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The magnitude and pace of anthropogenic climate change are increasing the likelihood of abrupt changes in terrestrial ecosystems worldwide. The Last Deglacial Transition (LDT) witnessed global and regional climate change and caused vegetation change globally. The recognition and attribution of deglacial abrupt vegetation conversion would certainly enhance our understanding on the survivability and resilience of ecosystems to climate change. Here, we conducted statistical analyses for a pollen record from Yilong Lake, southwestern China, focusing on the period of the LDT. Biome changes since the Last Glacial Maximum were reconstructed numerically by using a standard approach of pollen-plant functional type-biome assignment (biomization). Principal component analysis and structure change test were applied on pollen composition and diversity data. Modern vegetation and climate relationship was analyzed to discuss climatic conditions for the vegetation conversion in Yilong region during the LDT. Our results revealed a vegetation conversion occurring around 14.3 cal kyr BP, characterized by abrupt shifts in pollen compositions and biomes and also reduction in diversity indices. We suggested that the cumulative pressure of climate warming during the LDT was probably the critical climatic variable triggering the vegetation conversion in Yilong region, while precipitation played an important role in regulating the proportions or coverages of different vegetation types after the development of evergreen broadleaved forest. By the end of tthis century, climate under intermediate to very high greenhouse gas emission scenarios were projected to reach the thresholds for vegetation transitions from evergreen broadleaved forest to (monsoon) rainforest, or to Savanna-like vegetation. However, it is still a challenge to forecast accurately when or on what spatial scale vegetation change will happen because vegetation responses to climate change are complicated and the topography and habitats on Yunnan Plateau are extremely diverse. • An abrupt vegetation change during the Last Deglacial Transition in Yunnan, China. • Vegetation conversion from deciduous to evergreen broadleaved forests. • Climate warming contributed most to the vegetation conversion. • Precipitation regulated the proportions or coverages of different vegetation types. • Monsoon rainforest or Savanna-like vegetation may expand in the future. [ABSTRACT FROM AUTHOR]

Southwestern China, a biodiversity hotspot, underwent dramatic climate change following the Last Glacial Maximum and intensive human activity also exerted a major impact since the late Holocene. In this paper, we report a pollen record from Yilong Lake in Yunnan Province, southwestern China, to understand vegetation response to long-term climatic variation and human activities at a regional-level over the last 27,000 years. Findings show that temperate and coniferous taxa were dominant before 18 cal kyr BP reflecting the glacial climate. Between 18 and 14 cal kyr BP, thermophilic taxa increased in response to global deglaciation. A notable shift from deciduous to evergreen forests occurred at approximately 14 cal kyr BP, after which pollen concentration increased but pollen diversity decreased. Pollen assemblages indicated dense forests, primarily composed of evergreen oaks developed under warm and strong summer monsoon conditions from 13 to 8 cal kyr BP. High rates of vegetation change occurred during the middle Holocene before vegetation diversity gradually increased during the Holocene Thermal Optimum, with high variability of precipitation in the Yilong Lake region. Anthropogenic forcing progressively became the main factor affecting vegetation composition and vegetation change rates over the past three millennia. • We reported a pollen record from Yilong Lake in Yunnan province, China. • Cold-tolerant taxa dominated before 18 cal kaBP after which thermal-like taxa increased. • Evergreen forests replaced deciduous forests around 14 cal kaBP. • Vegetation change rates peaked in mid-Holocene with mega-thermal but frequent droughts. • Departure of vegetation and potential climax occurred in late-Holocene due to human activities. [ABSTRACT FROM AUTHOR]

Past plant diversity dynamics can provide a historical perspective on biodiversity change and ecosystem dynamics as a guide to conservation management in the future. Pollen analysis is one of the most widely used approaches to reconstruct plant diversity change through time, but the representativeness of pollen diversity to plant diversity is not yet fully understood and especially in open landscapes. In this paper, we compare pollen assemblages from topsoil in the open landscapes of the Tibetan Plateau with the surrounding vegetation to investigate their compositional similarity and the correlations between their diversity (richness and evenness), and to evaluate the influence of climate variables, landscape characteristics, and human disturbance on the pollen diversity. The results show that pollen assemblages vary obviously in different vegetation types and they can represent their surrounding plant communities at low taxonomic levels. Pollen richness boarders a better match with plant richness than pollen evenness with plant evenness across the whole study area, but the correlation is weak (r adj 2 < 0.2, p < 0.001). Transforming plants into their pollen equivalents has little improvement for the correlations between pollen and plant richness/evenness. Pollen richness and evenness can capture well the trend in plant richness and evenness along the vegetation gradient, suggesting that they can be used as gamma (landscape scale) rather than alpha (local scale) diversity metrics in the study area. Mean annual precipitation (MAP), mean annual temperature (MAT), and patch richness (PatchS) are positively associated with pollen richness. MAP, PatchS, and human disturbance (HD) are significantly predictors for pollen evenness. These confirm that pollen richness and evenness can provide insights into past plant diversity dynamics and help evaluating the effects of climate and habitat changes and human disturbance on long timescales. • Pollen assemblages represent surrounding plant communities at low taxonomic levels. • Pollen diversity is reliable proxy for plant diversity at the landscape scale. • Vegetation shift is an important prerequisite in studying past plant diversity. • Pollen-equivalent transformation cannot improve pollen-plant diversity correlations. • Pollen diversity can indicate changes in past climate and habitat conditions. [ABSTRACT FROM AUTHOR]

Vegetation composition has been greatly modified by human activity since Neolithic times, providing valuable insights into the evolution of human-landscape relationships. In this paper, we integrated 26 pollen records from the Zhejiang Province of China where a Neolithic culture of rice farming existed at an early date, to examine the dynamics of agricultural development and its impact on vegetation. Firstly, we synthesized the relative abundance of Oryza pollen and charcoal (Cpeak) using generalized additive models, to produce a record of agricultural development and the intensity of human activities. We found that changes in Oryza abundance and Cpeak were positively correlated, and identified three phases as follows: agricultural initiation before 8000 cal yr BP, agricultural development between 8000 and 6000 cal yr BP and the onset of intensive rice farming after 6000 cal yr BP. Pearson correlation between each pollen taxon and Oryza indicates that arboreal taxa exhibit an overall negative correlation with Oryza , but terrestrial herbs and ferns show a positive correlation, indicating that deforestation accompanied agricultural development. Rosaceae, Castanea , Fagus and Typha display positive correlation with Oryza during the earliest stage dominated by hunter-gathering, reflecting the protection and cultivation of food-producing vegetation. During the intensive farming stage, the Liangzhu ancestors reclaimed more farmland and began to pay attention on farmland management including clearing the fields of weeds. This is the main reason for the enhanced negative correlation between Artemisia , Chenopodiaceae, Brassicaceae, Asteraceae and Lamiaceae with Oryza at 6000–5000 cal yr BP. Finally, we confirm the potential of integrated Oryza abundance in pollen records as a human-impact index in the Zhejiang region, and emphasize that temporal dynamics in vegetation and human activities should be critically pre-examined when applying relevant human-impact indices. • Integrated charcoal and Oryza pollen reveal Neolithic human intensity and rice farming history. • Food-providing plants were protected during the hunter-gatherer stage. • During the intensive agriculture phase, weed taxa exhibited a strengthened negative correlation with Oryza correlation. • The application of anthropogenic pollen necessitates a critical evaluation of its temporal dynamics. [ABSTRACT FROM AUTHOR]