Relationship Between Surface Pollen Assemblage And The Vegetation In The Western Tianshan Steppe Region Of Xinjiang

The ecological and environmental effects caused by global warming will undoubtedly pose a huge threat to the sustainable development of human beings,especially in the arid regions of northwest China with sparse vegetation and fragile ecology.Land Use/Cover Change is one of the important influencing factors driving climate change in historical periods,and has an important feedback effect on ecological environment changes.Therefore,the study of its changing process has gradually become one of the hot topics in the scientific community.Vegetation change is the main form of land cover change,while pollen contains relatively complete plant community information.Therefore,researching the relationship between the two is an effective way to quantitatively reconstruct paleovegetation and explore climate change.However,different climatic regions and vegetation types have different transmission methods and pollen production.Therefore,it is an important prerequisite to correctly understand the relationship between vegetation and pollen to conduct research on the relative pollen production(RPP)of plants and relevant source area of pollen(RASP)in different regions.At present,no scholars have carried out research on quantitative reconstruction of paleovegetation based on pollen data in the desert steppe of western Xinjiang.However,these studies have important implications for explaining the fossil pollen assemblage of vegetation changes in the region and for a better understanding of the Holocene vegetation succession process.Based on the surface pollen and vegetation data of 46 sampling sites,this study calculates the pollen fall speed,and the ERV model of estimating the relative pollen productivity and its relevant source area of pollen of the six main pollen types in this area.On this basis,the reliability of the research results is tested,and the main results are as follows:(1)The surface vegetation coverage in the grassland area of the western Tianshan Mountains in Xinjiang is low,growing mainly with Ephedra,Tamarix and other shrub types and Chenopodiaceae,Artemisia,Asteraceae,Poaceae,Cyperaceae and Fabaceae and other herb types;The pollen assemblage is also dominated by herb and shrub pollen types.Affected by valley wind and hydraulic effects,a certain amount of tree plant pollen appeared in the samples.Surface pollen analysis revealed that Artemisia,Chenopodiaceae and Ephedra are generally more representative among herbaceous plants,while Poaceae are less representative.(2)Based on the length of ellipsoidal pollen and the diameter of spherical pollen,the pollen sedimentation rate of Cyperaceae(0.0273 m/s)was the highest in the study area,followed by Asteraceae(0.0206m/s),Poaceae(0.0189 m/s),Chenopodiaceae(0.0131 m/s),Ephedra(0.0123 m/s),and Artemisia(0.0105 m/s).(3)The ERV model showed that the sub-model 2 combined with the Prentice distance weighting method matched the vegetation-pollen data better,and it was concluded that the RSAP in western Xinjiang was about 600 m,which was less affected by wind speed.Taking Artemisia as the reference species(RPP=1),the ERV model showed that Chenopodiaceae(12.26±1.54)and Ephedra(4.56±1.12)had higher relative pollen production,Cyperaceae(0.61±0.22)and Asteraceae(0.56±0.22)followed,and Poaceae(0.28±0.20)was the smallest.In addition,we reconstructed regional and individual site plant cover using the Landscape Reconstruction Algorithm(LRA)to assess relative pollen production based on the ERV model.LRA analysis showed that,apart from Cyperaceae,the reconstructed vegetation simulation values of Artemisia,Asteraceae,Poaceae,Ephedra and Chenopodiaceae were closer to the original vegetation coverage than the pollen percentage,that is,the PRR value obtained in this study was relatively close to the original vegetation coverage.It is reliable and can be further used in the quantitative reconstruction of paleovegetation in the desert steppe region of western China.