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A 292 cm-long sediment core was collected from the center of Yukashigata Lagoon using a Mackereth air-pressure piston corer. Pollen analysis with radiocarbon dating of this sediment core was conducted to reconstruct the surrounding paleoenvironment. The results revealed a decrease in evergreen broadleaf tree pollen grains, an increase in herb pollen grains and fern spores, and a slight increase in charcoal fragments around 1100 cal CE, suggesting the onset of human impact on vegetation around this time. Furthermore, based solely on changes in the size of Poaceae pollen, it is estimated that rice cultivation began around 1250 cal CE. A major vegetation shift occurred around 1300 cal CE, marked by a rapid increase in Pinus pollen grains, herb pollen grains, and fern spores, along with a decrease in evergreen broadleaf tree pollen grains. The latter change suggested large-scale destruction of vegetation. Subsequently, tree pollen grains continued to decline, with a further decrease around 1550 cal CE, perhaps caused by the extensive use of Kumano timber for the construction of castles and temples by Sengoku-period warlords. Much of this timber was supplied by the Kishu Domain. However, as the Kishu supply of high-quality timber began to deplete, the warlords shifted to a policy of forest protection and cultivation, banning the felling of six tree species. As a result, the abundance of Pinus and Cryptomeria pollen grains sharply increased from around 1650 cal CE, as did that of evergreen broadleaf tree pollen grains which indicated a transition from compensatory vegetation to evergreen broadleaf forest from around 1950 cal CE. This vegetation recovery appears to have been linked to increasing reliance on plant-based fuels as fossil fuels became more widely adopted.
Research papers (academic journals)
