中国地方の湿原堆積物の花粉分析学的研究

I. 蛇ガ乢湿原

抄録

The present paper is the first of a series to the elucidation of the vegetational history done by pollen analysis of moor sediments taken from the Chugoku district, Japan.
Orogatawa moor is located in the Oroga pass at 700m above sea-level between Mt. Minagasen and Mt. Kami-Hirusen within the Chugoku Mountains, in the northern part of Okayama Prefecture. The profile of about 280cm sediments obtained from the deepest portion of the mooris divided into three layers; the lower one is silty clay, the middle one muck and the upper one terrestorial peat.
As a result of pollen analysis of these samples, three major vegetational changes for the last 6, 500 years are recognized by the fossil pollen data from 29 levels as follows;
1. Quercus, Fagus, Ilex stage (280-190cm) (6, 500-4, 000y.B.P.);
2. Quercus, Fagus, Carpinus stage (190-70cm) (4, 000-1, 500y.B.P.);
3. Fagus, Quercus, Pinus stage (70-0cm) (after 1, 500y.B.P.).
Quercus is the most dominant tree in the pollen diagram. The evergreen type is dominant at the lower part of the first stage. The frequency decreased gradually during the upper one of the first stage, and the second one. On the other hand the deciduous type increased during these stages, and the frequency is higher than the evergreen one at the third stage.
The destructions of natural forests by human activity may have started at third stage (ca 1, 100 y.B.P.) as shown by the sharp decrease of Quercus pollen, the gradual increase of Pinus one, and the great abundance of Gramineae one.
The sedimentation rate based on ¹⁴C dates in this moor is considerably great compared with some data taken from another moor in Japan. It rises gradually from the bottom to the surface as follows: 0.05cm/year (200-150cm), 0.06cm/year (150-100cm) and 0.07cm/year (50-0cm) with exception of a decrease (0.025cm/year: 100-50cm).