Non-arboreal Pollen Research Articles

The importance of local‐scale openness within regions dominated by closed woodland

AbstractNew and existing pollen data from Wales, UK, are used to assess the level of landscape openness at the regional and local scale. At the regional scale, the existing pollen data support the high‐forest model of vegetation structure by 6000 cal. yr. BC prior to any palynological signal for anthropogenic impact in the region. New data from two sites in southwest Wales follow the general regional pattern of early to middle Holocene vegetation succession, but are striking owing to maintenance of high non‐arboreal pollen percentages (NAPs) throughout the mid‐Holocene. It is argued that these NAPs indicate that a significant degree of openness can be found at the local level (and beyond the confines of the peat‐forming site) within regions characterised by closed woodland. It is possible that woodland development in these areas may have been suppressed by reduced drainage, although the role of grazing animals in maintenance of clearings cannot be assessed. Implications for this local degree of openness are discussed, in particular the significance of vegetation heterogeneity at the local scale for the construction of place or locale for prehistoric communities. Copyright © 2006 John Wiley & Sons, Ltd.

Surface pollen deposition on glacier forelands in southern Norway I: local patterns of representation and source area at Storbreen, Jotunheimen

The relationship between vegetation and surface pollen deposition is examined at Storbreen glacier foreland where a clear plant succession exists. The aim is to determine whether the distinct plant communities present produce characteristic pollen assemblages. The influence of environmental factors is also considered. Pollen assemblages from moss polsters, collected from 22 paired sampling sites across the foreland, are compared with local vegetation. Two-way indicator species analysis and detrended correspondence analysis are employed to identify clusters and sequences, initially in the vegetation data and subsequently in the pollen data sets. Vegetation and pollen data are compared simultaneously using canonical correspondence analysis. Three main plant communities are distinguished: pioneer, heath and snowbed. Broadly, each community produces characteristic pollen assemblages. Boundaries between groups are not clear-cut, reflecting the mosaic of plant communities present. Recognition of distinct plant communities is hampered by the prevalence of long-distance arboreal pollen and poor representation of entomophillously pollinated taxa. Late in the succession up to 78% of pollen could originate locally. Use of the non-arboreal pollen sum significantly improves correspondence with vegetation. The importance of indicator taxa is considered and both Salix and Empetrum are found to distinguish successfully early phases of succession from later phases. Strong correlations exist between the primary ordination axes of vegetation and pollen and with terrain age and altitude (for example, the correlation between altitude and total land pollen Axis 1 is r= -0.76). The surface data add new information to the interpretation of tree colonization in the area during the Holocene.

Late Glacial and Holocene vegetational history of the Altai Mountains (southwestern Tuva Republic, Siberia)

Two lakes of glacial origin (Grusha at 2413 m and Akkol at 2204 m) are located on a broad high-mountain plateau on the dry eastern end of the Russian Altai Mountains in the Republic of Tuva, just north of Mongolia. The present vegetation of the area is an open high-mountain tundra–steppe mosaic, with patches of Larix and Pinus sibirica forests on north-facing slopes 30 km northwest of the lakes. Alpine meadows occur near streams and snow patches. Pollen diagrams and radiocarbon dates (16 for Grusha and 12 for Akkol) were used to reconstruct the vegetational history since the last glaciation. The core from Grusha contains about 50 cm of Late Glacial sediment of relatively low organic content, mostly correlated with the Younger Dryas episode because of the high percentages of Artemisia, Gramineae, and Chenopodiaceae, along with a diversity of non-arboreal pollen types indicating tundra–steppe and meadow-steppe. In the earliest Holocene, starting with increased organic matter at about 195 cm (12,000 cal. yr BP), the Artemisia–Gramineae–Chenopodiaceae pollen assemblage continued, along with an increase in shrub Betula but without the diversity of minor non-arboreal types. The interpretation of dry and warm climate at this time is supported by the unconformity at Akkol, implying a dried lake. Then after about 1000 years the increase of Pinus sibirica, P. sylvestris, Picea obovata, and Abies sibirica suggests that forests developed in response to increased humidity, first at the higher-elevation Grusha, and then at Akkol. After about 6000 cal. yr BP the role of forests decreased sharply in the area. The Picea and Abies components almost disappeared, as they did also in more westerly areas of the Altai Mountains. Steppe elements increased along with alpine herbs, especially after 2000 cal. yr BP as a result of cooling or increased aridity, as well as probable human activity. Correlation of the vegetation sequence for the Tuva sites with those to the west in the central Altai Mountains indicates that the Late Glacial open landscapes persisted in the earliest Holocene but then were invaded by coniferous forests as a result of increased moisture and temperature associated with Atlantic storm systems as well as with insolation-enhanced Asian monsoon. Cooling and drying after about 6000 cal. yr BP brought the decline of Abies and Picea and the expansion of tundra–steppe.

