Modern Pollen Research Articles

Aerobiological studies – current state and future challenges

Aerobiology is the interdisciplinary science focused on the study of airborne organisms and biological materials, like pollen grains, fungal spores, bacteria, viruses, mycotoxins. The results of the aerobiological monitoring are practically employed in medicine, agriculture, beekeeping, meteorology, monument protection. The information of the current and predicted exposure is transmitted to patients and physicians through the electronic tools, applications, media, to compile the optimal therapy of respiratory diseases, especially pollen allergy. It is worth taking into account some confirmed phenomena to interpret the aerobiological data correctly: (i) many airborne particles occur seasonally and their amount and seasonal dynamics are more or less variable; (ii) threshold values for the airborne particles causing the threat for humans (e.g. for allergic individuals) are important, but the personal sensitivity must be also included; (iii) overlapping occurrence of different airborne particles, like pollen, spores, pollution makes clinical symptoms worsening; (iv) modern pollen and spores fall is affected in direct and indirect way by the climate changes, anthropogenic pollution, long range transport and the specific local environmental conditions. Currently the implementation of the automatic measurement systems and the analyses of allergen particles in the air are the main challenges for aerobiologists. Joined activity of this group of enthusiastic specialists of different interests is performed in frame of the multi centre networks and supported by the International Association for Aerobiology together with the regional.

Modelling the distribution of Amazonian tree species in response to long‐term climate change during the Mid‐Late Holocene

AbstractAimTo (a) assess the environmental suitability for rainforest tree species of Moraceae and Urticaceae across Amazonia during the Mid‐Late Holocene and (b) determine the extent to which their distributions increased in response to long‐term climate change over this period.LocationAmazonia.TaxonTree species of Moraceae and Urticaceae.MethodsWe used MaxEnt and inverse distance weighting interpolation to produce environmental suitability and relative abundance models at 0.5‐degree resolution for tree species of Moraceae and Urticaceae, based on natural history collections and a large plot dataset. To test the response of the Amazon rainforest to long‐term climate change, we quantified the increase in environmental suitability and modelled species richness for both families since the Mid‐Holocene (past 6,000 years). To test the correlation between the relative abundance of these species in modern vegetation versus modern pollen assemblages, we analysed the surface pollen spectra from 46 previously published paleoecological sites.ResultsWe found that the mean environmental suitability in Amazonia for species of Moraceae and Urticaceae showed a slight increase (6.5%) over the past 6,000 years, although southern ecotonal Amazonia and the Guiana Shield showed much higher increases (up to 68%). The accompanied modelled mean species richness increased by as much as 120% throughout Amazonia. The mean relative abundance of Moraceae and Urticaceae correlated significantly with the modern pollen assemblages for these families.Main ConclusionsIncreasing precipitation between the Mid‐ and Late Holocene expanded suitable environmental conditions for Amazonian humid rainforest tree species of Moraceae and Urticaceae, leading to rainforest expansion in ecotonal areas of Amazonia, consistent with previously published fossil pollen data.

Modern pollen and its relationship with vegetation and climate in the Mu Us Desert and surrounding area, northern China: Implications of palaeoclimatic and palaeocological reconstruction

