Juniperus Pollen Research Articles

Unified 200 kyr paleohydrologic history of the Southern Great Basin: Death Valley, Searles Valley, Owens Valley and the Devils Hole cave

We present a hydroclimate synthesis of the southern Great Basin over the last two glacial-interglacial cycles focused on paleolakes in Death Valley (core DV93-1), Searles Valley (core SLAPP-SRLS17), Owens Valley (core OL92), and the Devils Hole cave. There is close agreement between the occurrence of lakes in Death Valley and the height of the water table in the Devils Hole (50 km east of Death Valley) during the last 200 kyr. Death Valley and Devils Hole have adjacent, partly overlapping, drainage areas and most likely did over the last 200 kyr. When the water table in the Devils Hole was above the threshold level of ∼5 m higher than the modern, permanent lakes existed in Death Valley. At water table elevations less than 5 m above the modern, ephemeral lakes, saline pans, and mudflats occurred in Death Valley. The close temporal agreement between inferred paleoenvironments from the sediments in the Death Valley core and the paleowater table elevation in Devils Hole suggests a common forcing and provides insight into climate variability in the southwestern United States over the last 200 kyr. Owens Valley and Searles Valley, which derived inflow waters from the Sierra Nevada via the Owens River, contain paleohydrologic records which match those from Death Valley and the Devils Hole in terms of timing and direction of water availability over the last 200 kyr, indicating a similar paleohydrologic history for the entire southern Great Basin region. Near the end of Marine Oxygen Isotope Stage 6 (MIS 6), 140 ka - 130 ka, Lake Manly in Death Valley became shallow and hypersaline, and ultimately dried up at 127.1 ka ±4.3 ka. The transition from glacial to interglacial vegetation, which involved the loss of Juniperus pollen and an increase in Quercus (oak) pollen, occurred in Death Valley core DV93-1 at 131.3 ka ±4.0 ka. Following the glacial to interglacial pollen shift, a large alkaline lake formed in Death Valley. Similar conditions (freshwater, high productivity, and a mixed, deeply oxygenated water column indicated by biomarkers) existed in Searles Lake between 135.3 +2.7/-2.9 ka and 130.1+2.7/-2.6 ka, also following the juniper-oak pollen transition. Sr isotopes in calcite and sulfate minerals (gypsum, glauberite, thenardite), and the rare occurrence of the sodium carbonate mineral northupite with a low 87Sr/86Sr ratio in core DV93-1, together with organic geochemical proxies from Searles core SLAPP-SRLS17, all suggest that at this time, late MIS 6 Lake Manly in Death Valley received alkaline water via spillover from Searles Valley into Death Valley through Panamint Valley. The hydrologic connection between Searles Valley, Panamint Valley, and Death Valley at Termination II (130 ka) is documented here for this system of pluvial lakes for the first time. The Devils Hole water table decreased to +6.5 m at 140.8 ka ±3.2 ka, rose briefly to +8 m at 137.6 ka ±0.5 ka, and then dropped 8 m by 120.36 ka ±0.45 ka, when it reached an elevation similar to the modern. The pluvial lakes in Death Valley and Searles Valley may have coincided with the rise of the Devils Hole water table at ∼137.6 ka ±0.5 ka years ago, although the age models for core DV93-1 and core SLAPP-SLRS17 during the end of MIS 6 carry large uncertainties.

Multi-proxy paleoenvironmental data from Paulina Marsh inform human-environmental dynamics in the Northern Great Basin U.S.A.

