Woody debris contribution to the carbon budget of selectively logged and maturing mid-latitude forests

Woody debris (WD) is an important component of forest C budgets, both as a C reservoir and source of CO2 to the atmosphere. We used an infrared gas analyzer and closed dynamic chamber to measure CO2 efflux from downed coarse WD (CWD; diameter >= 7.5 cm) and fine WD (FWD; 7.5 cm > diameter >= 2 cm) to assess respiration in a selectively logged forest and a maturing forest (control site) in the northeastern USA. We developed two linear regression models to predict WD respiration: one based on WD temperature, moisture, and size (R-2=0.57), and the other on decay class and air temperature (R-2=0.32). WD respiration (0.28 +/- 0.09 Mg C ha(-1)year(-1)) contributed only approximate to 2% of total ecosystem respiration (12.3 +/- 0.7 Mg C ha(-1) year(-1), 1999-2003), but net C flux from CWD accounted for up to 30% of net ecosystem exchange in the maturing forest. C flux from CWD on the logged site increased modestly, from 0.61 +/- 0.29 Mg C ha(-1) year(-1) prior to logging to 0.77 +/- 0.23 Mg C ha(-1) year(-1) after logging, reflecting increased CWD stocks. FWD biomass and associated respiration flux were approximate to 7 times and approximate to 5 times greater, respectively, in the logged site than the control site. The net C flux associated with CWD, including inputs and respiratory outputs, was 0.35 +/- 0.19 Mg C ha(-1) year(-1)(net C sink) in the control site and -0.30 +/- 0.30 Mg C ha(-1)year(-1) (net C source) in the logged site. We infer that accumulation of WD may represent a small net C sink in maturing northern hardwood forests. Disturbance, such as selective logging, can enlarge the WD pool, increasing the net C flux from the WD pool to the atmosphere and potentially causing it to become a net C source.