@article{CaoTianLietal.2019, author = {Cao, Xianyong and Tian, Fang and Li, Furong and Gaillard, Marie-Jose and Rudaya, Natalia and Xu, Qinghai and Herzschuh, Ulrike}, title = {Pollen-based quantitative land-cover reconstruction for northern Asia covering the last 40 ka cal BP}, series = {Climate of the past : an interactive open access journal of the European Geosciences Union}, volume = {15}, journal = {Climate of the past : an interactive open access journal of the European Geosciences Union}, number = {4}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1814-9324}, doi = {10.5194/cp-15-1503-2019}, pages = {1503 -- 1536}, year = {2019}, abstract = {We collected the available relative pollen productivity estimates (PPEs) for 27 major pollen taxa from Eurasia and applied them to estimate plant abundances during the last 40 ka cal BP (calibrated thousand years before present) using pollen counts from 203 fossil pollen records in northern Asia (north of 40 degrees N). These pollen records were organized into 42 site groups and regional mean plant abundances calculated using the REVEALS (Regional Estimates of Vegetation Abundance from Large Sites) model. Time-series clustering, constrained hierarchical clustering, and detrended canonical correspondence analysis were performed to investigate the regional pattern, time, and strength of vegetation changes, respectively. Reconstructed regional plant functional type (PFT) components for each site group are generally consistent with modern vegetation in that vegetation changes within the regions are characterized by minor changes in the abundance of PFTs rather than by an increase in new PFTs, particularly during the Holocene. We argue that pollen-based REVEALS estimates of plant abundances should be a more reliable reflection of the vegetation as pollen may overestimate the turnover, particularly when a high pollen producer invades areas dominated by low pollen producers. Comparisons with vegetation-independent climate records show that climate change is the primary factor driving land-cover changes at broad spatial and temporal scales. Vegetation changes in certain regions or periods, however, could not be explained by direct climate change, e.g. inland Siberia, where a sharp increase in evergreen conifer tree abundance occurred at ca. 7-8 ka cal BP despite an unchanging climate, potentially reflecting their response to complex climate-permafrost-fire-vegetation interactions and thus a possible long-term lagged climate response.}, language = {en} } @article{CaoTianTelfordetal.2017, author = {Cao, Xianyong and Tian, Fang and Telford, Richard J. and Ni, Jian and Xu, Qinghai and Chen, Fahu and Liu, Xingqi and Stebich, Martina and Zhao, Yan and Herzschuh, Ulrike}, title = {Impacts of the spatial extent of pollen-climate calibration-set on the absolute values, range and trends of reconstructed Holocene precipitation}, series = {Quaternary science reviews : the international multidisciplinary research and review journal}, volume = {178}, journal = {Quaternary science reviews : the international multidisciplinary research and review journal}, publisher = {Elsevier}, address = {Oxford}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2017.10.030}, pages = {37 -- 53}, year = {2017}, abstract = {Pollen-based quantitative reconstructions of past climate variables is a standard palaeoclimatic approach. Despite knowing that the spatial extent of the calibration-set affects the reconstruction result, guidance is lacking as to how to determine a suitable spatial extent of the pollen-climate calibration-set. In this study, past mean annual precipitation (P-ann) during the Holocene (since 11.5 cal ka BP) is reconstructed repeatedly for pollen records from Qinghai Lake (36.7 degrees N, 100.5 degrees E; north-east Tibetan Plateau), Gonghai Lake (38.9 degrees N, 112.2 degrees E; north China) and Sihailongwan Lake (42.3 degrees N, 126.6 degrees E; north-east China) using calibration-sets of varying spatial extents extracted from the modern pollen dataset of China and Mongolia (2559 sampling sites and 168 pollen taxa in total). Results indicate that the spatial extent of the calibration-set has a strong impact on model performance, analogue quality and reconstruction diagnostics (absolute value, range, trend, optimum). Generally, these effects are stronger with the modern analogue technique (MAT) than with weighted averaging partial least squares (WA-PLS). With respect to fossil spectra from northern China, the spatial extent of calibration-sets should be restricted to radii between ca. 1000 and 1500 km because small-scale calibration-sets (<800 km radius) will likely fail to include enough spatial variation in the modern pollen assemblages to reflect the temporal range shifts during the Holocene, while too broad a scale calibration-set (>1500 km radius) will include taxa with very different pollen-climate relationships. