Spatial and temporal characteristics of Neogene palynoflora in China and its implication for the spread of steppe vegetation

This study reviews 17 published Neogene pollen records with independent age control to provide a better understanding of the vegetation evolution and climate change in China, especially of the past shifts of the arid-semiarid steppe. During the late Early Miocene to early Middle-Miocene period, most of East and South China was covered by woodland vegetation (e.g., Quercus, Carya, Alnus, and Juglans) while Northwest China was mainly steppe (e.g., Artemisia), generally indicating a warm and humid climate influenced by a strong East-Asian summer monsoon. Since the Early Miocene the vegetation boundary between both regions has moved through time as the climate has changed. During the late Middle to Late Miocene cooling, herbs and shrubs increased significantly in the vast region north to the Yangtze River of South China and major woodland vegetation retreated to south of the Yangtze River. In the context of this cooling, a drier season probably became established north to the Yangtze River, as is evident from the late Middle Miocene to Pliocene compiled palynoflora data. Nevertheless, a little resumption for woodland vegetation occurred during the Early Pliocene in North China, presumably corresponding to global climate amelioration. Thus, the stepwise declining pattern of modern vegetation distribution from southeast to northwest in China can be traced back to at least the late Middle Miocene. In the meanwhile, the Neogene vegetation and its inferred climate history in China indicated a general declining trend of East-Asian summer monsoon.