Spatial biome changes in southwestern Japan since the Last Glacial Maximum

Data from published palynological studies in southwestern Japan between 20 ka BP and the present were applied in a biomization procedure for Japan. The 20 biome maps obtained reveal a transition in biome from cool-mixed forest to warm-mixed/broadleaved evergreen forest and their migration routes. During the Last Glacial Maximum, southwestern Japan was covered with cool-mixed forest, and the climate was cooler than present. The warm-mixed/broadleaved evergreen forest was established in northern Kyushu Island and in the coastal areas of the Sea of Japan at 17 and 7 ka BP, respectively. There appears to have been a delay in its migration into the Chugoku region, caused by the environmental changes in the Sea of Japan. Before 8 ka BP, the relatively weak flow of the Tsushima warm current into the Sea of Japan created a climate resembling continental conditions and the winter temperatures were not high enough to permit the establishment of a warm-mixed/broadleaved evergreen forest. After 8 ka BP, warm-mixed/broadleaved evergreen forest spread into the Chugoku region, and reached higher altitudes 4 ka BP.