- 1Kyoto University, Kyoto, Japan
- 2University of Helsinki, Helsinki, Finland
Trees, typically large trees in upland forests, emit CH4 produced in their trunk by methanogenic archaea. In this case, spatial variability of emission can be more complicated than when tree trunks act as a passive conduit for CH4 produced in the soil. However, due to poor accessibility, CH4 emissions from the trunk above 3 m, where a researcher cannot reach without a ladder, scaffold or crane, have not been well studied. The vertical emission patterns from trunks, including the upper part, and the processes driving them, i.e., CH4 production and transport, remain unexplored.
Using a crane truck, we investigated vertical patterns of CH4 emissions, internal CH4 concentration and production up to 12 m above ground in six trees of three species in a cool-temperate upland forest. We also conducted a modelling study of CH4 transport within trunks to know whether CH4 emitted from the upper part of the trunk, if present, is produced locally at the same height of the trunk or is produced elsewhere and transported to that height.
CH4 was actively emitted from the trunk at a height greater than 3 m, with peak emissions at 4 to 6 m above ground in some trees. CH4 production was observed consistently up to the highest sampling point at 12 m height. CH4 production hotspots in Japanese beech and horse-chestnut trees were characterized as decaying wood due to their low density and high moisture content. In Japanese cedar, production hotspots were surrounded by wet sapwood, suggesting that limited oxygen diffusion to the tree centre stimulated CH4 production. According to CH4 transport modelling, axial CH4 transport from the production hotspot upwards is more likely in trees with low radial diffusion. However, within a realistic parameter range, such long-distance axial CH4 transport could not be realized.
The results highlighted the complexity of endogenously produced CH4 emissions in the trunk. Oxygen level and wood decay, as suggested by our results, could be key factors to explain the heterogeneity of CH4 production inside the trunk, which can efficiently predict the spatial variability of the emission along the trunk height.
How to cite: Mochidome, T., Hölttä, T., Dannoura, M., and Epron, D.: Significant CH4 production and emission in the upper part of the tree trunk, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14314, https://doi.org/10.5194/egusphere-egu25-14314, 2025.