Treeline composition and biodiversity change on the southeastern Tibetan Plateau during the past millennium, inferred from a high-resolution alpine pollen record

Abstract Climate variability has been impacting the terrestrial ecosystems. However, some important processes relating to the response of vegetation to climate change in alpine regions, such as treeline composition and associated plant diversity change, have not been well understood in terms of multi-centennial scales. Here, we present a well-dated high-resolution palynological record from Basomtso, southeastern Tibetan Plateau (TP), to discuss the vegetation change and the relevant climate forcing. Our results manifest that the treeline position, composition and plant diversity around Basomtso did change greatly during the past millennium. The cold events ( ca . 720-650 cal yr BP and ca. 400-50 cal yr BP) were considered crucial to force these changes. Cold temperature limited the growth of trees in the high elevations and thus led to downslope movement of treeline and conspicuous decrease of dominant tree species. Space and resource released from the upper forest triggered shrub and herb taxa expanded to lower elevations and even new species can dispersed to this area and survived, leading to changes in vegetation composition and diversity. Although the climate warming is pronounced since the 20th century, treeline distribution, vegetation composition and species diversity seem have not been recovered from the previous cold period. And the vegetation succession in the mountains of the southeastern TP will probably develop slowly in the coming decades. Our results highlight the need for long-term climate and vegetation monitoring and analysis in order to better understand the regional dynamics of treeline movement and plant diversity change during climate transition period.