Understanding the dynamics between climate change and human adaptive strategies is a longstanding question driving paleoecological and archaeological research in North America's Great Basin. We present multiproxy data from five sediment cores retrieved from Paulina Marsh in the Fort Rock Basin, Oregon, an area renowned for its archaeology but lacking the paleoenvironmental data needed to fully contextualize those records. Radiocarbon, pollen, particle size, elemental, and charcoal analyses of one core, and geochronological data from four additional cores, reveal fluctuating vegetation communities, hydrologic conditions, and fire histories during the Early and Late Holocene that are consistent with models proposed to explain changing settlement-subsistence patterns in the region. There was likely an emergent marsh or meadow and an absence of Juniperus at the core site during the Early Holocene. Middle Holocene deposits are not present due to a geologic unconformity, perhaps because of channel migration and climatic aridity. Late Holocene sediments record a more mesic meandering stream system between ∼3900 and 2200 years ago, followed by an increase in xeric-adapted vegetation in the last 2000 years. The lack of Juniperus pollen in the Early Holocene sediments inform ongoing debates about Juniperus spread in the Great Basin. These data represent the first Early Holocene pollen record from the Fort Rock Basin and are one of few lowland vegetation histories of this age in the region. This study contributes to our understanding of past ecology in semi-arid environments, provides new context for archaeological interpretations, and establishes a framework for future work in the region.

Holocene chemostratigraphy of spring sediments in Range Creek Canyon, Utah, USA

This study builds off the paleoclimatic reconstruction created by Hart et al. that used a multiproxy study to examine the role of moisture in the exodus of the Fremont from Range Creek Canyon in the 12th century. For this research, elemental ratios, weathering indices, and pollen data from two wetland spring sediment cores were used to compare with the existing Hart et al. paleoclimatic reconstruction (Objective 1). Elemental ratios and pollen data proved to be effective proxies for precipitation fluctuation, with the ratio of Pinus to Juniperus pollen representing effective moisture and increasing with the intensity of chemical weathering. Elemental data were additionally used to identify crypto tephra in the cores to validate Range Creek Canyon’s existing chronology (Objective 2). The XRF analysis of the sediment cores constrained the chronology of environmental change in the canyon by identifying the elemental signature of the Mazama eruption (7627 ± 150 cal. year BP). The concentration of Al, Y, and Ti were 50 times higher in this layer than elsewhere in the core, indicating a sudden depositional event, such as a volcanic eruption. Based on the multiproxy data and confirmed chronology, the Fremont entered the canyon during a period of elevated precipitation lasting until 600 AD. Precipitation levels remained steady until 1200 AD, after which precipitation levels decreased, causing drought conditions that coincide with the Fremont’s departure from Range Creek Canyon.

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.

Molecular approaches for the analysis of airborne pollen: A case study of Juniperus pollen

BackgroundPollen monitoring is a common and vital tool in the field of allergy, creating awareness in pollen sensitive individuals. Traditionally, pollen monitoring has been based on conventional microscopic counting techniques that are labor intensive and limited in the identification to the genus or family level. Molecular techniques provide an alternative approach that is less labor intensive and enable identification of any species by its genetic fingerprint. ObjectiveTo use quantitative polymerase chain reaction (qPCR) to evaluate pollen concentrations in air samples. MethodsJuniperus pollen was selected as our model because of the importance of this pollen in the southcentral United States. We analyzed 105 air samples collected with a Burkard spore trap from 2013 to 2015 using species-specific primers and probes. To evaluate the feasibility of a molecular approach, we used duplicate air samples that allowed us to compare results from classical identification based on light microscopy with our qPCR results. ResultsPollen concentrations from the qPCR data were significantly correlated with concentrations determined through light microscopy (R = 0.902, P < .001). We also confirmed an overlap in the pollination seasons between Juniperus ashei and Juniperus pinchotii and between J ashei and Juniperus virginiana. ConclusionWe found that this method correctly identified different Juniperus species present in mixed air samples in the southcentral United States, an accomplishment that cannot be achieved using microscopic identification. We conclude that the qPCR method is more accurate and sensitive than current pollen monitoring techniques and, therefore, has the potential to be used in various pollen monitoring stations.

