We compiled published peer-reviewed CO₂, CH₄, and N₂O 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 CO₂ EFs were found for temperate afforested agricultural lands and boreal forestry-drained sites with very low tree stand productivity. The highest CH₄ 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 N₂O 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.

The ability to accurately assess the impact of organic soil drainage on greenhouse gas emissions (GHG) is still limited. Methane (CH₄) emissions are characterized by significant variations, and GHG emissions from nutrient-rich organic soil in the region have not been extensively studied. The aim of this study was to assess CH₄ and nitrous oxide (N₂O) emissions from nutrient-rich organic soil in hemiboreal forests to provide insights into their role in regional GHG balance. Over the course of one year, CH₄ and N₂O emissions, as well as their affecting factors, were monitored in 31 forest compartments in Latvia in both drained and undrained nutrient-rich organic soils. The sites were selected to include forests of different ages, dominated by silver birch (Betula pendula Roth), Norway spruce (Picea abies (L.) Karsten), and black alder (Alnus glutinosai (L.) Gärtner), as well as clearcuts. Soil GHG emissions were estimated by collecting gas samples using the closed manual chamber method and analyzing these samples with a gas chromatograph. In addition, soil temperature and groundwater level (GW) measurements were conducted during gas sample collection. The mean annual CH₄ emissions from drained and undrained soil were −4.6 ± 1.3 and 134.1 ± 134.7 kg CH₄ ha⁻¹ year⁻¹, respectively. N₂O emissions from undrained soil (4.1 ± 1.4 kg N₂O ha⁻¹ year⁻¹) were significantly higher compared to those from drained soil (1.7 ± 0.6 kg N₂O ha⁻¹ year⁻¹). In most of the study sites, undrained soil acted as a CH₄ sink, with the soil estimated as a mean source of CH₄, which was determined by one site where an emission hotspot was evident. The undrained soil acted as a CH₄ sink due to the characteristics of GW level fluctuations, during which the vegetation season GW level was below 20 cm.

This study was designed to estimate the variation in non-volatile carbon (C) content in different above- and belowground tree parts (stem, living branches, dead branches, stumps, coarse roots and small roots) and to develop country-specific weighted mean C content values for the major tree species in hemiboreal forests in Latvia: Norway spruce (Picea abies (L.) H. Karst.), Scots pine (Pinus sylvestris L.), birch spp. (Betula spp.) and European aspen (Populus tremula L.). In total, 372 sample trees from 124 forest stands were selected and destructively sampled. As the tree samples were pre-treated by oven-drying before elemental analysis, the results of this study represent the non-volatile C fraction. Our findings indicate a significant variation in C content among the tree parts and studied species with a range of 504.6 ± 3.4 g·kg⁻¹ (European aspen, coarse roots) to 550.6 ± 2.4 g·kg⁻¹ (Scots pine, dead branches). The weighted mean C content values for whole trees ranged from 509.0 ± 1.6 g·kg⁻¹ for European aspen to 533.2 ± 1.6 g·kg⁻¹ for Scots pine. Only in Norway spruce was the whole tree C content significantly influenced by tree age and size. Our analysis revealed that the use of the Intergovernmental Panel on Climate Change (IPCC) default C content values recommended for temperate and boreal ecological zones leads to a 5.1% underestimation of C stock in living tree biomass in Latvia’s forests. Thus, the country-specific weighted mean C content values for major tree species we provide may improve the accuracy of National Greenhouse Gas Inventory estimates.

Impact of drainage of organic soils in forest land on soil carbon (C) stock changes is of high interest not only to accurately estimate soil C stock changes, but also to provide scientifically based recommendations for forest land management in context of climate change mitigation. To improve knowledge about long-term impact of drainage on nutrient-rich organic soils in hemiboreal forests in Latvia, 50 research sites representing drained conditions (Oxalidosa turf. mel. (Kp) and Myrtillosa turf. mel. (Ks) forest site types) and undrained conditions as control areas (Caricoso-phragmitosa, Dryopterioso-caricosa and Filipendulosa forest site types) were selected. Soil C stock changes after drainage was evaluated by comparing current C stock in drained organic soils to theoretical C stock before drainage considering impact of soil subsidence. During the 53-years period after drainage, the peat subsidence was higher in nutrient-rich Kp forest site type compared to moderate nutrient-rich Ks forest site type (peat subsided by 37.0 ± 4.8 and 23.3 ± 4.8 cm, respectively). In nutrient-rich Kp forest site type, soil C stock decreased by 4.98 ± 1.58 Mg C ha–1 yr–1 after drainage, while no statistically significant changes in soil C stock (0.19 ± 1.31 Mg C ha–1 yr–1) were observed in moderate nutrient-rich soils in Ks forest site type. Thus, in Ks forest site type, the main driver of the peat subsidence was the physical compaction, while in Kp forest site type contribution of organic matter decomposition and consequent soil C losses to subsidence of the peat was significant.

The impact of the moisture regime on the carbon budget of organic soils with different nutrient statuses has not been fully studied in hemiboreal forests thus far. This study evaluated soil carbon (C) stock changes in forests with drained and undrained nutrient-rich organic soils by estimating C loss through respiration and C input through the litter. The study sites included forest stands dominated by Norway spruce (Picea abies), silver birch (Betula pendula), black alder (Alnus glutinosa), and clear-cuts. Soil respiration was measured using the chamber method, and to estimate the soil C input by litter—the biomass and the C content of the foliar litter, ground vegetation, and fine-root production were measured. The soil in forest stands acted as a C sink. The carbon dioxide (CO₂) removal rates of 0.4 ± 0.4 t C ha⁻¹ year⁻¹ and 0.1 ± 0.4 t C ha⁻¹ year⁻¹ were estimated for undrained and drained soil in forest stands, respectively. The soil in the clear-cuts acted as a CO₂ source, and the annual emissions ranged from 0.4 ± 0.4 t C ha⁻¹ year⁻¹ in undrained to 0.9 ± 0.7 t C ha⁻¹ year⁻¹ in drained conditions. The reason for the soil in clear-cuts being a C source was increased C loss by respiration and reduced soil C input by litter. Furthermore, the mean soil C input by ground vegetation biomass in the clear-cuts was considerably higher than in the forest stands, which did not compensate for the increase in soil respiration and the absence of C input by foliar litter and the fine roots of trees. The results of the study on annual soil C stock changes can be used as an emission factor in national greenhouse gas inventories of forest land in the hemiboreal zone.

We determined the magnitude of instantaneous greenhouse gas (GHG) emissions from drainage ditches in hemiboreal peatlands in Latvia during the frost-free period of 2021 and evaluated the main affecting factors. In total, 10 research sites were established in drained peatlands in Latvia, including active and abandoned peat extraction sites and peatland forests. Results demonstrated that in terms of global warming potential, the contribution of CO₂ emissions to the total budget of GHG emissions from drainage ditches can exceed the CH₄ contribution. The average CO₂ and N₂O emissions from drainage ditches in peatland forests were significantly higher than those from ditches in peat extraction sites, while there was no difference in average CH₄ emissions from ditches between peatland forests and peat extraction sites. Emissions from ditches of all GHGs increased with increasing temperature. In addition, CO₂ and N₂O emissions from drainage ditches increased with decreasing groundwater (GW) level. They were also negatively correlated with water level in ditches, but positively with potassium (K) and total nitrogen (TN) concentrations in water. By contrast, CH₄ emissions from drainage ditches increased with increasing GW level and water level in ditches but were negatively correlated with K and TN concentrations in water.