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Reconstructing Holocene changes in regional sea level is useful for understanding future sea-level scenarios. In this paper we examined the sedimentology, pollen, foraminifera, and organic matter properties of a well-dated profile from the Subei Basin that spans the last 6.7 ka. By integrating our findings with the archaeological record, we investigated mid- to late Holocene vegetation responses to relative sea-level fluctuations and considered the impact of climatic variations on cultural development. In the middle Holocene, the rapid and abrupt expansion of salt marsh vegetation (Chenopodiaceae, Cyperaceae, and Poaceae) suggests a relative rise in sea level. From 5.7 to 4.2 cal ka BP, lowland swamps were settled by Neolithic communities, as indicated by peak levels of microscopic charcoal and a significant rise in herbaceous pollen species, such as Cyperaceae, Typha , Myriophyllum , and Poaceae. From 4.2 to 3.7 cal ka BP, a major increase in Chenopodiaceae abundance and a δ13C excursion were observed along with a decrease in Cyperaceae and Poaceae levels, which revealed that human activity significantly decreased following the 4.2 ka climate event. Evidence suggests that the area under investigation experienced a relatively high sea level between 6.7 and 6.0 ka, a relative decrease in sea level between 6.0 and 5.7 ka, a steady sea-level condition between 5.7 and 4.2 ka, and gradual replacement by a freshwater marsh between 5.7 and 4.2 ka. The pollen and δ13 C records demonstrate that the relative sea level rose quickly from 4.2 to 3.7 ka, which could correspond to the 4.2 ka event. Enhanced El Niño-Southern Oscillation (ENSO) variance and intense climatic events in eastern China were the driving forces behind the mid-late Holocene relative sea-level shift. The rise in relative sea level eventually led to the collapse of the Qingdun and Jiangzhuang sites in the Subei Basin. Our results provide independent vegetation evidence of the simultaneous changes in relative sea level and variations in climate. • Vegatation and environment changes are investigated from ∼6700 cal a BP. • The significant relative sea-level rise in the Subei Plain during 4.2–3.7 cal ka BP. • The rise in relative sea level led to the collapse of the Qingdun site and Jiangzhuang site in the Subei Basin. [ABSTRACT FROM AUTHOR]

In this paper, we summarize the Holocene environmental history of the lower Yangtze region, east China, based on the sedimentary records and microfossil diatom, pollen, fungal and charcoal data that were published in the past two decades. We then examine the linkage between changes in the coastal environment and the development of rice agriculture in the region, with reference to the available archaeological evidence and historical archives. Based on the sedimentary and archaeological evidence, we conclude that during the early Holocene sea-level movements and sedimentary processes significantly changed the region’s landscape from an open, brackish water environment to a largely enclosed, wetland system. This newly established freshwater marsh environment provided a habitat favourable to rice agriculture. The early Neolithic farmers took the opportunity presented to them and started rice cultivation in locations where freshwater wetland systems were established. During the middle Holocene, environmental conditions were largely stable, and the coastal wetlands evolved slowly. Environmental change was only a supportive player in the Neolithic cultural processes, because the Neolithic people were able to adapt to these changes and took advantages of the newly emerging marsh land for food collection and production. Around 4200 years ago, the prosperous Liangzhu society fell, but there is no evidence to suggest the fall was related to a significant environmental change. The coastal environment continued to evolve slowly during the late Holocene. But this period saw rapid technological development in irrigation and flood protection, and the environmental factor was reduced to background noise. Throughout the Holocene, the main strategy taken by the Neolithic people to cope with environmental change was migration to find better food sources. Along with this strategy was the development of technology in landscape management to ensure a more reliable food production in addition to food collection through hunting, gathering and fishing. [ABSTRACT FROM AUTHOR]

• 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]

Schematic figure showing climate driving mechanisms on wetland hydrological and vegetational evolution. The relatively strong East Asian summer monsoon (EASM) with high precipitation tends to generate a higher water-level condition with more hygrophilous herbaceous plants while blocking the deposition of coarse grain-size fractions (a), and vise versa for weak EASM stages (b). [Display omitted] • The late-Holocene hydrological and vegetational regimes were reconstructed. • An ecological lake-to-wetland transition occurred at ~4.5 ka BP. • The wetlands evolution was largely controlled by monsoonal precipitation. The responding mechanism of wetland ecosystem to climate change is currently unclear due to a lack of long-term records incorporating multiple ecological factors. This paper presents a well-dated and multi-proxy cored record from a natural freshwater wetland developed in a paleo-pingo-related depression on the Sanjiang Plain. The study aims to reconstruct the wetland water-level and vegetational regimes during the past ~6.0 ka BP and discuss the wetland evolution response to the East Asian summer monsoon (EASM) circulation. The results show that a shallow-water lake with hygrophilous herbs developed in the depression with a strong EASM during ~6.0–4.5 ka BP. The paleolake was succeeded by a wetland with a lowered mean water level and an increase in tree cover controlled by the weakened EASM during the past 4.5 ka BP. Such an ecological lake-to-wetland transition corresponds well to the sharp decline of the EASM around 4.5 ka BP which has been well documented in various geological records across the EASM domain. During the wetland developing stage over the past 4.5 ka BP, the water-level and vegetational changes in the studied depression were also closely related to the EASM variations. The strengthened EASM usually generated higher water levels with more hygrophilous herbs around 4.0 ka BP, 3.5 ka BP, 3.0 ka BP, 2.0 ka BP, and 1.3 ka BP. Considering the prevalent EASM climate serving as the predominant water supply for the wetlands on the modern Sanjiang Plain, we suggest the EASM circulation has played a critical role in driving the wetland ecological evolution during the mid-to-late Holocene Epoch. The past 0.4 ka BP is an exception as the local Trees/Herbs ratio visibly increased with the declined water level, while the monsoonal precipitation shows no equivalent shift. The wetland evolution at this stage was attributed to human interference. [ABSTRACT FROM AUTHOR]

• Holocene vegetation history was reconstructed in a mountain area of north China by pollen data. • Mountain forests responded more sensitively to temperature before 6.0 cal. kyr BP. • Mountain forests responded more sensitively to summer monsoon after 6.0 cal. kyr BP. • Human impact was not serious for vegetation until several centuries ago. Understanding Holocene vegetation response regimes will improve predictions of future vegetation dynamics in mountain areas of semi-arid north China. In this paper, we statistically analyzed the relationship between a pollen record in a mountain area of semi-arid north China and influencing variables independent of pollen data, in the hope that potential vegetation forcing and response regimes can be explored. Our result suggests that the cool deciduous forest (CDF) at high elevation and the temperate deciduous forest (TDF) at middle and lower elevation were sensitive in responding to temperature before 6000 cal. yr BP, but were not sensitive to the summer monsoon (SM). Since 6000 cal. yr BP, the CDF and TDF were sensitive in responding to the SM instead of temperature. Hence, a shift of response regimes can be placed at ∼6000 cal. yr BP, which happened to be consistent with the time that forest expansion changed to deforestation. The insensitive response to the SM during the early Holocene might be attributed to the vegetation elevational movement, the topographic barrier for forest migration from refugia, and/or the topographically related high resistance and resilience of mountain forests. The sensitive response of CDF and TDF to the weakening SM since 6000 cal. yr BP was mainly caused by the cumulative moisture deficit caused by the continual weakening of the SM. Human activity had little impact on mountain forests until several centuries ago. Mountain forest expansion in response to climate warming during the early to middle Holocene can provide analogues for the prediction of forest dynamics of future warming. [ABSTRACT FROM AUTHOR]