Changes Of Palaeovegetation Pattern In China During The Late Quaternary

Pollen as the best preserved and most abundant proxy reflecting the ecological differences among plant taxa,is often used for reconstructing the patterns and dynamics of palaeovegetation or palaeoclimate,aiming to illustrate the evolution of past environment and discover its driving factors.The pollen database based on enormous site-level pollen records has enabled researchers to study the evolution of past environment at regional even global scale.Quantitative reconstruction studies of large-scale palaeovegetation patterns require a complete,reliable and open-source pollen database while China possesses adequate and high-quality pollen site records but need effective organization.Therefore,in this study,we searched for every pollen-related research in China published or reported since the 1960 s,collected geographic and sampling information and compiled raw records or digitized data from published pollen diagram.We thus established the most complete late-Quaternary pollen dataset of China,including 4987 sites of modern pollen and 372 sites of sediment pollen.The sampling sites in the dataset are widely distributed at every vegetation zone in China,with various sample types and high quality.Based on our improved Biomization method,our study first examined the applicability of our method in Chinese regions by comparing the reconstructed biome from modern pollen records,and then we used sediment pollen records to quantitively reconstruct the vegetation pattern changes in China over 50,000 years.In addition,we calculated the rate of vegetation change in the past 30,000 years based on the quantitative reconstruction results of 271 selected sites.The main results are as follows:(1)The overall match on one-to-one comparison between the observed and reconstructed biomes is 58.4%.But the classification of mega-biome enhanced the overall matching to 61.4% and generally increased the matching rate of each biome,while the matching rate rose to 75.8% when considering the similarity among biomes.Results showed that our updated classification of plant function types and biomes can objectively represent the relationship between pollen taxa and biomes,as well as the characteristic of vegetation in Chinese regions,making it sufficient for the quantitative reconstruction at a very large territory.(2)The reconstruction results showed that with the dry and cold climate during the last glacial maximum,most vegetation types were transforming to dry and cold biomes.Extension of aridity indicating biomes such as tundra and desert to lower latitudes at ca 18 ka BP demonstrated the occurrence of Heinrich I rapid cooling events.The alpine tundra shrank to higher altitude in western China during this Late Glaciation with temperate grasslands and deserts shifting to above 30°N and the increasing proportion of subtropical forests in southern China.Under the warm and humid climate condition during the Holocene,the distribution of temperate desert communities was restricted to the northern Tibetan Plateau and arid regions in northwestern China while tropical forests increased in coastal areas.The distribution of biomes during late Holocene gradually resembled that of modern vegetation zones.(3)The rate of change(ROC)suggested that the slow increasing in global temperature during the Last Glacial Maximum caused more intense vegetation change.Also,the global temperature increased but with series of strong fluctuations in Late Glaciation,which made a high rate of vegetation change indicating the persistent succession of plant communities.Vegetational change was relatively stable during the early and mid-Holocene,most regions showing no significant respond to the series of short-term cooling events in Holocene.The late Holocene saw subtle climatic change but extremely strong changes in vegetation,which indicates that anthropogenic activities had significantly influenced the vegetation succession with its scope and influence even resembling and exceeding the series transition at the end of last glacial period.This study,based on high quality and sufficient amount of pollen records to reconstruct the palaeovegetation pattern in China with a suitable updated biomisation procedure,had considerable confidence in reconstruction results.The application of ROC calculation also allowed for a more accurate description of flora succession.In future studies,it’s still necessary to supplement pollen records from the blank sampling areas,further improve the data quality in our dataset,and continue to modify the classification of plant functional types and biomes to reduce the mis-matching rate,so as to conduct Chinese paleoenvironmental research based on a fully complete and comprehensive pollen database in the future.