Long-distance Pollen Transport Research Articles

Pollen long-distance transport associated with symptoms in pollen allergics on the German Alps: An old story with a new ending?

Pollen grains are among the main causes of respiratory allergies worldwide and hence they are routinely monitored in urban environments. However, their sources can be located farther, outside cities' borders. So, the fundamental question remains as to how frequent longer-range pollen transport incidents are and if they may actually comprise high-risk allergy cases. The aim was to study the pollen exposure on a high-altitude location where only scarce vegetation exists, by biomonitoring airborne pollen and symptoms of grass pollen allergic individuals, locally.The research was carried out in 2016 in the alpine research station UFS, located at 2650 m height, on the Zugspitze Mountain in Bavaria, Germany. Airborne pollen was monitored by use of portable Hirst-type volumetric traps. As a case study, grass pollen-allergic human volunteers were registering their symptoms daily during the peak of the grass pollen season in 2016, during a 2-week stay on Zugspitze, 13–24 June. The possible origin of some pollen types was identified using back trajectory model HYSPLIT for 27 air mass backward trajectories up to 24 h.We found that episodes of high aeroallergen concentrations may occur even at such a high-altitude location. More than 1000 pollen grains m−3 of air were measured on the UFS within only 4 days. It was confirmed that the locally detected bioaerosols originated from at least Switzerland, and up to northwest France, even eastern American Continent, because of frequent long-distance transport. Such far-transported pollen may explain the observed allergic symptoms in sensitized individuals at a remarkable rate of 87 % during the study period.Long-distance transport of aeroallergens can cause allergic symptoms in sensitized individuals, as evidenced in a sparse-vegetation, low-exposure, ‘low-risk’ alpine environment. We strongly suggest that we need cross-border pollen monitoring to investigate long-distance pollen transport, as its occurrence seems both frequent and clinically relevant.

Pollen Viability of Fraxinus excelsior in Storage Experiments and Investigations on the Potential Effect of Long-Range Transport

Fragmented ash populations due to ash dieback may lead to a limited gene flow and pollination success. Therefore, the viability of ash pollen plays a major role for the survival of the species. The extent to which the long-distance transport of pollen affects pollen viability was investigated with experiments in a climate chamber using ash pollen samples from a seed orchard in Emmendingen, Germany. Furthermore, experiments with a volumetric pollen trap were conducted. A suitable storage temperature for ash pollen was determined by using four viability tests; TTC test, pollen germination, Alexander’s stain and Acetocarmine. An optimization of the germination medium was performed. We found a strong influence of prevailing temperatures on pollen viability, which decreased faster under warmer conditions. At moderate temperatures, viable pollen could still be observed after 28 days. Thus, a possible successful pollination can also be associated to long-range transported pollen. Storage experiments showed that pollen viability could be maintained longer at temperatures of −20 °C and −80 °C than at 4 °C. In particular, the TTC test has proven to be suitable for determining viability. Therefore, properly stored pollen can be used for breeding programs to support the survival of Fraxinus excelsior.

Earlier Flowering of Betula pendula Roth in Augsburg, Germany, Due to Higher Temperature, NO2 and Urbanity, and Relationship with Betula spp. Pollen Season.

Flowering and pollen seasons are sensitive to environmental variability and are considered climate change indicators. However, it has not been concluded to what extent flowering phenology is indeed reflected in airborne pollen season locally. The aim of this study was to investigate, for the commonly represented in temperate climates and with highly allergenic pollen Betula pendula Roth, the responsiveness of flowering to different environmental regimes and also to check for commensurate changes in the respective pollen seasons. The region of Augsburg, Bavaria, Germany, was initially screened for birch trees, which were geolocated at a radius of 25 km. Random trees across the city were then investigated during three full flowering years, 2015–2017. Flowering observations were made 3–7 times a week, from flower differentiation to flower desiccation, in a total of 43 plant individuals. Data were regressed against meteorological parameters and air pollutant levels in an attempt to identify the driving factors of flowering onset and offset. Flowering dates were compared with dates of the related airborne pollen seasons per taxon; airborne pollen monitoring took place daily using a Hirst-type volumetric sampler. The salient finding was that flowering occurred earlier during warmer years; it also started earlier at locations with higher urbanity, and peaked and ended earlier at sites with higher NO2 concentrations. Airborne pollen season of Betula spp. frequently did not coincide locally with the flowering period of Betula pendula: while flowering and pollen season were synchronized particularly in their onset, local flowering phenology alone could explain only 57.3% of the pollen season variability. This raises questions about the relationship between flowering times and airborne pollen seasons and on the rather underestimated role of the long-distance transport of pollen.