This study establishes the spatial and quantitative relationship between modern pollen, vegetation and climate based on 84 surface pollen samples from a nature reserve and ecological restoration area in the Mu Us Desert and surrounding areas, including seven natural vegetation types. Pollen spectra, discriminant analysis and spatial distribution patterns of the main pollen types are used to explore the relationship between pollen assemblages and vegetation types. Results show that each vegetation type can be characterized by a distinct modern pollen assemblage as follows: (1) coniferous forest: Pinus Diploxylon-type and Picea; (2) deciduous forest: Pinus Diploxylon-type, Quercus, Artemisia and Poaceae; (3) deciduous shrub: Pinus Diploxylon-type, Artemisia and Poaceae; (4) grass meadow: Poaceae and Cyperaceae; (5) grass steppe: Poaceae and Artemisia; (6) desert steppe: Chenopodiaceae, Artemisia and Poaceae; and (7) desert: Chenopodiaceae, Nitraria and Artemisia. The higher percentage and lower concentration of Pinus pollen in the Mu Us Desert can be explained by effective long-distance transport from the mountain forest, while Picea has a limited pollen dispersal ability via wind-borne dispersal. Poaceae pollen is well represented and has a higher percentage in several different types of ecological conditions. Modern pollen–climate relationships are assessed using redundancy analysis and weighted averaging partial least squares regression. Significant relationships exist between pollen assemblages and mean annual temperature (R2 = 0.67; RMSEP 1.7 °C; max. bias 2.5 °C), July precipitation (R2 = 0.58; RMSEP 17.8 mm; max. bias 26.0 mm), and January precipitation (R2 = 0.82; RMSEP 0.9 mm; max. bias 1.8 mm). Furthermore, the climate variables obtained by spatial interpolation of data from meteorological stations are used to cross-check the data reconstructed by pollen-climate transfer functions. Our work provides a more comprehensive understanding of the qualitative and quantitative relationships between modern pollen and vegetation/climate and serves as a basis for the paleovegetation and paleoclimate reconstruction in arid and semiarid regions of northern China and similar areas.

Evaluating quantitative pollen representation of vegetation in the tropics: A case study on the Hainan Island, tropical China

Complex pollen-vegetation relationships in tropical environments have long been a challenge for the interpretation of pollen spectra in terms of vegetation cover. Here, we test the application of the widely-used Extended R-Value (ERV) model in the tropical secondary and planted woodlands of the Hainan Island (China) to estimate relative pollen productivities (RPPs) for common plant taxa occurring as pollen in surface and fossil samples of the region. We collected pollen (soil samples) and related vegetation data within 1500 m radius at 23 random distributed sites within an area of 50 km × 100 km. We found a large difference between the modern pollen assemblages and the related vegetation composition in terms of number and dominance of taxa. We tested the three existing ERV sub-models and three methods to distance-weight vegetation cover, i.e. 1/d, the Prentice’s model (using a Gaussian Plume dispersal model, GPM), and the Lagrangian stochastic dispersal model (LSM). The LSM appears to be inappropriate for our dataset. The combination of ERV sub-model 2 and Prentice’s model using nine anemophilous and zoophilous (or with “messy” pollination syndrome) taxa was found to provide the best results. The relevant source area of pollen (RSAP) of the soil samples was estimated to ca. 1000–1500 m. The ranking of RPPs is as follows: Castanopsis-Lithocarpus (19.44 ± 0.17) > Asteraceae (8.74 ± 0.05) > Moraceae (6.52 ± 0.08) > Euphorbiaceae (5.22 ± 0.1) > Papilionaceae (2.66 ± 0.05) > Mallotus-Macaranga (2.21 ± 0.08) > Anacardiaceae (1.77 ± 0.04) > Rubiaceae (1.29 ± 0.02) > Poaceae (=1). Violation of the ERV model assumptions of anemophily and stationarity of vegetation composition influenced the performance of the ERV analysis in this study and implied careful evaluation of the results. Nevertheless, the obtained RPPs are considered reliable and will allow to quantify the relative cover of the nine plant taxa in the past. Further studies of this kind will be worthwhile to obtain additional RPP values for a larger number of tropical taxa, even though quantification of past plant cover in the tropics will remain a challenge. The numerous zoophilous taxa may either be absent of the pollen record, or exhibit pollen-vegetation relationships for which the ERV-model is not successful in estimating RPPs. These plant taxa will require other approaches for their quantification in the past.

