SIMULATION OF SOIL CARBON CYCLING AND CARBON BALANCE FOLLOWING CLEAR-CUTTING IN A MID-TEMPERATE FOREST AND CONTRIBUTION TO THE SINK OF ATMOSPHERIC CO2

A simulation model of soil carbon cycling was developed based on the d ata observed in a mid-temperate forest in Yoshiwa, Hiroshima Prefectur e, Japan, and soil carbon cycling and carbon budget in a mature forest stand and following clear-cutting were calculated on a daily basis us ing daily air temperature and precipitation data. The seasonal change in the amount of the Ao layer was characterized by a decrease from spr ing to autumn due to rapid decomposition of litter, and recovery in la te autumn due to a large litterfall input. There was little change in the amount of humus in mineral soil. These estimates coincides closely with those observed in the field. Most flow rates and the accumulatio n of soil carbon decreased very markedly just after clear-cutting. The Ao layer reached its minimum in 10 years, and recovered its loss with in 50-60 years after cutting. A large loss of carbon was observed just after cutting, but the balance changed from negative to positive in 1 5 years after cutting. The total loss of soil carbon following cutting recovered within 30 years, and nearly the same amount of carbon as th at stocked in the timber before harvesting accumulated 70-80 years aft er cutting. The calculation by the simulation model was made using the assumption that the increase in atmospheric CO2 promoted the primary production rate by 10% over the last three decades. The result suggest s that about 8 t C ha(-1) was sunk into soils of the mid-temperate for est over the same period. It indicates that forest soils may be one of the main sinks for atmospheric CO2.