Relationship between surface pollen and vegetation on the northern slope of west Tianshan Mountains, China
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Abstract:
The Tianshan Mountains, one of the famous mountain ranges in northwest China, forms a complete geographic zone and divides Xinjiang province into two different natural geographic units: southern and northern Xinjiang. These two units display distinct vertical gradient distributions of climate, soil and vegetation types which impact on pollen transportation, dispersion, preservation and deposition. Based upon pollen assemblages of 50 modern pollen samples and the data of vegetation plots, both of which were collected from the northern slope of western Tianshan Mountains, we analyzed the relationship between vegetation and surface pollen assemblages and compared different pollen assemblages of the Tianshan Mountains. (1) We divide the pollen spectra into five pollen assemblage zones, i.e., mountain desert, steppe, forest, subalpine meadow, and alpine cushion, according to major vegetation types of the north slope of the western Tianshan Mountains. (2) When the percentage of Picea pollen is 25%–30%, the sample can be considered coming from the Picea forest. The dominance of Picea-Artemisia-Chenopodiaceae-Apiaceae assemblage indicates the existence of a forest vegetation. The subalpine meadow and steppe are dominated by Artemisia-Chenopodiaceae-Poaceae-Picea-Ephedra assemblage. High percentage of Chenopodiaceae-Artemisia pollen indicates mountain desert and alpine cushion vegetation. Picea pollen is representative, and its proportion in a sample is consistent with the distribution of modern vegetation, but is significantly affected by airflow. The distribution of Ephedra pollen is also affected by airflow, and its percentage cannot be used to infer whether the vegetation exists around the sample site or not. Artemisia and Chenopodiaceae pollen are super representative, but they are only of regional ecological significance, while Poaceae pollen shows low representativeness due to its low yield. (3) The vertical pollen spectra are the most complicated in the north slope of western Tianshan.