Pollen calendars and regional gradients as information tools in the Extremadura pollen monitoring network (SW Spain)

Pollen allergies are one of the most important problems among respiratory diseases in today’s society. The creation and development of aerobiological information tools are useful to provide information to patients and doctors. In this work, we analysed the pollen spectrum of Extremadura to generate pollen calendars for Badajoz, Caceres, Don Benito, Plasencia and Zafra. Additionally, we analysed regional pollen gradients and plotted the main pollen season (MPS) characteristics (start date, peak date, end date and duration) in each city. In Extremadura, 35–40 different types of pollen are frequently identified, the most abundant of which (in decreasing order) belong to Quercus, Poaceae, Olea, Cupressaceae, Platanus, Plantago and Pinus. The dates when the highest accumulation of pollen occurs in the air are from mid-April to the end of May in Badajoz and Caceres; from mid-March to early June for Don Benito; from mid-April to early June for Plasencia; and from mid-April to 10 June for Zafra. Moreover, it could be confirmed that in the Extremadura region, the start date and the peak date occur earlier in the cities in the south of the region and that the duration of the pollen season is longer in these cities. The differences observed among cities may be due to the varieties of urban species and their management (pruning and irrigation), the influence of peri-urban landscapes, medium- and long-distance pollen transport and climate. The representation and geolocation of pollen calendars obtained using geographic gradients provide information in a simple, fast and visual way and can be of great interest to allergic patients and health professionals.

A 24,000-year ancient DNA and pollen record from the Polar Urals reveals temporal dynamics of arctic and boreal plant communities

A 24,000-year record of plant community dynamics, based on pollen and ancient DNA from the sediments (sedaDNA) of Lake Bolshoye Shchuchye in the Polar Ural Mountains, provides detailed information on the flora of the Last Glacial Maximum (LGM) and also changes in plant community composition and dominance. It greatly improves on incomplete records from short and fragmented stratigraphic sequences found in exposed sedimentary sections in the western Russian Arctic. In total, 162 plant taxa were detected by sedaDNA and 115 by pollen analysis. Several shifts in dominance between and within plant functional groups occurred over the studied period, but most taxa appear to have survived in situ. A diverse arctic-alpine herb flora characterised the interval ca. 24,000–17,000 cal years BP and persisted into the Holocene. Around 17,000 cal years BP, sedges (e.g. Carex) and bryophytes (e.g. Bryum, Aulacomnium) increased. The establishment of shrub-tundra communities of Dryas and Vaccinium sp., with potentially some Betula pubescens trees (influx ∼290 grains cm2 year−1), followed at ca. 15,000 cal years BP. Forest taxa such as Picea and ferns (e.g. Dryopteris fragrans, Gymnocarpium dryopteris) established near the lake from ca. 10,000 cal years BP, followed by the establishment of Larix trees from ca. 9000 cal years BP. Picea began to decline from ca. 7000 cal years BP. A complete withdrawal of forest tree taxa occurred by ca. 4000 cal years BP, presumably due to decreasing growing-season temperatures, allowing the expansion of dwarf-shrub tundra and a diverse herb community similar to the present-day vegetation mosaic. Contrary to some earlier comparative studies, sedaDNA and pollen from Lake Bolshoye Shchuchye showed high similarity in the timing of compositional changes and the occurrence of key plant taxa. The sedaDNA record revealed several features that the pollen stratigraphy and earlier palaeorecords in the region failed to detect; a sustained, long-term increase in floristic richness since the LGM until the early Holocene, turnover in grass and forb genera over the Pleistocene-Holocene transition, persistence of a diverse arctic-alpine flora over the late Quaternary, and a variable bryophyte flora through time. As pollen records are often limited by taxonomic resolution, differential productivity and dispersal, sedaDNA can provide improved estimates of floristic richness and is better able to distinguish between different plant assemblages. However, pollen remains superior at providing quantitative estimates of plant abundance changes and detecting several diverse groups (e.g. Poaceae, Cyperaceae, Asteraceae) which may be underreported in the sedaDNA. Joint use of the two proxies provided unprecedented floristic detail of past plant communities and helped to distinguish between long-distance transport of pollen and local presence, particularly for woody plant taxa.

