Methane emission from stems of European beech (Fagus sylvatica) offsets as much as half of methane oxidation in soil.

Trees are known to be atmospheric methane (CH 4 ) emitters. Little is known about seasonal dynamics of tree CH 4 fluxes and relationships to environmental conditions. That prevents the correct estimation of net annual tree and forest CH 4 exchange. We aimed to explore the contribution of stem emissions to forest CH 4 exchange. We determined seasonal CH 4 fluxes of mature European beech (Fagus sylvatica) stems and adjacent soil in a typical temperate beech forest of the White Carpathians with high spatial heterogeneity in soil moisture. The beech stems were net annual CH 4 sources, whereas the soil was a net CH 4 sink. High CH 4 emitters showed clear seasonality in their stem CH 4 emissions that followed stem CO 2 efflux. Elevated CH 4 fluxes were detected during the vegetation season. Observed high spatial variability in stem CH 4 emissions was neither explicably by soil CH 4 exchange nor by CH 4 concentrations, water content, or temperature studied in soil profiles near each measured tree. The stem CH 4 emissions offset the soil CH 4 uptake by up to 46.5% and on average by 13% on stand level. In Central Europe, widely grown beech contributes markedly to seasonal dynamics of ecosystem CH 4 exchange. Its contribution should be included into forest greenhouse gas flux inventories.