Modern Pollen Distribution Pattern In China And Its Relationships With Vegetation And Climate

Pollen record is an essential basic data for reconstructing paleovegetation and paleoclimate,which is important for studying the paleoenvironmental evolution,past climate change and past biogeochemical cycles.To quantitatively reconstruct the palevegetation and paleoclimate change processes,to explore the relationship between vegetation evolution and climate change,as well as to reveal the process of human activities on vegetation,it is necessary to correctly understand modern pollen processes.All of these studies strongly depend on the accuracy of pollen identification and the completeness of modern pollen databases.In this study,we collected the modern pollen data records from published and unpublished literatures between 1960 to 2020,sorted out the pollen taxa and their percentage content data in each record,and processed the data for screening and standardization.We also recorded information including sampling locations,latitude,longitude and altitude of sampling sites,sample types,data sources,data types,surrounding vegetation information and references.This resulted in the updating,expansion and integration of the latest Chinese Modern Pollen Database.The modern pollen dataset of China consists of a total of 4987 modern pollen sampling sites,including 660 sites from the first version of Chinese Quaternary Pollen Database,2265 previously published sites and 2062 recently collected data.The dataset includes 668 pollen taxa.The sample type was mainly from surface soils(3840 sites),and others were from moss plosters,surface sediments from lakes and the ocean.All of the sites are widely distributed in different geographical regions and vegetation types all over China.The data can be divided into the raw data(62.4%)and numerical digitized data(37.6%)according to the data source,as well as by data type the original grain count(58.03%)and calculated pollen percentage(41.97%).On this basis,the spatial distribution pattern of modern pollen and its relationship with vegetation and climate were investigated in this study.The modern vegetation information of formation and formation group,and vegetation division data of all pollen sample sites were extracted using the GIS from the vegetation map of China(1:1,000,000 scale)and the vegetation division map of China(1: 1,000,000 scale),respectively.The climate data(10 factors)of all sample sites was extracted from an interpolated climate dataset of China using the thin plate smooth spline technique.We selected 28 important pollen taxa,including 8 gymnosperm taxa,12 woody angiosperm taxa and 8 herbaceous angiosperm taxa.The distribution of different pollen taxa and their relationships with vegetation and climate were illustrated with the modern vegetation and climate data of their distribution areas.The correspondence between pollen taxa and surrounding major vegetation groups revealed by using co-inertia analysis(Co IA),and the relationships between modern pollen and different climatic factors were further statistically analysed by means of principal component analysis(PCA),canonical correspondence analysis(CCA)and correlation analysis(CA).The main results are as follows:(1)The geospatial distribution patterns of 28 important pollen taxa in China showed that the geographical distribution ranges of most pollen taxa coincide with their current species distribution.However,most of pollen taxa are widely distributed at low levels of pollen percentages,and gradually occur in their main growth areas with increasing pollen content levels,which is more similar to the distribution range of their vegetation.For example,Taxodiaceae,Fagaceae and Euphorbiaceae with high pollen percentages are more located in tropical and subtropical areas.The high pollen percentage sample sites of Ephedra,Nitraria,Artemisia,and Chenopodiaceae are mostly found in the grassland and desert areas of northwestern China.The pollen taxa such as Cyperaceae and Picea with high pollen percentages are more concentrated in the Tibetan Plateau.However,there are also some pollen taxa affected by wind transportation,such as the pollen of Pinus is mostly distributed in eastern China,but in the interior northwestern China and the inland of the Tibetan Plateau where are not pine distribution areas,there still have relatively high pollen content in sample sites.This indicates that pollen of the genus Pinus deviates from its geographical distribution area of the taxa.(2)The results of co-inertia analysis showed that the eigenvalues of the first two axes of the matrix could explain most of the variation information(85.71% in total).Most of the sample sites had good correspondence between pollen and the surrounding major vegetation groups,such as the sample sites in the cold-temperate coniferous forest region and the temperate coniferous-deciduous broadleaf mixed forest region and other forest regions;however,there were also some sample sites with poor correspondence,especially in the sample sites within vegetation formation of Artemisia and Poaceae in temperate steppe and desert,and alpine vegetation zones.(3)The results of the relationships between 28 important pollen taxa and different climatic factors showed that distributions of most pollen taxa corresponded to certain climatic ranges,and had significant climatic indication at higher pollen contents.The results of PCA,CCA and CA showed that both precipitation and temperature have important influence on pollen distribution,and annual precipitation is the main climatic driver.The distributions of pollen such as Cyperaceae,Chenopodiaceae,Ranunculaceae,and Pinus are mainly influenced by annual precipitation,and the distributions of Salix,Larix,Rhizophoraceae,and Abies have strong relationships with mean annual temperature.However,due to other non-climatic factors,such numerical correlations between pollen and climate in the national scale were poor.For more than half a century,researchers have sampled and studied a large number of surface modern pollen in China.The modern pollen dataset of China only has partial records,but it has a good coverage of most areas in China.The establishment and sharing of this dataset,as well as the research of modern pollen – vegetation – climate relationships,provide not only data support for the further update of the Chinese Pollen Database and in-depth the palynological research,but also can be effectively used in the validations of the past vegetation and climate reconstructions.