日本の温帯落葉広葉樹林のフロラと植生の歴史─ブナ林を中心として─

抄録

Recent studies of paleobotany and phylogeography conducted on temperate deciduous genera were reviewed, and a new hypothetical scenario on the history of flora and vegetation of Japanese temperate deciduous forests was presented.　The flora of these forests originated not only from boreotropical flora, that is, the flora of subtropical and warm temperate forests existed between the late Paleocene and early Eocene, but also from the flora of cool temperate deciduous forests that were widely established from the late Eocene to Oligocene.　The boreo­tropical flora of East Asia is characterized by the abundant occurrence of deciduous species in addition to evergreen species.　The flora of Japanese warm temperate forests was basically formed owing to floral exchanges through a land bridge between continental East Asia and the western part of the Japanese Archipelago.　However, the flora of Oligocene cool temperate forests also remained in the northeastern part of the Japanese Archipelago because of the humid oceanic climate found here.　On the other hand, it mostly disappeared in continental East Asia after the late Miocene because of global cooling and increased aridity in the area.　The boundary between these warm temperate and cool temperate forests was constantly located in the Japanese Archipelago, shifting northward or southward during the glacial-interglacial cycle.　Therefore, the flora of Japanese temperate deciduous forests was formed as a mixture of these warm temperate and cool temperate floras.　The complex pattern of vegetation zonation observed in these forests can be partly explained as results of the above-mentioned floral exchange.　As for the remaining important issues, speciation processes in the extant Japanese beech species, i.e., Fagus crenata and F. japonica, must be solved.　The phytogeographical importance of the Fossa Magna area in the formation process of Japanese temperate flora needs to be further investigated.