Modern pollen source and spatial distribution from surface lake sediments in the southwestern Pampa grasslands, Argentina: Implications to interpret Holocene pollen records

In the Pampa grasslands of Argentina nothing is known about the transport, deposition and spatial distribution of pollen in lakes. To analyze and understand how well lake surface sediment pollen assemblages reflect the contemporary vegetation in relation to pollen source area, bathymetry and grain size sediments 36 surface sediment samples from Chasicó Lake and 5 from its only tributary were analyzed. Lake pollen assemblages showed two major patterns above and below the range between 4 and 6 m depth. Below this range the percentage and concentration of main pollen taxa are relatively homogeneous, without overrepresented taxa and with well-preserved pollen. They reflect the extra-local and regional source areas from Pampa grasslands and xerophylous forest and indicate that pollen from cores taken below this range will be suitable for paleocological studies. Isopoll of the main taxa and grain size distribution maps allowed understand how pollen and sediment was transported, deposited and distributed in the lake. The spatial distributions of main pollen taxa differ considerably among them, generating various pollen assemblages at different sampling points. There is no significant correlation between total pollen concentration and both depth and grain size, suggesting that there are not a totally pollen and sediment focusing in the lake. The pollen distribution indicates that wind and surface runoff are the primary transport vectors to the lake. However, tributary also contributes with the waterborne pollen, particularly around the river mouth. Implications of these processes will be of particular interest for reliable interpretation of fossil pollen records in similar environments.

표층퇴적물의 현생화분을 이용한 고식생 및 정량적 고온도 복원을 위한 연구방법 소개

표층퇴적물의 현생화분을 이용한 고식생 및 정량적 고온도 복원을 위한 연구방법 소개

Variations in pollen deposition of the main taxa forming the land cover along a NW–SE transect in European Russia: results of a ten year Tauber trap monitoring period

Annual pollen accumulation rates of the main tree and shrub taxa of European Russia (Picea, Pinus, Betula, Alnus, Quercus, Tilia, Fraxinus, Ulmus and Corylus), as well as several herbaceous taxa (Poaceae, Cyperaceae, Chenopodiaceae and Artemisia), were obtained using Tauber pollen traps which were placed along a northwest to southeast transect in European Russia. The work was carried out within the framework of the Pollen Monitoring Programme (PMP). The data were analysed using both traditional interpretations of PAR (pollen accumulation rate) values and numerical methods (linear regressions and canonical correspondence analysis, CCA). The various vegetation zones: broadleaved-coniferous forest, broadleaved forest and forest-steppe, differ from each other by the absolute pollen values (PARs) of forest-forming taxa and several wind-pollinated herbs. However, no statistical support for zonal differentiation based on these PARs has been found. The only obvious difference was observed between the forest zone and the forest-steppe. The climatic gradient along the NW–SE transect is reflected by changes in pollen values, but is smoothed due to human influence during past centuries and as a consequence of the dominance of secondary vegetation formations. The highest total PAR, as well as PARs of all the forest-forming taxa, was observed in the southern part of the mixed broadleaved-coniferous forest zone (RU-ZV). The PARs of thermophilic taxa (Tilia, Fraxinus, Acer, Ulmus, Quercus and Corylus), as well as of Picea correspond to warmth availability which is under the influence of a combination of latitude, continentality of climate and microclimatic conditions. According to linear regressions, Picea, Tilia, Quercus and Corylus PARs correspond to Tjul, the July temperature of the previous season. Canonical correspondence analysis indicates that temperature, in particular Tjul, is the main climatic parameter controlling the variation of modern pollen rain.

Modern pollen representation of the vegetation of the Tagus Basin (central Iberian Peninsula)

The study of modern vegetation–pollen relationships has long been recognized as crucial for the proper interpretation of fossil pollen records. Despite the quickly growing number of palynological studies from central Iberia and its adjacent Atlantic margin, comprehensive studies about modern pollen representation at broad spatial scales were still lacking. In this paper, we have studied the vegetation–pollen relationships in the Tagus Basin in 62 sites located along a wide environmental gradient from Thermomediterranean evergreen mixed thermophilous woodlands by the Atlantic coast to Oromediterranean shrublands above the treeline in the Guadarrama Mountains (central Spain). At each site, we analyzed pollen from moss polsters and conducted vegetation surveys. Most forested vegetation types (pinewoods, oak woods, evergreen mixed thermophilous woodlands) presented rather distinct pollen assemblages dominated by the pollen equivalents of the major tree species. Nevertheless, enhanced taxonomic resolution within Pinus and Quercus ilex-type would represent significant progress, e.g., enabling to separate Mediterranean and mountain pinewoods. Pollen spectra from shrubland and steppic communities are in general less differentiated, due to high regional pollen input associated with low local pollen production and/or the dominance of insect-pollinated species (e.g., Cytisus oromediterraneus in mountain shrublands). The results presented here will readily assist the interpretation of regional fossil pollen records from small mires/bogs/lakes and forest hollows, given their comparable pollen catchments. Comparison of modern pollen assemblages with pollen records from larger lakes and marine settings is not so straightforward, but our results suggest that marine pollen assemblages might average the pollen signature of the entire basin.

