Modern Pollen Dataset Research Articles

Assessing the importance of climate variables for the spatial distribution of modern pollen data in China

To assess the importance of climate variables for the distribution of modern pollen data in China, we present a continental-scale dataset consisting of 1374 samples. Boosted regression trees and constrained ordination techniques are employed to quantify the importance of six climate variables (annual precipitation, PANN; actual/potential evapotranspiration ratio, Alpha; mean annual temperature, TANN; mean temperature of the warmest month, MTWA; mean temperature of the coldest month, MTCO; annual sum of the growing degree days above 5°C, GDD5) for the distribution of individual pollen taxa and modern pollen assemblages. The results show that taxon-specific responses to the climate variables display a wide regional diversity and that the climate variables with low collinearity that best account for the spatial variability of modern pollen assemblages differ regionally. PANN is the most important variable in northwestern and northeastern China and the Tibetan Plateau, while MTWA and MTCO are the dominant variables in east-central and southern China. This suggests that the climate variables that can be optimally reconstructed from fossil pollen data vary in different bioclimatic regions of China. This feature is typical to many continental-scale modern pollen datasets and needs to be considered in pollen-based climate reconstructions.

A modern pollen–climate dataset from China and Mongolia: Assessing its potential for climate reconstruction

A modern pollen dataset from China and Mongolia (18–52°N, 74–132°E) is investigated for its potential use in climate reconstructions. The dataset includes 2559 samples, 229 terrestrial pollen taxa and four climatic variables — mean annual precipitation (Pann): 35–2091mm, mean annual temperature (Tann): –12.1–25.8°C, mean temperature in the coldest month (Mtco): –33.8–21.7°C, and mean temperature in the warmest month (Mtwa): 0.3–29.8°C. Modern pollen–climate relationships are assessed using canonical correspondence analysis (CCA), Huisman–Olff–Fresco (HOF) models, the modern analogue technique (MAT), and weighted averaging partial least squares (WA-PLS). Results indicate that Pann is the most important climatic determinant of pollen distribution and the most promising climate variable for reconstructions, as assessed by the coefficient of determination between observed and predicted environmental values (r2) and root mean square error of prediction (RMSEP). Mtco and Mtwa may be reconstructed too, but with caution. Samples from different depositional environments influence the performance of cross-validation differently, with samples from lake sediment-surfaces and moss polsters having the best fit with the lowest RMSEP. The better model performances of MAT are most probably caused by spatial autocorrelation. Accordingly, the WA-PLS models of this dataset are deemed most suitable for reconstructing past climate quantitatively because of their more reliable predictive power.

A comparison of remotely sensed and pollen‐based approaches to mapping Europe's land cover

AbstractAimRemote sensing coupled with direct observation allows recent changes in vegetation to be investigated but, in order to extend our understanding of land‐cover change further back in time, different proxies for vegetation are required. The pseudobiomization (PBM) approach has been developed to transform fossil pollen data into land‐cover classes (LCCs) in order to reconstruct broad‐scale anthropogenic land‐use change through time. The aim of this study was to test and refine the PBM approach through application to an extensive modern pollen dataset and comparison with remotely sensed CORINE land‐cover maps for Europe.LocationThe study area comprised 2471 modern pollen sites from across Europe.MethodsPollen sites were assigned to one of eight LCCs using the pollen‐based PBM method, which draws upon biomization techniques to transform pollen data into records of land‐cover change. Five of the LCCs were ‘pure’ classes (e.g. broad‐leaf forest) and three of them were mixed vegetation. Remotely sensed CORINE land‐cover maps were used to assign LCCs to sites, and the results were compared with pollen‐assigned LCCs.ResultsThe results revealed a good correspondence between the proportions of different LCCs that were registered using CORINE and pollen‐based PBM, when data were aggregated at a pan‐European scale. However, the match between the two datasets was much less close at a site‐specific level. The overall results were improved to c. 60% when the target was broadened to include similar as well as identical LCCs. The spatial correspondence was best across north‐central Europe and least good in south‐west Europe, the Mediterranean and northern Scandinavia.Main conclusionsThe ability of distinct data types to sense actual vegetation is limited by various sources of error; for example, both pollen and remote sensing vary in terms of spatial and temporal heterogeneity and taxonomic resolution. It is likely that many of the main sources of error are common to both methods, rather than being approach‐specific. We conclude that pollen‐based methods of intermediate complexity can be used as a proxy for broad‐scale land‐cover change across most of temperate Europe, but may be less reliable at a site‐specific scale.

