Spatial distribution of anemophilous pollen and its correlation with the Asian summer monsoon on the southeastern Tibetan Plateau

Abstract

Previous studies have discovered arboreal pollen in non-forested areas on the Tibetan Plateau, which are mostly anemophilous type and regarded as a result of the Asian summer monsoon. However, the relationship between the spatial distribution of wind-pollinated pollen and monsoon has seldom been illustrated quantitatively. Here, we used 676 surface samples (647 compiled, 29 new samples) to examine the characteristics of the spatial distribution patterns of 13 anemophilous pollen taxa on the southeastern Tibetan Plateau, by employing the spatial interpolation technique. Then, we quantified the correlation between the distributions of these taxa and monsoon wind via Mantel test. The results show that the anemophilous pollen represents at least half percentage of the total pollen assemblages in most areas of the study region. Anemophilous tree pollen mainly distributes in the south and southeastern part, while anemophilous non-tree pollen does in the opposite and perpendicular direction. The distributional pattern of non-anemophilous pollen reflects that their corresponding plants most likely constitute the understory components of different forests or the minorities of non-forests communities. Mantel tests indicate that the anemophilous tree pollen has a highest correlation with the Asian summer monsoon. Anemophilous pollen, overall pollen assemblages and anemophilous pollen with air sacs have higher correlations with summer monsoon. Contrarily, non-anemophilous pollen has relatively weak correlation. Furthermore, we found that the relationships between various pollen groups or separate taxa and the Asian summer monsoon are dependent on sample types. The lake sediment surface samples had the strongest signal of the Asian summer monsoon among the different sample types. Our findings provide the strong evidence of the Asian summer monsoon influencing the pollen distribution patterns. More importantly, the quantification of this correlation between anemophilous tree pollen and the Asian summer monsoon offers the fundamentally theoretical basis of reconstructing paleo-monsoon by the proxy of windborne pollen taxa.