Methane and Carbon Dioxide Fluxes from Stems, Soils, and Coarse Woody Debris in a Temperate Forest

Abstract:

Quantifying the magnitude and variability of greenhouse gas fluxes from different terrestrial carbon pools is necessary for enhancing understanding of terrestrial carbon cycling. While much more is known about variability CO₂ fluxes, we have little information on how CH₄ fluxes vary across multiple carbon pools within terrestrial ecosystems. We measured fluxes of CH₄ and CO₂ from living tree stems, soils, and coarse woody debris within a temperate forested watershed during the growing season (May-November). Fluxes of both CH₄ and CO₂ were significantly different among carbon pools. Living tree stems were weak sources of both CH₄ and CO₂ with seasonal means (± 1 SD) of 0.08 ± 0.19 nmol CH₄ m^-2 s^-1 and 1.16 ± 1.21 µmol CO₂ m^-2 s^-1. Soils were sinks of CH₄ and sources of CO₂ with seasonal means (± 1 SD) of -2.00 ± 1.41 nmol CH₄ m^-2 s^-1 and 3.07 ± 2.10 µmol CO₂ m^-2 s^-1. Fluxes of CH₄ and CO₂ from coarse woody debris were largely variable relative to the other pools with seasonal means (± 1 SD) of -0.21 ± 0.76 nmol CH₄ m^-2 s^-1 and 2.61 ± 2.50 µmol CO₂m^-2 s^-1. Gas fluxes varied significantly (p < 0.05) between sampling sites for both living stems and coarse woody debris, but not for soils. For living stems, this variability was explained by differences in tree species, where N. sylvatica had largest seasonal mean flux of CH₄ and L. tulipifera had the largest seasonal mean flux of CO₂. For woody debris sites, the variability was explained wood density, with dense, fresh wood acting as CH₄ sources, and less dense, decayed wood acting as CH₄ sinks. Our results show homogeneity in soil CH₄ and CO₂ fluxes, but a large heterogeneity in fluxes from tree stems and coarse woody debris. These results provide insights on how forest management strategies could influence greenhouse gas emissions from forested watersheds.