Plant flowering mirrored in airborne pollen seasons? Evidence from phenological observations in 14 woody taxa

Abstract Flowering and pollen seasons are sensitive to environmental variability and are considered climate change indicators. However, it has not been concluded to what extent flowering phenology is indeed reflected in airborne pollen season locally. The aim of this study was to investigate, for a wide spectrum of plant species, the responsiveness of flowering to different environmental regimes and also to check for commensurate changes in the respective pollen seasons. Fourteen taxa were selected representing the families of Corylaceae, Cupressaceae, Fagaceae, Oleaceae, Pinaceae and Platanaceae. Each was studied for at least one full flowering year and in at least two sampling stations differing in elevation or direction within the period 2004–2011. Flowering observations were made 2–3 times a week, from flower differentiation to flower desiccation; >1000 daily observations were made in 225 plant individuals, in total. Data were regressed against meteorological parameters in an attempt to identify the driving factors of flowering onset and offset. Flowering dates were compared with dates of the related airborne pollen seasons per taxon; airborne pollen monitoring took place daily using a Hirst-type volumetric sampler. For all taxa, flowering started earlier at lower elevations or southern direction. Cumulative temperature proved to be the factor most significantly affecting flowering onset and end for all species (p 0.70). For the majority of the taxa examined, airborne pollen season did not coincide locally with the respective flowering periods of the selected species: flowering could precede pollen season, even for more than one month (as in C. avellana), or start after the pollen season onset (as in P. brutia). The strong sensitivity of flowering to air temperature is not the case in the respective pollen seasons. This raises questions on the relationship between flowering times and airborne pollen seasons and on the rather underestimated role of long-distance transport of pollen.

Surface pollen distribution in alpine zone of the higher Himalaya: a case study from the Kalla glacier valley, India

ABSTRACT In order to understand the relationship between modern pollen spectra and vegetation, we analysed 20 surface sediment samples collected from the alpine zone of Kalla Bank glacier valley, Dhauliganga Basin, India covering an elevational stretch of c. 3600 to 5000 m asl and vegetation zones like the alpine scrub, alpine meadow and alpine barren. This study also provides insights into the vertical pollen transport along the elevational gradient of the glacier valley. Numerical analyses such as cluster analysis (CA), discriminant analysis (DA) and detrended correspondence analysis (DCA) are used to explore and discuss the modern pollen deposition patterns in the alpine settings. Despite the inconsistencies observed between modern vegetation and surface palynoassemblages, a good agreement is noticed between CA and DA classifications and DCA ordination results which reveal signature of upslope wind transport. High percentages of pine, cedar, alder and birch pollen grains in the above tree-line surface pollen assemblages are indicative of their upslope wind transport from a lower elevation. The inconsistencies may be attributed to the differential pollen representation between species, differential flowering and pollination of herbaceous taxa. The present study suggests altitude and monsoonal winds might be the two most influential factors that attributed changes in the surface palynoassemblages of the alpine vegetation in the Kalla Bank glacier (Kunti-Banar) valley. Therefore, while interpreting the fossil pollen spectra from any high altitude mountainous zone, long-distance pollen transport should always be taken into account, especially for anemophilous plant taxa.

