| Summary: | The ability to accurately assess the impact of organic soil drainage on greenhouse gas emissions (GHG) is still limited. Methane (CH<sub>4</sub>) 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 CH<sub>4</sub> and nitrous oxide (N<sub>2</sub>O) 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, CH<sub>4</sub> and N<sub>2</sub>O 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 (<i>Betula pendula</i> Roth), Norway spruce (<i>Picea abies</i> (L.) Karsten), and black alder (<i>Alnus glutinosai</i> (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 CH<sub>4</sub> emissions from drained and undrained soil were −4.6 ± 1.3 and 134.1 ± 134.7 kg CH<sub>4</sub> ha<sup>−1</sup> year<sup>−1</sup>, respectively. N<sub>2</sub>O emissions from undrained soil (4.1 ± 1.4 kg N<sub>2</sub>O ha<sup>−1</sup> year<sup>−1</sup>) were significantly higher compared to those from drained soil (1.7 ± 0.6 kg N<sub>2</sub>O ha<sup>−1</sup> year<sup>−1</sup>). In most of the study sites, undrained soil acted as a CH<sub>4</sub> sink, with the soil estimated as a mean source of CH<sub>4</sub>, which was determined by one site where an emission hotspot was evident. The undrained soil acted as a CH<sub>4</sub> sink due to the characteristics of GW level fluctuations, during which the vegetation season GW level was below 20 cm.
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