTRACT FROM AUTHOR]

We compiled published peer-reviewed CO 2 , CH 4 , and N 2 O data on managed drained organic forest soils in boreal and temperate zones to revisit the current Tier 1 default emission factors (EFs) provided in the IPCC (2014) Wetlands Supplement: to see whether their uncertainty may be reduced; to evaluate possibilities for breaking the broad categories used for the IPCC EFs into more site-type-specific ones; and to inspect the potential relevance of a number of environmental variables for predicting the annual soil greenhouse gas (GHG) balances, on which the EFs are based. Despite a considerable number of publications applicable for compiling EFs being added, only modest changes were found compared to the Tier 1 default EFs. However, the more specific site type categories generated in this study showed narrower confidence intervals compared to the default categories. Overall, the highest CO 2 EFs were found for temperate afforested agricultural lands and boreal forestry-drained sites with very low tree stand productivity. The highest CH 4 EFs in turn prevailed in boreal nutrient-poor forests with very low tree stand productivity and temperate forests irrespective of nutrient status, while the EFs for afforested sites were low or showed a sink function. The highest N 2 O EFs were found for afforested agricultural lands and forestry-drained nutrient-rich sites. The occasional wide confidence intervals could be mainly explained by single or a few highly deviating estimates rather than the broadness of the categories applied. Our EFs for the novel categories were further supported by the statistical models connecting the annual soil GHG balances to site-specific soil nutrient status indicators, tree stand characteristics, and temperature-associated weather and climate variables. The results of this synthesis have important implications for EF revisions and national emission reporting, e.g. by the use of different categories for afforested sites and forestry-drained sites, and more specific site productivity categories based on timber production potential. [ABSTRACT FROM AUTHOR]

In peatlands drained for forestry, the soil carbon (C) or carbon dioxide (CO 2) balance is affected by both (i) higher heterotrophic CO 2 -C release from faster decomposing soil organic matter (SOM) and (ii) higher plant litter C input from more vigorously growing forests. This balance and other greenhouse gas (GHG) sinks and sources in managed lands are annually reported by national GHG inventories to the United Nations Climate Change Convention. In this paper, we present a revised, fully dynamic method for reporting the CO 2 balance of drained peatland forest soils in Finland. Our method can follow temporal changes in tree biomass growth, tree harvesting and climatic parameters, and it is built on empirical regression models of SOM decomposition and litter input in drained peatland forests. All major components of aboveground and belowground litter input from ground vegetation as well as live trees and trees that died naturally are included, supplemented by newly acquired turnover rates of woody plant fine roots. Annual litter input from harvesting residues is calculated using national statistics of logging and energy use of trees. Leaching, which also exports dissolved C from drained peatlands, is not included. The results are reported as time series from 1990–2021 following the practice in the GHG inventory. Our revised method produces an increasing trend of annual emissions from 0.2 to 2.1 t CO 2 ha -1 yr -1 for the period 1990–2021 in Finland (equal to a trend from 1.4 to 7.9 Mt CO 2 yr -1 for the entire 4.3 Mha of drained peatland forests), with a statistically significant difference between the years 1990 and 2021. Across the period 1990–2021, annual emissions are on average 1.5 t CO 2 ha -1 yr -1 (3.4 Mt CO 2 yr -1 for 2.2 Mha area) in warmer southern Finland and - 0.14 t CO 2 ha -1 yr -1 (- 0.3 Mt CO 2 yr -1 for 2.1 Mha area) in cooler northern Finland. When combined with data on the CO 2 sink created by the growing tree stock, in 2021 the drained peatland forest ecosystems were a source of 1.0 t CO 2 ha -1 yr -1 (2.3 Mt CO 2 yr -1) in southern Finland and a sink of 1.2 t CO 2 ha -1 yr -1 (2.5 Mt CO 2 yr -1) in northern Finland. We compare these results to those produced by the semi-dynamic method used earlier in the Finnish GHG inventory and discuss the strengths and vulnerabilities of the new revised method in comparison to more static emission factors. [ABSTRACT FROM AUTHOR]

