Comparing Measurement Approaches for Quantifying CO2 Flux from Downed Woody Debris with a Dynamic Chamber Method

Validating methodology for quantifying of carbon (C) loss from dead wood is critical for understanding C turnover in forest ecosystems. We compared estimates of CO2 fluxes with a closed dynamic chamber method using an infrared gas analyzer with: 1) small chambers installed on the downed woody debris (DWD) surface and 2) DWD segments placed in large chambers. The fluxes were measured from 6 intermediately decayed DWD fragments, wood and bark of Betula pubescens and Populus tremula and calculated on the surface area, volume and mass bases. For most DWD fragments, the tendency with an underestimation of CO2 flux in the first approach up to 90% was observed due to a barrier effect of a thick bark layer and possible gas leakages. Our results demonstrate the importance of taking into account contribution of bark into total DWD respiration rates especially in upscaling the piece-level results into ecosystem level.