Spatial variation in respiration from coarse woody debris in a temperate secondary broad-leaved forest in Japan

We measured the rates of respiration from snags and logs (“coarse woody debris”, CWD) of Japanese red pine (Pinus densiflora Sieb. et Zucc.) to examine the rate of decomposition and CO2 efflux from these materials in a temperate secondary broad-leaved forest in Japan. At this site, a high quantity of CWD of P. densiflora had accumulated as a result of pine wilt disease during the 1970s. Respiration rates were measured using a dynamic closed chamber method combined with an infrared gas analyzer. We measured the respiration rate of 7 samples of snags and 10 samples of logs from August 2003 to January 2004. The responses of the respiration rates of snags (Rsnag) and logs (Rlog) to changing temperature were both exponential and the responses to water content were quadratic, and the same function could be used to estimate annual values of both Rsnag and Rlog. Intensive measurements of water contents of snags and logs showed a marked difference in water content. The mean water content of snags was 20% of log water content. This difference was likely responsible for the observed difference in annual Rsnag and Rlog. The decay rate constants estimated from the respiration rates measurement of snags and logs were 0.019 and 0.081 year−1, respectively. Despite being lower than Rlog, Rsnag was a significant compartment of the CWD carbon budget at this site.