Comparing Pollen Assemblages From Surface Soil And Interpreting Vegetation Variation Of Lushan During 1959-2020

On the study of paleo-vegetation based on pollen proxy,the characteristics of pollen assemblages have been proved to reflect the vegetation environment within a certain region at a specific period,which has been widely used to illustrate the history of vegetation evolution.The accurate pollen-vegetation relationship can provide a correct baseline for quantitative reconstruction of paleo-vegetation.Lushan Mountain is located in the subtropical climate zone,with rich and transitional vegetation types.Different succession series of the same group occur in Lushan,so it is a good area to investigate vegetation succession and ecological protection.In this study,we collected 32 surface sediments samples from various vegetations along altitudes on Lushan in 2020,and obtained pollen assemblages data from these samples by pollen analysis.We discussed the relationship between the modern pollen assembladges and current potential natural vegetation.Furthermore,we compared the varation of pollen assembladges between 1959 and 2020 and reconstructed vegetations of these two years by the biomization method to understand the vegetation succession of Lushan during this period.Finally,we used temporal beta‐diversity index to discover the plant diversity changes of vegetation communities with a vertical gradient in the past 60 years.The results show that the characteristics of topsoil sporopollen assemblages in 2020 can generally reflect the subtropical evergreen broad-leaved forest type in Lushan Mountain,although there is a certain degree of difference between reconstructed vegetation and actual vegetation.The percentage of pine pollen in the sporopollen assemblage in this area is too high,leading to low proportion for other pollen taxa.In addition,the dominant pteridophyte spores change from Hicriopteris in 1959 to Dicranopteris in 2020,which may be related to the strong acidity of soil p H in the process of community succession.According to the similarity coefficient index,it is concluded that the corresponding relationship between the sporopollen assemblage of topsoil and the surrounding vegetation is relatively weak in Lushan,and the classification grade and the range of plant records have a certain influence on the results.The composition of vegetation in Lushan is complex and the dividing lines of vegetation zones are not obvious,so it is difficult to distinguish these zones along vertical direction by biome method.However,it can basically reflect the vegetation composition of sampling sites,indicating that this method is feasible in mountain areas.Vegetation reconstruction based on biomization show that the vegetation types of three sampling sites during 1959-2020 changed from evergreen broad-leaved forest/mixed forest to coniferous and broad-leaved mixed forest.Using the beta diversity analysis,we draw a conclusion that the sporopollen taxa diversity for these six sampling sites has increased in the past 60 years.The diversity increase is not affected by altitude,but is related to the increase of vegetation diversity in Lushan Mountain.Among the sampling sites,only the sporopollen diversity of Qixian Temple decreased,which may be the result of allelopathy and human interference on the dominant species in the succession process.