日高山脈東側における2,000年前以降の花粉相の推移と特徴 : ナウマンゾウの時代を経て

概要

The Tokachi Plain in Hokkaido, Japan, has always been a stable food supply base for Japan, supported by large-scale agriculture, including dry-field farming, mainly of beans and potatoes and dairy husbandry since 1875. In 2021, the authors performed pollen analysis, AMS14C dating, vegetation and soil property surveys on a 1.6 m deep borehole obtained in a wetland forest at an altitude of 275 m in Memuro-cho, Fushimi, at the foot of the eastern Tokachi side of the Hidaka Mountains in 2002. The study clearly shows the characteristics of vegetation changes. In regard to the changes that occurred in the Fushimi wetland, tephra released from volcanoes in the distance was thickly piled up, changing into a wetland with Lysichiton camtschatcense, on which a cool-temperate deciduous broad-leaved forest was established, and the pollen zone D was formed. The AMS14C age at a depth of 1.44 m is 2310–2112 cal BP ± 2σ (95.4%) (NUTA2-27097). Below this point, in the pollen zone A, coniferous trees receded and deciduous broad-leaved trees predominated. Samples from 1.0 m depth (sample No. 51) to 1.4 m depth (sample No. 69) contain a small amount of Selaginella selaginoides spore (pollen zone B). In addition, the C pollen zone includes a little more spruce (maximum value of 35% at a depth of 72 cm, sample No. 39) and Abies sachalinensis. On the other hand, in Churui, located 40 km southeast of the aforesaid site, the molar teeth and almost the entire bodyʼbone of the Palaeoloxodon naumanni’ were excavated in 1969. The result from the pollen analysis on the stratum 17c-5, performed by Ohe and Kosaka (1972) and Hoshino et al. (2021), where the bones were discovered, indicates that the climate of Churui was milder than that of Fushimi, because there used to be a Fagus crenata forest there. The period turned out to be 120,000 years ago. 　In recent years, while global warming has become a serious social issue, there was a time in the past when the climate was much warmer.

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