2023 Volume 129 Issue 1 Pages 289-305
Two chronologically distinct plant macrofossil assemblages, the Late Miocene Tokachihoroka and the Early Pleistocene Taushubetsu floras, are recognized in the Lake Nukabira area of eastern central Hokkaido on the northernmost island of the Japanese Archipelago. The Tokachihoroka flora from the lacustrine Tokachihoroka Formation comprises 47 taxa in 18 families and 27 genera. The Taushubetsu flora from the lacustrine Taushubetsu Formation comprises 42 taxa in 20 families and 26 genera. The dominant arboreal taxa of these two floras is Betula maximowicziana-relative birch, which is associated with other deciduous broadleaf Betulaceae species, as well as Acer spp. and an evergreen conifer, Picea sp. The compositions of these floras, ecologies of their contemporary counterparts, and results of quantitative climate analysis based on CLAMP (the Climate Leaf Analysis Multivariate Program) indicate that the floras represent a combination of lakeside, slope, and subalpine vegetation types under humid and cool temperate climate conditions. Although the Taushubetsu flora represents a more modern species composition than the Tokachihoroka flora, the physiognomies of both floras reflect volcanic influences under similar humid and cool temperate climatic conditions.
