Abstract
We carried out a phytolith analysis of soil sequences of three regions, Haboro, Sarobetsu, and Tonbetsu, in the northern part of Hokkaido to discuss the fluctuation of Sasa since the Last Interglacial period and evaluate Sasa as an index of past snowfall and temperature. The phytolith record suggests that Sasa has continuously existed after the Last Interglacial in Haboro. On the other hand, Sasa almost disappeared during the Last Glacial period in Sarobetsu and Tonbetsu. Previous research shows that Sasa drastically decreased in the northern and eastern parts of Hokkaido during the Last Glacial period. The present geographical distribution of Sasa shows that Sasa needs conditions of a warmth index of more than 17·°C month and a snow depth of less than 50 cm for its existence. Other paleobotanical information suggests that Hokkaido satisfied the condition of a warmth index of more than 17·°C month during the Last Glacial period. Thus, the decrease of Sasa must have been caused by the lack of enough snow. Considering the slow migration speed of Sasa by vegetative reproduction, Sasa seems to have existed sporadically in refugia such as Haboro with an enough snow fall during the Last Glacial period and spread over the whole Hokkaido in the Holocene period.