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{HerzschuhCaoLaeppleetal.2019, author = {Herzschuh, Ulrike and Cao, Xianyong and Laepple, Thomas and Dallmeyer, Anne and Telford, Richard J. and Ni, Jian and Chen, Fahu and Kong, Zhaochen and Liu, Guangxiu and Liu, Kam-Biu and Liu, Xingqi and Stebich, Martina and Tang, Lingyu and Tian, Fang and Wang, Yongbo and Wischnewski, Juliane and Xu, Qinghai and Yan, Shun and Yang, Zhenjing and Yu, Ge and Zhang, Yun and Zhao, Yan and Zheng, Zhuo}, title = {Position and orientation of the westerly jet determined Holocene rainfall patterns in China}, series = {Nature Communications}, volume = {10}, journal = {Nature Communications}, publisher = {Nature Publ. Group}, address = {London}, issn = {2041-1723}, doi = {10.1038/s41467-019-09866-8}, pages = {8}, year = {2019}, abstract = {Proxy-based reconstructions and modeling of Holocene spatiotemporal precipitation patterns for China and Mongolia have hitherto yielded contradictory results indicating that the basic mechanisms behind the East Asian Summer Monsoon and its interaction with the westerly jet stream remain poorly understood. We present quantitative reconstructions of Holocene precipitation derived from 101 fossil pollen records and analyse them with the help of a minimal empirical model. We show that the westerly jet-stream axis shifted gradually southward and became less tilted since the middle Holocene. This was tracked by the summer monsoon rain band resulting in an early-Holocene precipitation maximum over most of western China, a mid-Holocene maximum in north-central and northeastern China, and a late-Holocene maximum in southeastern China. Our results suggest that a correct simulation of the orientation and position of the westerly jet stream is crucial to the reliable prediction of precipitation patterns in China and Mongolia.}, language = {en} } @article{TianCaoDallmeyeretal.2018, author = {Tian, Fang and Cao, Xianyong and Dallmeyer, Anne and Lohmann, Gerrit and Zhang, Xu and Ni, Jian and Andreev, Andrei and Anderson, Patricia M. and Lozhkin, Anatoly V. and Bezrukova, Elena and Rudaya, Natalia and Xu, Qinghai and Herzschuh, Ulrike}, title = {Biome changes and their inferred climatic drivers in northern and eastern continental Asia at selected times since 40 cal ka BP}, series = {Vegetation History and Archaeobotany}, volume = {27}, journal = {Vegetation History and Archaeobotany}, number = {2}, publisher = {Springer}, address = {New York}, issn = {0939-6314}, doi = {10.1007/s00334-017-0653-8}, pages = {365 -- 379}, year = {2018}, abstract = {Recent global warming is pronounced in high-latitude regions (e.g. northern Asia), and will cause the vegetation to change. Future vegetation trends (e.g. the "arctic greening") will feed back into atmospheric circulation and the global climate system. Understanding the nature and causes of past vegetation changes is important for predicting the composition and distribution of future vegetation communities. Fossil pollen records from 468 sites in northern and eastern Asia were biomised at selected times between 40 cal ka bp and today. Biomes were also simulated using a climate-driven biome model and results from the two approaches compared in order to help understand the mechanisms behind the observed vegetation changes. The consistent biome results inferred by both approaches reveal that long-term and broad-scale vegetation patterns reflect global- to hemispheric-scale climate changes. Forest biomes increase around the beginning of the late deglaciation, become more widespread during the early and middle Holocene, and decrease in the late Holocene in fringe areas of the Asian Summer Monsoon. At the southern and southwestern margins of the taiga, forest increases in the early Holocene and shows notable species succession, which may have been caused by winter warming at ca. 7 cal ka bp. At the northeastern taiga margin (central Yakutia and northeastern Siberia), shrub expansion during the last deglaciation appears to prevent the permafrost from thawing and hinders the northward expansion of evergreen needle-leaved species until ca. 7 cal ka bp. The vegetation-climate disequilibrium during the early Holocene in the taiga-tundra transition zone suggests that projected climate warming will not cause a northward expansion of evergreen needle-leaved species.