Surface pollen and its relationships with modern vegetation and climate in the Tianshan Mountains, northwestern China

Abstract

A dataset consisting of 70 surface pollen samples from forest, alpine meadow, alpine steppe, temperate steppe, desert steppe, shrub/semi-shrub steppe and desert sites in the Tianshan Mountains, northwestern China provides an opportunity to study the relationships between surface pollen assemblages and modern vegetation and climate in this region. Redundancy analysis (RDA), the human influence index (HII) and pollen ratios were used to facilitate analysis of the pollen data. The modern pollen assemblages are primarily composed of Picea, Artemisia, Chenopodiaceae, Poaceae, Asteraceae, Nitraria and Ephedra. The results suggest that the surface pollen assemblages of different vegetation types largely represent the modern vegetation in terms of the primary taxa and dominant types. The RDA indicates that the mean annual precipitation (MAP) and the July temperature (T July ) are the major climate variables that control the modern pollen assemblages. Picea, Artemisia, Poaceae, Cyperaceae, Fabaceae, Asteraceae, Polygonaceae and Apiaceae pollen assemblages are positively correlated with MAP and negatively correlated with T July , while the pollen ratios for certain other types, such as Chenopodiaceae, Ephedra and Nitraria, are negatively correlated with MAP and positively correlated with T July . The arboreal/non-arboreal ratios are notably high in the forest samples, indicating a sensitive response to forest vegetation. Moreover, the Artemisia/Chenopodiaceae pollen ratios are generally correlated with the vegetation type and annual precipitation change, suggesting that these factors could be useful indicators of moisture variability in arid regions. However, it is difficult to distinguish between steppe and steppe desert based on this ratio, due partly to human disturbance. The HII is significantly correlated with certain pollen taxa, including Poaceae, Plantago, Polygonaceae and Elaeagnaceae, particularly in the alpine meadow and steppe samples. Our results have implications for interpreting the available fossil pollen data in the study region and other arid and semi-arid regions.

Modern pollen assemblages from surface lake sediments and their environmental implications on the southwestern Tibetan Plateau

“…This is because most areas in the eastern TP have more precipitation than those in the western TP. However, in arid and semi-arid areas on the TP and in northwestern China, precipitation mostly controls vegetation cover and composition and, thus, pollen assemblages (Zhang et al 2012;Wei & Zhao 2015). As shown by the RDA results in our study, MAP is the most important factor controlling variations in the modern pollen distributions on the southwestern TP.…”

“…Sanderson et al (2002) developed this modern global data set for HII by integrating the human population density, land use and infrastructure, and human access. This data set has been successfully used for exploring the relationship between human effect and surface pollen assemblages (Li et al 2014;Wei & Zhao 2015).…”

“…Thus, assessing the influence of human activities on modern pollen assemblages is very helpful for fully understanding environmental changes and quantitative climate reconstructions based on pollen data. Wei & Zhao (2015) explored the relationships between human effects and surface pollen assemblages in the Tianshan Mountains in northwestern China. Some of the sampling sites were from Tibetan Plateau along the main roads.…”

“…Some of the sampling sites were from Tibetan Plateau along the main roads. Wei & Zhao (2015) explored the relationships between human effects and surface pollen assemblages in the Tianshan Mountains in northwestern China. However, there have been very few studies on the influence of humans on the modern pollen spectra over the TP.…”

Assessing the impact of human activities on surface pollen assemblages in Qinghai Lake Basin, China

“…Artemisia pollen was present at high percentages in surface pollen samples from alpine meadow steppe and alpine steppe while Chenopodiaceae was present frequently but at low percentages (up to 7.3%) in each vegetation zone. It has been previously recognized that Artemisia pollen dominates in steppes while Chenopodiaceae pollen is enriched in deserts (El‐Moslimany, ; Herzschuh, ; Li et al ., ; Wei et al ., ; Lu et al ., ; Zhao et al ., ; Wei and Zhao, ). Poaceae pollen (<35 µm) had a relatively low percentage (average <16.1%) in the samples even though Poaceae plants were abundant (coverage >50%) in the alpine steppe vegetation zones, suggesting that Poaceae is under‐represented.…”