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.

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.

Assessments of net greenhouse gas (GHG) emissions in forest land with drained organic soils conducted within the scope of National GHG inventories requires reliable data on litter production and carbon (C) input to soil information. To estimate C input through tree above-ground litter, sampling of above-ground litter was done in 36 research sites in Latvia representing typical forests with drained organic soils in hemiboreal region. To estimate C input through tree below-ground litter and litter from ground vegetation, modelling approach based on literature review and data on characteristics of forest stands with drained organic soils in Latvia provided by National Forest Inventory (NFI) was used. The study highlighted dependence of C input to soil through litter production from the stand characteristics and thus significant differences in the C input with litter between young and middle age stands. The study also proves that drained organic soils in middle age forests dominated by Silver birch, Scots pine and Norway spruce may not be the source of net GHG emissions due to offset by C input through litter production. However, there is still high uncertainty of C input with tree below-ground litter and ground vegetation, particularly, mosses, herbs and grasses which may have crucial role in C balance in forests with drained organic soils. Key words: forests, drained organic soils, litter production, carbon input, National GHG inventory

This study investigates the soil organic carbon (SOC) and whole tree biomass carbon (C), soil bulk density (BD) as well as changes in these parameters in afforested areas in Latvia. The study covered 24 research sites in afforested areas—juvenile forest stands dominated by Scots pine, Norway spruce and Silver birch. The initial measurements were conducted in 2012 and repeated in 2021. The results show that afforestation mostly leads to a general decrease in soil BD and SOC stock in 0–40 cm soil layer and an increase in C stock in tree biomass across afforested areas with various tree species, soil types, and former land uses. The physical and chemical properties of the soil could explain the differences in changes in soil BD and SOC caused by afforestation, as well as the impact of past land use may have persisted. When comparing the changes in SOC stock with the increase in C stock in tree biomass due to afforestation, taking into account the decrease in soil BD and the resulting elevation of soil surface level, the afforested areas at juvenile development stage can be considered a net C sink.

In the Northern Hemisphere, forests play an important role in carbon storage. During the past few decades in the eastern Baltic and Nordic regions, forest drainage has been a common occurrence, which also has an effect on carbon stock. Most of the studies on this issue were carried out in boreal zones and were focused on short-term effects. Thus, our aim was to evaluate the long-term (after 54 years) effect of drainage on carbon stock (CS) changes in organic soil (Fibric histosols) in hemiboreal forests. Three forest types were selected in drained (Myrtillosa turf. mel (Mmel)) and undrained (Caricoso–phragmitosa (CP) and Sphagnosa (Sph)) parts of the same area. Surface level changes, soil penetration resistance, and soil and tree biomass carbon stock were assessed to evaluate the drainage effect. Drainage caused an average surface level drop of 25 cm, but did not deplete the soil carbon pool, resulting in significantly and substantially higher (2 to 6 times) tree biomass carbon stock. The drainage of organic soils in managed wet forests leads to an increased long-term contribution to climate change mitigation, thus such areas should be established or maintained in conjunction with areas that maximize other ecosystem services to ensure the sustainability of forest landscapes.

Scots pine (Pinus sylvestris L.) is one of the most widespread and economically most important tree species in Latvia. Scots pine forest health and element flow changes have been monitored in Latvia within the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) with assessment of crown condition and damaging agents at 115 Level I monitoring sites (mostly oligothrophic and mesotrophic Vacciniosa, Myrtillosa and Hylocomiosa forests) and with sampling and analyses of environmental samples at three Level II monitoring sites representing typical Scots pine forests (Myrtillosa) in hemiboreal conditions in Latvia. This study summarizes the background information and presents the trends of forest health, carbon turnover and environment condition in Scots pine forest since 2009. In general, defoliation rate in Scots pine stands remains stable for the studied period, with some yearly fluctuations, possibly related to regional insect outbreaks, especially well demonstrated in two Level II plots. The share of damaged trees varied by year from 12.8% to 19% of the total number; the main cause of damage was direct action of man. Chemical element flows in Scots pine forests in Level II monitoring plots have been relatively stable as well except the decreasing trend in total N concentration in deposition and SO4-S concentration in soil solution and increasing trends in DOC concentration in soil solution that is in line with common trends in Europe. Carbon input with above-ground litter was relatively stable during the whole period; however, interannual variations were rather wide.