Elevational gradients during the Late-Glacial/Holocene vegetational transition in southern Bulgaria

The Late Glacial and early-Holocene vegetational history of a newly dated pollen and macrofossil diagram from Besbog, a cirque lake at 2250 m just above the forest limit in the Pirin Mountains of southwestern Bulgaria, is compared with a newly dated pollen diagram for the mire Shiroka Polyana at 1400 m in the conifer forest of the nearby Rhodope Mountains in order to investigate the chronology of major changes in the vegetation at different elevations. In the Lake Besbog record the non-arboreal pollen assemblage of the Late Glacial changed abruptly to that of Betula, Quercus and other deciduous types. The date for this change is about 11.6 ka cal b.p. The Quercus assemblage may be composed of pollen blown from intermediate elevations, to which deciduous forest had expanded because of higher summer temperatures related to high summer insolation. At Shiroka Polyana (1400 m) in the modern conifer belt, a similar change did not occur until about 8.8 ka cal b.p. The persistence of the dry steppe or steppe forest in the early Holocene at this lower site can also be attributed to high summer insolation. Thus as atmospheric temperature increased at the end of the Late Glacial, deciduous forests expanded first at intermediate elevations in the Pirin Mountains and only later in the Rhodope Mountains at lower elevations as summer insolation decreased.

Natural and anthropogenic forcing of aquatic macrophyte development in a shallow Danish lake during the last 7000 years

AbstractAim To investigate the long‐term changes in aquatic vegetation in a lowland, shallow lake, and to assess the relationship between aquatic vegetation and natural and anthropogenic catchment changes.Location Gundsømagle Sø, Zealand, Denmark: a shallow (mean depth 1.2 m), hypereutrophic lake (mean annual total phosphorus (TP) c. 700 μg TP L−1) located in a predominantly agricultural catchment (88% cultivated land). The lake is presently devoid of macrophytes.Methods One hundred and forty‐seven contiguous samples from a sediment core (taken in 2000) were analysed for macrofossil remains together with loss‐on‐ignition and dry weight. From an earlier sediment core (taken in 1992), 67 samples were analysed for pollen and the two cores were correlated using the ignition residue profiles. Core chronology was determined by 210Pb and 137Cs dating of the recent lake sediments, while older sediments were dated by pollen‐stratigraphical correlation, as 14C dating proved problematical. Aquatic macrofossil abundance was used to reconstruct past changes in the lake's plant community and water‐level. The contemporary catchment land‐use change was inferred from sedimentary pollen data, and soil erosion to the lake was deduced from the minerogenic content of the lake sediments.Results The macrofossil record covers the last 7000 years, but aquatic plant remains were scarce prior to c. 1300 bc. After this date the abundance of submerged and emergent macrophyte remains increased dramatically, paralleled by an increase in sediment minerogenic matter and non‐arboreal pollen (NAP). Aquatic plant remains were abundant for more than 3000 years until the mid 1900s. Macrofossils of Linum usitatissimum (L.) (flax) and high pollen percentages of ‘Cannabis type’ (hemp) were recorded in periods between c. 1150 bc and 1800 ad.Main conclusions Our study suggests that, between c. 5000 bc and 1300 bc, the submerged plant community was confined to the littoral zone. From 1300 bc onwards, the submerged macrophyte vegetation expanded rapidly across the lake bed, presumably as a response to lake shallowing caused by a combination of climatic‐induced water‐level lowering and enhanced erosional infilling of the lake basin due to intensified anthropogenic activities in the catchment. The lake was meso‐eutrophic and had an extensive and diverse aquatic flora for more than 3000 years, until the middle of the twentieth century. In periods between c. 1150 bc and 1800 ad, the lake experienced direct anthropogenic impact from retting of fibre plants (Linum and Cannabis). Over the last 200 years, erosional infilling of the lake basin increased drastically, probably as a result of agricultural intensification. In the twentieth century, the lake was strongly affected by nutrient enrichment from both point sources (sewage from built‐up areas) and diffuse agricultural run‐off which led to hypertrophic conditions and the collapse of the submerged vegetation c. 1950–60. The concept of ‘naturalness’ and the implications for lake conservation are discussed.