A modern pollen–climate calibration set from central‐western Mongolia and its application to a late glacial–Holocene record

AbstractAimFossil pollen spectra from lake sediments in central and western Mongolia have been used to interpret past climatic variations, but hitherto no suitable modern pollen–climate calibration set has been available to infer past climate changes quantitatively. We established such a modern pollen dataset and used it to develop a transfer function model that we applied to a fossil pollen record in order to investigate: (1) whether there was a significant moisture response to the Younger Dryas event in north‐western Mongolia; and (2) whether the early Holocene was characterized by dry or wet climatic conditions.LocationCentral and western Mongolia.MethodsWe analysed pollen data from surface sediments from 90 lakes. A transfer function for mean annual precipitation (Pann) was developed with weighted averaging partial least squares regression (WA‐PLS) and applied to a fossil pollen record from Lake Bayan Nuur (49.98° N, 93.95° E, 932 m a.s.l.). Statistical approaches were used to investigate the modern pollen–climate relationships and assess model performance and reconstruction output.ResultsRedundancy analysis shows that the modern pollen spectra are characteristic of their respective vegetation types and local climate. Spatial autocorrelation and significance tests of environmental variables show that the WA‐PLS model for Pann is the most valid function for our dataset, and possesses the lowest root mean squared error of prediction.Main conclusionsPrecipitation is the most important predictor of pollen and vegetation distributions in our study area. Our quantitative climate reconstruction indicates a dry Younger Dryas, a relatively dry early Holocene, a wet mid‐Holocene and a dry late Holocene.

Reconstruction of Holocene vegetation, tree cover dynamics and human disturbances in central European Russia, using pollen and satellite data sets

This paper presents an assessment of Holocene tree cover densities and forest disturbance in European Russia using the best-modern-analogue (BMA) technique of quantitative reconstruction and an innovative approach, which combines modern pollen datasets with remotely sensed data from moderate-resolution imaging spectroradiometer satellite images. The test of the accuracy of the applied method using a database of 450 sets of surface pollen assemblages shows that it can reproduce present day characteristics of woody cover in Europe correctly (R 2 = 0.57, standard error = 10.8 %), and it is sufficient for reconstruction of major changes of woodland vegetation in the past. Application of the BMA technique to fossil pollen data from two key regions in the central part of European Russia demonstrates that changes in regional woody cover are useful for the reconstruction of prehistoric human disturbance.

Pollen-based vegetation and climate reconstruction of the Ferdynandovian sequence from Łuków (eastern Poland)

ABSTRACT Early middle Pleistocene deposits from Łukow, correlated with the Cromerian complex, represent rare bi-partite Ferdynandovian pollen sequence encompassing two interglacial warmings (F1 and F2) separated by F1/2 cooling/glaciation and related to MIS 15-13. The paper presents pollen-based palaeoecological and palaeoclimate investigations in which plant climate indicators were applied. Additionally modern pollen dataset from the Roztocze region was used to evaluate vegetation history in terms of forest communities and presence and abundance of tree taxa sensitive to air temperature and humidity. Climate changes derived from pollen data indicate strong oceanic features of the climate of the first interglacial (F1) resembling those typical for the beginning of the Eemian, followed by cooling (F 1/2) with plant communities typical of the Pleistocene steppetundra, which undoubtedly indicate strong continentality, and subsequent return of more oceanic climate (F2) with mean remperature of the warmest month exceeding 18°C. Both pollen succession and climate changes recorded in the Łukow sediments correlate well with other bi-partite successions known from eastern part of European Lowlands.

