過去一万二千年間-日本の植生変遷史 : II.新しい花粉帯

抄録

The late-glacial period, characterized by plentiful pines and/or birches, contains two distinct pollen zones, i.e., LI (ca. 15,000-12,000 years B.P., with abundant boreal conifers) and LII (ca. 12,000-10,000 years B.P., with a rapid rise of beech and other cool-temperate species). This is especially clear south of about 37°N latitude. The Holocene consists of five pollen zones, RIa, RIb, RII, RIIIa and RIIIb. RI, generally including RIa and RIb, is a transitional zone from late-glacial to mid-postglacial RII vegetation. The RIa/RIb zonal boundary (about 8,500 years B.P.) is defined by a slight increase of plants which develop fully in RII. RII (ca. 7,000-4,000 years B.P.) shows the maximum development of the laurilignosa in southwestern Japan and the deciduilignosa in northestern Japan. RIIIa (the maximum Neoglacial period) is distinguished by a small expansion of the cool-temeprate forest in southwestern Japan, and by downward and southward migration of the boreal forest in central and northeastern Japan. RIIIb (after ca. 1,500 years B.P.) is the pine period. The high correlation coefficient (0.938) between the first continuous occurrence of buckwheat pollen and the beginning of RIIIb's pine increase suggests that Pinus densiflora forest was established as a result of intensified prehistoric shifting agriculture.