This study examined the orbital-scale vegetation response to seasonal climate changes related to the East Asian monsoon and ocean currents during the last glacial–interglacial cycle based on a new continuous pollen record from Lake Biwa, western Japan. During MIS 6, 4, and 2, pinaceous conifer forests were present in both inland and Japan Sea coastal areas around Lake Biwa, influenced by cold and dry conditions in both summer and winter. In contrast, deciduous broadleaved forests and evergreen forests grew during interglacial periods in MIS 5e and 1 under relatively warm and humid conditions in summer, as well as in winter. Fagus crenata, a tree endemic to the Japanese archipelago, was especially widely distributed during MIS 5e due in part to winter snowfall caused by warm current inflows in the Sea of Japan. During MIS 5 and 3, temperate conifer trees were dominant. During periods of low summer insolation in MIS 5, the endemic tree Cryptomeria japonica became dominant in both inland and coastal areas of the region, likely as a result of high precipitation in early summer related to southward shifts of the summer monsoon front and moderate winter climate conditions. In contrast, Sciadopitys verticillata, which is also an endemic tree, had own habitat around inland areas of western Japan during the periods of high summer insolation in MIS 5. Climate fluctuations during the glacial–interglacial cycles created several ecological niches in time and space for each endemic tree in the Japanese archipelago.
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