3Ma以来华北地区植被演化特征及其驱动因素

第四纪冰期与间冰期旋回的形成过程，及其陆生植被系统的响应及演化过程是研究地质时期全球变化的重点问题，本文通过对华北地区北部LN1钻孔的121个高质量孢粉数据重建了过去3 Ma以来的区域植被演化过程。研究结果显示，区域植被经历了4个主要发展过程，约3~2 Ma气候相对温暖湿润，主要为以松、桦、栎、胡桃、榆等组成的落叶阔叶林；约2 Ma，区域植被急剧变化，主要表现为针叶林扩张，阔叶林比例的减少，在2~1. 2 Ma转变为以松、云杉、桦为主的针阔叶混交林。在中更新世全球气候转型期，区域植被再次发生迅速改变，在约1. 2~0. 7 Ma转变为稀树的灌丛草原，0. 7 Ma以后区域气候进一步干旱化，在最近0. 7 Ma内区域环境转变为典型草原为主的植被景观。区域的植被变化反映了华北平原区近3 Ma以来整体上呈现出干旱化与寒冷化的趋势，其中2. 0 Ma，1. 2 Ma， 0. 7 Ma气候事件最为突出。上述结果反映了华北地区植被的演变过程及季风降水的逐渐减少与北极冰盖在近3 Ma以来的迅速扩张期同步对应。

Characteristics of vegetation evolution and its driving factors since 3 Ma in North China

The formation process of the Quaternary glacial and interglacial cycles, and the response and evolution process of the terrestrial vegetation system are key issues in global research on geological timescales. This paper reconstructs the regional vegetation evolution process since the past 3 Ma by using 121 high quality pollen data from borehole of LN1 in the north part of North China. The study results indicate that the regional vegetation has experienced four major development processes. The climate was relatively warm and humid during the 3~2 Ma and the vegetation was deciduous broad leaved forest, mainly composed of pine, birch, alfalfa, walnut, and alfalfa. The vegetation changed sharply such that the proportion of coniferous forest expanded and the broad leaved forest decreased in the area around 2 Ma. The vegetation changed to coniferous and broad leaved mixed forest dominated by pine, spruce and birch during 2~1.2 Ma. During the mid Pleistocene global climate transition period, the regional vegetation changed rapidly, transforming into a shrubland of sap trees at about 1.2~0. 7 Ma. After 0. 7 Ma, the regional climate was further dry and the regional environment changed to typical grassland vegetation landscape around 0.7 Ma. The vegetation changes in the region reflect the trend of aridification and cooling in the North China Plain with prominent climate events at 3 Ma 2. 0 Ma, 1. 2 Ma, and 0. 7 Ma. These results reflect that the vegetation evolution process and the gradual decrease of monsoon coincide with the rapid expansion of the Arctic ice sheet since nearly 3 Ma in North China.