兵庫県氷ノ山のササ植生下にみられる土壌の母材の累積性と生成環境 Cumulative Property of the Soil Parent Materials and Soil Forming Environments under Bamboo-grass Vegetation on Mt. Hyono-sen, Hyogo Prefecture, Central Japan
Ando-soils with thick and humic A horizon derived from tephra materials are widely distributed in Japan. Recent studies are make it clear that these thick and humic A horizons have developed upward cumulatively. On the other hand, these soils are very sparsely distributed in the Kinki district of central Japan. One of the reasons may be that the parent material in this area are generally poor in tephra materials. In addition to the parent material factor, other factors, such as continuous supply of plentiful organic matter, topographic stability, and a suitable climate, may be necessary for the formation of a thick and humic A horizon.<br>To elucidate the pedogenetic processes, especially the cumulative properies of parent materials and the vegetational environments in the past, we researched Ando-like soils in Mt. Hyono-sen, Hyogo Prefecture. Three soil profiles are surveyed: one (H1) is located in a grassland of bamboo-grass (<i>Sasa kurilensis</i>); the other two profiles (H2, H3) in beech (<i>Fagus crenata</i>) forest with bamboo-grass as undergrowth. In addition to these soil samples, gravel of bedrock (andesite), peaty deposits in the vicinity, and volcanic glass were used as the mineralogical references. Microscopic mineral analysis for fine sand fraction and X-ray diffraction analysis for silt and clay fractions were carried out to investigate the origin of parent materials. Plant opal analysis and pollen analysis were used for the elucidation of past vegetational history.<br>Primary mineral composition of the fine sand fraction showed a mixture of tephra-origin particles (volcanic glass, hypersthene, hornblende) and bedrock-origin particles (groundmass fragments of andesite) in all horizons of each profile except the BC horizon of H1 profile. Mineralogy of silt and clay fractions also showed the mixed distribution of bedrockorigin minerals (feldspar, cristobalite) and foreign materials like eolian dust (quartz) in all horizons of each profile. A large number of plant opal grains have accumulated in each profile; most of them are considered to originate from bamboo-grass, and they were more strongly weathered in the deeper horizons. From these results, we conclude that the thick and humic A horizon in this area developed upward cumulatively under the balanced accumulation of organic matter and mineral materials. The results of pollen analysis suggested that bamboo-grass vegetation has been maintained for a long time, since the beginning of pedogenesis, and even the present beech forest has changed gradually from an open site with sparse forest or grassland to a closed forest. From the results mentioned above, it is inferred that the Ando-like soils in this area were formed under the strong influence of long-maintained bamboo-grass vegetation, as well as that of parent material and topographic and climatic factors.
第四紀研究 35(4), 313-323, 1996-10-31
Japan Association for Quaternary Research