Pollen distribution along climatic and biogeographic gradients in northern Central America

Environmental reconstructions based on fossil pollen rely on the understanding of modern pollen distribution along climatic and biogeographic gradients. This study analyses the modern pollen spectra of Central America using three basic approaches: (1) the evaluation of using modern pollen spectra to differentiate the main vegetation types of the region, (2) the usage of non-linear regression to predict individual pollen abundances as a function of climate, and (3) the construction of pollen—climate transfer functions. Standard pollen analysis was carried out on mud—water interface samples from 81 lakes in the Yucatan Peninsula and adjacent mountains of Guatemala and Mexico. Detrended correspondence and cluster analyses were used to evaluate the biogeographic patterns revealed by this modern pollen data set. Non-parametric locally weighted scatterplot smoothing (LOESS) regression was used to construct pollen—climate functional relationships. Five modern vegetation types were clearly identifiable through their associated pollen spectra: Pinus forest, Quercus forest, mountain mesophyllous forest, tropical rainforest, and tropical seasonal forest. The last group includes three subcategories (evergreen seasonal, tropical semi-deciduous, and tropical deciduous forests), which were not separable via this analysis. Precipitation and temperature trends were consistent and robust for at least 28 and 30 taxa, respectively, in the LOESS regression. While floristic patterns driven by temperature were clearly reflected by the pollen spectra, those driven by precipitation were less sharply defined. Nevertheless, pollen data from the study area offered good resolution to identify broad biogeographic patterns. Furthermore, individual taxa showed high predictability along precipitation and temperature gradients, allowing the theoretical construction of pollen—climate transfer functions. This study provided valuable tools for the interpretation of fossil pollen sequences from Central America.

The origin and temporal development of an ancient cultural landscape

AbstractAim To reconstruct the Late Glacial and Holocene vegetation history of western Tasmania and to test the long‐held notion of a replacement of forest by moorland during the mid to late Holocene in western Tasmania, Australia.Location Western Tasmania, Australia.Methods Fossil pollen data were screened with a modern pollen dataset using detrended correspondence analysis and charcoal data were analysed using significance tests.Results At the landscape scale, the distribution of vegetation types in western Tasmania has remained remarkably stable through the post‐glacial period. Open moorland has dominated the landscape since the Late Glacial, while rain forest expanded at that time in to areas which it occupies today. Vegetation development in the Holocene is markedly different and charcoal values are significantly higher when compared with those in previous interglacial periods.Main conclusions The dominant paradigm of a replacement of rain forest by moorland across western Tasmania during the mid to late Holocene is not supported by this regional analysis. The arrival of humans in Tasmania during the Last Glacial Stage provided an ignition source that was independent of climate, and burning by humans through the Late Glacial period deflected vegetation development and facilitated the establishment of open moorland in regions occupied by rain forest during previous interglacial periods. It is concluded that the present dominance of the landscape of western Tasmania by open moorland is the direct result of human activity during the Late Glacial and that this region represents an ancient cultural landscape.

A potential of pollen-based climate reconstruction using a modern pollen–climate dataset from arid northern and western China

To improve the interpretation of fossil pollen records, we analyzed the relationships between modern pollen taxa and climate data and established a pollen–climate calibration using the northern and western Chinese modern pollen dataset to demonstrate its potential for the reconstruction of past climate dynamics in the semi-arid and arid regions of China. Analysis of pollen and climate data involved Pearson's correlation ceofficient and other transfer functions, as well as the "best modern analogues" method. We also applied a technique for error estimation to calibrate reconstructed values into a probability distribution and a confidence interval for the observed values. The percentage representations of 24 pollen taxa in 546 surface pollen samples collected in northern and western China were correlated with modern climate characteristics. The relationships between individual pollen types and climate were appraised over a large spatial scale in the study area. Of investigated taxa, 41.7% had linear, 45.8% had unimodal (orthogonal polynomial), and 12.5% had monotonic (Log) distribution in response to annual precipitation. Both taxa and plant functional types (PFTs) provided similar results using the best modern analogues method for modern pollen and climate data at the 546 sites in northern and western China. Precipitation reconstructions were more accurate than climate reconstructions of any thermal parameters, suggesting that available moisture was the most important factor controlling plant distribution in the primarily semi-arid to arid study region. Climate reconstruction performed using the modern analogues technique for 112 taxa was not significantly better than reconstruction with only 37 selected taxa. Climate reconstruction based on PFTs was more accurate when using only the main pollen taxa than when using most of the taxa. Our test of the best modern analogues method with the northern and western Chinese surface pollen dataset demonstrated its reliability for reconstructing modern climate variables.