The urgent need to mitigate climate change has evoked a broad interest in better understanding and estimating nitrous oxide (N2O) emissions from different ecosystems. Part of the uncertainty in N2O emission estimates still comes from an inadequate understanding of the temporal and small-scale spatial variability of N2O fluxes. Using 4.5 years of N2O flux data collected in a drained peatland forest with six automated chambers, we explored temporal and small-scale spatial variability of N2O fluxes. A Random forest with conditional inference trees was used to find immediate and time-lagged relationships between N2O flux and environmental conditions across seasons and years with different environmental conditions. The temporal variation of N2O flux was large, and the daily mean flux varied between –11 and 1760 µg N2O m⁻² h⁻¹. Three of the six measurement chambers had a maximum N2O flux of less than 400 µg N2O m⁻² h⁻¹, while the fluxes in the other three chambers exceeded 1000 µg N2O m⁻² h⁻¹. Spatial differences in the flux persisted over time, and despite the high small-scale spatial variability, the temporal patterns of the fluxes were relatively similar across the chambers. Soil moisture as well as air and soil surface temperature were the most important variables in the random forest, with lagged soil moisture also considered important. N2O flux responded to soil wetting with a time lag of 1–7 days, but the length of the time lag varied spatially and between seasons indicating interactions with other spatially and temporally variable environmental conditions. The high temporal variation in N2O flux was related to a) seasonally variable environmental conditions, with the highest N2O fluxes measured after summer dry-wet cycles and winter soil freezing, and b) to annually variable seasonal weather conditions, which lead to high year-to-year variability in N2O budget. Changes especially in the frequency of summer precipitation events and in winter temperature and snow conditions may increase the variability of annual N2O emissions if the variability in summer and winter weather conditions increases due to climate change. [ABSTRACT FROM AUTHOR]

Reporting the greenhouse gas (GHG) emissions from the LULUCF sector in the GHG inventory requires sound methods for estimating both the inputs and outputs of carbon (C) in managed ecosystems. Soil CO2 balance of forests consists of the CO2 released from decomposing soil organic matter (SOM) and the C entering 15 the soil through aboveground and belowground plant litter input. Peatlands drained for forestry release soil C as CO2 because the drainage deepens the oxic peat layer prone to SOM decomposition. IPCC Guidelines provide default CO2 emission factors for different climatic zones and the defaults or locally adapted static emission factors are commonly in use in GHG inventory reporting for drained peatlands. In this paper, we describe a new dynamic method to estimate the CO2 balance of drained peatland forest soils in Finland. Contrary to static emission factors, the annual CO2 release from soil is in our method estimated using empirical regression models driven by time series of tree basal area (BA), derived from the national forest inventories in Finland, time series of air temperature and the drained peatland forest site type. Aboveground and belowground litter input is also estimated using empirical models with newly acquired turnover rates for tree fine roots and BA as a dynamic driver. All major components of litter input from ground vegetation and live, harvested and naturally died trees are included. Our method produces an increasing trend of emissions from 1.4 to 7.9 Mt CO2 for drained peatland forest soils in Finland for the period 1990-2021, with a statistically significant difference between years 1990 and 2021. Across the period 1990-2021, annual emissions are on average 3.4 Mt and -0.3 Mt in southern and northern parts of Finland, respectively. When combined with data of the CO2 sink created by trees, it appears that in 2021 drained peatland forest ecosystems were a source of 2.3 Mt CO2 in southern Finland and a sink of 2.5 Mt CO2 in northern Finland. We compare the emissions produced by the new method with those produced by the old GHGI method of Finland and discuss the strengths and vulnerabilities of our method in comparison to static emission factors. [ABSTRACT FROM AUTHOR]