中更新世以来华北平原植被演化及其气候响应

中更新世以来气候转型与陆地植被生态系统演变是近年来全球变化研究领域关注的热点问题。基于华北平原东部G3孔上部的孢粉分析结果、磁性地层年代,对中更新世以来华北平原植被演化及其气候响应过程进行研究。结果显示华北平原地区近1.6Ma以来植被演化可分为4个阶段:1.6~1.2Ma为密度较高的暖温带针阔叶混交林,1.2~0.7Ma为开阔的暖温带落叶阔叶林,0.7~0.3Ma为阔叶疏林草原,0.3Ma以来为暖温带落叶阔叶林。华北平原地区中更新世植被转型期对应O同位素36阶段,显示转型开始发生于1.2Ma,与全球中更新世转型期对应良好。其主要特征表现为林地减少,针叶林比例下降,藜科、蒿属、禾本科等草地面积显著增加。0.7Ma前后华北平原林地进一步退化,区域植被由原来的落叶阔叶林向疏林草原转变,0.3Ma后区域乔木比例可能有所回升。周期性气候变化对植被的影响在花粉谱中也有一定显示,1.2Ma之前主要表现为植被林地类型的交替发展,而1.2Ma则主要表现为草原与森林交替发展。

Palaeovegetation evolution and its response to the climate change since Middle Pleistocene in the North China Plain

The climate transition and the terrestrial vegetation ecosystem evolution since Middle Pleistocene are outstanding hotspot in recent global change studies. Based on pollen analysis and the magnetostratigraphy in G3 core in the eastern part of the North China Plain (NCP), the palaeovegetation since Mid Pleistocene was reconstructed. It reveals the vegetation evolution process and climatic response of NCP during the same time. The results show that the process of regional vegetation evolution can be divided into four stages: 1.6~1.2Ma, warm temperate coniferous and broad-leaved mixed forest with relative high density; 1.2~0.7Ma, mainly open warm temperate deciduous broad-leaved forest; 0.7~0.3Ma, broadleaf woody grassland; 0.3~0Ma, alternate appearance of mainly deciduous broad-leaved forest and woody grassland. The most significant vegetation change in NCP occurred at the time point 1.2Ma, which was around oxygen isotope stage 36 corresponding with the so-called Mid Pleistocene climate transition. At the time point, both broadleaf and coniferous forest proportions declined, while grassland dominated by Chenopodiaceae, Artemisia and Gramineae increased significantly. At about 0.7 Ma, the forest in NCP deteriorated further and regional vegetation transformed from deciduous broad-leaved forest to woody grassland. Since 0.3 Ma, the proportion of arbores has risen again. The impact of climate cycles on vegetation is also shown in the pollen spectrum. Before 1.2Ma, the vegetation represented mainly the alternate development of warm temperate and temperate forest types, and after 1.2Ma, the vegetation mainly represented the alternate development of forest and grassland.