Scottish early Holocene vegetation dynamics based on pollen and tephra records from Inverlair and Loch Etteridge, Inverness-shire

This paper presents the results of an investigation of early Holocene cryptotephra layers recovered from sediments in two kettle-hole basins at Inverlair (Glen Spean) and Loch Etteridge (Glen Fernisdale). Electron probe micro-analysis (EPMA) of shards from two cryptotephra layers revealed that the uppermost layer in both sequences has a composition similar to the An Druim tephra, first reported from a site in Northern Scotland. We present evidence that distinguishes the An Druim from the chemically very similar early Holocene Ashik tephra. The lowermost layer at Inverlair matches the composition of the Askja-S tephra found in the Faroe Islands, Ireland, Sweden, Germany and Switzerland. This is the first published record of the Askja-S tephra from mainland Scotland. As at other sites, the Askja-S seems to mark a short-lived climatic deterioration, most likely the Pre-Boreal Oscillation: at Inverlair it occurs just above an oscillation represented by a reduction in LOI values and in the abundance of Betula pollen, and by a peak in Juniperus pollen. The lowermost layer at Loch Etteridge has a Katla-type chemistry and extends through the upper part of the Loch Lomond (Younger Dryas/GS-1) Stadial to the Stadial/Holocene transition; it may represent a composite layer which merges the Vedde and Abernethy tephras. One of the key conclusions is that the glacial-melt deposits in the vicinity of Inverlair (kames and kame terraces) were ice-free by c. 10.83ka (the age of the Askja-S), providing a limiting age on the disappearance of LLR ice in Glen Spean.

Rapid Quantification of Juniperus Pollen Proves Overlapping Pollen Seasons

Rashmi Prava Mohanty, Mark A. Buchheim, PhD, Estelle Levetin, PhD, FAAAAI; University of Tulsa, Tulsa, OK, University of Tulsa. RATIONALE: Microscopic analysis of air samples fails to determine the pollination season overlap between various species with morphologically similar pollen such as members of the Cupressaceae and Poaceae. Previously, we showed it was possible to use PCR to identify Juniperus ashei pollen from air samples. The present study was undertaken to determine if qPCR could be used to determine airborne pollen counts for three Juniperus species and define the pollination season overlap. METHODS: The atmosphere in Tulsa, OK(USA) was monitored with a Burkard sampler and analyzed by microscopy using standard methods. A second Burkard sampler was used from 2013 to 2015 for molecular analysis; 109 samples were tested with species-specific primers and probes designed for J.ashei, J.pinchotii and J.virginiana. Numbers of pollen grains obtained from microscopy were compared with numbers obtained from qPCR by Spearman correlation coefficient. RESULTS: Cupressaceae pollen was detected in the Tulsa atmosphere from October through April. The qPCR counts for total Juniperus pollen showed a significant correlation with the microscope counts, R50.92, p<0.001. Quantitative PCR data showed overlapping pollen seasons. In the fall, data indicated five days (in two years) with both J.pinchotii and J.ashei pollen. Similarly, in January and February eight days (in two years) indicated both J.ashei and J.virginiana pollen in the air. CONCLUSIONS: This approach is a rapidmethod to identify and quantify specific pollen types and the pollen season overlap where species and genera cannot be distinguished by microscopy. Defining the exact pollination season will be a benefit for patients sensitive to pollen from specific taxa.

Detection of Airborne Juniperus Pollen By Conventional and Real-Time PCR from Burkard Air Samples

M O N D A Y 746 Detection of Airborne Juniperus Pollen By Conventional and Real-Time PCR from Burkard Air Samples Rashmi Prava Mohanty, MS, Mark A. Buchheim, PhD, James Anderson, Estelle Levetin, PhD, FAAAAI; University of Tulsa, Tulsa, OK, University of Tulsa, oshtech inc. RATIONALE: Microscopic detection of pollen requires considerable expertise, and identification is limited to genus or family level. Cupressaceae pollen is detected in the Tulsa atmosphere for seven months each year; however, local members of this family only pollinate from February throughApril. Here, we developedmolecularmethods to identify multiple Juniperus species from air samples. METHODS: Air samples from January to March were collected with a Burkard 7-day sampler located in Tulsa, OK. One-day segments of exposed Melenex tape were cut into smaller pieces and DNA extracted. Species-specificmatK primers for J.ashei and J.virginianawere developed for conventional PCR and leafy primers/probe pairs were developed for real-time PCR for Juniperus. An air sample collected on 15 January in London, Ontario(CANADA) using a Buck Bioslide sampler was also analyzed. RESULTS: Serial dilution of J.asheii pollen demonstrated that specific matK primers were able to detect the presence of 2 to 3 pollen grains indicating this method would be useful for Burkard samples. Using matK primers, J.ashei pollen was confirmed from air samples collected in Tulsa in January as well as from Canada. Primers for matK in J.virginiana confirmed the presence of that pollen in Tulsa air sampled in February and March. Primer/probe pairs for leafy were successful in real-time PCR and can be used to quantify Juniperus pollen from Burkard samples. CONCLUSIONS: This study provides an effective alternative to microscopy for identification of pollen from Burkard air samplers and Bioslide samplers. These data also confirm the long distance transport of J.ashei pollen up to 2400 km.

