The defoliation of Cryptomeria japonica is observed in shrine forests around Hikone, Japan. Here, moisture content, soil pH, exchangeable Mg, Ca and Al of soil in shrine forests of C. japonica were examined in order to assess the relationship between these factors and defoliation. There was no relationship between soil pH, exchangeable Mg and Ca in soil and the degree of defoliation in shrine forests. Exchangeable Al in the soil of shrine forests increased with decreasing soil pH below pH 5.0,

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... ut there was no relationship between exchangeable Al and degree of defoliation in shrine forests. Soil moisture content differed between severely defoliated forests and forests with no defoliation. Soil moisture is thought to play a large role in inducing defoliation of C. japonica. Based on results from previous studies, the declining forests in the basin of the Kuzuryu River in Fukui Prefecture and in the basin of the Koito River in Chiba Prefecture reported by Yambe (1973) were considered to have been caused by the construction of dams. On these rivers, dams were constructed several years before the forest decline researched by Yambe. Dam construction is thought to have caused the low moisture content in the basins.