Monsoonal climate of East Asia in Eocene times inferred from an analysis of plant functional types

The spatio-temporal vegetation patterns of East Asia in the Eocene remain uncertain. In this present paper, we conduct numerical analyses of plant functional types (PFTs) for 80 Eocene floras, subdivided into three-time intervals: the early, middle, and late Eocene. Based on PFT diversity spectra, five groups are identified from cluster analysis and interpreted in terms of vegetation type. These PFT-based vegetation reconstructions suggest a northwestward retreat of dry shrub or open woodland from early to late Eocene times, coupled with the expansion of humid broadleaved forest from the southeast. This hydrological distribution is consistent with mammal distribution, lithological indicators and geochemical proxies. An overall vegetation pattern of largely east-west differentiation is detected and we note that no unequivocal tropical vegetation is observed in low-latitudes during the Eocene. Our results indicate that a monsoonal climate shaped the Eocene spatio-temporal evolution of vegetation in East Asia along with the global cooling, and rain-shadow effects by the central and southwestern China highland, as well as basin extensions in the Pacific coast in the east.