Alder pollen concentrations in the air during snowfall

The focus of our study was airborne alder pollen because it is one of the main causes of inhalant allergies in many countries in the Northern Hemisphere. The main research setback was pollen concentrations during snowfall. Analyses from a 21-year database showed that the hourly patterns of occurrence of airborne Alnus pollen during snowfall differ. Snowfall can cause a decrease in pollen concentrations in the air that may persist for several hours. However, during the snowfall period of 2018, an increase in pollen concentrations was observed. High temperatures during the days preceding snowfall stimulate thermal currents, and pollen could become airborne. During snowfall, airborne pollen grains are supposedly washed out of the atmosphere and numerous pollen grains are deposited on the snow surface. Hypotheses about the long-distance transport of pollen have also been verified. Back-trajectory analysis has revealed that air masses from Belarus and Ukraine were transported to Rzeszow. We found that the influence of snowfall on pollen concentrations is ambiguous and individuals prone to allergies also notice symptoms on days with snowfall and temperatures below zero.

Modern pollen spectra from the Pala Wetland Reserve Forest, Siaha District, Southern Mizoram, north-eastern India

This study is an attempt to evaluate the relationships between vegetation and modern pollen rain in Siaha District, Southern Mizoram, India, as a contribution to palaeoecological research. A set of 21 pollen substrates (surface soil and moss pollsters) were obtained from the vicinity of Pala Lake, the biggest natural lake in Mizoram. Two thick spider web samples were also incorporated to measure the degree of trapped airborne palyno-debris as compared to the moss-soil data. The total pollen rain reflects the site-to-site variation in the pollen assemblages as shown by their abundances – 38%, 26% and 27% from the forest, forest margin and open land, respectively. The spider web samples also contribute 9% of palynomorphs to the total pollen assemblage. The total pollen rain revealed the dominance of non-arboreal pollen (NAP: 56%) over arboreal pollen (AP: 27%). The data showed a partial correlation with the extant woody vegetation; however, two major arboreal taxa – Dipterocarpus and Xerospermum – are under-represented despite their prominence in the near vicinity. The presence of highland taxa such as Tsuga and Carya indicates long-distance pollen transport. The abundance of monolete and trilete ferns also suggests a prevalent humid depositional environment. Fungal spores mainly constitute the non-pollen palynomorphs (NPP) assemblage. Low representation of dominant tree taxa in the pollen assemblages, even in the samples proximal to the forest, can be attributed to the entomophilous nature of the trees (Emblica and Artocarpus species). The extant palynoflora recovered in different surface substrates are suggestive of differential pollen production, dispersal and deposition.

Aran Islands, Western Ireland: Farming History and Environmental Change, Reconstructed from Field Surveys, Historical Sources, and Pollen Analyses

The Aran Islands are exceptional cultural landscapes at the Atlantic fringe of Europe. They are strongly influenced by human settlement and small-scale farming that is still pursued according to traditional practices. Reconstruction of changes in farming from the beginning of the early 20th century onwards, and demographic changes beginning in the early 19th century, are discussed in the light of official statistics. Field surveys, aimed mainly at documenting the extent of Secale cereale (rye) cultivation, provide more precise information on the extent of rye cultivation in recent decades and give fresh insights into present-day flora, vegetation, and plant biodiversity. Results from a previously published, lake sediment-based Holocene pollen profile from Inis Oirr are re-assessed in the light of modern-day pollen deposition studies that we carried out. We discuss the implications of long-distance pollen transport for the interpretation of Holocene pollen diagrams in relation to the history of trees, including Pinus sylvestris (Scots pine), in Ireland, and we emphasize the importance of supporting traditional farming practices, particularly as regards cereal growing, on the Aran Islands.

Carpinus betulus pollen accumulation rates in Roztocze (SE Poland) in relation to presence of Carpinus in Ferdynandovian pollen diagrams

Carpinus pollen has been recorded in fossil pollen diagrams of different interglacials. In case of the Ferdynandovian pollen sequence it is of particular importance to know if scattered presence of Carpinus pollen at the decline of Ferdynandovian 1 interglacial represents long distance transport of pollen or small isolated Carpinus populations. The study aims to trace the pollen-vegetation relationship in Roztocze (SE Poland) using Tauber-style pollen traps to understand better the pattern of Carpinus pollen dispersal and deposition. High and low pollen deposition years were recorded for Carpinus betulus in the period 1998–2010. Deposition was extremely high in 2002. Average annual pollen accumulation rate was calculated at 1348 grains cm -2 year -1 , which was 4.1% of total pollen spectrum. The study confirms that the earlier pollen presence/absence threshold values of about 5% for the presence of Carpinus trees in vegetation (Huntley & Birks 1983) were too high. The pollen monitoring data from Roztocze support the opinion of Ralska-Jasiewiczowa et al. (2004) that low values of about 0.5% may reflect the presence of Carpinus trees in the forests. These data, in comparison to the scattered Carpinus pollen grains in the last part of the Ferdynandovian 1 interglacial seem to indicate that single trees of this genus may nave occurred in the vegetation at the decline of interglacial optimum.

