Three buried forests of the Last Glacial Stage and middle Holocene at Ooyazawa on northern Honshu Island of Japan

Abstract

Three extensive buried forests of the Late Quaternary were unearthed at Ooyazawa, Aomori, in the northern part of Honshu Island of Japan during construction of a flood water reservoir. The lower and middle buried forests were formed by activities of the Towada Volcano and dated from the early period of the Last Glacial Maximum and the Late Glacial Period, respectively. The upper buried forest was formed as a result of sea level changes and dated from the Early Jomon Period of middle Holocene. Picea and Larix dominated in the lower and middle buried forests of the Last Glacial Maximum and the Late Glacial Period, accompanied by occasional Abies. In the middle buried forest Picea and Larix grew evenly intermixed, and Larix trees were larger (up to 84 cm in stem diameter) than Picea trees (up to 33 cm in stem diameter). The taxonomic composition of the lower and middle forests was similar to that of the buried forests on the eastern slope of the Towada Volcano of the Late Glacial Period. The buried forests of northern Honshu Island, as well as those of south to central Honshu Island, indicate that Picea–Larix forests were the dominant vegetation through the Last Glacial Maximum to the Late Glacial Period on central to northern Honshu Island. In the upper buried forest of the middle Holocene, Fraxinus and Alnus dominated, accompanied by Juglans, Castanea, Quercus, Fagus, Magnolia, Hydrangea, and Acer. This upper buried forest contemporaneously formed woody peat below the forest floor. According to a pollen analytical study at Ooyazawa, similar buried forests continually established themselves after frequent destructions by flooding for at least 1000 years of middle Holocene. Lowland forests of Fraxinus and Alnus that simultaneously formed woody peat grew extensively in the Kanto Plain of central Honshu Island during the middle Holocene. The upper buried forest at Ooyazawa was the first record of this type of lowland forest outside the Kanto Plain and showed that the establishment of marsh forests with contemporaneous woody peat was a general phenomenon in a large area of Honshu Island during the middle Holocene.