Vegetation and climate history inferred from a Qinghai Crater Lake pollen record from Tengchong, southwestern China

A palynological investigation of a 514 cm long continuous core section from Qinghai Crater Lake, western Yunnan Province, southwestern China, was performed in order to reconstruct regional vegetation and climate from 15.8 cal kyr BP to the present. The results show that the area was covered with deciduous broadleaved forest dominated by deciduous Quercus between 15.8 and 12.8 cal kyr BP, suggesting slightly cold and dry conditions. From 12.8 to 8.3 cal kyr BP, the vegetation continued to be dominated by deciduous broadleaved forest, but there was also a sudden increase in Castanopsis/Lithocarpus and a slight drop in deciduous Quercus and Alnus, reflecting a gradual increase in both temperature and humidity. During the period 8.3–4.6 cal kyr BP, the mixed deciduous forests became more diverse and dense, with thermophilous and hygrophilous species expanding to their maximum extents, implying a warm and rather humid climate. From 4.6 to 0.5 cal kyr BP, the vegetation was succeeded by open mixed deciduous forest dominated by Alnus, with a retreating evergreen broadleaved forest, indicating a cool and slightly dry climate. After 0.5 cal kyr BP, the vegetation became less diverse and more open, but evergreen broadleaved trees increased their spread markedly, suggesting that the climate had become warmer and drier. In recent decades, human activity resulted in a large increase in Alnus and Pinus around this lake basin. Specifically, we concluded that the warm and moist climate detected between 8.3 and 4.6 cal kyr BP may have occurred in response to the high sea surface temperatures and high sea levels in the Bay of Bengal existent at that time.