23,000 yr of vegetation history of the Upper Lerma, a tropical high-altitude basin in Central Mexico

Pollen analysis on a 9.54-m sediment core from lake Chignahuapan in the upper Lerma basin, the highest intermontane basin in Central Mexico (2570 m asl), documents vegetation and limnological changes over the past ∼23,000 14C yr. The core was drilled near the archaeological site of Santa Cruz Atizapán, a site with a long history of human occupation, abandoned at the end of the Epiclassic period (ca. 900 AD). Six radiocarbon AMS dates and two well-dated volcanic events, the Upper Toluca Pumice with an age of 11,600 14C yr B.P. and the Tres Cruces Tephra of 8500 14C yr B.P., provide the chronological framework for the lacustrine sequence. From ca. 23,000 14C yr B.P. to ca. 11,600 14C yr B.P. the plant communities were woodlands and grasslands based on the pollen data. The glacial advances MII-1 and MII-2 correlate with abundant non-arboreal pollen, mainly grasses, from ca. 21,000 to 16,000 14C yr B.P., and at ca. 12,600 14C yr B.P. During the late Pleistocene, lake Chignahuapan was a shallow freshwater lake with a phase of lower level between 19,000 and 16,000 14C yr B.P. After 10,000 14C yr B.P., tree cover in the area increased, and a more variable lake level is documented. Late Holocene (ca. 3100 14C yr B.P.) deforestation was concurrent with human population expansion at the beginning of the Formative period (1500 B.C.). Agriculture and manipulation of the lacustrine environment by human lakeshore populations appear at 1200 14C yr B.P. (550 A.D.) with the appearance of Zea mays pollen and abundant charcoal particles.

Vegetation and environmental record in the northern East China Sea during the late Pleistocene

In order to understand fluctuations in terrestrial and marine environments influenced by the East Asian Monsoon during the last 42 kyr, we investigated a sedimentary core MD982195 collected from the northern East China Sea (ECS), one of the largest marginal seas in the world. The total abundance of pollen and spores varies from 4.8 to 22.3×10 3 grains g −1. The pollen and spores can be grouped to represent six local zones of pollen assemblage based on their abundance and assemblages. Pollen assemblage found in the modern condition (zone MD2195-6) is consistent with the present vegetation found in Kyushu, Japan. Cooler condition with high rainfall can be estimated in zone MD2195-1 (42–40.5 ka). Larger area of continental shelf in the ECS and Yellow Sea was exposed to the land during the large drop in the sea level in zones MD2195-2 (40.5–17 ka) and -3 (17–14 ka). High abundance of nonarboreal pollen in Zones MD2195-2 and -3 is attributed to reduced distance, exposed continental shelf and ocean current system. Rainfall could have been diminished in zone MD2195-2. Climate could begin to warm up in zone MD2195-3. Sharp decrease in abundance of nonarboreal pollen due to rapid transgression characterizes zone MD2195-4 (14–8 ka). Warm temperate-subtropical evergreen broad-leaved pollens developed in zone MD2195-5. The occurrence of Phyllocladus, originating from high land of New Guinea, Indonesia Maritime Continent and Philippines, between upper zone MD2195-2c and zone MD2195-4 suggests that Kuroshio Current flowed through the ECS during the last glacial times.

