Abstract
The purpose of this study is to clarify the reason for changes in the soil carbon contents depending on the conversion of the forest management type from natural deciduous broad-leaved forests (broad-leaved forests) to artificial Japanese cypress and Japanese cedar forests (coniferous forests). In the coniferous forests, Japanese cypress (Chamaecyparis obtusa) was planted on the upper slop and Japanese cedar (Cryptomeria japonica) was planted on the lower slope. In this study, comparisons of the results were made between the broad-leaved forest and coniferous forest in each slope position. The soil carbon content in the cypress forest was about 0.6 times lower than that of the broad-leaved forest on the upper slope. On the other hand, the soil carbon content in the cedar forest was almost the same to that of the broad-leaved forest on the lower slope. The amounts of soil microbial biomass C and soil respiration rates, metabolic activity of the soil microorganisms, cellulose decomposition rates and the amounts of nitrogen mineralization of the cypress forest was 0.3-0.5 times lower than that of the broad-leaved forest. The amounts of soil microbial biomass C and soil respiration rates, metabolic activity of the soil microorganisms, cellulose decomposition rates and the amounts of nitrogen mineralization of the cedar forest was 0.6-1.3 times than that of broad-leaved forest. These tendencies reflected the soil carbon contents. The carbon mineralization rate of the cypress litter was 1.2 times higher than that of the broad-leaved litter on the upper slope. The carbon mineralization rate of cedar litter was 0.8 times lower than that of the broad-leaved litter on the lower slope. This suggested that the cypress litter had been easily mineralized and had been difficult to accumulate relative to the litter in the broad-leaved forest on the upper slope, while the cedar litter had been mineralized with difficulty which provided a rapid accumulation relative to the litter in the broad-leaved forest on the lower slope.