}, language = {en} } @article{TianHerzschuhDallmeyeretal.2013, author = {Tian, Fang and Herzschuh, Ulrike and Dallmeyer, Anne and Xu, Qinghai and Mischke, Steffen and Biskaborn, Boris}, title = {Environmental variability in the monsoon-westerlies transition zone during the last 1200 years - lake sediment analyses from central Mongolia and supra-regional synthesis}, series = {Quaternary science reviews : the international multidisciplinary research and review journal}, volume = {73}, journal = {Quaternary science reviews : the international multidisciplinary research and review journal}, number = {2}, publisher = {Elsevier}, address = {Oxford}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2013.05.005}, pages = {31 -- 47}, year = {2013}, abstract = {A high resolution multi proxy (pollen, grain size, total organic carbon) record from a small mountain lake (Lake Khuisiin; 46.6 degrees N, 101.8 degrees E; 2270 m a.s.l.) in the south eastern Khangai Mountains of central Mongolia has been used to explore changes in vegetation and climate over the last 1200 years. The pollen data indicates that the vegetation changed from dry steppe dominated by Poaceae and Artemisia (ca AD 760-950), to Larix forest steppe (ca AD 950-1170), Larix Betula forest steppe (ca AD 1170-1380), meadow dominated by Cyperaceae and Poaceae (ca AD 1380-1830), and Larix Betula forest steppe (after similar to AD 1830). The cold-wet period between AD 1380 and 1830 may relate to the Little Ice Age. Environmental changes were generally subtle and climate change seems to have been the major driver of variations in vegetation until at least the early part of the 20th century, suggesting that either the level of human activity was generally low, or the relationship between human activity and vegetation did not alter substantially between AD 760 and 1830. A review of centennial scale moisture records from China and Mongolia revealed that most areas experienced major changes at ca AD 1500 and AD 1900. However, the moisture availability since AD 1500 varied between sites, with no clear regional pattern or relationship to present day conditions. Both the reconstructions and the moisture levels simulation on a millennium scale performed in the MPI Earth System Model indicate that the monsoon-westerlies transition area shows a greater climate variability than those areas influenced by the westerlies, or by the summer monsoon only.}, language = {en} } @article{ZhangCaoXuetal.2022, author = {Zhang, Naimeng and Cao, Xianyong and Xu, Qinghai and Huang, Xiaozhong and Herzschuh, Ulrike and Shen, Zhongwei and Peng, Wei and Liu, Sisi and Wu, Duo and Wang, Jian and Xia, Huan and Zhang, Dongju and Chen, Fahu}, title = {Vegetation change and human-environment interactions in the Qinghai Lake Basin, northeastern Tibetan Plateau, since the last deglaciation}, series = {Catena}, volume = {210}, journal = {Catena}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0341-8162}, doi = {10.1016/j.catena.2021.105892}, pages = {14}, year = {2022}, abstract = {The nature of the interaction between prehistoric humans and their environment, especially the vegetation, has long been of interest. The Qinghai Lake Basin in North China is well-suited to exploring the interactions between prehistoric humans and vegetation in the Tibetan Plateau, because of the comparatively dense distribution of archaeological sites and the ecologically fragile environment. Previous pollen studies of Qinghai Lake have enabled a detailed reconstruction of the regional vegetation, but they have provided relatively little information on vegetation change within the Qinghai Lake watershed. To address the issue we conducted a pollen-based vegetation reconstruction for an archaeological site (YWY), located on the southern shore of Qinghai Lake. We used high temporal-resolution pollen records from the YWY site and from Qinghai Lake, spanning the interval since the last deglaciation (15.3 kyr BP to the present) to quantitatively reconstruct changes in the local and regional vegetation using Landscape Reconstruction Algorithm models. The results show that, since the late glacial, spruce forest grew at high altitudes in the surrounding mountains, while the lakeshore environment was occupied mainly by shrub-steppe. From the lateglacial to the middle Holocene, coniferous woodland began to expand downslope and reached the YWY site at 7.1 kyr BP. The living environment of the local small groups of Paleolithic-Epipaleolithic humans (during 15.3-13.1 kyr BP and 9-6.4 kyr BP) changed