A Preliminary Study On The Relationship Between Surface Pollen Assemblage And Modern Vegetation In Northwest Of Sichuan

Surface pollen assemblages and their relationships with the modern vegetation and climate are the foundation for the recovering palaeo-environment and palaeo-vegetation. In order to investigate the relationship between the surface pollen and modern vegetation, surface soil samples collected from35sites in Northwest of Sichuan were analyzed, and then the pollen assemblages of every zone were obtained. Different vegetation types show different characters in the combination of pollen in surface soil. In the steppe communities, the herbs pollen percentages are more than77%, trees are near7.94%while shrubs are less than2%. In the shrub communities, the shrubs pollen percentages are about11.49%, the herbs pollen percentages among45to70%, trees pollen percentages are near31.68%. In the meadow communities, the herbs pollen percentages are more than78%, the trees pollen percentages are less than20%while the shrubs pollen are about1.65%. In the trees communities, the trees pollen percentages are near39.76%, the herbs are56.90%while the shrubs are less than5%. In the marsh, mud and Marsh surface sediments, the herbs pollen percentages are over80%, Cyperaceae as the main pollen type, trees pollen percentages are less than15%while the shrubs are less than2%.The representation of pollen in surface soil is different. The pollens such as Pinus, Artemisia, Picea are over-represented, Quercus, Gramineae, Cyperaceae, are under-represented. The pollens of Picea and Cyperaceae have good indication.The result of the comparison of comprehensive surface pollen indexs of different communities shows that, in non-forest communities, herbs pollen percentages are superiority which higher than70%while the content of arboreal pollen percentages are less than20%, AP/NAP<1, in the forest area has the high pollen concentration.The high ratio of A/C shows that the study area is wet.The result of relationship between the surface pollen and altitude shows that, the altitude (3000-4000m) occurred the plant of Cyperaceae consistent with the samples altitude(3400-3810m) over50%percentages of Cyperaceae. The comparison between the percentages of Artemisia pollen from surface samples and their distribution altitude then found that Artemisia pollen percentages decreasing with the increase of altitude.The trend of pollen concentration and pollen percentage is similar in ecological vegetation, show that the surface pollen assemblages are relatively stable in Northwest of Sichuan. The concentration of pollen changes marked of the dominant species.The results of the Clustering Analysis divide the samples into3groups. The first axis shows the relationship between the samples and humidities based on the ecological environments of each group; the second axis shows the relationship between the samples and altitudes based on the altitudes of each sample.Surface soil samples collected from multiple vegetation types, the high herbs pollen percentages are the general feature of surface pollen,4samples of herbs pollen percentages are less than50%, and the content of arboreal pollen percentages are over50%only in Coniferous forest and Coniferous-broad-leaf mixed forest.