Pollen Analytical Studies of the Megata Peatland in Akita Prefecture

The paucity of reports on the vegetational history of the alluvial peatland overlooked the Japan Sea in Tohoku district encouraged us to study it. In this paper the pollen analytical features of the Megata peatland situated at an altitude of above 10m in Akita Prefecture are described with a view to discussion of the vegetational history in the peatland and its surroundings from 3, 500y. B.P.The results are summarized as follows.1. The profile at the north of the peatland from which samples were taken for pollen analysis was mostly composed of autochthonous peat, of which the ages were calculated to be 3, 180±85y. B.P. (N-2003) at the 500cm depth and 2, 080±80y. B.P. (N-2004) at the 300cm depth on the basis of 14C dating.2. Pollen diagram derived from peat profile is characterized by the occurrence of Cryptomeria, Fagus, Quercus and Alnus with a high frequency of pollen and a gradual increasing of Cryptomeria from 3, 000y.B.P. of the initial layer. In pollen diagram three pollen assemblage zones on the basis of the prosperities of these dominant genera are differentiated as follows:I) Fagus-Quercus-Alnus zone (630-420cm)II) Cryptomeria-Fagus-Quercus-Alnus zone (420-70cm)III) Pinus-Cryptomeria-Alnus zone (70-0cm)3. The pollen diagram suggests a gradual change from the forests dominated by Fagus and Quercus, to Cryptomeria-Fagus forests now found locally in Akita Prefecture. An increasing of Pinus and Cryptomeria at the zone III seems to be influenced by plantation in the neighbourhood of the peatland.