Late Pleistocene-Holocene vegetation and climate change in Ebinur Betula wetland, Xinjiang, NW China

The work was supported by the National Natural Science Foundation of China (Grant No. 41971121 and 41572331), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA19050103), and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.Late Pleistocene-Holocene has been regarded as one of the most important periods in the history of climate change. The specific objectives of this study were to restore vegetation change and climatic evolution in the Ebinur Betula wetland of Xinjiang in China over the past 16,000 years based on 15 surface and 70 fossil pollen data. Research results revealed that a relatively humid climate existed from 12,230 to 9,260 cal. aBP, followed by a reducing humidity period between 9,260 cal. aBP and 3,303 cal. aBP. After 3,303 cal. aBP, the aridity increased further, especially in the last 600 years. Additionally, three high peaks of the Betula pollen in this wetland occurred at the end of the Last Glacial Maximum, at the beginning of early Holocene and during the Medieval Warm Period, all of which pointed to the amelioration of climatic conditions. However, the percentage of Betula has also been on a declining trend in the past 600 years, indicating a drying climate and intensified human activities. Therefore, these findings are conducive to exploring the impacts on wetland vegetation caused by climate change and anthropogenic disturbance in different periods, and providing the reference frame for wetland restoration and ecological construction in China.Publisher PDFPeer reviewe

Changes in wetland salinity, human activity and wetland vegetation abundances over the past 900 years

The birch wetland is an important type of oasis ecosystem in Xinjiang, China, which is extremely vulnerable to climate change and other disturbances. In this study, we aimed to understand the history of vegetation in such wetlands and find the key factors driving changes in the abundance of species inhabiting the wetlands of arid and semi-arid regions for over the past 900 years. Surface pollen samples were collected from 21 sites at altitudes between 750 m and 210 m, and 183 fossil samples were collected from the Ebinur and Caotanhu wetlands in north Xinjiang, China. Three different ground and surface water samples were collected from birch wetlands and the saline Ebinur Lake. The pollen and hydrochemical data were compared to examine the current interactions, and the knowledge thus gained was used to interpret historical changes in vegetation abundance in different regions (Ebinur and Caotanhu). The modem wetland landscape, surface pollen assemblage, and fossil pollen data from these areas together with hydrochemistry data concerning ground and surface water indicated that a local wetland ecosystem dominated by freshwater plants has been prevalent since 900 cal. a BP. The records show that Betula microphylla dominated the vegetation in the Caotanhu wetland from 900 to 700 cal. a BP; it subsequently declined and has now disappeared. In the Ebinur wetland, the vegetation cover of B. microphylla was at its highest between 270 and 220 cal. a BP; it is currently facing extirpation in the region. Our results, together with data concerning salinity and population statistics, indicate that both salinity and human activity have influenced wetland vegetation over the past 900 years. The two wetland ecosystems were dominated by freshwater plants during this period. At present, high salinity in the wetlands might be a key factor in driving the susceptible B. microphylla to extirpation. Increased human activity is an additional factor influencing changes in wetland vegetation. Overall, the results of our study on the interactions between wetland water and vegetation in different time periods (past and modern) and regions (Ebinur and Caotanhu) should be helpful for devising conservation strategies and conservation measures for B. microphylla in the semi-arid and arid areas of China

Airborne pollen patterns and their relationship with meteorological factors in the Betula microphylla-dominated wetland of Ebinur Lake, Xinjiang, China