Variations in organic matter composition in sediments from Lake Huguang Maar (Huguangyan), south China during the last 68 ka: implications for environmental and climatic change

This study presents a continuous and long-term palaeoenvironmental and palaeoclimatic record from a lacustrine sediment core (Lake Huguang Maar) at the northern coast of the South China Sea, extending back to about 68 cal ka BP. We provide a comprehensive ecosystem analysis from the opportunity to combine organic geochemical and palynological data. Several climatically induced changes to the flora and fauna have been recognised. From 68 to 58 and 48 to 40.5 cal ka BP, relatively depleted δ 13C TOC (−31.3 to −25.0‰) and δ 13C values of mid- and long-chain n-alkanes (−34.3 to −30.2‰), as well as high percentages of tropical pollen, indicate a vegetation dominated by subtropical/tropical forest (C 3 plants). An expansion of a mixed C 3/C 4 open grassland between 58 and 48 and particularly after 40.5 cal ka BP mirrors drier climatic conditions, in conjunction with a lowering of atmospheric CO 2 concentrations; δ 13C TOC (−24.1 to −16.8‰) and δ 13C values of n-alkyl lipids (−28.9 to −24.1‰) are heavier, higher percentages of non-arboreal pollen were observed and the wood/grass lignin index (WGLI) from open pyrolysis (Py–GC) indicates a higher input of grass lignin. Abundant oxidised terrigenous particles that resulted from increased fire activity and/or greater erosion rates are a further hint of enhanced dryness. The clear drop in moisture availability suggests that this site is sensitive in fluctuations of the summer and winter monsoon activity in accordance with other proxy records in south-east Asia. The response of the aquatic ecosystem is documented by an extremely large δ 13C shift of algal-derived botryococcenes from −35.4 to −6.2‰, which records a change towards a bicarbonate carbon source at low dissolved CO 2 concentrations.

Palaeogeographic and palaeoclimatic evolution of the Po Plain from 150-ky core records

Integrated sedimentological and micropalaeontological (foraminifers, ostracods, pollen) analyses of eight continuously cored boreholes, up to 140 m deep, reveal the depositional history and the palaeoclimatic evolution of southeastern Po Plain (northern Italy) over the last 150 ky. Age assignments are supported by the chronostratigraphic sequence framework calibrated by radiocarbon and pollen data, allowing detailed correlation with the oxygen-isotope record. Facies analysis (including identification of 12 distinct microfossils associations) and detailed stratigraphic correlations across several tens of km document a cyclic sedimentation pattern (including continental, coastal and shallow-marine deposits), which defines two transgressive–regressive sequences, deposited over the last two interglacial–glacial cycles. Two prominent stratigraphic markers, corresponding to wedge-shaped coastal sand bodies, are recorded between 0–30 and 100–125 m core depths. These sedimentary bodies were deposited during the two major transgressive pulsations and subsequent sea-level highstands of the last 150 ky, assigned to the Holocene and the Tyrrhenian (oxygen-isotope Substage 5e), respectively. The stratigraphic architecture of post-Substage 5e deposits shows consistent patterns of coastal evolution with changing sea-level position. Lowering of sea level between 125 and 70 ky (onset of Substages 5d and 5b, and Stage 4) resulted in extensive and repeated basinward shifts of facies, which can be observed across closely spaced unconformity surfaces associated to alluvial plain sedimentation (falling-stage systems tract). The general phase of sea-level fall was punctuated by short transgressive phases (Substages 5c, 5a and Stage 3 interstadials), which led to widespread deposition of organic-rich (lagoonal and swamp) deposits. Upper Stage 3 and Stage 2 deposits (lowstand systems tract) are replaced across a significant part of the study area by a hiatal surface. Holocene interglacial deposits are characterized by a retrogradational stacking pattern of coastal plain and littoral facies (transgressive systems tract), reflecting invariably the landward migration of a barrier–lagoon–estuary system. Subsequent highstand deposition (highstand systems tract) was characterized by extensive progradation of wave-influenced deltas and strandplains. The two major transgressive surfaces, of Tyrrhenian and Holocene age, are considerably easier to identify than the other key surfaces for sequence stratigraphic interpretation. The lowermost transgressive deposits display a pollen signature diagnostic of warm climate (interglacial) periods, showing wide forest development and relatively high pollen concentrations. By contrast, the deposits overlying the unconformable surfaces related to successive phases of sea-level fall are fingerprinted by pollen spectra dominated by Pinus and non-arboreal pollen types, with very low pollen concentrations, reflecting the onset of a stable cold climate vegetation characteristic of stadial to fully glacial conditions. The good match between facies architecture, pollen distribution and global sea-level evolution strongly suggests that Late Quaternary sedimentation in the Po Basin developed under a predominantly glacio-eustatic control. Stratigraphic architecture of the Po Basin thus can provide a useful analog for interpretation and correlation in the stratigraphic record of very rapid glacio-eustatic (fourth-order) cycles, with frequencies of about 100 ky.

