摘要：Soil profiles under natural forest vegetation on four islands of the Ogasawara Islands, Japan, were compiled and evaluated based on chemical analysis to learn about the natural habitats of the past and determine adequate management measures for conserving the respective ecosystems. The majority of the soils could be characterized as high acidity (high exchangeable acidity, low pH(H2O) with low pH(KCl)), high cation exchange capacity (CEC) and high proportions of exchangeable Mg over exchangeable Ca and K, and those soils are in fairly early stages of weathering, differing from “laterite” and/or “laterite-like soils.” Available P for plants in the soils is bimodal: very low or very high. The very high level of soil-available P was caused by seabird activities in the past. The high proportion of exchangeable Mg would induce Ca and K deficiency in plants, and this situation would have prevailed in the Ogasawara Islands. Available N for plants in the surface horizons of the soils is generally high and does not limit the ecosystem productivity in many cases of natural forest. Soil erosion would cause fatal effects on the ecosystem by removing the surface horizons and exposing subsoil horizons with extremely high levels of soil acidity, high proportions of exchangeable Mg and low levels of available P and N, with inappropriate permeability and aeration ability for plant growth. Such subsoil horizons would provide very poor conditions for growing plants. Conserving soils is essential and important to the recovery and restoration of the natural vegetation and ecosystems.
关键词：available N for plants;available P for plants;cation exchange capacity (CEC);exchangeable acidity;exchangeable Ca;exchangeable K;exchangeable Mg;soil erosion;soil profile
