Modern Pollen Data Research Articles

A preliminary study of the modern pollen of Tripura, Northeast India

The vegetation distribution in Tripura, Northeast India was studied from the modern pollen assemblages at various sites in the region. Sediment samples and moss cushions were collected along transects from North to South Tripura to assess the modern pollen taxa dominant in the region. A number of taxa showing a modern day distribution of moist deciduous mixed vegetation dominant in Tripura were observed in the modern pollen data. Statistical significance of the modern–pollen data was verified using one–way ANOVA technique. Despite the limited pollen taxa recorded in the surface samples the analysis proved the potential of the pollen data and scope for future palynological studies. The impact of anthropogenic activity is clearly visible through the low sample yield and presence of taxa such as Poaceae, Amaranthaceae, Solanaceae, etc. Other factors such as entomophilous tendency and/or low yield of pollen in tropical plants, excessive rainfall, sediment distribution and jhum cultivation could contribute to the lack of pollen preservation in the region.

Improving the quality of pollen-climate calibration-sets is the primary step for ensuring reliable climate reconstructions

Pollen-based climate reconstructions have been widely applied in China as an essential way to investigate quantitatively past climate change, which is necessary to improve the reliability of future climate predictions. However, their usefulness is often doubted, particularly for those regions with a long history of civilization (e.g. East China), where both the modern and past vegetation are heavily disturbed by human activities.Which factors influence the integrity of pollen-based climate reconstructions and how to improve their reliability are rigorous challenges for palynologists. Previous work focusing on these two questions has used modern pollen data from China or eastern continental Asia and mainly concludes that past climate reconstruction is quite sensitive to the quality of the calibration-set.

A Review of Relative Pollen Productivity Estimates From Temperate China for Pollen-Based Quantitative Reconstruction of Past Plant Cover.

Model-based quantitative reconstruction of past plant cover in Europe has shown great potential for: (i) testing hypotheses related to Holocene vegetation dynamics, biodiversity, and their relationships with climate and land use; (ii) studying long term interactions between climate and land use. Similar model-based quantitative reconstruction of plant cover in China has been restricted due to the lack of standardized datasets of existing estimates of relative pollen productivity (RPP). This study presents the first synthesis of all RPP values available to date for 39 major plant taxa from temperate China and proposes standardized RPP datasets that can be used for model-based quantitative reconstructions of past plant cover using fossil pollen records for the region. We review 11 RPP studies in temperate China based on modern pollen and related vegetation data around the pollen samples. The study areas include meadow, steppe and desert vegetation, various woodland types, and cultural landscapes. We evaluate the strategies of each study in terms of selection of study areas and distribution of study sites; pollen- and vegetation-data collection in field; vegetation-data collection from satellite images and vegetation maps; and data analysis. We compare all available RPP estimates, select values based on precise rules and calculate mean RPP estimates. We propose two standardized RPP datasets for 31 (Alt1) and 29 (Alt2) plant taxa. The ranking of mean RPPs (Alt-2) relative to Poaceae (= 1) for eight major taxa is: Artemisia (21) > Pinus (18.4) > Betula (12.5) > Castanea (11.5) > Elaeagnaceae (8.8) > Juglans (7.5) > Compositae (4.5) > Amaranthaceae/Chenopodiaceae (4). We conclude that although RPPs are comparable between Europe and China for some genera and families, they can differ very significantly, e.g., Artemisia, Compositae, and Amaranthaceae/Chenopodiaceae. For some taxa, we present the first RPP estimates e.g. Castanea, Elaeagnaceae, and Juglans. The proposed standardized RPP datasets are essential for model-based reconstructions of past plant cover using fossil pollen records from temperate China.

Predictive pollen-based biome modeling using machine learning.