Central African biomes and forest succession stages derived from modern pollen data and plant functional types

Abstract. New detailed vegetation reconstructions are proposed in Atlantic Central Africa from a modern pollen data set derived from 199 sites (Cameroon, Gabon and Congo) including 131 new sites. In this study, the concept of plant functional classification is improved with new and more detailed plant functional types (PFTs) and new aggregations of pollen taxa. Using the biomisation method, we reconstructed (1) modern potential biomes and (2) potential succession stages of forest regeneration, a new approach in Atlantic Central African vegetation dynamics and ecosystem functioning reconstruction. When compared to local vegetation, potential biomes are correctly reconstructed (97.5% of the sites) and tropical rain forest (TRFO biome) is well identified from tropical seasonal forest (TSFO biome). When the potential biomes are superimposed on the White's vegetation map, only 76.4% of the sites are correctly reconstructed. But using botanical data, correspondence and cluster analyses, the 43 sites from Congo (Mayombe) evidence more affinities with those of central Gabon and so they can also be considered as correctly reconstructed as TRFO biome and White's map should be revised. In terms of potential succession stages of forest regeneration, the mature forest (TMFO) is well differentiated from the secondary forest (TSFE), but inside this latter group, the young and the pioneer stages are not clearly identified due probably to their low sampling representation. Moreover, linked to their progressive and mosaic character, the boundaries between two forest biomes or two forest stages are not clearly detected and need also a more intensive sampling in such transitions.

Spatial pattern of Abies and Picea surface pollen distribution along the elevation gradient in the Qinghai–Tibetan Plateau and Xinjiang, China

In this study we examine the relationships between Abies and Picea abundance in surface pollen and sub‐alpine coniferous forest (SCF) distribution, elevation and climate in the Qinghai–Tibetan Plateau using a large modern pollen data set consisting of 857 samples. Results indicate that Abies and Picea pollen are abundant in the southern and eastern Qinghai–Tibetan Plateau, where SCF dominates the landscape. Pollen percentages of both Abies and Picea show a unimodal pattern with changes in elevation and climate, and their optima occur at elevations from 2500 to 4000 m a.s.l., mean annual temperature from −1 to 10 °C and mean annual precipitation from 450 to 850 mm. The optimal elevation of Abies and Picea pollen distribution decreases with latitude from c. 4000 m in the south (21–32°N) to c. 2500 m in the north (43–49°N). The spatial pattern of Abies and Picea pollen abundance is highly correlated with the modern distribution of these taxa, which is largely controlled by elevation and climate. These relationships could provide a practical reference for interpretation of fossil pollen data in terms of climate and elevation in the Qinghai–Tibetan Plateau.