Juniper Pollen Hotspots in the Southwest

Rationale: Juniperus pollen is a major allergen in Texas, Oklahoma, and New Mexico. While the bulk of pollen may be released in rural areas, large amounts of pollen can be transported to urban areas. Major juniper species in the region include: Juniperus ashei, J. virginiana, J. pinchotii, and J. monosperma. Pollen release is virtually continuous beginning in late September with J. pinchotii and ending in May with J. monosperma. Urban areas in the region were evaluated for the potential of overlapping seasons in order to inform sensitive individuals. Methods: Burkard volumetric pollen traps were established for two consecutive spring seasons at 6 sites in northern New Mexico and 6 sites for two consecutive winter and fall seasons in Texas and Oklahoma Standard methods were used in the preparation and analysis of slides. Results: The Dallas-Fort Worth Metroplex is home to over 6 million people. It is adjacent to populations of J. pinchotii, J. virginiana, and J. ashei. Peak concentration near Dallas for J. ashei in 2011 was 5891 pollen grains/m3 in January 7th. The peak date for J. pinchotii at an upwind sampling location in San Marcos, TX was November 1, 2010 and peak for J. virginiana at a nearby station in Tulsa, OK was November 1, 2010 and peak for J. virginiana at a nearby station in Tulsa, OK was February 20, 2011. Amarillo, TX is adjacent to J. pinchotii, J. ashei, and J. monosperma populations and may be subject to juniper pollen from September through May. Conclusions: Considering the overlapping distributions of juniper trees and the overlapping temporal release of pollen, sensitive patients may benefit from avoiding hotspots.

Vegetation responses to rapid warming and to minor climatic fluctuations during the Late-Glacial Interstadial (GI-1) at Gerzensee (Switzerland)

High-resolution pollen analyses made on the same samples on which the ratios of oxygen isotopes were measured that provided the time scale and a temperature proxy after correlation to NorthGRIP.(1)A primary succession: The vegetation responded to the rapid rise of temperatures around 14,685yr BP, with a primary succession on a decadal to centennial time scale. The succession between ca 15,600 and 13,000yr BP included:(1.1.)The replacement of shrub-tundra by woodland of Juniperus and tree birch (around 14,665yr BP)(1.2.)The response of Juniperus pollen to the shift in oxygen isotopes in less than 20yr,(1.3.)A sequence of population increases of Hippophaë rhamnoides (ca 14,600yr BP), Salix spp. (ca 14,600yr BP), Betula trees (ca.14,480yr BP), Populus cf. tremula (ca. 14,300yr BP), and Pinus cf. sylvestris (ca. 13,830yr BP).(2)Biological processes: Plants responded to the rapid increase of summer temperatures on all organisational levels:(2.1)Individuals may have produced more pollen (e.g. Juniperus);(2.2)Populations increased or decreased (e.g. Juniperus, Betula, later Pinus), and(2.3)Populations changed their biogeographical range and may show migrational lags.(2.4)Plant communities changed in their composition because the species pools changed through immigration and (local) extinction. Some plant communities may have been without modern analogue.These mechanisms require increasing amounts of time.(2.5)Processes on the level of ecosystems, with species interactions, may involve various time scales. Besides competition and facilitation, nitrogen fixation is discussed.(3)The minor fluctuations of temperature during the Late-Glacial Interstadial, which are recorded in δ18O, resulted in only very minor changes in pollen during the Aegelsee Oscillation (Older Dryas biozone, GI-1d) and the Gerzensee Oscillation (GI-1b).(4)Biodiversity: The afforestation at the onset of Bølling coincided with a gradual increase of taxonomic diversity up to the time of the major Pinus expansion.

