Vegetation dynamics and its response to climate change during the past 2000 years in the Altai Mountains, northwestern China

Over the past 2000 years, a high-resolution pollen record from the Yushenkule Peat (46 degrees 45 '-46 degrees 57 ' N, 90 degrees 46 '-90 degrees 61 ' E, 2374 m a.s.l.) in the south-eastern Altai Mountains of northwestern China has been used to explore the changes in vegetation and climate. The regional vegetation has been dominated by alpine meadows revealed from pollen diagrams over the past 2000 years. The pollen-based climate was warm and wet during the Roman Warm Period (0-520 AD), cold and wet during the Dark Age Cold Period (520-900 AD), warm and wet during the Medieval Warm Period (900-1300 AD), and cold and dry during the Little Ice Age (1300-1850 AD). Combined with other pollen data from the Altai Mountains, we found that the percentage of arboreal pollen showed a reduced trend along the NW-SE gradient with decreasing moisture and increasing climatic continentality of the Altai Mountains over the past 2000 years; this is consistent with modern distributions of taiga forests. We also found that the taiga (Pinus forest) have spread slightly, while the steppe (Artemisia, Poaceae and Chenopodiaceae) have recovered significantly in the Altai Mountains over the past 2000 years. In addition, the relatively warm-wet climate may promote high grassland productivity and southward expansion of steppe, which favors the formation of Mongol political and military power.