Biomization and quantitative climate reconstruction techniques in northwestern Mexico—With an application to four Holocene pollen sequences

New paleovegetation and paleoclimatic reconstructions from the Sierra Madre Occidental (SMO) in northwestern Mexico are presented. This work involves climate and biome reconstruction using Plant Functional Types (PFT) assigned to pollen taxa. We used fossil pollen data from four Holocene peat bogs located at different altitudes (1500‑2000 m) at the border region of Sonora and Chihuahua at around 28° N latitude (Ortega-Rosas, C.I. 2003. Palinología de la Ciénega de Camilo: datos para la historia de la vegetación y el clima del Holoceno medio y superior en el NW de la Sierra Madre Occidental, Sonora, Mexico. Master Thesis, Universidad Nacional Autónoma de México, México D.F.; Ortega-Rosas, C.I., Peñalba, M.C., Guiot, J. Holocene altitudinal shifts in vegetation belts and environmental changes in the Sierra Madre Occidental, Northwestern Mexico. Submitted for publication of Palaeobotany and Palynology). The closest modern pollen data come from pollen analysis across an altitudinal transect from the Sonoran Desert towards the highlands of the temperate SMO at the same latitude (Ortega-Rosas, C.I. 2003. Palinología de la Ciénega de Camilo: datos para la historia de la vegetación y el clima del Holoceno medio y superior en el NW de la Sierra Madre Occidental, Sonora, Mexico. Master Thesis, Universidad Nacional Autónoma de México, México D.F.). An additional modern pollen dataset of 400 sites across NW Mexico and the SW United States was compiled from different sources (Davis, O.K., 1995. Climate and vegetation pattern in surface samples from arid western U.S.A.: application to Holocene climatic reconstruction. Palynology 19, 95–119, North American Pollen Database, Latin-American Pollen Database, personal data, and different scientific papers). For the biomization method (Prentice, I.C., Guiot, J., Huntley, B., Jolly, D., Cheddadi, R., 1996. Reconstructing biomes from paleoecological data: a general method and its application to European pollen data at 0 and 6 ka. Climate Dynamics 12, 185–194), we modified the pollen-PFT and PFT-biomes assignation of Thompson and Anderson (Thompson, R.S., Anderson, K.H., 2000. Biomes of western North America at 18,000; 6000 and 0 14C yr BP reconstructed from pollen and packrat midden data. Journal of Biogeography 27, 555–584) for a better representation of the modern vegetation of NW Mexico. The biome reconstruction method was validated with the modern pollen sites and applied to the fossil sites. Our results show that, during the early Holocene, a cool conifer forest extended at least down to 1700 m, while today this biome is present above 2000 m in the Chihuahua state. The Younger Dryas event was recorded in one site with cold and dry conditions. The reconstructed annual temperature for this period was 3°–6 °C colder than today, and annual precipitation was 250 mm lower than at present (900 mm/yr). The middle Holocene after 9200 cal yr BP was marked by a warming trend, reaching temperatures 2 °C warmer than today at 7000 cal yr BP, and by the installation of a warm mixed forest, the present day biome, at 1700 m elevation, while at higher elevations (1900 m) the cool conifer forest was still present. Summer precipitation was 200 mm/yr above the early Holocene values, suggesting that monsoon-like conditions strengthened since 9200 cal yr BP at this region. During the last 4000 yr, the same warm mixed forest was reconstructed below 1700 m and a conifer forest above 1700 m. A great variability of vegetation and climate patterns was recorded for the last 3000 yr particularly at high elevation sites, where warming and cooling trends would be coeval of the Medieval warm period and Little Ice Age, likely related to ENSO variability.

A pre‐European settlement pollen–climate calibration set for Minnesota, USA: developing tools for palaeoclimatic reconstructions