Molecular analysis confirms the long-distance transport of Juniperus ashei pollen.

Although considered rare, airborne pollen can be deposited far from its place of origin under a confluence of favorable conditions. Temporally anomalous records of Cupressacean pollen collected from January air samples in London, Ontario, Canada have been cited as a new case of long-distance transport. Data on pollination season implicated Juniperus ashei (mountain cedar), with populations in central Texas and south central Oklahoma, as the nearest source of the Cupressacean pollen in the Canadian air samples. This finding is of special significance given the allergenicity of mountain cedar pollen. While microscopy is used extensively to identify particles in the air spora, pollen from all members of the Cupressaceae, including Juniperus, are morphologically indistinguishable. Consequently, we implemented a molecular approach to characterize Juniperus pollen using PCR in order to test the long-distance transport hypothesis. Our PCR results using species-specific primers confirmed that the anomalous Cupressacean pollen collected in Canada was from J. ashei. Forward trajectory analysis from source areas in Texas and the Arbuckle Mountains in Oklahoma and backward trajectory analysis from the destination area near London, Ontario were completed using models implemented in HYSPLIT4 (Hybrid Single-Particle Lagrangian Integrated Trajectory). Results from these trajectory analyses strongly supported the conclusion that the J. ashei pollen detected in Canada had its origins in Texas or Oklahoma. The results from the molecular findings are significant as they provide a new method to confirm the long-distance transport of pollen that bears allergenic importance.

Biogeographical estimates of allergenic pollen transport over regional scales: Common ragweed and Szeged, Hungary as a test case

Abstract Long-distance pollen transport can substantially raise local pollen levels, but their relative contribution has not yet been quantified temporally or spatially in ragweed infested regions. Using common ragweed (Ambrosia artemisiifolia) pollen accumulation at a ragweed infested area, Szeged, Hungary as a test case, this study attempted to: (1) identify, using cluster analysis, biogeographical regions that contribute to long-range transport of ragweed pollen to Szeged; (2) quantify the relative contribution of ragweed pollen from these regions; (3) determine the relative contribution of “local” and “transported” pollen for Szeged. Using the HYSPLIT model, three-dimensional backward trajectories were produced daily over a 5-year period, 2009–2013 for ragweed pollen accumulation at Szeged. A k-means clustering algorithm using the Mahalanobis distance was applied in order to develop trajectory types. Nine back-trajectory clusters were identified. Cluster 1 (direction: from the Channel area south of Great Britain) and cluster 5 (direction: from Northern Mediterranean) were found the most relevant potential long-distance sources for Ambrosia pollen transport to Szeged. Potential source contribution function (PSCF) and concentration weighted trajectory (CWT) values indicated additional potential source areas including the central and eastern part of France, the northern part of Italy and the Carpathian Basin. For Szeged on non-rainy days, medium-range transport is important, while on rainy days the two transport ranges have equal weights. Based on the Granger causality, annual pollen amount transported by the atmospheric circulation is 27.8% of the annual total pollen at Szeged. From this quantity, 7.5% is added to (due to transport), while 20.3% is subtracted from (e.g. because of wash-out by frontal rainfalls going towards Szeged) local sources.

