Reconstruction of the Biome Pattern since 20, 000 yr BP Using Biomization Method

-(I) Kyushu Island-

Abstract

In order to construct past biome distributions on Kyushu Island, we compiled fossil pollen data that record vegetation changes during the past 20, 000 years. Age models estimated using 14C dates and/or Tephrochronology allowed the data digitized from published pollen diagrams to be compiled in 1000-year intervals from 20, 000 years ago to the present day.
We applied a method for identifying biomes from Japanese modern pollen data (Gotanda et al., 2002) to the fossil pollen data set. We obtained 20 biome maps that show the spatial changes in biome distribution through time. During the Last Glacial Maximum, Kyushu Island was covered with cool-mixed forest, and therefore the climate was estimated to be about 7°C cooler than the present. After 17, 000 yr BP cool-mixed forest retreated and warm-mixed forest migrated northward in western Kyushu. In eastern Kyushu, warm-mixed forest had not yet become established, and temperate deciduous forest started grewing. The appearance of warm-mixed forest in eastern Kyushu was delayed until 7, 000 yr BP This late appearance suggests that the refugia of warm-mixed forest during the Last Glacial Maximum not only existed in Yaku Island and southern Kyushu, but also on the Koshiki Islands in western Kyushu. Warm-mixed forest spread over the Kyushu Island, and its maximum coverage occurred at 4, 000 yr BP, which is much later than the interpreted climatic optimum at 6, 000 yr BP. This time lag may reflect the fact that winter temperature at 6, 000 yr BP was too cold for warm-mixed forest to grow and only became warm enough by 4, 000 yr BP.