Abstract
Spatio–temporal distribution of vegetation during the late Holocene at Oninuma, Fukushima Prefecture (northeastern Honshu) was reconstructed from pollen and fossil wood assemblages and by radiocarbon dating. Circa 2500 years ago, Alnus sect. Gymnothyrsus dominated the fan swamp forest in this area, while Quercus grew on the surrounding hills. By ca. 1500 years ago, Fraxinus and Fagus increased on the fan and the hills, respectively. By ca. 800 years ago, an Alnus-dominated swamp forest covered the fan, accompanied by Thujopsis dolabrata and Chamaecyparis pisifera. The distribution of fossil woods showed that T. dolabrata mainly grew in the center of the fan, whereas C. pisifera grew throughout it. The 120–180 tree rings and the horizontal spread of the roots of C. pisifera trees implied that the swamp forest continued for at least 200 years on the peaty land. It is probable that T. dolabrata and C. pisifera were once significant components of the swamp forest in northeastern Honshu similar to Cryptomeria japonica that formed buried forests of the late Holocene in western Honshu. Probably, C. japonica also grew on the mountains around the site.