This paper investigates suitability of supervised machine learning classification methods for classification of biomes using pollen datasets. We assign modern pollen samples from Africa and Arabia to five biome classes using a previously published African pollen dataset and a global ecosystem classification scheme. To test the applicability of traditional and machine-learning based classification models for the task of biome prediction from high dimensional modern pollen data, we train a total of eight classification models, including Linear Discriminant Analysis, Logistic Regression, Naïve Bayes, K-Nearest Neighbors, Classification Decision Tree, Random Forest, Neural Network, and Support Vector Machine. The ability of each model to predict biomes from pollen data is statistically tested on an independent test set. The Random Forest classifier outperforms other models in its ability correctly classify biomes given pollen data. Out of the eight models, the Random Forest classifier scores highest on all of the metrics used for model evaluations and is able to predict four out of five biome classes to high degree of accuracy, including arid, montane, tropical and subtropical closed and open systems, e.g. forests and savanna/grassland. The model has the potential for accurate reconstructions of past biomes and awaits application to fossil pollen sequences. The Random Forest model may be used to investigate vegetation changes on both long and short time scales, e.g. during glacial and interglacial cycles, or more recent and abrupt climatic anomalies like the African Humid Period. Such applications may contribute to a better understanding of past shifts in vegetation cover and ultimately provide valuable information on drivers of climate change.

History and conservation of Tunisia's largest freshwater wetland: Garâa Sejenane

The Garâa Sejenane is an ancient lake in northern Tunisia that currently houses a mosaic of temporary wetlands. Comparison of modern pollen data and field vegetation surveys shows both a weak regional pollen signal and the homogenization of pollen assemblages at the scale of the garâa. Despite a hiatus between 19,000 and 2230 cal. BP, fossil pollen analyses provide the first Tunisian LGM record and attest to the ancient origin of the lake, which housed some taxa still present locally in the 1950s. The originality of the Pleniglacial surrounding landscape dominated by a juniper steppe contrasted with the mountain conifer forests in Kroumiria. Lastly, analyses of aerial photographs (1948, 1962, 1984), recent satellite photographs and previous botanical descriptions reveal that the lake has been drying since 1960 because of important anthropogenic activities (drainage, groundwater pumping, cultivation, grazing…). These disturbances have generated profound changes in hydrophytic plant communities (fragmentation, diversity loss, introduction of invasive species…) that are likely to threaten their long-term survival.

Reconstructing past arboreal cover based on modern and fossil pollen data: A statistical approach for the Gredos Range (Central Spain)

Quantifying and reconstructing past vegetation changes is an important step to fully understand human-environment interactions in the past. In this study we present a reconstruction of arboreal cover of six study sites in the Gredos Range (central Spain) over the last 3000 yr based on multivariate statistical analysis (cluster analysis and non-metric multidimensional scaling, NMDS) of 186 modern pollen samples, modern vegetation data and six detailed fossil pollen records. The integrated approach allows distinguishing eight modern vegetation communities and linking the fossil pollen records with these vegetation communities as modern analogues. The information of the arboreal cover of the modern pollen sites was used to estimate the past arboreal cover of the fossil pollen sites in the Gredos Range. This estimated arboreal cover shows a higher level of landscape openness than suggested by the original pollen percentages data. Our results show that the evolution of the arboreal cover through time differs along an altitudinal gradient, with a decrease in arboreal cover during the Roman and Visigoth periods (2000–1240 cal BP) at low altitudes and only during the Christian/Feudal period (850–500 cal BP) at high altitudes. The applied methodology, integrating fossil pollen data with modern pollen and vegetation data in one NMDS, allows reconstructing past arboreal cover in a quantitative way.