Climate change on the northeastern Tibetan Plateau during the past ~ 600 years inferred from peat pollen records

A 600-year high-resolution pollen record from a peat core (FS-2010) on the Zoigê Plateau was obtained to reconstruct vegetation and climate changes on the northeastern Tibetan Plateau. Surface pollen data reveal that vegetation differences are reflected in different modern pollen assemblages. Fossil pollen data indicate that alpine meadow was the dominant vegetation type on the Zoigê Plateau during the Little Ice Age (LIA) from ~1400 to ~1900 AD. Pollen-based climatic reconstructions indicate climatic fluctuations during this period consistent with records from neighboring areas. Specifically, relatively “warm-wet” conditions persisted from ~1400 to ~1500 AD and ~1800 to ~1900 AD, but generally “cool-dry” conditions from ~1500 to ~1800 AD. The reconstructed temperature variations during the LIA (i.e., ~1400 to ~1900 AD) were attributed to variations in total solar irradiation. This study casts further doubt on the FG/MG (subalpine forest and shrub group/alpine meadow group) ratio as a reliable indicator of temperature reduction during the Current Warm Period (CWP; post ~1900 AD) due to significant anthropogenic impacts including deforestation and swamp drainage. The reconstructed patterns of precipitation in the Zoigê Plateau including Flower Swamp are shown to be contingent on variations in the strength of the Asian Monsoon.

Holocene vegetation and climate change on the Colorado Plateau in southern Utah, USA

AbstractPollen, plant macrofossils, and sedimentary analyses from archaeological deposits at North Creek Shelter (NCS) on the Colorado Plateau provide data on vegetation and climate change during the Holocene. From 11,300–10,200 cal yr BP, NCS was embedded in a mixed conifer forest of cool-adapted species (e.g.,Abies,Pseudotsuga menziesii, andPinus ponderosa) with anArtemisiaunderstory. During this interval, NCS pollen corresponds to modern pollen fromPicea–Abiesforests that reside 950 m higher in elevation. Rapid deposition rates of NCS sediments indicate that climatic conditions during the Early Holocene were more mesic than today, with increased precipitation. The onset of warmer conditions at NCS began at 10,200 cal yr BP, and pollen and plant macrofossils indicate that a semiarid woodland and scrub mosaic dominated byPinus edulis,Juniperus osteosperma, and Amaranthaceae surrounded NCS by 9300 cal yr BP. This is corroborated by fossil pollen that is similar to modern pollen fromP. edulis–J. osteospermawoodlands and Amaranthaceae scrub that currently surround NCS. Sedimentary analyses suggest that during this time, accumulation rates were very low due to low precipitation and a drier climate overall. Migration ofP. edulisinto southern Utah is directly dated to 8100 cal yr BP, thus confirming recently proposed patterns of northward expansion.

Exine morphometric analysis as a new tool for Citrus species identification: a case study from Oplontis (Vesuvius area, Italy)

