Nitrous oxide (N2O) and methane (CH4) fluxes from tree stems in birch and black alder stands - a case study in forests with deep peat soils

The aim of the study is to evaluate greenhouse gas (GHG) fluxes from stems in black alder (Alnus glutinosa (L.) Gaertn.) and birch (Betula pendula Roth) stands with drained and naturally wet nutrient rich peat soils, as well as to evaluate correlation between the GHG fluxes, soil temperature and groundwater level. The study was implemented in 8 forest stands – three black alder stands with nutrient rich peat soil (stand types according to national classification – Dryopterioso-caricosa and Filipendulosa) and 5 birch stands with peat soil (stand type Oxalidosa turf. mel. and Dryopterioso-caricosa). Measurement of GHG fluxes was continued for 12 months using Gasmet DX4040 FTIR analyser and removable non-transparent chambers of fixed volume and area. GHG fluxes were measured at 0.5, 1.0 and 1.5 m height on 3 trees in every stand. According to the study results the average CH4 emissions from stem surface in birch stands are 6.9 ± 6.2 g CO2 eq m·yr and in black alder stands 1.0 ± 3.2 g CO2 eq m·yr. Groundwater level significantly effects CH4 emissions – if it remains above 15 cm during summer, the CH4 emissions from stem increases to 84.0 ± 25.2 g CO2 eq. m·yr. Tree stems in drained peat soils are not a source of CH4 emissions. According to the study results tree stems in peat soils are not producing N2O emissions.