Modern pollen–vegetation relationships in traditionally mown and unmanaged boreal rich-fen communities in central Norway

Knowledge of the relationship between vegetation and modern pollen deposition is necessary to improve the interpretation of fossil pollen samples. We compared the cover of plant species and the modern pollen deposition in surface moss samples in 49 plots in rich-fen vegetation from the boreal vegetation zone in Norway in two areas (one oceanic and one more continental). These rich fens were used for traditional hay cutting until ca. 1950. Three management regimes are used: 1) biennial mowing, 2) quadrennial mowing and 3) unmown. The unmown areas were traditional hay fens, with no management since the 1950s. Of the 89 plant taxa and corresponding 65 taxa of pollen and spores, 29 and 22, respectively, were sufficiently represented in both vegetation and as pollen, to allow direct comparisons of the two data sets. Most of the plant and pollen taxa were found in the plots from both study areas and in plots with different mowing frequencies. Therefore, quantitative differences in vegetation cover and pollen percentages were the main focus in this investigation of plant–pollen relationships in mown and unmown vegetation. The relative difference in plant cover was largest between biennially and unmown plots. 12 species showed a significant positive correlation with difference in plant cover between mown and unmown areas (p<0.05; Wilcoxon signed rank test), most pronounced for Molinia caerulea (most common in unmown plots), and Carex dioica and Thalictrum alpinum (most common in mown plots). A significant positive plant–pollen correlation (Spearman rank-correlation) was found for 10 pollen taxa. Thalictrum alpinum is a very good pollen indicator, and Cyperaceae, Eriophorum-type and Pedicularis-type are good pollen indicators of mowing. Poaceae/M. caerulea and Succisa pratensis are negatively correlated with mowing. The impact of mowing on species composition was similar in both study areas. Mown and unmown areas were differentiated in the vegetation data and could be identified by modern pollen data. These results will improve the interpretation of past land-use practices using pollen analysis of rich-fen vegetation.

Modern pollen deposition in glacial settings in the Himalaya (India): abundance of Pinus pollen and its significance

ABSTRACTThirty-five surface sediment samples from three glacial sites – [Chorabari Glacier (Kedarnath), Hamtah and Chhatru glaciers (Lahaul-Spiti)] – situated in the western Himalaya, India, were palynologically analysed to explore the relationship between the modern pollen assemblages and the extant vegetation. The Chorabari Glacier is located in the Greater Himalaya and influenced by the Southwest Summer Monsoon; whereas the Hamtah and Chhatru glaciers are located in the Trans-Himalaya and affected more by the Western Disturbances (winter precipitation). The area around Chorabari Glacier receives abundant rainfall, while the Hamtah and Chhatru glaciers are in a high-altitude cold desert. Palynological studies have revealed an overwhelming dominance of Pinus pollen in all the samples. Though the sampling sites are 2 to 8 km away from the treeline and characterised by herbaceous ground vegetation, the marked predominance of arboreal pollen (especially Pinus) in the sediments stresses the importance of a proper interpretation of modern pollen data, so as to have an appropriate standard for deciphering the pollen–vegetation relationship in the respective study areas.

Pollen‐derived biomes in the Eastern Mediterranean–Black Sea–Caspian‐Corridor

AbstractAimTo evaluate the biomization technique for reconstructing past vegetation in the Eastern Mediterranean–Black Sea–Caspian‐Corridor using an extensive modern pollen data set and comparing reconstructions to potential vegetation and observed land cover data.LocationThe region between 28–48°N and 22–62°E.MethodsWe apply the biomization technique to 1,387 modern pollen samples, representing 1,107 entities, to reconstruct the distribution of 13 broad vegetation categories (biomes). We assess the results using estimates of potential natural vegetation from the European Vegetation Map and the Physico‐Geographic Atlas of the World. We test whether anthropogenic disturbance affects reconstruction quality using land use information from the Global Land Cover data set.ResultsThe biomization scheme successfully predicts the broadscale patterns of vegetation across the region, including changes with elevation. The technique discriminates deserts from shrublands, the prevalence of woodlands in moister lowland sites, and the presence of temperate and mixed forests at higher elevations. Quantitative assessment of the reconstructions is less satisfactory: the biome is predicted correctly at 44% of the sites in Europe and 33% of the sites overall. The low success rate is not a reflection of anthropogenic impacts: only 33% of the samples are correctly assigned after the removal of sites in anthropogenically altered environments. Open vegetation is less successfully predicted (33%) than forest types (73%), reflecting the under‐representation of herbaceous taxa in pollen assemblages and the impact of long‐distance pollen transport into open environments. Samples from small basins (&lt;1 km2) are more likely to be reconstructed accurately, with 58% of the sites in Europe and 66% of all sites correctly predicted, probably because they sample an appropriate pollen source area to reflect regional vegetation patterns in relatively heterogeneous landscapes. While methodological biases exist, the low confidence of the quantitative comparisons should not be over‐emphasized because the target maps themselves are not accurate representations of vegetation patterns in this region.Main ConclusionsThe biomization scheme yields reasonable reconstructions of the broadscale vegetation patterns in the Eastern Mediterranean–Black Sea–Caspian‐Corridor, particularly if appropriate‐sized sampling sites are used. Our results indicate biomization could be used to reconstruct changing patterns of vegetation in response to past climate changes in this region.