In the Mediterranean area, the occurrence of citrus plants in ancient times is clearly attested in Sardinia and along the southern Tyrrhenian coasts through the presence of pollen grains and organic residues dating back to the sixth century bc. The presence of Citrus pollen was also detected in soil sediments from Pompeii (ad 79), in marine sediments from the ancient harbour of Naples (first century ad), in Rome (27 bc–ad 14) as well as in a garden soil at the Villa di Poppea in Oplontis (first century bc). The first citrus tree to be identified was citron (Citrus medica L.), but even if the presence of other citrus species was supposed, identification was limited by the difficulty of discriminating the exine characteristics through optical microscopy. Exine micromorphology of eight citrus species, including primitive to cultivated, was studied by SEM and optical microscope observations. By means of the image analysis method, the morphometry of lumina and brochi was evaluated. Results indicate that the size of lumina and brochi increases from primitive, wild to cultivated citrus up to lemon. In addition, there is an overall correspondence between brochi dimension and hybridization history. The morphometric analysis on modern pollen material and comparison with the fossil grains found at Oplontis allowed attesting for the first time the presence of C. limon and C. reticulata in the Roman Age. The statistical methods used for the analysis of exine ornamentations proved to be a useful tool for interpreting the complex citrus hybridization history and for shedding light on the scenario of citrus fruits introduction in the Roman period.

Soil-surface pollen assemblages and quantitative relationships with vegetation and climate from the Inner Mongolian Plateau and adjacent mountain areas of northern China

We statistically analyzed 396 soil-surface pollen samples from the Inner Mongolian Plateau and its adjacent mountain areas of northern China to gain insights into pollen–vegetation–climate. The results of indicator species analysis, canonical correspondence analysis (CCA) and boosted regression tree (BRT) analysis suggest that: 1) soil-surface pollen assemblages can differentiate between desert, steppe, meadow steppe, cool broadleaved forest, cool conifer forest, and temperate forest, but fail to differentiate between steppe and forest steppe; shrub and temperate forest; and temperate broadleaved forest, temperate mixed conifer-broadleaved forest, and eurythermic conifer forest; 2) pollen taxa, with low percentages but frequent occurrences, strongly indicate presence in the vegetation; 3) mean annual precipitation (MAP) is the most dominant variable influencing soil-surface pollen assemblages and the most promising climate variable for quantitative reconstructions. Weighted averaging partial least squares regression (WA-PLS), modern analogue technique (MAT), and boosted regression trees (BRT) were used to construct a series of pollen-climate calibration sets. WA-PLS and MAT outperform BRT under leave-one-out cross-validation. WA-PLS models are less susceptible to spatial auto-correlation than MAT models, making WA-PLS models generally the best choice. Our soil-surface pollen data will contribute to modern pollen data in eastern Asia.

Hydroclimate influences on modern pollen rain of upland southeastern Amazonia

For accurate interpretations of palaeopalynological data, it is important to understand the influence of the current vegetation composition and characteristics on the formation of the palynological assemblage recorded in artificial or natural pollen traps. Therefore, in this study, modern pollen rain was characterized using artificial pollen traps under different ecological conditions and climatic seasons in Trilha da Mata Lake, Carajás North Ridge, southeastern Amazonia. The collection of pollen rain data comprises the total period from September 2015 to August 2016. There were two periods of low rainfall (September to December 2015 and May to August 2016) and one period of high rainfall (January to April 2016). The first two periods were represented by a predominance of canga vegetation pollen relative to forest pollen. Under dry conditions, the associations among the taxa Aparisthmium/Alchornea, Myrcia and Bellucia dichotoma were considered important for forest ecosystems, while those among Pleroma, Hyptis parkeri, Borreria and Perama carajensis were considered important for canga ecosystems. Under wet conditions, the forests were well represented by Schefflera, Anthurium lindmanianum, Pseudopiptadenia suaveolens and Glycydendron, and the most represented canga vegetation in the pollen rain were Poaceae undif., Miconia, M. acutistipula var. ferrea and Psychotria. Aparisthmium/Alchornea and Poaceae undif. Aparisthmium/Alchornea was related to periods of low water availability, and Poaceae undif. was associated with marshy or flooded environments. Thus, an increase in the influx of Poaceae undif. pollen grains was determined by variations in the extension of flooded areas, indicating an increase in the amount of rainfall and not the opposite case. Thus, future studies on vegetation reconstruction must consider modern pollen assemblages to precisely determine paleoenvironmental and paleoclimate conditions during sediment deposition.