Vegetation, climate and fire in the eastern Andes (Bolivia) during the last 18,000 years

A c. 18kacal BP long sediment record from Laguna Khomer Kocha Upper (4153m asl), Bolivia, shows that fire regime, governed by climatic variation, has long been a transformative agent in the eastern Andes. Before c. 14.5kacal BP, warming and relatively moist conditions free from fire, facilitated the expansion of high Andean Polylepis woodland. Fire onset at c. 14.5.kacal BP, quickly transformed the local vegetation and the woodlands became restricted to areas protected from fire. A major increase in burning, c. 10.1–6.4kacal BP removed Polylepis woodland locally and this coincided with a region-wide Holocene dry event (HDE) which caused falling lake levels and allowed fire intensification. A decline in burning at c. 6.4kacal BP and an increase in marsh–woodland (Alnus) marked the termination of the HDE and a return to wetter conditions. As well as recording the environmental history of local vegetation dynamics, long-distance pollen transport provides evidence of changes in the Yungas montane forests, highlighting their sensitivity to climate and burning regimes. Simultaneous adjustments in both Andean and Yungas montane taxa suggest that vegetation dynamics in the two environments are linked to a common climatic driver. There is no evidence to indicate that human activity had any impact on the local landscape.

Palynological and satellite-based MODIS observations of modern vegetational gradients in China

The MODIS-based estimates of woody, herbaceous and bare cover percentages within a 21 × 21, 11 × 11 and 0.5 × 0.5 km window around pollen sampling sites were attributed to the respective modern pollen spectra. Reconstructions of modern woody cover using the pollen–MODIS reference data set and the modern analogue approach matched well to the original MODIS-based estimates for three selected land-cover fractions. The best of all correspondence between the reconstructed and observed values was obtained for the 21 × 21 km window, including woody ( r = 0.83), herbaceous ( r = 0.80) and bare ( r = 0.90) cover. Discrepancies in the pollen–MODIS cross-validation may be caused by long-distance pollen transport, patchy vegetation, particularly in the densely populated eastern areas and along the steep mountain slopes, under-representation of curtain woody taxa (e.g. Larix and Populus in pollen records), and possible uncertainties in the MODIS data. A series of tests performed with the reference data set including 1452 surface-pollen spectra and representing all vegetation and climatic units of China show the pollen-based reconstructions correspond well to the MODIS-based estimations of land-cover percentages within a 21 × 21 km window, supporting previously obtained results from northern Asia and North America. Results obtained for the smaller window sizes are less accurate, particularly when reconstructing woody cover. The pollen–MODIS-based modern analogue approach can reproduce present-day characteristics of land cover in China with a reasonably high degree of accuracy despite the complexity of the topography and regionally intensive land use. The generally strong correlations encourage the application of the approach to Chinese fossil pollen records.

Directionality of Pollinator Movements in Watermelon Plantings

Insect pollinators such as honeybees (Apis mellifera L.) and bumble bees (Bombus spp.) are strongly directional in their movements among flowers and typically move to the nearest neighboring inflorescence, which is often in the same row. Pollinator movements in watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] were determined by tracking pollen flow with the incompletely dominant lobed-leaf trait of ‘Crimson Sweet’ (Nl) as the pollen donor and the incompletely recessive ‘Sunshade’ (nl) as the recipient. Mature ‘Sunshade’ watermelon fruit were collected at 3-m increments down selected rows and across all rows in both directions from the central donor plants that made up 1% of the planting. The resulting progenies from each fruit collected were screened to determine the directionality of pollinator movements by the occurrence of the Nlnl genotype (or lobed-leaf phenotype). The row that went through the central donor plant block had higher percentages of lobed-leaf seedlings compared with the other rows evaluated. However, lobed-leaf seedlings were observed on rows at significant distances (greater than 10 m) from the donor block. This resulted most likely from long-distance pollen transport, in-hive pollen transfer, or multiple transfers of pollen to staminate (male) and/or pistillate (female) flowers by pollinators before reaching the final destination on a stigmatic surface at a substantial distance from donor plants. Because watermelon vines grow out in all directions, including across rows, a pollinator can easily move to adjacent flowers on a vine growing across rows; thus, the movements of pollinators in watermelon (and most likely other vining cucurbits) are not as simple as maintaining a linear direction down the row.

