The Surface Pollen Assemblages And Their Relationships With Modern Vegetation And Climate In North China

The records from terrestrial ecosystems play a key role to the understanding of the history and mechanisms of the past global changes. Pollen is one of the best proxies to recover the changes of ecological environment. However, due to the complicated pollen sediment and dispersal process, the relationship between pollen assemblages and vegetation is not linear, therefore the research of surface pollen assemblages and their relationships with modern vegetation and climate provide a foundation for reco nstructing palaeo-environment by fossil pollen.A dataset consisting of130surface pollen samples from forest, marsh, marsh meadow, steppe, shrub, steppe desert and desert from Zoige Basin, Loess Plateau and surrounding deserts and north Xinjiang provides an opportunity to study the relationships between surface pollen assemblages and modern vegetation and climate in this region. The principle components analysis (PCA), correlation analysis and pollen ratios were used to help analyze the pollen data. The modern pollen assemblages are mostly composed of Artemisia, Chenopodiaceae, Cyperaceae, Poaceae, Betula, Pinus, Picea, non-Artemisia Asteraceae, Stellara, Polygonum, Nitraria and Ephedra. The results suggest that the surface pollen assemblages of different vegetation types faithfully represent the modern vegetation in terms of main composition taxa and dominant types. PCA results indicate that MAP is the major climate variable that controls the modern pollen assemblages. Pollen taxa and environment variable correlation analysis shows that Pinus, Betula, Poaceae, Asteraceae and Artemisia pollen percentages are positively related with mean annual precipitation (MAP), while some other types, such as Chenopodiaceae and Ephedra pollen percentages are negatively related with MAP. Correspondance ananlysis results of pollen ratio to climate and vegetation change indicate that the Arboreal/Non-Arboreal and Artemisia/Chenopodiaceae pollen ratios are positively associated with mean annual precipitation and decreased from forest to desert. Artemisia/Cyperaceae pollen ratio are weakly positively related to July temperature and negtivelly related to mean annual precipitation and could identify the marsh and meadow vegetation types from other vegetation types, suggesting that pollen ratios could be used as good indicators of moisture variability. Our results have implications for interpreting the fossil pollen data in the study region.