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The vegetation history of the central Tibetan Plateau over the last two millennia provides an important baseline for exploring future vegetation evolution. In this paper, we analyze high-resolution records of pollen, grain-size, total organic carbon (TOC) and total nitrogen (TN) for a 66.5 cm deep sediment core collected from Beilei Co on the central Tibetan Plateau. Between ca. 210 CE and 1988 CE, pollen spectra together with other proxies show that the Beilei Co region was covered by alpine steppe and experienced a relatively stable environment, with only slight changes in vegetation composition and minor climatic variations. However, since 1988 CE, abundances of Artemisia and Cyperaceae have begun to increase, while those of Chenopodiaceae (current accepted Latin name is Amaranthaceae) and Asteraceae have decreased sharply. Both the pollen assemblages and other proxies show that the study area is currently undergoing a major change and that the period of vegetation stability that has characterized the past two millenia has now ended. We argue that the recent changes in the vegetation may be caused by increasing precipitation and/or thawing permafrost due to global warming. In the future, the alpine steppe around Beilei Co may be replaced by alpine meadow. • High-resolution pollen spectra covering last two millennia completed for the central Tibetan Plateau. • Vegetation of the central Tibetan Plateau is stable for most of the time until the last few decades. • The central Tibetan Plateau is experiencing an unprecedented phase of wetting. [ABSTRACT FROM AUTHOR]

Abstract: Studies of vegetation successions related to climate changes during previous interglacial periods provide important insights into the mechanisms of climate change during the current interglacial and enable predictions of future climate impacts on ecosystems. The Chinese Loess Plateau (CLP), which is particularly sensitive to climate warming, presents an excellent site for such studies. However, few detailed records exist of vegetation and climate variations during interglacial periods on the CLP. This study obtained a series high resolution pollen records from the Luochuan loess-paleosol section on the CLP, and the paper discusses the vegetation and climate histories during three previous interglacial periods (MIS 9, MIS 7 and MIS 5). The Artemisia-Chenopodiaceae steppe vegetation that covered this area between 342 ka and 312 ka changed to Humulus-Chenopodiaceae steppe between 312 ka and 302 ka, and then reverted to Artemisia-Chenopodiaceae steppe after 302 ka. From 250 ka to 237 ka, the vegetation type remained Artemisia-Chenopodiaceae steppe, and then changed to Artemisia-Humulus steppe between 237 ka and 227 ka. Between 227 ka and 195 ka, the vegetation returned to Artemisia-Chenopodiaceae steppe. During MIS 5, vegetation of the study area changed from Pinus-Rosaceae-Chenopodiaceae forest-steppe between 129 ka and 117 ka, to Artemisia-Humulus-Ranunculaceae steppe from 117 ka to 96 ka. After 96 ka, the vegetation types changed to Pinus-Betula-Chenopodiaceae forest-steppe. Comparing these pollen records with other climatic proxies from the CLP and the oxygen isotope records from the Pacific Ocean suggests that vegetation and climate change features around the study site were synchronous with East Asian monsoon variations near 65°N. The regional tectonic uplift probably provided only a subordinate influence on vegetation and climate variation on the CLP during MIS 5. [Copyright &y& Elsevier]

• Identify ancient flood events, which may be the reason for decline of the culture. • Pollen and heavy metals can be used to reflect the strength of human activities. • Pollen and heavy metals revealed the process of culture from prosperity to decline. • This paper defined the chronology from prosperity to decline of Shijiahe culture. • Climate change has been revealed by pollen and heavy metals since 4800 cal. yr BP. The Shijiahe Culture (ca. 4800–4100 yr BP), which originated in the middle Yangtze Basin, was a milestone of prehistoric Chinese civilization. To reveal the interactions between climatic changes and human activities during this time interval, the geochronology and multiple proxies (pollen and heavy metals) of samples from a 220-cm-deep outer wall at the Sanfangwan Site (a typical site of the Shijiahe Culture) were analyzed. Radiocarbon dating indicates that the age range of the Sanfangwan Site is ca. 4800 to 4100 cal. yr BP. From ca. 4800 to 4600 cal. yr BP (the early Shijiahe Culture), pollen assemblages were dominated by Gramineae and an anthropogenic plant community (e.g. Ranunculaceae, Chenopodiaceae, Labiatae, and Cruciferae), indicating an expansion in rice agriculture during this interval. High metal concentrations in the same interval indicate a large flux of metals from smelting and farming activities. Between ca. 4600 and 4100 cal. yr BP (the middle and late Shijiahe Culture), decreases in Gramineae and anthropogenic pollen mirrored the recession of farming. Concurrent decreases in heavy metals may be attributable to a decline in the smelting industry. Three episodes of high pollen concentrations and visible increases in hygrophyte pollen, Pinus pollen, and fern spores at 4600–4550, 4450–4350, and 4200–4100 cal. yr BP probably indicate the occurrence of several flooding events during the middle and late Shijiahe Culture, resulting in the migration of local inhabitants. This study highlights the driving effect of flood events on the collapse of the Shijiahe Culture. [ABSTRACT FROM AUTHOR]

Improved studies of past vegetation change are required to better understand the variation of alpine ecosystems on the Qinghai-Tibetan Plateau (QTP) in response to future climate change. Spatial and temporal variations of past vegetation can be traced by fossil pollen data mapping. In this paper, we synthesized 57 continuous pollen records on the QTP covering the past 15 kyr to depict large-scale vegetation change and its response to climate variations. In order to minimize potential chronological biases, age-depth models were revised using a state-of-the-art and consistent method for all the records. The spatial and temporal variation of major pollen taxa were examined based on interpolated pollen maps at 1000-year intervals. The arboreal pollen (AP, mainly of Pinus , Betula and Abies / Picea) content expressed significant climate signals over a broad spatial and temporal gradient. During the late glacial period, high proportions of AP widely occurred in regions that are presently unforested owing to the sparse local vegetation coverage. For the Holocene period, AP showed relatively high contributions in records from the southeastern margin of the QTP, with a decreasing gradient in abundance towards the northwest. The transportation of AP to unforested regions corresponds closely to the intensity of monsoon wind, which can be used to track the Holocene evolution of the summer monsoon. The dominant shrub and herbaceous taxa (including Artemisia , Chenopodiaceae, Cyperaceae, Poaceae and Ephedra) generally represent developments of local vegetation responding to climate variations. In addition, the persistent increase in Poaceae pollen during the mid to late Holocene correlates possibly to regional human activities. The inferred spatial and temporal patterns of major pollen types on the QTP provide significant knowledge about long-term vegetation change and its potential response to climate variations. • An initial plateau-scale examination of fossil pollen records on the Tibetan Plateau. • Spatial and temporal patterns of major pollen types were mapped at 1000-year interval. • Arboreal pollen from unforested plateau surface represents intensity of summer monsoon. • Herbaceous pollen reveals local vegetation development in response to climate change. [ABSTRACT FROM AUTHOR]