Regional peculiarities in the importance of precipitation and temperature on mid-to-late Holocene arboreal degradation on the eastern Tibetan Plateau

Existing pollen records reveal that a shift from tree-rich to herb-dominated vegetation occurred on the eastern Tibetan Plateau (TP) during the mid-to-late Holocene, which gave rise to the modern vegetation pattern. However, given the complex climatic regulation of vegetation growth, the main climatic controls on arboreal vegetation in the eastern TP still need to be explored. In this study, a 387.5 cm sediment core covering the last 12.6 cal ka was recovered from Emu Co on the eastern TP. Based on pollen analysis in conjunction with the modern analogue technique, the role of various climate factors influencing past vegetation changes was modelled. Our results show that, during 12.6–9.5 cal ka BP, the study area experienced an arid and cold climate, with a sparse vegetation cover, as evidenced by the high abundance of herbaceous pollen and low total pollen concentration. A cold-tolerant deciduous broadleaved arboreal component, dominated by Betula, began to expand at ca. 9.5 cal ka BP, replacing herbaceous vegetation habitat, suggesting a gradual warming and wetting trend. Controlled mainly by rising temperatures, evergreen coniferous tree components develop from 8.7 to 5 cal ka BP, with Picea pollen reaching its maximum abundance. After 5 cal ka BP, the herbaceous vegetation re-expands under the combined pressure of lower temperatures and reduced precipitation. Declining arboreal pollen abundance in the mid-to-late Holocene is prevalent in the available fossil pollen records, but the main drivers have regional peculiarities: in the east-central region of the TP near Emu Co, lower temperatures may have played a more important role in the retreat of trees than reduced precipitation. Conversely, arboreal retreat and vegetation change in the north-east and south-east regions may be related to the weakening of the Asian summer monsoon circulation and seasonal climate changes caused by the East Asian winter monsoon and Indian summer monsoon, respectively.