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Establishing a quantitative relationship between modern pollen and vegetation remains a pivotal but intricate pursuit within the field of Quaternary palynology. The R-value, a well-established and traditional metric characterized by its simplicity and direct applicability, serves to calibrate the nonlinear disparities between surface pollen and modern vegetation. This study entails the construction of a comprehensive pollen R-value dataset for China derived from R-values published between 1987 and 2021. The dataset, compiled after rigorous screening, calibration, and standardization processes, encompasses 898 modern pollen sampling sites and 2115 pollen R-value data entries, encapsulating 152 pollen taxa spanning 65 families and 113 genera. Synthesizing the extracted R-values yielded the following insights: (1) A macrospatial analysis validates previously established knowledge at a site-specific scale. Evidently, pollen R-value variations across China are statistically significant. Approximately two-thirds of pollen taxa exhibit underrepresentation (e.g., Taxodiaceae, Corylus, Nitraria, Tamarix, Cyperaceae, Poaceae, and Fabaceae), while the remaining one-third display overrepresentation (e.g., Pinus, Picea, Betula, Ephedra, Chenopodiaceae, and Artemisia). The degree of underrepresentation surpasses that of over-representation, and the representation patterns of Castanea, Quercus, Polygonaceae, and Asteraceae are contingent upon vegetation types. (2) Pollen R-values follow distinct spatial distribution patterns within China. In the woody vegetation region of eastern China, R-values progressively decline from north to south, correlating with rising temperatures and precipitation. Conversely, in herbaceous vegetation regions of northern and western China, R-values decrease from east to west and from northeast to southwest, corresponding to increased aridity. Nevertheless, pollen R-values manifest variation contingent on pollen taxa, vegetation types, and climatic regions, even differing for the same taxa across varying vegetation types and climatic conditions. This highlights the intricate nature of pollen R-values and their interpretation of pollen-vegetation relationships. (3) Pollen R-values and relative pollen production estimates exhibit resemblances and a modest positive correlation. However, adjudicating between them as representatives of vegetation requires nuanced consideration, as both metrics convey pollen representation within vegetation, demonstrating the multifaceted relationships they share with modern vegetation. Further recommendations suggest that when assessing pollen representation in modern vegetation, fossil pollen content should be weighted using either the median or log-transformed R-value. This approach underscores the necessity of comprehensively accounting for divergences and convergences across various spatial scales and vegetation types, particularly the disparities observed within identical pollen taxa across dissimilar regions. [ABSTRACT FROM AUTHOR]

This paper presents a multi-proxy reconstruction of the climate change in Caotanhu wetland using pollen, phytolith and charcoal records, and the data of loss of ignition (LOl), grain size analysis, and susceptibility. Results reveal that between 4550 and 2500 cal. a BP, a dry climatic condition was not favorable for the accumulation of peat. Since 2500 cal. a BP, the climate became humid and the wetland developed with abundant freshwater aquatic plants, which contributed to peat accumulation. Nevertheless, alternate periods of rain and dry climate occurred during that period. Between 2500 and 1810 cal. a BP (550 BC-140 AD), the climate was more humid than at present. A lot of emerged plants, such as Phragmites, Typha and Sparganium, and freshwater green algae grew in the wetland which was surrounded by desert-steppe vegetation composed mainly of Chenopodiaceae, Artemisia, Compositae and Thalictrum. However, from 1810 to 1160 cal. a BP (140-790 AD), the water level started to decrease and hydrophyte species reduced greatly, but some Phragmites still grew in the wetland and around it was desert vegetation with high proportion of Chenopodiaceae and Artemisia. Then from 1160 to 650 a BP (790-1300 AD), it entered a period of desert-steppe with abundant mesic and xerophytic plants. And a lot of aquatic plants prevailed in the wetland. Here, what is noticeable is that percentages of arboreal pollen, consisting mainly of Betula and Picea, increased greatly and reached a maximal value of 27.2%, in which, Betula percentages rose to 23.2%. Hence, it is reasonable to conclude that Betula grew in the highland of the wetland, or Picea timberline shifted downward resulting in the increase of percentages of Betula and Picea pollen, which were transported into the wetland by flood or wind. But since 650 cal. a BP, desert vegetation prevailed around the wetland again with dominant Chenopodiaceae and Artemisia, and the climate was similar to modern one. Despite some aquatic plants still growing in the wetland at that time, their amounts diminished greatly. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Quantitative proxy-based and high-resolution palaeoclimatic datasets are scarce for the lower reaches of the Yangtze River (LYR) basin. This region is in a transitional vegetation zone which is climatologically sensitive; and as a birthplace for prehistorical civilization in China, it is important to understand how palaeoclimatic dynamics played a role in affecting cultural development in the region. We present a pollen-based and regionally-averaged Holocene climatic twin-dataset for mean total annual precipitation (PANN) and mean annual temperature (TANN) covering the last 10,000 years for the LYR region. This is based on the technique of weighted averaging-partial least squares regression to establish robust calibration models for obtaining reliable climatic inferences. The pollen-based reconstructions generally show an early Holocene climatic optimum with both abundant monsoonal rainfall and warm thermal conditions, and a declining pattern of both PANN and TANN values in the middle to late Holocene. The main driving forces behind the Holocene climatic changes in the LYR area are likely summer solar insolation associated with tropical or subtropical macro-scale climatic circulations such as the Intertropical Convergence Zone (ITCZ), Western Pacific Subtropical High (WPSH), and El Niño/Southern Oscillation (ENSO). Regional multi-proxy comparisons indicate that the Holocene variations in precipitation and temperature for the LYR region display an in-phase relationship with other related proxy records from southern monsoonal China and the Indian monsoon-influenced regions, but are inconsistent with the Holocene moisture or temperature records from northern monsoonal China and the westerly-dominated region in northwestern China. Overall, our comprehensive palaeoclimatic dataset and models may be significant tools for understanding the Holocene Asian monsoonal evolution and for anticipating its future dynamics in eastern Asia. [ABSTRACT FROM AUTHOR]