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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]

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 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]

1 In a glasshouse experiment we studied the effect of raised C[O.sub.2] concentration (720 p.p.m.) on C[H.sub.4] emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17-20 [degrees] C). The potential for C[H.sub.4] production and oxidation was measured at the end of the emission experiment. 2 The vascular cores ('Sedge') consisted of a moss layer with sedges, and the moss cores ('Sphagnum') of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6-12 times higher from the Sedge cores than from the Sphagnum cores. The release of C[H.sub.4] from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures. 3 In both Sedge and Sphagnum samples, C[O.sub.2] treatment doubled the potential C[H.sub.4] production but had no effect on the potential C[H.sub.4] oxidation. A raised concentration of C[O.sub.2] increased C[H.sub.4] efflux weakly and only at the highest peat temperatures (1720 [degrees] C). 4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised C[O.sub.2] concentrations, and would thus retard any consequent increase in C[H.sub.4] emission. Keywords: C[O.sub.2] enrichment, glasshouse experiment, methane efflux, production and oxidation potentials

1 C[O.sub.2] emissions in boreal peatlands were measured during two seasons on various mire site types representing different nutrient statuses and water tables. In order to examine the long term effects of water table draw-down on the C[O.sub.2] fluxes, the sites also included 25-50-year-old drainages. 2 On virgin sites the lowest C[O.sub.2] fluxes were measured at ombrotrophic sites dominated by Sphagnum fuscum (78-127mg C[O.sub.2] [m.sup.-2] [h.sup.-1] at 12 [degrees] C, 60-200g C[O.sub.2]-C [m.sup.-2] [year.sup.-1]) and the highest C[O.sub.2] fluxes were at ombrotrophic sites with abundant under-storey vegetation (183-259 mg C[O.sub.2] [m.sup.-2] [h.sup.-1] at 12 [degrees] C, 290-340 g C[O.sub.2]-C [m.sup.-2] [year.sup.-1]). 3 Lowering of the water table by 1 cm increased C[O.sub.2] fluxes by an average of 7.1 mg C[O.sub.2] [m.sup.-2] [h.sup.-1] at 12 [degrees] C and 9.5g C[O.sub.2]-C [m.sup.-2] [year.sup.-1]. In some cases the effect of ditches on the water table, and correspondingly on C[O.sub.2] fluxes, was small. However, effective draining caused [approximately equal to] 100% increase in C[O.sub.2] fluxes. Drainages had higher C[O.sub.2] fluxes compared with virgin subsites at the same temperature and water table. 4 The effect of temperature on C[O.sub.2] fluxes depended on the water table, the average [Q.sub.10] value being 2.9 with water tables of 0-20 cm and 2.0 with water tables below 20 cm. 5 C[O.sub.2] fluxes are compared with primary production figures, and peat carbon stores and the carbon balance in changing climate are discussed. Keywords: C[O.sub.2] flux, drainage, peatland, temperature, water table