from shrub-steppe to coniferous forest-steppe. The pollen record shows no evidence of pronounced changes in the vegetation community corresponding to human activity. However, based on a comparison of the local and regional vegetation reconstructions, low values of biodiversity and a significant increase in two indicators of vegetation degradation, Chenopodiaceae and Rosaceae, suggest that prehistoric hunters-gatherers likely disturbed the local vegetation during 9.0-6.4 kyr BP. Our findings are a preliminary attempt to study human-environment interactions at Paleolithic-Epipaleolithic sites in the region, and they contribute to ongoing environmental archaeology research in the Tibetan Plateau.}, language = {en} } @article{ZhangXuGaillardetal.2016, author = {Zhang, Shengrui and Xu, Qinghai and Gaillard, Marie-Jose and Cao, Xianyong and Li, Jianyong and Zhang, Liyan and Li, Yuecong and Tian, Fang and Zhou, Liping and Lin, Fengyou and Yang, Xiaolan}, title = {Characteristic pollen source area and vertical pollen dispersal and deposition in a mixed coniferous and deciduous broad-leaved woodland in the Changbai mountains, northeast China}, series = {Vegetation History and Archaeobotany}, volume = {25}, journal = {Vegetation History and Archaeobotany}, publisher = {Springer}, address = {New York}, issn = {0939-6314}, doi = {10.1007/s00334-015-0532-0}, pages = {29 -- 43}, year = {2016}, abstract = {Pollen influx (number of pollen grains cm\&\#8722;2 year\&\#8722;1) can objectively reflect the dispersal and deposition features of pollen within a certain time and space, and is often used as a basis for the quantitative reconstruction of palaeovegetation; however, little is known about the features and mechanisms of vertical dispersal of pollen. Here we present the results from a 5 year (2006-2010) monitoring program using pollen traps placed at different heights from ground level up to 60 m and surface soil samples in a mixed coniferous and deciduous broad-leaved woodland in the Changbai mountains, northeastern China. The pollen percentages and pollen influx from the traps have very similar characteristics to the highest values for Betula, Fraxinus, Quercus and Pinus, among the tree taxa and Artemisia, Chenopodiaceae and Asteraceae among the herb taxa. Pollen influx values vary significantly with height and show major differences between three distinct layers, above-canopy (\&\#8805;32 m), within the trunk layer (8 \&\#8804; 32 m) and on the ground (0 m). These differences in pollen influx are explained by differences in (i) the air flows in each of these layers and (ii) the fall speed of pollen of the various taxa. We found that the pollen recorded on the ground surface is a good representation of the major part of the pollen transported in the trunk space of the woodland. Comparison of the pollen influx values with the theoretical, calculated "characteristic pollen source area" (CPSA) of 12 selected taxa indicates that the pollen deposited on the ground surface of the woodland is a fair representation with 85-90 \% of the total pollen deposited at a wind speed of 2.4 m s\&\#8722;1 coming from within ca. 1-5 km for Pinus and Quercus, ca. 5-10 km for Ulmus, Tilia, Oleaceae and Betula, ca. 20-40 km for Fraxinus, Poaceae, Chenopodiaceae, Populus and Salix, and ca. 30-60 km for Artemisia; it is also a good representation with 90-98 \% of the total pollen deposited coming from within 60 km at a wind speed of 2.4 m s\&\#8722;1, or 100 km at a wind speed: 6 m s\&\#8722;1, for the 12 selected taxa used in the CPSA calculation. Furthermore, comparison with the vegetation map of the area around the sampling site shows that the pollen deposited on the ground represents all plant communities which grow in the study area within 70 km radius of the sampling site. In this study, the pollen percentages obtained from the soil surface samples are significantly biased towards pollen taxa with good preservation due to thick and robust pollen walls. Therefore, if mosses are available instead, soil samples should be avoided for pollen studies, in particular for the study of pollen-vegetation relationships, the estimation of pollen productivities and quantitative reconstruction of past vegetation. The results also indicate that the existing model of pollen dispersal and deposition, Prentice's model, provides a fair description of the actual pollen dispersal and deposition in this kind of woodland, which suggests that the application of the landscape reconstruction algorithm would be relevant for reconstruction of this type of woodland in the past.}, language = {en} }