Based on pollen analysis conducted at Lake Harutori from 9,500 to 3,200 cal BP, paleovegetation was reconstructed. Throughout this period, the presence of conifer fossil pollen grains was minimal, while fossil pollen grains from deciduous broadleaf trees were predominant. Notably, there was an increase in fossil pollen grains from deciduous broadleaf trees during the mid-Holocene, suggesting a warmer environment compared to the last glacial. Particularly during the warm mid-Holocene period, there was an increase in deciduous broadleaf trees. Furthermore, the expansion of the Juglans genus during the mid-Holocene suggests a pioneering occupation of river floodplains due to increased rainfall and snowfall associated with warming. It is suggested that from the mid-Holocene to the late Holocene, the environment around Lake Harutori may have been conducive to the establishment of Betula forests. After 4,000 cal BP, fossil pollen grains of Quercus subgen. Lepidobalanus decreased slightly, while conifer fossil pollen grains increased slightly. This supports the idea of a transition from a warmer to a cooler environment in the area around this lake, consistent with previous studies.