Examining bias in pollen-based quantitative climate reconstructions induced by human impact on vegetation in China

Abstract. Human impact is a well-known confounder in pollen-based quantitative climate reconstructions as most terrestrial ecosystems have been artificially affected to varying degrees. In this paper, we use a human-induced pollen dataset (H-set) and a corresponding natural pollen dataset (N-set) to establish pollen–climate calibration sets for temperate eastern China (TEC). The two calibration sets, taking a weighted averaging partial least squares (WA-PLS) approach, are used to reconstruct past climate variables from a fossil record, which is located at the margin of the East Asian summer monsoon in north-central China and covers the late glacial Holocene from 14.7 ka BP (thousands of years before AD 1950). Ordination results suggest that mean annual precipitation (Pann) is the main explanatory variable of both pollen composition and percentage distributions in both datasets. The Pann reconstructions, based on the two calibration sets, demonstrate consistently similar patterns and general trends, suggesting a relatively strong climate impact on the regional vegetation and pollen spectra. However, our results also indicate that the human impact may obscure climate signals derived from fossil pollen assemblages. In a test with modern climate and pollen data, the Pann influence on pollen distribution decreases in the H-set, while the human influence index (HII) rises. Moreover, the relatively strong human impact reduces woody pollen taxa abundances, particularly in the subhumid forested areas. Consequently, this shifts their model-inferred Pann optima to the arid end of the gradient compared to Pann tolerances in the natural dataset and further produces distinct deviations when the total tree pollen percentages are high (i.e. about 40 % for the Gonghai area) in the fossil sequence. In summary, the calibration set with human impact used in our experiment can produce a reliable general pattern of past climate, but the human impact on vegetation affects the pollen–climate relationship and biases the pollen-based climate reconstruction. The extent of human-induced bias may be rather small for the entire late glacial and early Holocene interval when we use a reference set called natural. Nevertheless, this potential bias should be kept in mind when conducting quantitative reconstructions, especially for the recent 2 or 3 millennia.

A modern pollen–climate dataset from the Darjeeling area, eastern Himalaya: Assessing its potential for past climate reconstruction

Relying on the ability of pollen assemblages to differentiate among elevationally stratified vegetation zones, we assess the potential of a modern pollen-climate dataset from the Darjeeling area, eastern Himalaya, in past climate reconstructions. The dataset includes 73 surface samples from 25 sites collected from a c. 130–3600 m a.s.l. elevation gradient along a horizontal distance of c. 150 km and 124 terrestrial pollen taxa, which are analysed with respect to various climatic and environmental variables such as mean annual temperature (MAT), mean annual precipitation (MAP), mean temperature of coldest quarter (MTCQ), mean temperature of warmest quarter (MTWQ), mean precipitation of driest quarter (MPDQ), mean precipitation of wettest quarter (MPWQ), AET (actual evapotranspiration) and MI (moisture index). To check the reliability of the modern pollen-climate relationships different ordination methods are employed and subsequently tested with Huisman–Olff–Fresco (HOF) models. A series of pollen–climate parameter transfer functions using weighted-averaging regression and calibration partial least squares (WA-PLS) models are developed to reconstruct past climate changes from modern pollen data, and have been cross-validated. Results indicate that three of the environmental variables i.e., MTCQ, MPDQ and MI have strong potential for past climate reconstruction based on the available surface pollen dataset. The potential of the present modern pollen-climate relationship for regional quantitative paleoclimate reconstruction is further tested on a Late Quaternary fossil pollen profile from the Darjeeling foothill region with previously reconstructed and quantified climate. The good agreement with existing data allows for new insights in the hydroclimatic conditions during the Last glacial maxima (LGM) with (winter) temperature being the dominant controlling factor for glacial changes during the LGM in the eastern Himalaya.