Insights into a hydration regulating system in Cupressus pollen grains

Hydration, rupture and exine opening due to the sudden and large expansion of intine are typical of taxoid-type pollen grains. A hemispheric outgrowth external to the exine was observed on Cupressus and Juniperus pollen grains before the intine swelling and exine release. However, the actual existence of this permanent or temporary structure and its precise role in pollen hydration is still being debated. The aim of this paper is to collect information on the actual presence of this peculiar outgrowth on the surface of the Cupressus pollen grain, its structure, composition and function. Pollen grains of several Cupressus species were observed using various techniques and methodologies, under light and fluorescence microscopy, phase-contrast microscopy, confocal microscopy, scanning electron microscopy, and an environmental scanning electron microscope. Observations were also performed on other species with taxoid-type pollen grains. A temporary structure located just above the pore was observed on Cupressus pollen grains, as well as on other taxoid-type pollens. It is hemispheric, layered, and consists of polysaccharides and proteins. The latter are confined to its inner part. Its presence seems to regulate the entrance of water into the grains at the beginning of pollen hydration. The presence of a temporary structure over the pore of taxoid-type pollen grains was confirmed and its structure was resolved using several stains and observation techniques. This structure plays a role in the first phases of pollen hydration.

Northern New Mexico Spring Pollen Levels

RATIONALE: Juniperus pollen has been reported as a major spring allergen in Albuquerque and surrounding areas. Much of northern New Mexico is vegetated with mixed stands that contain Juniperus scopulorum and/or Juniperus monosperma. The present study was undertaken to document spring pollen levels and types and to aid in the development of a pollen forecast and warning system for Juniperus.

The historical dynamics of calcareous grasslands in the central and southern Franconian Jurassic mountains: a comparative pedoanthracological and pollen analytical study

We present a thematic set on pedoanthracological research. In this paper a comparative analysis of soil wood charcoal from calcareous grasslands and pollen from an alluvial sediment profile has been carried out to reconstruct the history of calcareous grassland habitats in the Franconian Jura. Seven tree and shrub species (groups) were recorded from soil charcoal. Charcoal from Pinus dominated all spectra, indicating open forests or even less intensively grazed grasslands, which is supported by findings of remains of Juniperus and Ligustrum. Charcoals from Fagus, Quercus and Abies, indicating more closed forests, were comparatively rare. AMS radiocarbon datings assigned the charcoals to the period of the Roman Empire, the late Middle Ages and the early Modern Times correlating with the peaks of microcharcoals in the sediment profile. Juniperus pollen was used as indicator of calcareous grasslands. Plantago lanceolata, Galium type, Apiaceae, Ranunculaceae and Ballota/ Galeopsis pollen-types were significantly correlated with the occurrence of Juniperus and identified as further indicators. Pinus was selected as an indicator for open forests. Pollen of all indicator species occurred throughout the pollen profile starting in the Iron Age. The main peak of grassland indicator species pollen types was in the high Middle Ages. Maxima of Pinus pollen have been recorded in the periods of the Roman Empire and the late Middle Ages. We suggest extension maxima of less intensively grazed calcareous grasslands during the Roman Empire period and during the late Middle Ages and of intensively grazed grasslands in the high Middle Ages in the latter case correlated to intensive mining activities north of the study region. Increase in Pinus and the conversion of open into woody grasslands in the late Middle Ages/beginning of Modern Times was triggered by the abandonment of arable farming due to the decline of human population caused by pest diseases.

