Remaining Evergreen Conifer Tsuga in Hokkaido, Japan : Pollen analysis and AMS14C dating

• Main Authors: 星野, フサ, Hoshino, Fusa, 萩原, 法子, Hagiwara, Noriko, 春木, 雅寛, Haruki, Masahiro, 南, 雅代, Minami, Masayo, 北川, 浩之, Kitagawa, Hiroyuki, 中村, 俊夫, Nakamura, Toshio
• Language: Japanese
• Published: 名古屋大学宇宙地球環境研究所年代測定研究部 2024
• Subjects: AMS14C dating; pollen analysis; Tsuga; Ishikari district; paleo-vegetation; Sakhalin
• Online Access: https://nagoya.repo.nii.ac.jp/record/2010371/files/020-027_2023.pdf

Tsuga (Tsuga sieboldii, Tsuga diversifolia) is one of the representative evergreen conifers that had remained in Hokkaido from the earliest times to recent years, although its distribution has not been observed in Hokkaido today. Its pollen remained in the Paleocene coal fossils and was extracted in Kushiro, the eastern part of Hokkaido, in the warm period. Tsuga sieboldii is currently abundant in the southwestern area of Japan, while Tsuga diversifolia lies scattered in mountainous areas from the Kanto region to the Tohoku region. Tsuga pollen has been found in strata 14,000 to 7,000 years old in Sakhalin as well as in various parts of Hokkaido. In regard to the transition and the characteristics of Tsuga (Tsuga sieboldii, Tsuga diversifolia) in various parts of Hokkaido, based on the results of pollen analysis and AMS14C dating, the authors studied chronological changes in the occurrence rates of Tsuga and of its companion species (Picea, Taxodiaceae, Abies), and consequently, they also discussed the relationship with Picea, whose establishment environments approximate those of Tsuga, the relations between the paleo-vegetation as far back as the ancient times and the present forest vegetation, and the path to the extinction of the genus Tsuga. Pollen of Tsuga, along with that of tree species in the warm-temperate district zones, was found in the Paleocene coal fossils from the Kushiro coalfield in Hokkaido, which indicates 36-15% occurrence rate for all areas of eastern Hokkaido 13 million years ago, during the Neogene. In the Ishikari area, central Hokkaido, the occurrence rate was 30-25% between 500,000 and 300,000 years ago, and after 50,000 years ago, the rate dropped to 30-20% in some places and to only a few percents in others. On the whole, Tsuga is considered to have dwindled due to the momentum of Picea, whose establishment environments approximate those of Tsuga. It is confirmed that Palaeoloxodon naumanni appeared in Hokkaido until 40,000 to 50,000 years ago, which suggests the warm period ...