Main conclusion <p>Methane was rarely produced in the stems of living trees in the upland forests. However, it was largely produced in the swollen lower stems in the wetland forests.</p> Abstract <p>The methane (CH₄) fluxes on aboveground living trees have been widely observed over the last decades. However, aboveground living tree-based CH₄ production has been rarely studied in terrestrial ecosystems. Thus, it is essential to study aboveground CH₄ production in multiple tree species. In this study, we aimed to understand the CH₄ production in the stems of living trees in the subtropical forests from 445 individual living tree stems (1335 upper, middle, and lower tree stem segments). We found that substantial CH₄ concentrations of ≥ 1000 μL L⁻¹ and detectable CH₄ production of ≥ 0.2&#xa0;ng&#xa0;g⁻¹ dry weight (DW) h⁻¹ occurred only in ~ 5% of all sampled living tree stems in the upland forests. Substantial CH₄ concentrations and detectable CH₄ production occurred frequently in the swollen lower stems (a kind of eco-physiologic adaptation) but rarely in the straight stems of living trees in the wetland forests. Particularly, CH₄ production was significantly higher in the swollen lower stems compared to in the straight stems, with a mean rate of 22.2&#xa0;ng&#xa0;g⁻¹ DW h⁻¹, and the produced CH₄ was demonstrated to be microbial according to its highly depleted ¹³C abundance and its exponential kinetics in response to time. In global wetland forests, the existing eco-physiologic adaptations of living trees are potentially a distinctive CH₄ source, and thereby more research is required for understanding their CH₄ processes and fluxes.</p>