Carbon Dioxide and Methane Fluxes From Tree Stems, Coarse Woody Debris, and Soils in an Upland Temperate Forest

Abstract

Forest soils and canopies are major components of ecosystem CO₂ and CH₄ fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO₂ and CH₄ fluxes. We measured CO₂ and CH₄ fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO₂ sources (4.58 ± 2.46 µmol m⁻² s⁻¹, mean ± 1 SD) and net sinks of CH₄ (−2.17 ± 1.60 nmol m⁻² s⁻¹). Coarse woody debris was a CO₂ source (4.23 ± 3.42 µmol m⁻² s⁻¹) and net CH₄ sink, but with large uncertainty (−0.27 ± 1.04 nmol m⁻² s⁻¹) and with substantial differences depending on wood decay status. Stems were CO₂ sources (1.93 ± 1.63 µmol m⁻² s⁻¹), but also net CH₄ sources (up to 0.98 nmol m⁻² s⁻¹), with a mean of 0.11 ± 0.21 nmol m⁻² s⁻¹ and significant differences depending on tree species. Stems of N. sylvatica, F. grandifolia, and L. tulipifera consistently emitted CH₄, whereas stems of A. rubrum, B. lenta, and Q. spp. were intermittent sources. Coarse woody debris and stems accounted for 35% of total measured CO₂ fluxes, whereas CH₄ emissions from living stems offset net soil and CWD CH₄ uptake by 3.5%. Our results demonstrate the importance of CH₄ emissions from living stems in upland forests and the need to consider multiple forest components to understand and interpret ecosystem CO₂ and CH₄ dynamics.