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Holocene paleoclimate reconstructions and comparisons largely rely on accurate age-depth modeling. However, uncertainties in chronology, such as those caused by sparse radiocarbon dates, will hamper inter-core comparisons and correlations, and might result in misleading "cause and consequence" conclusions. This study aimed to find a solution to increase the comparability and minimize the uncertainty of wetland chronology as much as possible. Sediment cores were recovered and radiocarbon dated from the Lianhuachi wetland located in Southeastern China. Humification degree and loss-on-ignition (LOI) were determined using colorimetric and combustion methods respectively. Our data were compared with previously published datasets obtained in the same wetland. The results show that independent humification profiles from the Lianhuachi wetland displayed high similarities. This high similarity between the humification profiles allowed us to transfer radiocarbon ages from one core to another using sequence slotting correlation. Applying the humification-based chronology refinement method to all sediment cores resulted in an improvement in the correlation coefficients between the same but independently measured proxy sequences from the wetland, which suggests both the inter- and intra-core comparability was improved. Because determining peat humification degree is easy, inexpensive, and time-saving, we suggest that humification can serve as a tool that can be used to correlate different cores and to transfer published radiocarbon ages within the same wetland (peatland) or in a comparable geological setting, to establish a more robust chronology of these comparable cores. The degree of peat humification can thus serve as a relative dating technique to refine the chronology of wetland (including peatland) records. [ABSTRACT FROM AUTHOR]

An improved understanding of past interactions between terrestrial vegetation and various forcings, such as climate change, human impact, and paleofire, is crucial for assessing impacts of future global change on terrestrial ecosystems. This study seeks to find the key factor or factors that have driven Holocene vegetation change along the East Asian monsoon margin. Several high-resolution pollen records are reviewed and new phytolith-based paleovegetation reconstructions and physical geochemical datasets are presented from a peatland in northeastern China. Using 108 modern topsoil samples as a training set, canopy cover and vegetation composition are estimated for the period since 5100 cal. yr BP. Variation partitioning analysis (VPA) is used to determine the relative importance of climate change, human impacts, and paleofire disturbance. The generalized dynamic vegetation model LPJ-GUESS is forced with climate anomaly output from an atmospheric general circulation model to simulate vegetation dynamics during the mid-Holocene and the pre-industrial era. The proxy-based estimates are compared to modelling output. Results indicate that regional tree cover varied from 10% to 40% during the past five millennia. The single-core, phytolith-based reconstructions are generally consistent with stacked tree pollen z-scores calculated from different records along the East Asian monsoon margin, implying that mid-Holocene tree cover decrease was persistent and almost synchronous over extensive areas. VPA demonstrates that long-term monsoon marginal vegetation successions were mainly caused by climate effects. Numerical modelling suggests that since the mid-Holocene the retreat of forests along the monsoon margin was primarily associated with precipitation deficits. Our investigation highlights that the precipitation associated with the East Asian monsoon system has exerted a stronger influence than the westerlies on the monsoon margin climate and vegetation change. With ongoing global change, close attention to variations in precipitation patterns and amounts should be especially helpful in efforts aimed at ecological monitoring, change prediction, and restoration. • Phytoliths provide complementary paleovegetation evidence to pollen for the monsoon margin area in northeastern China. • Phytolith-based quantitative tree coverage reconstructions suggest persistent forest cover since the mid-Holocene. • Vegetation dynamics within the monsoon margin area is strongly associated with East Asian monsoon variability. • DGVMs modelling suggests the dominant role of precipitation in regulating vegetation change. [ABSTRACT FROM AUTHOR]