Modern pollen–vegetation relationships within tropical marshes of Lopé National Park (Central Gabon)

In the Congo Basin, paleoenvironmental data are scarce, due to the lack of natural lakes. Using marshes sedimentary deposits as alternative archives requires the calibration of modern pollen assemblages, which are totally absent for these type of deposits. The aim of this study is to understand and qualify how well surface marsh sediment pollen assemblages reflect the contemporary vegetation. We compare pollen assemblages at the surface of 23 sedge marshes disseminated in an enclave of savanna in the Gabonese forest and vegetation surveys along transects from sampling areas. Very high diversity of forest pollen taxa is recorded, with a gradient of diversity from most open environments to those where the forest is closer, however savanna taxa remains low. The surface samples surprisingly reveal general weak percentages of Poaceae pollen grains that never exceed 25%. The low proportion of Poaceae is consistent with the deposition mode of pollen in these specific sites but challenges the common interpretation of a straightforward relationship between this percentage and savanna/forest balance.

A comparative assessment of pollen in modern vegetation and bat guano in Pipulbari Cave of Meghalaya, India

This study presents a palynological examination of modern bat guano to understand the quality of pollen preservation in relation to the extant vegetation in and around the vicinity of the Pipulbari Cave. Surface soil samples from the nearby forest, cropland and wetland areas were also studied for the comparison of pollen rain in relation to the current vegetation and landscape in the region. The pollen data recovered from the forest are indicative of tropical mixed deciduous forest composed of Shorea, Salmalia, Mesua, and Duabanga which exactly conforms to the extant vegetation in the region. The wetland vegetation was characterized by the consistent recovery of marshy and aquatic taxa including Cyperaceae, Polygonum, and Nymphaea in the pollen assemblage. The pollen preserved in cropland was characterized by the presence of cereal and Brassica. The pollen data from the modern bat guano samples display a relative dominance of the forest constituents as compared to wetland and cropland vegetation which reflects the preferential foraging of bats in dense forest areas. A multivariate principal component analysis (PCA) was applied to quantify data obtained from pollen frequency analyses of different areas inside Pipulbari Cave, which clearly revealed a significant group variation in vegetation type on the basis of dispersal and deposition of pollen in surface soil and bat guano samples. The pollen data from the modern bat guano samples are shown to provide a reliable basis for paleoecological reconstructions if they were to be based on the modern pollen analog method.

Роль атмосферной циркуляции в формировании современного пыльцевого и альгологического состава атмосферных осадков Центральной Якутии

Роль атмосферной циркуляции в формировании современного пыльцевого и альгологического состава атмосферных осадков Центральной Якутии

Responses of the mangrove ecosystem to Holocene environmental change in the Sundarban Biosphere Reserve, India

Abstract The Sundarban Mangrove Forest in the Sundarban Biosphere Reserve, located at the mouth of the Ganga–Brahmaputra Delta in India, is the most diverse mangrove ecosystem in the world. Sediment cores were taken from two widely separated islands in that reserve: Chamta (CMT) and Sudhyanyakhali (SDK). Pollen analysis and radiocarbon dating were used to study the Holocene development and dynamics of this unique ecosystem. Modern pollen rain study reveals a strong relation between modern pollen rain and the present vegetation, as well as a high rate of Phoenix palludosa pollen production.The pollen records indicate that man-grove existed at CMT from ~5960 and at SDK from ~1520 cal yr BP. Changes in relative sea level, including the frequency and intensity of inundation as well as fluctuating precipitation, have been the major factors along with geomorphic processes that control the development and dynamics of the mangrove in the area during the Holocene. The mid Holocene mangrove at CMT declined, to be progressively replaced by successive communities, and eventually reached climax stage, while the SDK site is transitional in nature. The mangrove responds rapidly to changes in environmental conditions at both locations. Because of large-scale anthropogenic interventions, it is unlikely that similar rapid responses will occur in the future.

