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Understanding the response of wetlands to climate changes could provide useful insights toward predicting the wetlands future in a warmer world. Here, we present a well-dated peat/mud profile with multiple proxies to reconstruct the historic development of Honghe wetland and discuss its response to the East Asian monsoon variations during the Holocene. The results show that the Honghe wetland developed as a shallow-water lake in the mid-early Holocene during a time of high precipitation from the East Asian monsoon. At 4600 years BP, peat layers appeared with sharp increases in the accumulation rate, grain-size Md and arboreal plants, marking a decline in water levels with the relative dry climate. Moreover, the transition corresponds well to the mid-Holocne monsoon weakening event and we suggest the decrease of the monsoon associated precipitation plays a critical role in driving the lake-peatland transition in Honghe. Facing the intensified summer monsoon in future, we suggest some practical measures should be taken to protect the present wetlands from changing back to lakes. [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]

An integrated view of wetland's evolution is currently poorly understood due to a lack of knowledge on long-term interactions of multiple ecological factors. Here, we present a cored palynological record covering the Holocene Epoch from a depressional wetland on Heixiazi Island (China). With the aid of principal component analysis and cluster analysis of the palynological data, the historical vegetation regime has been well reconstructed for wetlands on the island. With further assistance from the published data on local hydrology and regional East Asian summer monsoon (EASM) variations, the interactions of vegetation, hydrology, and climate in the island's wetlands have been thoroughly analyzed with correlation analysis of the three factors. The results indicate that a strong EASM generally led to a high water level in the wetlands from increased monsoonal precipitation, causing an increase in arboreal vegetation and a decrease in herbs. Alternatively, a weak EASM generally led to low water levels due to decreased monsoonal precipitation, causing a decrease in arboreal vegetation and an increase in herbs. The local vegetation regime during the early Holocene was marked by an increase in tree/herb ratio due to rising water levels under the influence of an increasingly strengthened EASM. Subsequently, a general decline of the tree/herb ratio occurred from a gradual decrease in water level during the mid and late Holocene when the EASM gradually retreated. The wettest stage marked by the highest water level and tree/herb ratio occurred 8.0–4.6 ka BP with the strongest EASM. The driest stage occurred during the last 0.4 ka BP, which was attributed to both the weakest EASM influence and anthropogenic disturbance. Our study provides an integrated view of the wetlands' ecological dynamics incorporating multi-factor interactions, which further sheds light on the EASM driving mechanisms on wetlands evolution during the Holocene Epoch. Schematic figure showing the historical interactions of vegetation, hydrology, and climate in a typical wetland on Heixiazi Island, NE China. The relatively strong East Asian summer monsoon (EASM) with high atmospheric precipitation tends to generate a higher water level with less herbaceous plants (a), while a weaker EASM stage with less precipitation leads to a lower water level and more herbaceous plants (b). The light blue and gray arrows indicate the separate pollen contributions of arboreal trees in elevated areas and herbs within the depressional wetland, respectively. Unlabelled Image • A palynological methodology aided in reconstructing vegetation history. • Holocene climatological and hydrological regimes were determined. • Holocene interactions of vegetation, hydrology, and climate were presented. • Wetland evolution was largely controlled by monsoonal precipitation. [ABSTRACT FROM AUTHOR]

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 A high-resolution pollen record in a peat sequence from the Altai Mountains of Xinjiang, China, allows reconstruction of the regional vegetation and climate changes that occurred during the Holocene. Pollen distributions from the sequence indicate that the vegetation community in the Altai Mountains region transitioned through five general phases: forest and desert steppe, wet steppe, desert steppe, steppe, and finally forest and desert steppe. These vegetative phases imply that the regional climate changed from a cold and dry early Holocene to a warmer and wetter early-mid Holocene and then to a cold and rather dry mid-Holocene that was followed by a cool and wet late Holocene and finally by warm and dry conditions for the last millennium. These regional changes in climate are roughly consistent with local changes previously reconstructed from organic geochemical paleoclimate proxies in the same peat sequence by Zhang et al. (2016), but with some minor but important differences that reflect local factors. Regional comparisons reveal that the Holocene climate changes in the Altai Mountains are generally consistent with those of most arid central Asian regions that are influenced mainly by westerlies. However, they are out-of-phase with the climate histories of regions controlled by the Asian monsoons, indicating that the Asian monsoons did not extend to the high-altitude mountain regions of arid central Asia during the Holocene. We postulate that the regional Holocene moisture variations have been mainly modulated by NAO variations that affected transport of water vapor from the North Atlantic Ocean by the westerlies. Moreover, local factors that include topography of the mountains and glacial meltwater events in the high-altitude regions also contributed to the climate changes in the Altai Mountains. In addition, air temperatures related to summer insolation of the Northern Hemisphere might have played an important role in modulating moisture in the region, but only after the local montane ice-sheets had disappeared by the mid-Holocene. Highlights • Pollen records from a peat sequence from Xinjiang Altai Mountains reveal Holocene vegetation changes. • Pollen-based reconstruction of Holocene climate changes in the Altai Mountains. • Comparisons of Holocene climate changes in Altai Mountains with arid central Asian and monsoonal Asian regions. • Explanations proposed for Holocene vegetation and climate changes in the Altai Mountains. [ABSTRACT FROM AUTHOR]