青藏高原上新世以来植被与气候研究进展

PROGRESSES IN THE STUDY OF VEGETATION AND CLIMATE CHANGES SINCE PLIOCENE IN THE QINGHAI-XIZANG PLATEAU

由于青藏高原的特殊大气环流形势，夏半年受印度洋热带海洋季风──西南季风控制，向高原内部、尤其西北部，水份逐渐减弱；冬半年高原面受干冷西风环流影响，致使气候寒冷干燥。从而使高原植被由东南向西北发生递交。上新世早、中期在冈底斯山和念青唐古拉山以南地区发育常绿硬叶林，而北部则生长山地常绿针叶林，到更新世早期藏南以亚热带针阀混交林为主，北部出现灌丛和草原植被。自更新世晚期以来，青藏高原除东南部及喜马拉雅山以南的一部分地区保留部分亚热带针阔混交林外，大部分地区为高山草甸、灌丛草原或荒漠草原。

Vegetation and climate changes since Miocene were studied preliminarily in terms of palynological and paleobotanical records in the Qinghai -Xizang plateau in Miocene,subtropical alpine sclerophyllous oak forest existed in the most parts of Xizang,espicially southern Xizang. Meanwhile,the altitudinal zones of vegetation appeared and the alpine shrubbery was found firstly.The climatic characteristic was middle moist with annual temperature at above 2～ 10℃. In Early and Middle Pliocene,due to that rising mountains gradually hindered the India Ocean Monsoon's entering,the subtropical alpine sclerophyllous oak forest distributing widely in Miocene moved southward,main vegetation was evergreen sclerophyllous oak-cedra forest found in the regions south to the Gangdisi and Nianqingtanggula Mt., where the annual temperature was above 10℃ higher than today estimated by its modern distributing altitude, montane evengreen coniferous forest existed in the most of regions north to Gangdisi and Nianqingtanggula Mt, where the annual temperature was about 7℃.Since Late Pliocene,evergreenoak and cedra decreased, deciduous and herberous elements increased, main vegetation was subtropical mixed coniferous,and broadleaved forest in the north slopes of the Himalaya Mt, and regions south to Nianqingtanggula Mt., where the temperature Was 5.2～8.1℃ higher than present,in the regions north to the Himalaya 's north slopes and Nianqingtanggula Mt. ,drought became worse gradually, which resulted in appearence of shrubbery and steppe,where annual temperature was about 4 ℃ higher than today. Drought was serious since Late Pleistocene in the interior of the Plateau,alpine shrubberysteppe was found in the most part of Xizang, subtropical mixed coniferous and broadleaved forest,subtropical evergeen season rainforest and rainforest only existed in the Zhangmu,Kada,Yadong,Jilong, Cayu and Mutuo in the south slopes of the Himalaya Mt.,Holocene vegetation was similar to the Present.