Effects of sample size and temperature on coarse woody debris respiration from Quercus variabilis logs

Measuring coarse woody debris (CWD) respiration (R (CWD)) may have advantages over other approaches in determining CWD decomposition rates to accurately estimate forest carbon budgets and effects of warm temperatures on decomposition; however, studies on R (CWD) are insufficient. The R (CWD) from Quercus variabilis logs of different sizes (e.g., different surface area to weight ratios or weights) was measured under homogeneous conditions by using a closed-chamber system with a non-dispersive infrared sensor. The size effect on R (CWD) measured on a weight or volume basis was not significant, but it was significant on a surface area basis. This indicates that R (CWD) on a weight or volume basis would be a reliable measure, regardless of the size and cross-sectional area effects, while R (CWD) on a surface area basis must vary geometrically according to the change in sample size. R (CWD) did not change significantly over time until 122 h after sampling. An exponential model with a Q (10) of 2.34 was fitted only at temperatures below 22.6 A degrees C because R (CWD) was suppressed at high temperatures due to constantly decreasing moisture. Instead, a logistic model was applied for all temperatures. The annual R (CWD) and the decay rate constant were estimated to be 53.4 g C kg(-1) year(-1) and 0.107 year(-1), respectively. The decomposition rate estimate through R (CWD) might not correspond to that using the mass loss approach. It remains uncertain whether the methodological differences may lead to potential errors in measuring the actual CWD decomposition rate; therefore, a multiple approach study for CWD decomposition should be conducted.