Some tree trunks in upland forests emit methane (CH₄), the second strongest anthropogenic greenhouse gases. Wood in tree trunk is thought to be a site of CH₄ productions and CH₄ diffusion. To understand mechanisms leading to the emission, we investigated the variation in trunk CH₄ emission, trunk internal CH₄ production, and gas volumetric fraction of wood (GVF) in 13 species.
Most tree trunks emitted CH₄ consistently. The difference in trunk CH₄ emission among species was significant (Kruskal-Wallis test: p < 0.001). There was a tendency that the wood of diffuse-porous species produced more than the wood of ring-porous species, but the difference was not significant. From the relationship of production and emission of CH₄, one Yachidamo tree emitted CH₄ at high rate with virtually no production, implying CH₄ was coming from the soil. In contrast, trees of several species produced a large amount of CH₄, but emission rate was low, suggesting that CH₄ radial diffusion was limited. The GVF did not explain so much the difference between production and emission among species. For further research, quantification of CH₄ diffusivity and anatomical characteristic of wood and bark will provide better estimation of CH₄ transport in wood, both radially and axially.