Identification of arid phases during the last 50 cal. ka BP from the Fuentillejo maar‐lacustrine record (Campo de Calatrava Volcanic Field, Spain)

AbstractGeochemical (element analysis, molecular analysis of organic compounds), physical, palynological, mineralogical and sedimentary facies analysis were performed to characterise the sedimentary record in Fuentillejo maar‐lake in the Central Spanish Volcanic Field of Campo de Calatrava, in order to reconstruct the palaeoenvironmental and palaeoclimatic processes which controlled vegetation patterns and deposition of different sedimentary facies. The upper 20 m of core FUENT‐1 show variations in clastic input, water chemistry, vegetation and organic fraction sources in the lake throughout the Late Pleistocene and Holocene. The temporal framework provided by 14C accelerator mass spectrometry dating allows assigning the sequence to the last 50 cal. ka BP. Arid phases identified in the FUENT‐1 sequence are correlated to Heinrich events (HE) and to stadials of the Dansgaard/Oeschger (D/O) cycles. Siliciclastic facies with high magnetic susceptibility values, high Juniperus pollen content, a low Paq index (aquatic macrophysics proxy index), a decrease in the relative percentage of the n‐C27 and an increase in the n‐C31 alkanes are indicative of arid and colder climatic events related to HE 2, HE 1 and the Younger Dryas (YD). Similar short cold and arid phases during the Holocene were identified at 9.2–8.6, 7.5–7 and 5.5–5 cal. ka BP. In dolomite–mud facies, the pollen data show an increase in the herbs component, mainly – Chenopodiaceae, Artemisia and Ephedra – steppe taxa; a low Paq index, a decrease in the relative percentage of the n‐C27 alkane and an increase in the n‐C31 alkane are also observed. This facies was probably the result of lower lake levels and more saline–alkaline conditions, which can be interpreted as linked to arid–warm periods. These warm and arid phases were more frequent during Marine Isotope Stage (MIS) 3 and the interstadials of MIS 2. HE 4, HE 2, HE 1 and the YD in core FUENT‐1 were immediately followed by increases of warm steppe pollen assemblages that document rapid warming similar to the D/O cycles but do not imply increasing humidity in the area. Fuentillejo hydrology is controlled by changes in the atmospheric and oceanic systems that operated on the North Atlantic region at millennial scale during the last 50 cal. ka BP. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Palaeoecological and experimental evidence of former forests and woodlands in the treeless desert pastures of Southern Tibet (Lhasa, A.R. Xizang, China)

Palaeoecological and palaeopedological investigations around Lhasa (3650 m, 29°40′N/91°04′E, A.R. Xizang, China) provide evidence of human induced environmental changes which have occurred over the past 4600 years. The present desert pastures of Southern Tibet most probably replaced forests of Juniperus convallium, J. tibetica and Cupressus gigantea along with Prunus mira and Buddleja crispa in the understorey. Paleosol investigations and determined charcoal indicate a likeliness of forest destruction followed by increased erosion and sedimentation of colluvial soils. For the first time cereal pollen types could be clearly distinguished in southern Tibet. Juniperus pollen has been proved to have only a short dispersal range. The presence of cereal pollen and other human indicator pollen proves that it is more likely that human activity rather than climatic changes caused the forest decline during the younger Holocene. Successful non-irrigated reforestation trial experiments since 1997 on southern slopes around Lhasa with indigenous Cupressaceae have demonstrated that desertification of southern Tibet is a reversible process. As Lhasa receives 443 mm annual precipitation and has summer temperatures of above 10 °C it follows that the natural vegetation should be a forest, as opposed to the desert status quo that presides at present.

Reinvestigation of the interglacial pollen flora at Leveäniemi, Swedish Lapland

The till‐covered organic sediments at Leveäiemi, Swedish Lapland have been reinvestigated by pollen analysis in order to gather more detailed information on vegetation history and climatic conditions during the interglacial period represented at this site. A partly different picture of the vegetation succession has arisen compared to earlier studies and results. The organic sequence is still correlated with the Eemian, but the forests were probably more open during the initial and later parts of the interglaciation than suggested earlier. This is based on the higher values of Juniperus pollen noted, and a continuous curve for Populous pollen during the PAZ representing the later part of the interglaciation. Comparisons are made with other sites in northern Sweden, Finland and northern Norway, and the possibilities of separating Eeinian deposits from those formed during the Holsteinian interglaciation are discussed.