AbstractAim The bias in modern North American pollen assemblages by landscape disturbance from Euro‐American settlement has long been overlooked in the construction of pollen–climate transfer functions. Our aim is to examine this problem and to develop an unbiased pre‐settlement pollen–climate transfer function, and to test its performance and inference power in comparison with commonly used techniques.Location Minnesota, USA, is of palaeoclimatic interest because within the state are located two continental‐scale ecotones, controlled by temperature and available moisture. Shifts of these ecotones can be tracked using palaeoecological techniques.Methods Using a data set of pre‐settlement pollen assemblages from 133 lakes, which were coupled to climate data from the earliest instrumental records (i.e. 1895–1924), a pre‐settlement pollen–climate data set was developed that lacked the influence of anthropogenic landscape disturbance. A corresponding modern pollen data set (from lake sediment core tops) and a modern climate (i.e. 1961–90) data set were also developed. The two pollen sets were compared to demonstrate the effects of landscape disturbance from human activities. Ordination (redundancy analysis with Monte Carlo permutation tests) and regression techniques (generalized linear modelling) were used to establish the relationships between the early instrumental climate variables and pre‐settlement pollen assemblages and individual taxa, respectively. Transfer functions for the most suitable climate variables (i.e. those forming a minimal set of non‐collinear climate variables that explained the greatest amount of pollen variance) were developed from the pre‐settlement data set using bootstrapping.Results Comparison of pre‐settlement pollen and modern pollen showed an over‐representation of Ambrosia, Chenopodiaceae and Poaceae, and an under‐representation of arboreal taxa (e.g. Pinus, Quercus, Ostrya) in the modern assemblages. Not surprisingly, ordination and regression techniques showed a strong relationship between the early instrumental climate variables and pre‐settlement pollen assemblages and taxa. Transfer functions were developed for May and February mean temperature and available moisture. Pre‐settlement transfer functions substantially improved the root mean squared error by 37–72% in comparison with modern transfer functions inferring pre‐settlement conditions, suggesting that the modern transfer functions have poorer predictive abilities.Main conclusions For climatic reconstructions, there can be a serious distortion of inferences based solely on modern pollen–climate data sets in regions where anthropogenic landscape disturbance has occurred. By using historical climate data, coupled with pre‐disturbance pollen assemblages, robust transfer functions for temperature and effective moisture were developed.

Pollen-inferred precipitation time-series from equatorial mountains, Africa, the last 40 kyr BP

Palaeoclimatic estimates of mean annual rainfall in the equatorial highlands of Central East Africa have been established for the last 40 kyr. The values are inferred from nine fossil pollen sequences, collected from six peat bogs located between 2° and 4°S latitude, in the forest belt, from 1800 to 2240 m a.s.l. The transformation of pollen data into climatic parameters is achieved by the best analogues statistical method, using a modern pollen data set of East and Central Africa and calibration by meteorological data. The climatic reconstructions are first performed for each individual sequences. They are transformed into time-series using 88 of the 125 available radiocarbon dates (including 41 AMS dates). The synthesis of the results is presented as a single curve, illustrating the precipitation values obtained for 682 dated stratigraphic layers plotted on a radiocarbon timescale. The precipitation changes are presented at about a century resolution during the Holocene, and about a millennium for the glacial period. The most characteristic feature of the synthetic curve is the changing variability through time. During the last glacial period (30 to 15 kyr BP interval), our results indicate a ca. 450 mm/yr (32%) precipitation decrease relative to the present. Two maxima decrease periods are registered at ca. 19 kyr BP (700 mm/yr, ca. 45%) and between 18 and 16 kyr BP (608 mm/yr, ca. 42%). Several abrupt positive peaks of higher precipitation are noticed pre 35 kyr BP and ca. 22–20 kyr BP. During the lower Holocene (10–7 kyr BP), the mean calculated precipitation estimate is 30 mm/yr (2%) below the present-day value, with several abrupt positive shifts; the maximum at ca. 8 kyr BP reaches 600 mm/yr (42%). Great variations between low and high precipitation values are expressed post ca. 4 kyr BP. These results are discussed in light of other climatic indicators extracted either from the same sedimentary record, isotopes, microfauna, or from other geological palaeoclimatic proxy in the concerned region, and pattern of the monsoon record in marine cores. Anthropogenic disturbance on past vegetation, as well as humidity signal as a better response of forest to climatic forcing, and possible CO 2 effect need more investigation in the future. We feel confident that the greater variability at the century scale registered in the equatorial highlands provides a good explanation for increased aridity in the desertic region of Sudan and Egypt during the last 4 kyr. The possibility that such greater variability could be induced by high variability or instability of the Atlantic Ocean or global sea surface temperature instability should be explored.