Early Last Glacial forest vegetation reconstructed from fossil wood assemblages around Lake Toya, southern Hokkaido, Japan

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  • 洞爺湖周辺における 最終氷期前期の木材化石群集と森林植生の復元
  • トウヤコ シュウヘン ニ オケル サイシュウヒョウキ ゼンキ ノ モクザイ カセキ グンシュウ ト シンリンショクセイ ノ フクゲン

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Abstract

Early Last Glacial fossil wood assemblages were found in and below the Toya Pyroclastic Flow Deposits (Tpfl) around Lake Toya (Toya Caldera), Hokkaido. Among the assemblages, three fossil zones were recognized (in an ascending order): Zone I consisting of Picea, Larix and Abies, accompanied with Salix and Lonicera; Zone II of deciduous trees and shrubs such as Alnus, Salix, Rosa, and Lonicera; and Zone III of Betula and Picea. A boreal coniferous forest mixed with Salix and Lonicera was reconstructed from Zone I assemblage. Zone II reflected wetland vegetation. A preliminary pollen analysis of Zone II indicated that Picea, Abies, and Betula dominated boreal coniferous forests on adjacent upland of the fossil wood sites. Zone III also indicated boreal coniferous forest. Zone I - III were correlated to Oxygen Isotope Stages 5d - 5c based on the age of Toya Tephra and proposed pollen zones in Hokkaido. A good correlation of wood assemblages with known pollen assemblages indicates that the forest was composed mainly of taxa detected by pollen analyses. Drastic vegetation change from the Last Interglacial to Last Glacial reconstructed in Hokkaido may be attributed to its location near the cool-temperate forest/boreal coniferous forest boundary.

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