Variability in Stem Methane Emissions and Wood Methane Production of Different Tree Species in a Cold Temperate Mountain Forest

The role of trees, in addition to that of the soil, must be considered in CH 4 budget for forests. Although trees can emit CH 4 through their stems, there are uncertainties about the main factors that explain inter- and intraspecific variations, which impedes upscaling of measurements from the stem to the ecosystem level. This study aimed to characterize the variability in CH 4 emissions ( F_CH_4 ) from stems between species and individuals, and within individuals. We measured F_ CH_4 in situ during the snow-free period in five species in a temperate mountain forest, using individuals of different sizes and chambers at different heights along the stems. One coniferous species emitted almost no CH 4 , whereas four broadleaved species exhibited high intraspecific variability in F_ CH_4 (0–3.7 nmol m −2 s −1 ). Increasing trends in F_ CH_4 with tree diameter were observed for four species. The vertical patterns in F_ CH_4 were complex. Seasonal variations in F_ CH_4 , measured on two trees per species, were well explained by air temperature with apparent temperature sensitivity coefficients ( Q 10 ) between 1.2 and 2, which were not related to the antecedent precipitation indices, whether calculated over 7 or 30 days. Potential CH 4 production was detected in wood core segments incubated under anoxic conditions in the majority of individual trees of all species. Our results suggest that the CH 4 emitted by trunks can originate either from soil or internal sources. Scaling F_ CH_4 from trees at the stand level and developing process-based models of F_ CH_4 will remain challenging until the sources of variation are better explained.