EARLY HOLOCENE OPENLANDS IN SOUTHERN NEW ENGLAND

The pre-historical vegetation structure in temperate forest regions is much debated among European and North American ecologists and conservationists. Frans Vera's recent hypothesis that large mammals created mosaics of forest and openland vegetation in both regions throughout the Holocene has been particularly controversial and has provoked new approaches to conservation management. Thirty years earlier, American paleoecologists Herb Wright and Margaret Davis debated whether abundant ragweed pollen at Rogers Lake, Connecticut at 9500 yr BP signified local forest openings or long-distance transport of pollen from Midwestern prairies. Using new pollen records from Harvard Forest and the North American Pollen Database, we address this question and offer insights to the openland discussion. Ragweed and other forbs exceed 3.5% at five sites in a restricted area of southern New England between 10,100 and 7700 yr BP. Strong evidence suggests this pollen originated from the landscapes surrounding these sites (supporting Davis), as ragweed pollen percentages do not increase with longitude from New England to the Midwest. Ragweed pollen percentages are also unrelated to basin size and therefore unrelated to the proportion of extraregional pollen in New England. High forbs values were associated with increases in oak, decreases in white pine, and relatively high charcoal values. Modern pollen records with similar forb and tree percentages occur along the Prairie Peninsula region of the Upper Midwest. However, the closest analogue to the southern New England early Holocene assemblages comes from Massachusetts' Walden Pond in the early 18th century. These results and the affiliation of ragweed for open, disturbed habitats suggest that oak-pine forests with large openings persisted for over 2000 years due to dry conditions and perhaps increased fire frequency. This conclusion is corroborated by independent lake level and climate reconstructions. Because these early Holocene openlands have no detectable analogue in New England for the past 7000 years before European settlement, we suggest that all important openlands today are almost exclusively a legacy of Colonial agriculture and should be managed accordingly. Nonetheless, our results may have implications for forest dynamics accompanying projected climate change to more arid conditions in New England over the next century.

New evidence of long distance pollen transport to southern Greenland in late spring

New observations of long-distance pollen transport to southern Greenland are recorded during the last 2 weeks of May, 2003. The results indicate northeastern North America as the source area of the transported pollen grains as shown in earlier investigations. Backward trajectories indicate that transport occurred twice during the first week corresponding to a time of maximum pollen flux emitted to the atmosphere in the source area. A large percentage of exotic pollen grains were identified, about 11% of the total counted. However, transport during the second week appears to have occurred during a single day at a time of reduced pollen emission into the atmosphere, which was subjected later to severe washout. As a result, only 1% of the total pollen spectra was identified as exotic grains. The back trajectories modeled by the HYSPLIT application differ somewhat from those previously identified in 2002. Although in both years air passing over southern Greenland at 3000 m carried out the main transport, additional transport could have occurred at a much lower altitude in 2003.

Pollen record of rapidly changing air trajectories to the North Pole

Tracing modern atmospheric dynamics is important for constraining models used in past climate reconstruction. However, these models must be verified by modern observations. We present the rapid changeover of two different air trajectories to the North Pole determined by studying the long distance transport of pollen. Samples were collected on a manned floating capsule drifting southward on the sea ice from the North Pole in 2002. It was observed that an air mass at 3000 m altitude transported birch and pine pollen released in Western Europe during week 22 (May 27). Two weeks later, during week 24 (June 10), alder, birch and willow pollen from eastern Siberia reached the drifting station with an air mass at 1000 m altitude. These particular patterns support independent investigations of air trajectories in the Arctic, especially the transport of anthropogenic pollutants such as sulfate and nitrate.

Long distance transport of pollen to Greenland

Four pollen traps were recently placed at coastal sites in East and West Greenland in order to assess long distance transport of pollen to the Arctic domain. By identifying potential vegetation source areas associated with air mass pathways we were able to produce the first detailed record of pollen transport from eastern North America to Narsarsuaq, southern Greenland. The record is based on observations and on a transport and dispersion model used to calculate back trajectories of the air masses. The evidence points to the pollen being transported northward by the air mass over Newfoundland and the Labrador Sea before reaching Narsarsuaq. At this point, the air mass was at an altitude of 3000 m. Deposition of pollen grains occurred with downward air movements associated with a 0.5 mm/h rain. The source areas for these pollen grains differ from those of dust and certain other aerosols that reach the summit of the Greenland Ice Sheet. The results demonstrate the need for continued maintenance and analysis of the Greenland pollen trap data in order to improve our understanding of atmospheric circulation and transport to high northern latitudes.