臺灣之古生態研究（5）──頭社盆地

Paleoecological Study of Taiwan (5)–Toushe Basin

In order to investigate the vegetational history, paleoclimatic changes and the activity of early man in Central Taiwan, the Toushe Basin was selected as a site for palynological study. From the sediments extending down to 82 m and through 31m of thick peat, 40 samples were taken for this study. The palynomorphs were extracted by chemical deflocculation, then permanent slides were prepared by sealing with paraffin. Based on the examination of the permanent slides, a hypothesis for the vegetational history and past climate is proposed as follows: A warm temperate period has prevailed in this area ever since the formation of the lake. Except for scanty pollen zones such as Zone A (8200-7100 cm), Subzone C1 (5900-5300 cm), Subzone C3 (5150-4800 cm) and Subzone C5 (4200-3900 cm), successive series of plant communities have been found as follows: starting at a depth of 71 m, we find that Subzone B1 (7100-6750 cm), has a Quercus-Symplocos-Pasania-Alnus association, Gramineae-Compositae-Typha subassociation; Subzone B2 (6750-5900 cm), Quercus-Pasania-Alnus-Salix-Carpinus association, Gramineae-Cyperaceae subassociation; Subzone C2 (5300-5150 cm), Pasania-Quercus-Myrica-Symplocos association, Gramineae-Cyperaceae subassociation; Subzone C4 (4800-4200 cm), Pasania-Quercus-Myrica-Symplocos-Ligustrum-Engelhardtia association, Gramineae-Cyperaceae subassociation; Subzone C6 (3900-3100 cm), Pasania-QuercusMyrica-Symplocos-Ilex-Salix-Engelhardtia association, Gramineae-Cyperaceae subassociation; Subzone D1 (3100-1600 cm), Alnus-Symplocos association, Gramineae-Cyperaceae subassociation; Subzone D2 (1600-1350 cm), Alnus-Symplocos-Ligustrum-Ilex association, Gramineae-Compositae subassociation; Subzone D3 (1350-975 cm), Pasania-Quercus.-Alnus-Symplocos-IlexSalix-Ulmaceae-Mallotus association, Gramineae-Cyperaceae subassociation; and Zone E (975 cm-surface), Liquidambar-Mallotus-Pinus-Ulmus/Zelkova association, Gramineae-Cyperaceae subassociation. From the evidences of charcoal at 670 cm (ca. 3850 years B. P.), and wood fragments with burning traces at 580 cm (ca. 3400 years B. P.) and a steep rise in deposit ion rate of sediments since 4500 years ago, we suggest that early man may have come into this district to clear the forest as early as 4500 years ago.