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Influences of forest decline on various properties of soils on Mt. Hirugatake, Tanzawa Mountains, Kanto District, Japan

Abstract At Mt. Hirugatake, Tanzawa Mountains, the deciduous broadleaved forest has declined rapidly since the 1970s. Six study sites under different degrees of forest decline were selected at Mt. Hirugatake, Tanzawa Mountains as follows: site with healthy deciduous broadleaved forest (DBF), site with slight forest decline (SFD), site with distinct forest decline (DFD), sites with heavy forest decline 1 and 2 (HD1 and HD2), and site with Sasa-type grassland (SG). In the present study, the changes in the physical and chemical properties of the surface soil to the depth of 10 cm with that order of forest decline were investigated in nine sub-samples from each quadrat (10 m × 10 m) at each site. With forest decline, the bulk density tended to increase, and porosity, especially macropores, tended to decrease significantly. Although the soil pH decreased at the SFD site, no significant differences were found in the soil pH between the DBF site and the other sites. The amount of exchangeable aluminum was well correlated with the soil pH, but showed no significant differences between the DBF site and other sites, except for the SFD site. Thus, forest decline at Mt. Hirugatake, Tanzawa Mountains was not caused by aluminum stress, as suggested in the previous study (Higashi et al.: Soil. Sci. Plant Nutr., 49, 161'169, 2003). The amount of total carbon of soils markedly decreased at the early and the latest stages of forest decline; a decrease of about 34% was observed at the SG site compared with the DBF site.