论文部分内容阅读
本文对黄土高原西部渭源黄土剖面作了系统的孢粉分析.结果表明,末次盛冰期研究区植被主要为蒿属、蓝刺头型菊科、禾本科、藜科和麻黄属等草和灌木,以及少量以云杉为主的针叶树,表明气候寒冷干燥.全新世早一中期,针叶树消失,草本和灌木植物花粉含量增加,植被以蒿属为主,其次有紫菀、蓝刺头型菊科、菊苣-蒲公英型菊科、十字花科、禾本科和伞形科等植物,藜科和麻黄属植物只零星出现.显示气候较为温暖湿润.全新世晚期,藜科、茄科和十字花科等“伴人植物”增加.表明人类活动增强.整体上看,末次盛冰期以来渭源地区发育以蒿属为主的草原植被,即便在温暖湿润的全新世适宜期亦未见森林发育. “,”Pollen analyses were conducted on loess deposits at Weiyuan, the western Loess Plateau. Results show that during the Last Glacial Maximum (LGM), herbs and shrubs dominated the Weiyuan region, mainly composed of Artemisia, Echinops type, Gramineae, Chenopodiaceae, and Ephedra, together with small amounts of conifers (mainly Picea). This vegetation assembly indicates a cold and dry climate for the LGM. During the early-mid Holocene, conifers disappeared, herbs and shrubs increased. Artemisia was predominant, followed by Aster, Echinops type, Taraxacum type, Cruciferae, Gramineae, and Umbelliferae. The disappearance of Picea and decreases in Chenopodiaceae and Ephedra suggest a wanner and wetter climate in the early-mid Holocene than in the LGM. During the late Holocene, anthropogenic plants such as Chenopodiaceae, Solanaceae and Cruciferae rose, indicating increased human activity. In general, the study area was dominated by steppe vegetation (mainly Artemisia) in both the LGM and the Holocene Optimum. Extensive tracts of forests have not occurred on the western Loess Plateau at least since the LGM.