Changes and characteristics of paleo-vegetation in the Ishikari district of Hokkaido since 100,000 years ago

On the basis of the composition of spores and pollen, columnar section, modern forest vegetation, and the results of soil survey at seven survey sites in the Ishikari district of Hokkaido, the authors examined and discussed the flow from paleo-vegetation to modern forest vegetation, factors of the formation of forest vegetation, and the continuity of forest vegetation. In Nakayamatoge Pass, located more than 600 m above sea level in the western part of Ishikari district, Hokkaido, warm-temperate tree species including Fagus japonica, Fagus crenata, Cryptomeria japonica, Tsuga and Metasequoia glyptostroboides appeared in the Middle Tertiary Miocene, 13 million years ago. At the present time, evergreen conifer trees including Picea and Abies, and deciduous broadleaf trees such as Quercus, Betula, Alnus, Ulmus, Juglans mandschurica, Carpinus, and Corylus are observed. During the Middle Tertiary Miocene, in addition to warm-temperate tree species aforementioned, evergreen conifer trees and deciduous broadleaf trees as predecessor species of the present modern forest vegetation appeared. 　As for the formation and transition of paleo-vegetation and modern forest vegetation, the samples obtained at the 7 survey sites that were dated up to 888 calAD, the most recent values obtained by 14C dating in the Ishikari district, indicate that forest vegetation until around 2 million years ago was spread over tephra deposits that appeared as a result of volcanic activities and led to a diverse modern forest vegetation with wind-dispersed tree species joined by bird and beast dispersal tree species from the perspective of seed dispersal patterns.