Background/Question/Methods We have initiated a replicated, long-term, large-scale field experiment designed to test the effects of old-growth structural features on the biodiversity, productivity and nutrient cycling in a second-growth northern hardwood forest in northern Wisconsin. We specifically are testing the effects of canopy gaps and coarse woody debris (CWD) on these processes. Coarse woody debris is known to be an important C reservoir but is also a source of CO2 to the atmosphere though this flux is infrequently measured. We are measuring C respired from the surface of both freshly added and decaying wood within canopy openings created in January 2007 and beneath closed canopy conditions. Although we do not expect CO2 flux from newly added CWD to significantly increase total surface (soil and downed CWD) CO2 loss in the near term, the flux from existing cwd will comprise a significant fraction of total surface CO2 flux in both the mid and long term. We inventoried CWD distribution according to decay categories across this site in 0.2 ha plots. CO2 flux has been measured using PVC collars attached to either bark or wood surface and an infrared gas analyzer. Air and wood temperature and wood moisture have been measured simultaneously. Since CO2 flux from CWD is influenced by decay class, temperature, and moisture we selected 3-7 pieces in each combination of classes to measure CO2 flux at least monthly. Additionally we measured flux from newly cut stumps.
Results/Conclusions
CO2 flux is positively correlated with wood and air temperature (p-values <.0001). Respiration rates of logs are similar in both treatments (gap addition and intact canopy), but differed by decay class with the mean CO2 flux increasing from logs in early to later stages of decay (decay class 1 flux=3.78, 2 flux=4.33 and 3 flux=5.77 µmol m-2 s-1). The temperature of CWD differed by treatment but air temperature did not. Overall stumps respired at a rate 67% higher than logs. Over time canopy openings may significantly affect CO2 flux through their influence on decomposition rates.
