Methane fluxes from tree stems and soils along a habitat gradient

Abstract

Forests are major sources of terrestrial CH₄ and CO₂ fluxes but not all surfaces within forests have been measured and accounted for. Stem respiration is a well-known source of CO₂, but more recently tree stems have been shown to be sources of CH₄ in wetlands and upland habitats. A study transect was established along a natural moisture gradient, with one end anchored in a forested wetland, the other in an upland forest and a transitional zone at the midpoint. Stem and soil fluxes of CH₄ and CO₂ were measured using static chambers during the 2013 and 2014 growing seasons, from May to October. Mean stem CH₄ emissions were 68.8 ± 13.0 (mean ± standard error), 180.7 ± 55.2 and 567.9 ± 174.5 µg m⁻² h⁻¹ for the upland, transitional and wetland habitats, respectively. Mean soil methane fluxes in the upland, transitional and wetland were − 64.8 ± 6.2, 7.4 ± 25.0 and 190.0 ± 123.0 µg m⁻² h⁻¹, respectively. Measureable CH₄ fluxes from tree stems were not always observed, but every individual tree in our experiment released measureable CH₄ flux at some point during the study period. These results indicate that tree stems represent overlooked sources of CH₄ in forested habitats and warrant investigation to further refine CH₄ budgets and inventories.