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Harvard Forest Symposium Abstract 2005

• Title: The Effects of Selective Management on Carbon in Woody Debris: Measurements of Respiration and Environmental conditions.
• Primary Author: Wendy Liu (University of California - Berkeley)
• Additional Authors: Alfram Bright (Harvard University); John Budney (Harvard University); Daniel Curran (Harvard University); Bruce Daube (Harvard University); Lucy Hutyra (Boston University); Christine Jones (Harvard University); J. William Munger (Harvard University); Elizabeth Hammond Pyle (Harvard University); Scott Saleska (University of Arizona); Steven Wofsy (Harvard University)
• Abstract:

  Woody debris is an important component of the forest carbon (C) budget as both a C reservoir and source. Harvesting of trees results in inputs of coarse woody debris (CWD) and Fine woody debris (FWD). The effects of selective management on the CWD are investigated using (1) repeated CWD field surveys, (2) chamber-based respiration measurements, and (3) automated environmental measurements. During a selective harvest in the Simmes plot, adjacent to Harvard Forest, we found large inputs of CWD (from 8.01± 0.56 MgC ha-1 to 13.37 ± 1.05 MgC ha-1), followed by significant decomposition during the initial 2-year recovery period (net loss of ~1.60 MgC/ha/yr from CWD). How much of this decomposition resulted in Carbon released directly to the atmosphere depends on respiration rates, yet woody debris respiration rates are poorly quantified. To assess CWD and FWD respiration, we developed a method using an infrared gas analyzer and a closed dynamic chamber to measure CO2 efflux from downed CWD and FWD. We also created a framework to scale up from individual respiration rates to C fluxes for the whole ecosystem. Respiration measurements indicated much of the carbon lost from CWD was released directly to the atmosphere, with an estimated flux of 0.74 +- 0.21MgC ha-1 yr-1 due to respiration of CWD on the logged site. Fine woody debris biomass was ~7 times greater in the logged site than the unlogged site and released an additional 0.68 ± 0.27 MgC ha-1 yr-1 in the logged site in 2001, and bringing the total C flux for woody debris to 1.42 ± 0.34 MgC ha-1yr-1. Observed respiration rates imply mean turnover times of 13 years for CWD and 10 years for FWD. Respiration rates were well-represented by a linear model using natural log-transformed wood moisture, air temperature, their interaction, and size class (R2= 0.57). To quantify the effects of selective logging on the environmental conditions influencing CWD respiration, an integrated, low-maintenance, automated measurement system was designed, allowing continuous measurements to be made on CWD stocks. Initial results showed significant differences between logged and undisturbed sites in temperature and moisture. Hotter and drier conditions prevailed at the logged site, most likely as a result of the reduced canopy coverage. We infer that woody debris represents a weak C sink in undisturbed northern hardwood forests with C sources from CWD and FWD becoming significant after selective logging; significant elevated respiration will persist a relatively short time (2 –18 years).
  
  
  
  
  
  

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