Abstract
Fagus crenata and F. japonica (Fagaceae), both endemic to Japan, are representative trees of Japanese temperate deciduous broad-leaved forests. To examine the development processes of their dominant forests, we studied the morphology of fossil beech leaves and their occurrence from the Plio-Pleistocene strata in Japan. In an Early Pleistocene leaf fossil assemblage of ca. 1.65 Ma obtained from the Sayama Formation of the Kazusa Group in the Sayama Hills, western Tokyo, beech leaves accounted for ca. 40% of the fossil leaves. Morphological features of their venation and leaf margins showed co-occurrence of three beech species, F. crenata, F. japonica, and F. stuxbergi, in the fossil assemblage, among which F. crenata was the most dominant, accounting for 22.3 % of the leaves of tree taxa. This assemblage clearly represents the oldest fossil evidence of the modern Japanese beech forest dominated by F. crenata and F. japonica. Considering their present distribution, we assumed that, around the Kanto sedimentary basin, F. stuxbergi together with F. japonica grew with evergreen broad-leaved trees at lower altitudes, whereas F. crenata grew with F. japonica and other deciduous broad-leaved trees at higher altitudes.
