Vegetation changes in the Hengduan Mountains, China since the Last Glacial Maximum

Mountainous areas experience significant variations in temperature, humidity, and vegetation over short distances, thus mountain ecosystems are particularly sensitive to climate change. The Hengduan Mountains, located to east of the Tibetan Plateau, are characterized by a diverse terrain that includes plateau surfaces, alpines and lake basins. In this study, we present two pollen records from two cores in the Hengduan Mountains. Core YL from Lake Tianchi spans the last 23 ka, while core XMLT-1 from Lake Ximenlongtan covers the last 9.4 ka.

Around Lake Tianchi, the Tsuga dumosa forest zone migrated at least 650 m upward from 23 to ~7 ka, indicating a gradual increase in mean annual temperature exceeding 3.9 °C. In response to this warming, there was a successive colonization of different tree communities: grass and deciduous broadleaved trees dominated from 23 to 15 ka; warm deciduous broadleaved trees prevailed from 15 to 8 ka; and finally, warm coniferous trees (primarily Tsuga dumosa) and subtropical evergreen broadleaved trees dominated from 10 to 5 ka. After 5 ka, there was an increase in deciduous trees and grass, while evergreen trees decreased. Around the Lake Ximenlongtan area, tropical evergreen broadleaved trees dominated from 9.4 to 5 ka. However, after 5 ka, subtropical evergreen trees and grass increased at the expense of tropical evergreen trees.

At both sites, a significant shift in vegetation took place ~5 ka. The concurrent decline of subtropical evergreen trees around Lake Tianchi and tropical evergreen trees around Lake XMLT suggest a notable cooling event in western Yunnan, highlighting a trend toward decreasing monsoon intensity.