Neogene zonal vegetation of China and the evolution of the winter monsoon

When considering global change in China, it is important to understand how the strength of the monsoon has responded to changes in climate in the past. Here, we use a semi-quantitative reconstruction method, the Integrated Plant Record (IPR) vegetation analysis, to reconstruct the Neogene vegetation of China. The IPR method focuses on the taxonomic, physiognomic and autecological characteristics of fossil plants, whatever the organs concerned, such as palynomorph, diaspore, leaf and wood. Our study includes 107 Neogene fossil assemblages from 74 localities. There is an increase in the broad-leaved deciduous component in the northern areas during the Neogene. This is consistent with global cooling in the Neogene. At the same time, an increase of sclerophyllous and herbaceous components in west, central and north China occurs, which is indicative of aridification. There is no noticeable change in the vegetation of south China at that time. The Pliocene is characterised by an increasing contrast in vegetation between south and north China. The aridification of north China is due to a strengthening of the winter monsoon. Because there is no major change in the vegetation of south China, the weakening of East Asian summer monsoon is improbable. The Pliocene cooling is responsible for colder winters in Siberia, and the winter high pressure over Siberia becomes higher. As a result, the winter monsoon winds are stronger. The evolution of the summer and winter monsoons is not coupled.