VEGETATION EVOLUTION RECORDED BY LAKE SEDIMENT DURING LATE HOLOCENE ON THE SOUTHERN TIBETAN PLATEAU
As a significant ecological security buffer of China,the preservation of the ecosystem on the Tibetan Plateau(TP)is vital for sustainable development.Vegetation coverage is crucial in assessing the health of the flora on the TP,hence it is essential to comprehensively investigate the evolutionary processes and underlying mechanisms.In this study,a 120cm-long sedimentary core was collected from Ngamring Co(29° 17′～29°20′N,87°09′～87° 13′E;4304 m a.s.l.),at a water depth of 13 m.We chose AMS 14C and 210Pb/137Cs approaches to establish the age-depth model.Dating results indicate that the reservoir effect was 1999 years for AMS 14C dates,and the core covered the last 3600 years.Pollen analysis was conducted to reconstruct the historical evolution of vegetation with a temporal resolution of 30 years per sample.Utilizing the Modern Analogue Technique(MAT),a calibration-set was established based on modern pollen percentages and vegetation coverage from 614 sampling sites on the southern TP(unpublished data from our team).The"leave-one-out"cross-validation results indicate that this model is reliable(R2=0.71,RMSE=8.51％)and can be used to quantitatively reconstruct changes in vegetation coverage.In total,64 pollen taxa have been identified in the 120 fossil pollen samples.The pollen spectra were dominated by herbaceous pollen taxa,including mainly Cyperaceae,Artemisia,Chenopodiaceae,Poaceae,and Ranunculaceae.The proportions of tree pollen were lower,and Pinus,Betula,Tsuga,and Quercus occur commonly.The shrub pollen types include mainly Rosaceae,Nitraria,Hippophae,and Ephedra.During 3600～850 cal.a B.P.,the pollen spectra were primarily composed of Cyperaceae,with the A/Cy ratio(ratio of Artemisia to Cyperaceae)＜1,indicating the presence of alpine meadow vegetation around the lake with relatively high vegetation coverage(mean 16.9％)in a wet climatic condition.Additionally,the scores of the first axis of PCA were significantly negative at ca.3300 cal.a B.P.,and the vegetation coverage was significantly reduced,which should correspond to a dry climatic event.Since ca.1100 cal.a B.P.,a gradual increase in the percentage of Artemisia and a decrease in the percentage of Cyperaceae occurred.After 850 cal.a B.P.,Artemisia emerged as the dominant pollen type with A/Cy ratios＞1,indicating the vegetation changed to alpine steppe with lower vegetation coverage(mean 11.1％),possibly related to the dry climate conditions.The observed changes in vegetation types and coverage since 850 cal.a B.P.together with the dry climatic event at 3300 cal.a B.P.should be affected by the gradual weakening of the Indian Summer Monsoon(ISM).
万方数据
维普
