Vegetation And Environment Change Based On High Resolution Pollen Record During The Last 2400 Years In Dingbian, Shanxi, China

Based on the chronology of seven AMS ¹⁴C,two ¹⁴C dates,and the modem pollen data,a detailed history of vegetation and climate change during the last 2400 years was reconstructed by a high-resolution pollen record from Gouchi,Dingbian,at the Desert-Loess transition in Northern China.The study for modem pollen shows:1) Each vegetation community can be characterized by a distinctive modern pollen assemblage;2) the pollen of Pinus,Picea and Artemisia are over-represented;The Chenopodiaceae exists mainly in desert steppe;Although Poaceae is under-represented,higher percentages(over10%) may be found in the grassland where the natural vegetation is better preserved.41 families and 57 genera of fossil pollen were identified.Three pollen assemblage zones and seven sub-zones were divided based on the variations of main pollen percentages,pollen concentration and the result of CONISS analysis from the bottom to the top.Based on the modem pollen data,a detailed history of vegetation and climate changes during the past 2400 cal.B.P.was reconstructed by a high-resolution pollen record from Dingbian.It shows:between 2400 and 1740 a BP the vegetation was forest steppe dominated by Oak and the climate was warmer and moister;during 1740-1610 a BP the steppe expanded at the expense of the forest regression and the climate turned to be drier;during 1610-1240 a BP arboreal plants increased,open forest steppe developed and the climate became mild and moister;1240-1010 a BP the forest retreated while steppe expanded,suggesting a drier climate;1010-690 a BP the steppe further developed and a general warm and dry climate prevailed;690-500 a BP the deciduous broadleaved plants increased and the climate was temperate;500-190 a BP the vegetation was steppe and the climate was drier;190～0 a BP arboreal plants increased,indicating a moister climate.The climate by pollen record shows three warm periods in Dingbian.The warmer and moister period(2400-1740 cal.B.P.) being in accord with Qin-Han Dynasty Warm Period;the mild and moister period(1610-1240 cal.B.P.) corresponds with Sui-Tang Dynasty Warm Period; and the dry period(1010～690 cal.B.P.) can correlative with the Medieval Warm Period.In addition,the ecosystem degradation interval(500～190 cal.B.P.) maybe be compare with "Little Ice Age",though the climate fluctuation of warm/cold reoresent not obviously.