Spruce and broadleaved trees pollen percentages and PAR values in the European part of Russia: 9 years of pollen trap monitoring implemented to the fossil data

Abstract. 9-years results of modern pollen monitoring in the Central European Russia are presented. We discuss some implementations of modern pollen data to the interpretation of fossil distribution for Picea and broadleaved trees pollen.

Modern pollen data from the Canadian Arctic, 1972\u20131973

This data descriptor reports results of a 1972–73 baseline study of modern pollen deposition in the Canadian Arctic to originally aid interpretation of Holocene pollen diagrams from that region, especially focussed on the arctic tree-line. The data set is geographically unique due to its extent, and allows the assessment of the effects of modern climate change on northern ecosystems, including fluctuations of the a arctic tree-line. Repeated sampling was conducted along an interior transect at 29 sites from the Boreal Forest to the High Arctic, with five additional coastal sites covering a total distance of 3,200 km. Static pollen samplers captured both local pollen and long-distance pollen wind-blown from the Boreal Forest. Moss and lichen polsters provided multi-year pollen fallout to assess the effectiveness of the static pollen samplers. The local vegetation was recorded at each site. This descriptor provides information on data archived at the World Data Center PANGAEA, which includes spreadsheets detailing site and sample information as well as raw and processed pollen data obtained on over 500 samples.

Modern pollen assemblages in topsoil and surface sediments of the Xingyun Lake catchment, central Yunnan Plateau, China, and their implications for interpretation of the fossil pollen record

Modern pollen data from topsoils and surface lake sediments are commonly used as modern analogues and as climate calibration data for reconstructing vegetation and climate history from fossil pollen profiles. However, the potential differences and biases in pollen assemblages from these two sample types, as well as the processes of pollen sedimentation in lake basins, have received relatively little attention. Here we present the results of the analysis of modern pollen assemblages in 10 surface sediment samples and 25 topsoil samples from Xingyun Lake and its catchment, a shallow alpine lake site in the central Yunnan Plateau, southwest China. The modern pollen assemblages from both types of samples are mainly composed of Pinus, evergreen and deciduous oaks, Alnus, Poaceae, Artemisia, Brassicaceae and Amaranthaceae, and are consistent with the modern vegetation. Although the pollen assemblages of topsoil samples vary with the type of modern local vegetation, in general they are representative in term of the composition of the main pollen taxa, with some significant differences in the case of some vegetation types. With regard to the surface lake sediment samples, the pollen assemblages are relatively constant with no significant changes with sample location and water depth. The main pollen taxa are Pinus (around 40%), Alnus (around 18%) and Poaceae (around 11%), with relatively high percentages of evergreen and deciduous oaks, Betula (2–4%), and low percentages of Ulmus, Rosaceae, Corylus, Cupressaceae, Euphorbiaceae, Myrica and Elaeagnaceae. This composition is a good representation of the main types of catchment vegetation. The relative uniformity of the pollen assemblages from the lake surface samples may partly result from the effect of currents in redistributing the pollen input to the lake by rivers and wind. Therefore, we suggest that it is better to use pollen data from surface lake sediments, rather than from topsoils from the lake catchment, for interpreting fossil pollen assemblages of lake sediment cores. Our results indicate that the pollen assemblages in a sediment core from any part of Xingyun Lake are likely to provide a reliable record of the regional vegetation history and thus climatic change. Our modern pollen results, together with modern pollen data from other surface lake sediment samples along a large altitudinal gradient from Yunnan to southwest Sichuan Province, were used to reanalyze fossil pollen assemblages during the Last Glaciation period at Xingyun Lake. The results show that the vertical vegetation belts decreased in altitude from late Marine Isotope Stage 3 (late MIS3) to the Last Glacial Maximum (LGM) and then increased during the Last Deglaciation.

