Role of coarse woody debris in the carbon cycle of Takayama forest, central Japan

Coarse woody debris (CWD) is an important component of the forest carbon cycle, acting as a carbon pool and a source of CO₂ in temperate forest ecosystems. We used a soda-lime closed-chamber method to measure CO₂ efflux from downed CWD (diameter ≥5 cm) and to examine CWD respiration (R_CWD) under field conditions over 1 year in a temperate secondary pioneer forest in Takayama forest. We also investigated tree mortality (input to the CWD pool) from the data obtained from the annual tree census, which commenced in 2000. We developed an exponential function of temperature to predict R_CWD in each decay class (R² = 0.81-0.97). The sensitivity of R_CWD to changing temperature, expressed as Q₁₀, ranged from 2.12 to 2.92 and was relatively high in decay class III. Annual C flux from CWD (F_CWD) was extrapolated using continuous air temperature measurements and CWD necromass pools in the three decay classes. F_CWD was 3.0 (class I), 17.8 (class II), and 13.7 g C m^-2 year^-1 (class III) and totaled 34 g C m^-2 year^-1 in 2009. Annual input to CWD averaged 77 g C m^-2 year^-1 from 2000 to 2009. The budget of the CWD pool in the Takayama forest, including tree mortality inputs and respiratory outputs, was 0.43 Mg C ha^-1 year^-1 (net C sink) owing to high tree mortality in the mature pioneer forest. The potential CWD sink is important for the carbon cycle in temperate successional forests.