Climate sustained the evolution of a stable postglacial woody cover over the Tibetan Plateau

Abstract

The Tibetan Plateau (TP) is referred to as the world's “Third Pole” and the “Asian Water Tower”. It is dominated by herbaceous plants, with sparse to no vegetation cover in its central and western parts. Only 12% of the TP land mass is covered by forest on its eastern edge where most of the human population is distributed. Understanding forest evolution and its driving forces in this region is essential to sustainable development in east, southeast, and south Asia. In this study, we built a database of 622 topsoil pollen samples and 24 fossil pollen sites, and reconstructed the postglacial evolution of woody and herbaceous cover using the modern analogy technique (MAT) and the random forest (RF) methods. We found that postglacial woody cover was sustained at ~17% (13–21%) on the eastern TP (ETP) and ~ 5% (3–9%) on the central and western TP (CWTP). The change in woody cover on the ETP was mainly driven by the East Asian summer monsoon (EASM) precipitation (42%) and summer temperature (30%), while the change in herbaceous cover on the CWTP was mainly driven by the summer temperature (54%) and moisture-laden westerlies (16%). Humans only slightly affected the woody cover after 3600 cal. yr BP, even when large populations started to settle on the TP. Future climate warming might be beneficial for increasing the forest cover on the TP.