North American paleoclimate reconstructions for the Last Glacial Maximum using an inverse modeling through iterative forward modeling approach applied to pollen data

AbstractThe inverse modeling through iterative forward modeling (IMIFM) approach was used to reconstruct Last Glacial Maximum (LGM) climates from North American fossil pollen data. The approach was validated using modern pollen data and observed climate data. While the large‐scale LGM temperature IMIFM reconstructions are similar to those calculated using conventional statistical approaches, the reconstructions of moisture variables differ between the two approaches. We used two vegetation models, BIOME4 and BIOME5‐beta, with the IMIFM approach to evaluate the effects on the LGM climate reconstruction of differences in water use efficiency, carbon use efficiency, and atmospheric CO2 concentrations. Although lower atmospheric CO2 concentrations influence pollen‐based LGM moisture reconstructions, they do not significantly affect temperature reconstructions over most of North America. This study implies that the LGM climate was very cold but not very much drier than present over North America, which is inconsistent with previous studies.

Migration of legacy data to new media formats for long-time storage and maximum visibility: Modern pollen data from the Canadian Arctic (1972/1973)

This Data Management Plan (DMP) was created using the DMPTool. It describes modern pollen data collected along a 2500 mile (~4000 km) transect in the Canadian Arctic in 1972/73 as part of an NSF funded research project (GB-33497). The project was undertaken at the Institute of Arctic and Alpine Research at the University of Colorado Boulder. This legacy dataset originally stored as a paper copy and on 35-mm film will be migrated to digital formats that allow upload of the dataset to an international open-access library for permanent storage and visibility. This DMP was submitted to the 2015 Best Digital Data Management Plan and Practices - Competition (https://data.colorado.edu/cudmpguidance). The study provides a baseline pollen dataset for the interpretation of Holocene pollen diagrams from this region and for comparison with modern surface pollen samples, allowing the assessment of the effects of modern climate change on Arctic and subarctic ecosystems.

Modern pollen assemblages from surface lake sediments and their environmental implications on the southwestern Tibetan Plateau

The relationships amongst modern pollen assemblages, vegetation, climate and human activity are the basis for reconstructing palaeoenvironmental changes using pollen records. It is important to determine these relationships at regional scales due to the development of vegetation under different climatic conditions and human activities. In this paper, we report on an analysis of modern pollen assemblages of 31 surface lake samples from 31 lakes (one sample per lake) on the southwestern Tibetan Plateau where the knowledge of modern pollen and their relationships with vegetation, climate and human activities is insufficient. The region includes five vegetation zones: sub‐alpine shrub steppe, alpine steppe, alpine meadow and steppe ecotone, mountain desert and alpine desert. The lakes span a wide range of mean annual precipitation (50–500 mm) and mean annual temperature (−8 to 6 °C). Modern pollen assemblages from our samples mainly consist of herb taxa (Artemisia, Cyperaceae, Poaceae, Chenopodiaceae, etc.) and some tree taxa (Pinus, Fagaceae, Alnus, etc.). The results indicate that modern pollen assemblages are able to reflect the main vegetation distribution. Redundancy analysis for the main pollen types and environmental variables shows that precipitation is the leading factor that influences the pollen distribution in the study area with the first axis capturing 13.7% of the variance in the pollen data set. The Artemisia/Chenopodiaceae ratio is valid for separating the desert component (&lt;2) from the steppe and other vegetation zones (&gt;2) but is unable to distinguish moisture variations. The Artemisia/Cyperaceae ratio is able to identify meadows (&lt;1) and steppes (&gt;1) and can be used as a moisture index on the southwestern Tibetan Plateau. Our results show that an appropriate range is needed for a modern pollen data set in order to perform pollen‐based quantitative climate reconstructions in one region. It is essential to perform modern studies before using pollen ratios to reconstruct palaeovegetation and palaeoclimate at a regional scale.