Late‐glacial and early Holocene vegetation of Snowdonia

summaryDetailed pollen and lithostratigraphic analyses of lake deposits at Clogwyngarreg provide a comprehensive record of vegetational and environmental change in the lowlands of Snowdonia, north Wales during the late‐glacial and early Holocene. A radiocarbon determination suggests that the low lands were ice free by at least c. 13 500 BP. and thiit by that time open habitat herhaceous taxa, including abundant Rumex spp. were colonizing the recently deglaciated ground. The initial pioneer grassland communities Were gradually invaded by Juniperus and Betula, hut the development of birch woodland was limited. An interstadial episode, the lute‐glacial lnterstadial (Windermere Interstadial) is recognized in the sequence of plant succession that culminated m the establishment of juniper. A significant decline in Juniperus pollen frequencies and an increase in Cramineae, in the absence of an expansion in birch woodland, suggests that environmental conditions in the mid‐ to late‐late ‐glacial Interstadial were less favourable m juniper than those of the early‐middle Interstadial. Towards the top of the Interstadial organic sequence fluctuations in the Juniperus pollen curve, coupled with high Isoetes spore values and the deposition of a stone horizon, suggest local instability and re‐working prior to the deposition of Loch Lomond (Younger Dryas) Stadial mini‐rofjenic sediments. By c. 11 000 BP widespread solifluction and increasingly severe environmental conditions led to a breakup of existing plant communities and a proliferation of open habitat and disturbed ground taxa. During the Loch Lomond (Younger Dryas) Stadial, glaciers reoccupied the higher cwms of Snowdonia. Climatic amelioration, marking the Holocene at c. 10 000 yr BP, was characterized by a rapid expansion of Juniperus at Clogwyngarreg and evidence for early Holocene woodland development is presented.

Modern pollen rain and vegetation on the edwards plateau, texas

Abstract Modern pollen samples were collected from seven major woody plant communities across the Edwards Plateau, Texas. Arboreal pollen averaged 70% of the total pollen, and Quercus, Juniperus and Pinus were dominant arboreal types. Pinus and Quercus were overrepresented in the modern pollen spectra in comparison to their abundance in the vegetation, while Juniperus pollen was underrepresented. Predominant non‐arboreal pollen types were Gramineae, Chenopodiaceae‐Amaranthaceae and Compositae. Arboreal and non‐arboreal pollen were significantly correlated to vegetation canopy cover. Quercus was the only arboreal genus that showed a significant relationship between canopy cover and pollen. Results from this study were compared to modern pollen data from the Post Oak Savanna and western Edwards Plateau. No samples from any region equalled the abundance of Quercus found in this study. Two modern pollen samples showed strong similarities to several fossil pollen records from the western Edwards Plateau. Data ...

AN EARLY FLANDRIAN VEGETATIONAL RECORD FROM THE FLOOR OF THE BRISTOL CHANNEL

SUMMARYA palynological and plant macrofossil study of a short core of organic sediment from the floor of the Bristol Channel at –36 m (–120 feet) O.D. is presented and discussed. The fossil assemblages were deposited in a freshwater pond and reedswamp. This sediment, the deepest yet examined for Flandrian pollen in the Bristol Channel, is overlain by what are interpreted as intertidal sediments and indicates the approximate sea level and position of the coastline of South Wales about 9500 years B.P. The open nature of the vegetation in the area around the site of deposition is indicated by the presence of Juniperus pollen. Of the only two tree pollen types present Betula is far more frequent than Pinus, a feature common to the early Flandrian of southwest England and northwest France. The age ascribed to this deep sediment is consistent with other observations on submerged deposits both in the Bristol and English Channels.

LATE‐GLACIAL DEPOSITS NEAR CAPEL CURIG, CAERNARVONSHIRE

SummaryInvestigations into former lake basins in the region to the north of Capel Curig (SH 721581) in Caernarvonshire have revealed deposits of Late‐glacial age. Pollen analysis of the deposits permits subdivision of the sequence into the standard Late‐glacial zones I, II and III together with some sub‐zones based upon recurring pollen assemblages. Some of the ecological implications of these assemblages are discussed, in terms of vegetation, climate and soils. High Rumex* pollen values characterize pollen zone I. A wide range of herbs and Betula pollen dominate in zone II. Zone III is characterized by high Artemisia pollen values. A transition zone III–IV is included to cover the Empetrum and Juniperus pollen peaks, prior to the rapid rise in Betula pollen values in zone IV.