Long-term changes in the chemical properties of Japanese cedar (Cryptomeria japonica) forest soils under high precipitation in southwest Japan

Abstract

There is insufficient direct evidence of long-term changes in the chemical properties of forest soils to provide information for forestry management plans for sustainable site productivity. To understand changes in the chemical properties of forest soils in a specific high-precipitation climate in Japan, we re-investigated, in 1997, soil pits within a Japanese cedar (Cryptomeria japonica) forest in the Yanase region of Kochi Prefecture which had previously been surveyed in 1976. Comparison of the 1976 and 1997 results revealed significantly lower pH of surface and subsurface soils, and fewer exchangeable cations over time. In contrast, subsoil pH, concentrations of total carbon and nitrogen, and cation-exchange capacity (CEC) had not changed over the 21-year period. Estimation of proton and cation budgets in the forest ecosystem over 21 years, using data for the amounts in soil, biomass accumulation, and input through precipitation, revealed that biomass accumulation did not explain the cation depletion in soils. This suggests that cations were leached from the ecosystem. In contrast with previous reports, which showed Ca accumulation in Japanese cedar forest soils, our results indicated that high precipitation of more than 4,000 mm combined with acid deposition resulted in soil acidification and leaching of cations from soils, following the decrease in base saturation.