Phytolith Records from Tephra-soil Sequence since the Last Interglacial in the Southern Ishikari Lowland, Hokkaido, Japan: With Special Reference to the Fluctuation of the Sasa Group (Dwarf Bamboo) in Paleo-vegetation

We carried out phytolith analysis of the tephra-soil sequence since the Last Interglacial period in the southern Ishikari Lowland, Hokkaido. The Sasa group of so-called dwarf bamboo, one of the representative modern taxa, was a main component of the vegetation from Marine Oxygen Isotope Stage (MIS) 5e to the early half of MIS 5b. However, the Sasa group declined from the horizon of Aso-4 tephra (the late half of MIS 5b) to that of Kuttara-6 tephra (MIS 5b/5a), and then almost disappeared during the Last Glacial period when Pooideae was the most dominant of the Gramineae flora. Meanwhile the sub-boreal coniferous forests were estimated to have occurred at MIS 5b and MIS 3. The former was accompanied by the Sasa group like the present sub-boreal coniferous forest in Hokkaido, but the latter was not. It was after the early Holocene period that the Sasa group became a main component of the vegetation again.