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

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.