Calibrating the pollen signal in modern rodent middens from northern Chile to improve the interpretation of the late Quaternary midden record

The use of rodent middens from northern Chile as paleoecological archives has at times been questioned due to concerns about their biogenic origin and the degree to which their record represents vegetation composition rather than rodent habits. To address such concerns, we carried out a modern calibration study to assess the representation of vegetation by pollen records from rodent middens. We compared vegetation censuses with soil-surface and midden (matrix and feces) pollen samples from sites between 21° and 28°S. The results show that (1) the pollen signal from the midden matrix provides a more realistic reflection of local vegetation than soil-surface samples due to the pollen-deposition processes that occur in middens; and (2) in contrast to feces pollen assemblages, which feature some biases, rodent dietary habits do not seem to influence midden matrix pollen assemblages, probably because midden agents are dietary generalists. Our finding that modern pollen data from rodent middens reflect vegetation patterns confirms the reliability of midden pollen records as paleoecological archives in northern Chile.

Database of Subfossil Pollen Spectra from Territory of Russia and Adjacent Countries as a Tool for Paleoecological Research

Modern pollen samples provide necessary research tool that help to interpret the Holocene fossil pollen record, allow to investigate the relationship between pollen as the proxy and the environmental parameters such as vegetation, land-use, and climate that the pollen proxy represents. The Russian Modern Pollen Database is a new initiative of Russian Palynological Commission to establish a publicly accessible repository of modern (surface sample) pollen data. The Database is freely available online to the scientifi c community (http://pollendata.org) and currently has information on almost 700 pollen samples from territory of European Russia and Western Siberia. The database contains information about the name of the section; its location – coordinates, altitude; the type of the sample for pollen analysis (surface soil, moss, pillows, etc.); area relief (lake basin, fl oodplain, etc); local vegetation; regional vegetation (landscape zone or subzone); climate data, information about researchers and references. The database is constantly updated.

Modern pollen assemblages from surface lake sediments in northwestern China and their importance as indicators of vegetation and climate

The modern pollen assemblages of surface lake sediments and topsoils in northwestern China were studied to understand the relationship of modern pollen data with contemporary vegetation and climate, and the differences between the pollen assemblages of surface lake sediments and topsoils. The results show that Chenopodiaceae and Artemisia are dominant elements in the pollen assemblages of northwestern China. Additionally, Ephedra, Cyperaceae, Asteraceae, Poaceae, Picea, Pinus, and Betula are also important pollen taxa. Both pollen assemblages and principal component analysis indicate that pollen data from surface lake sediments and topsoils can be used to differentiate the main vegetation types of this region (desert, steppe, meadow and forest). However, differences exist between modern pollen assemblages of the two types of sediments due to the different relevant source areas of pollen and degrees of pollen preservation. For example, the larger relevant source area of surface lake sediment results in a higher abundance of Betula in pollen assemblage from surface lake sediment, whereas the tendency to disintegrate thin-walled pollen types in topsoil leads to a higher proportion of resistant pollen, such as Asteraceae. Linear regression analysis indicates that the Artemisia/Chenopodiaceae (A/C) ratio in pollen assemblages of surface lake sediments can be used to indicate humidity changes in the study area. However, the A/C ratio in topsoils should be used carefully. Our results suggest that pollen data from surface lake sediments would be better references for interpreting the fossil pollen assemblages of lake cores or lacustrine profiles.