Modern pollen rain, vegetation and climate along elevation gradients in the upper-middle Yellow River: numerical approaches for quantitative environmental reconstruction

A total of 245 modern pollen samples available in the East Asian Pollen Database and our unpublished pollen data (n = 204 and 41, respectively) were compiled to determine the correlation between modern pollen rain and vegetation in the watershed regions along the upper and middle Yellow River (UMYR) using principle component analysis (PCA). Despite considerable geographical differences and an uneven spatial vegetation distribution, pollen assemblages could differentiate major vegetation and climate zones. The PCA result reveals a high correlation between pollen taxa and key environmental factors, suggesting the high potential of this database for quantitative climate reconstruction. After screening, 199 samples were finally used to quantitatively reconstruct climate parameters with three methods namely, the weighted averaging partial least squares (WA-PLS) method, locally weighed weighted averaging (LWWA) method, and modern analogue technique (MAT).The comparison of multiple reconstructions indicates that WA-PLS provides quite accurate climate reconstructions from limited pollen data, whereas LWWA and MAT appear more suitable for large pollen datasets associated with a broad geographic range. We also discovered that the selection of sub-divided watershed areas yielded significant reduction in prediction errors and, in turn, improved accuracy of the quantitative climate reconstruction. The statistical results indicate that the transfer functions are reliable for both climate variables and elevation that is controlled mainly by the lapse rate of the altitudinal temperature. The current study provides evidence that modern pollen data in the UMYR can be used as a reliable reference dataset for pollen-based quantitative climate reconstructions.

Representation of modern pollen assemblage to vertical variations of vegetation and climate in the Yadong area, eastern Himalaya

The presence of arboreal pollen grains in pollen assemblages collected from alpine meadow and steppe sites in the central Tibetan Plateau affects the reliability of pollen-based investigations of past vegetation and climate conditions, but their origin remains uncertain. In this study, we present a 39-sample modern pollen dataset from the Yadong area on the southern slope of the Himalayas and investigate the relationships between pollen assemblages and the vertical variations in vegetation and climate and the upward transport of arboreal pollen. Our results reveal that surface soil pollen assemblages were influenced heavily by local vegetation components; however, their variations along the elevation gradient generally reflect vertical variations in vegetation and climate. For instance, arboreal pollen abundances were high at low-elevation sites, whereas herbaceous pollen abundances were high at cold and dry sites. Arboreal pollen grains (dominantly Pinus, Betula and Picea) can be transported by wind to unforested areas, and the southern slope of the Himalayas is likely a source of the arboreal pollen grains in alpine meadows and alpine steppes in the central Tibetan Plateau. Thus the arboreal pollen grains should be treated with caution in the reconstructions of past vegetation and climate in the central Tibetan Plateau.

Representation of modern pollen assemblages with respect to vegetation and climate in Northeast China

The characterization of modern pollen–vegetation–climate relationships forms the basis of past environmental and climatic reconstructions from fossil pollen records. Northeast China, which is located in a high-latitude temperate zone, is an ideal area for investigating the relationship between modern pollen assemblages and climate. However, a scarcity of datasets and detailed research on surface pollen in Northeast China prohibits high-resolution quantitative climate reconstructions in China. Here, a total of 43 surface moss samples from forest regions in the eastern part of Northeast China were collected and analyzed for pollen content. The pollen-vegetation-climate relationship was investigated by calculating distance-weighted vegetation abundances, cluster analysis, indicator species analysis, ordination analysis, correlation analysis and biomization. Pollen assemblages were compared with vegetation types recorded at the sampling sites on different scales. The combination of cluster analysis, indicator species analysis and biomization identified which forest types the surface pollen assemblages represented. Our results showed that: 1) Surface pollen assemblages from the forest region of Northeast China can be used to distinguish mixed forest types from coniferous forest at a regional scale. Indicator taxa of coniferous forest include Alnus and Betula, while the indicator taxa of mixed forest are the combinations of Juglans, Tilia, Ulmus, Quercus and Pinus. 2) Principal Component Analysis (PCA) indicates that the pollen assemblages are mainly controlled by temperature and precipitation, while the mean temperature of the coldest month (Mtco) is the most significant factor controlling vegetation change. 3) The Betula/Quercus ratio drops dramatically from coniferous forest to mixed forest with an increasing Mtco and can thus be used as an indicator of vegetation types at a regional scale and as an index to reconstruct temperature.