Grassland and fire history since the late-glacial in northern part of Aso Caldera, central Kyusyu, Japan, inferred from phytolith and charcoal records

Abstract Phytoliths and charcoal preserved in two soil sections in northern part of Aso Caldera, central Kyusyu, Japan revealed grassland and fire history since the late-glacial. The phytolith assemblages were divided into two significant zones, respectively. Phytolith assemblages show that the grassland vegetation, composed mainly of Sasa species, has continued since the late-glacial. The grassland compositions changed from Sasa type to Pleioblastus type around 7.5 cal ka. Charcoal records indicate that fire occurred at least in the early Holocene and continued to the present. Judging from the phytolith and charcoal records, the establishment of grassland may have been affected by not only climate changes and volcanic activities, but also fire since the early Holocene. Around the Aso Caldera, numerous prehistoric archaeological sites since the late-glacial have been discovered. Therefore, the occurrence of fire during the Holocene was possibly caused by human activities, and fire influenced the establishment of grassland. The results are important for understanding the relation between the fire and grassland vegetation in the regions where human activity has continued.