Abstract: Subtropical evergreen broad-leaved forest (EBLF) is the predominant vegetation type in eastern China. However, the majority region it covers in eastern China was an arid area during the Paleogene. The temporal history and essential factors involved in the evolution of subtropical EBLFs in eastern China remain enigmatic. Here we report on the niche evolution of Quercus section Cyclobalanopsis, that appeared in south China and Japan during the Eocene and became a dominant component of subtropical EBLFs since the Miocene in eastern Asia, using integrative analysis of occurrences, climate data and a dated phylogeny of 35 species in Cyclobalanopsis. Species within clades Cyclobalanoides, Lamellosa, and Helferiana mainly habitat in the Himalaya-Hengduan Region, adapting to a plateau climate, while species within the other clades mainly live in eastern China under the control of the East Asian monsoon. Reconstructed history showed that significant divergence of climatic tolerance in Cyclobalanopsis began around 19 Mya in the early Miocene. Simultaneously, the disparity in precipitation of wettest/warmest quarter and annal precipitation were remarkably enhanced in Cyclobalanopsis, especially in the recent eastern clades. During the Miocene, the remarkable radiation of Cyclobalanopsis and many other dominant taxa of subtropical EBLFs strongly suggest the rapid formation and expansion of subtropical EBLFs in eastern China. Our research highlights that the intensification of the East Asian monsoon and subsequent occupation of new niches by the ancient clades already present in the south may have jointly promoted the formation of subtropical EBLFs in eastern China since the early Miocene.

Key words: Quercus, climate, Miocene, niche evolution, East Asian monsoon