No abstract

Soil carbon cycling was studied in Japanese cedar plantations with different stand ages after clear-cutting and was analyzed by a compartment model. The amount of biomass and the litterfall rate increased rapidly with the growth of Japanese cedar, which were approximated by a simple logistic function of stand age. The accumulation of A 0 layer decreased from 21 t ha -1 to 5 t ha -1 during the 10 years following clearcutting, and then recovered to nearly the same level as before clear-cutting within 20 years after clear-cutting, although the amount of soil carbon in the mineral soil recovered more than 40 years after clear-cutting. The total and mineral soil respiration rates increased rapidly after clear-cutting and gradually decreased in young stands and stabilized in old stands. The relative decomposition rate of the A 0 layer and organic matters in mineral soil was high in the young stands because of the relatively high soil temperature rather than the soil moisture content. After the closing up of the canopy, the relative decomposition rates of the A 0 layer and humus in the mineral soil stabilized at 0.14 to 0.16 y -1 and 0.005 to 0.013 y -1 , respectively. Consequently, soil carbon cycling was strongly affected by clear-cutting. The amount of soil carbon rapidly decreased because of the cessation of litterfall and the increase of the relative decomposition rate of the A 0 layer and humus, and recovered gradually to the level before clear-cutting with the growth of the cedar plantation. The change in soil carbon cycling with stand development was partly caused by the change in soil temperature and moisture content but was mainly caused by the amount of cedar litterfall which changed significantly in the early stage of the stand following clear-cutting, and became slower and leveled off in the late stage with stabilization of the environmental conditions and litterfall rate.