Airborne pollen is indicative of vegetation and climatic conditions. This study investigates airborne pollen trapping in the Betula microphylla-dominated wetland of Ebinur Lake in Northwestern China from September 2012 to August 2015 using Pearson correlation analysis and the Hybrid Single-particle Lagrangian Integrated Trajectory model. Higher temperatures and moderate precipitation during the flowering period facilitated an increase in birch pollen with more exotic spruce pollen carried from the Tianshan Mountains by airflows, leading to the highest arbor pollen concentrations from September 2012 to August 2013. Peak pollen concentrations from September 2013 to August 2014 were possibly due to an increase in herbaceous pollen resulting from higher temperatures, lower precipitation and more exotic pollen from the desert of southwest Ebinur Lake and Central Asia in summer and autumn. Between September 2014 and August 2015, unfavorable climate conditions in summer and autumn decreased the pollen dispersal of xerophytes such as Artemisia and Chenopodiaceae, with little pollen transported from the Kazakh hilly area in late summer, resulting in the lowest pollen concentrations. Climatic parameters and air mass movements both greatly affected the atmospheric pollen concentration. The results provide information concerning the dispersion and distribution of birch pollen, paleoenvironmental reconstruction and wetland conservation

Multivariate analysis of modern and fossil pollen data from the central Tianshan Mountains, Xinjiang, NW China

To interpret past vegetation and climate changes from pollen data, we need to reveal the degree of similarity between modern analogues and fossil pollen spectra, which would help us predict the future climate and vegetation. Ninety surface pollen samples across six vegetation zones along an altitudinal gradient from 460 to 3510 m and 44 fossil samples at Caotan Lake were collected in the central Tianshan Mountains, northern Xinjiang, China. Discriminant analyses results, fossil pollen and phytolith assemblages were then used to reconstruct palaeovegetation and palaeoclimate in the area. The 90 surface samples were divided into six pollen zones (alpine cushion, alpine and subalpine meadow, montane Tianshan spruce forest, forest-steppe ecotone, Artemisia desert, typical desert), corresponding to the major vegetation types in the area. These zones follow a climatic gradient of increasing precipitation with increasing elevation. Paleovegetation reconstructed from 44 fossil pollen assemblages through discriminant analysis reflects the regional vegetation shifted from typical desert to Artemisia desert since 4640 cal. year BP in the Caotan Lake wetland. The fossil pollen and phytolith record also reveal the arid climate has not fundamentally changed in the period. But a dry-wet-dry local climate oscillation since 2700 cal. year BP has a fundamental influence on local wetland vegetation dynamics and peat accumulation of the Caotan wetland. Modern wetland landscape and surface pollen assemblages from the Ebinur Lake Wetland Nature Reserve provide further evidence for ferns and Betula growing in the Caotan Lake wetland during the historical period

Holocene climate events inferred from modern and fossil pollen records in Butuo Lake, Eastern Qinghai–Tibetan Plateau

Expansion of the spatial coverage of pollen data is essential to improve understanding of Holocene climate variation. To address this, we collected 25 surface and 72 fossil samples from Butuo Lake in the eastern Qinghai-Tibetan Plateau, China. We reconstructed the vegetation history of the region through detrended correspondence analysis (DCA) of the pollen data. Based on the results of this analysis, we divided the samples into five pollen zones (alpine sparse cushion vegetation, alpine scrub, alpine meadow, montane scrub meadow, and montane coniferous forest) corresponding to the major vegetation types. The observed temporal changes in vegetation (as indicated by the DCA of surface and fossil pollen spectra results, ratios of Artemisia to Cyperaceae (A/Cy), the sum of percentages of dryness indicators (SDI), and percentages of main pollen types) and modern pollen-climate transfer function (developed using the weighted averaging partial least squares regression method (WAPLS)) yield a sensitive record of Holocene monsoonal climate change in the area. During 11,140-8700, 8000-6000, and 5600-1780 cal. yr BP, the climate was wet and the vegetation was dominated by alpine meadow, indicating the occurrence of a strong southwest Asian monsoon that spanned almost the entire Holocene. Notably, two major cold and drought episodes are detected at 8700-8000 and 6000-5600 cal. yr BP, with vegetation dominated by alpine steppe, suggesting that the southwest Asian monsoon was extremely weak during these periods. The data will improve understanding of long-term variations of the southwest Asian monsoon in the region