Paleoecology and History of Metasequoia in Japan, with Reference to its Extinction and Survival in East Asia

Abstract

The occurrence of fossil Metasequoia Miki in and around Japan was reviewed based on recent stratigraphic and paleoenvironmental data to reconstruct the regional ecology and discuss the processes that led to the extinction of Metasequoia in Japan during the late Miocene and its survival in eastern Asia. The frequent and abundant occurrence of Metasequoia fossils with wetland plants during the Eocene indicates that Metasequoia was one of the dominant components of the flood plain wetland forests of Japan. In the Paleogene, Metasequoia was widely distributed in the vegetation zones located between the Paratropical Rain Forest and polar Mixed Coniferous Forest zones. Metasequoia populations in East Asia were limited by a mild maritime climate and were absent from the subtropical regions where fossil assemblages were represented by semi-arid sclerophyllous forests. Climatic cooling may have exterminated Metasequoia populations in northeastern China and the Russian Far East during the late Miocene. However, Metasequoia survived up until the latest early Pleistocene in central and southwestern Japan. Metasequoia was less common in the small subsiding basins than in the wide sedimentary basins that were associated with contiguous fluvial flood plain ecosystems. Thus, orogenic and volcanic induced changes in topography in the flood plains were also assumed to have influenced the distribution of Metasequoia since the late Miocene. These topographic changes culminated during the late early Pleistocene and were accompanied with eustatic events and likely exterminated Metasequoia populations in the alluvial lowlands in southwestern Japan and hindered the post-glacial migration of the genus.