Late‐glacial and early Holocene changes in vegetation and lake‐level at Hauterive/Rouges‐Terres, Lake Neuchâtel (Switzerland)

AbstractPalynological and sedimentological analyses of a sedimentary sequence sampled at Hauterive/Rouges‐Terres, Lake Neuchâtel (Switzerland) provide documentation of changes in vegetation and lake‐level during the Bølling, Younger Dryas and Preboreal pollen zones, and have allowed a comparison with sequences covering the same period from other sites located in the western part of the Swiss Plateau. The Juniperus–Hippophaë zone (regional pollen assemblage zone (RPAZ) CHb‐2, first part of the Bølling, ca. 14 650–14 450 cal. yr BP) was characterised by a generally low lake‐level. A weak rise occurred during this zone. The Juniperus–Hippophaë to Betula zone transition coincided with a lake‐level lowering, interrupted by a short‐lived but marked phase of higher lake‐level recorded at the neighbouring site of Hauterive‐Champréveyres, but not present at Hauterive/Rouges‐Terres owing to an erosion surface. Shortly after the beginning of the Betula zone (RPAZ CHb‐3, second part of the Bølling, ca 14 450–14 000 cal. yr BP), a marked rise in lake‐level occurred. It was composed of two successive periods of higher level, coinciding with high values of Betula, separated by a short episode of relatively lower lake‐level associated with raised values in Artemisia and other non‐arboreal pollen. The last part of RPAZ CHb‐3 saw a fall in lake‐level. The lower lake‐levels during RPAZ CHb‐2 to early RPAZ CHb‐3 can be correlated with the abrupt warming at the beginning of the Greenland Interstadial (GI) 1e thermal maximum. The successive episodes of higher lake‐level punctuating the GI 1e might be linked to the so‐called Intra‐Bølling Cold Oscillations identified from several palaeoclimatic records in the North Atlantic area, and also documented in oxygen‐isotope data sets from Swiss Plateau lakes. The Hauterive/Rouges‐Terres lake‐level record provides evidence for marked climatic drying through the second part of the Younger Dryas event (GS1), during the GS1–Preboreal (RPAZ CHb‐4b–4c) transition (except for a rise at ca. 11 450–11 400 cal. yr BP), and at the RPAZ CHb‐4c–5 (Preboreal–Boreal) transition, following the Preboreal Oscillation (after 11 150 cal. yr BP). The Preboreal Oscillation coincided with higher lake‐levels, its end being followed by a rapid expansion of Corylus, Quercus, Ulmus and Tilia. The Hauterive/Rouges‐Terres lake‐level record suggests that radiocarbon plateau at 12 600, 10 000 and 9500 14C yr BP corresponded to periods of generally lower lake‐level. This suggests that an increase in solar activity may have contributed to both climatic dryness and a decrease in atmospheric radiocarbon content. Copyright © 2002 John Wiley & Sons, Ltd.

A high resolution stable isotope record of the penultimate deglaciation in lake sediments below the city of Amsterdam, The Netherlands

A detailed record of the deglaciation history of the penultimate glacial to interglacial transition is given, mainly based on the stable isotopes of calcium carbonate-containing lake sediments in a glacially excavated depression below the city of Amsterdam. Initially, this depression, the Amsterdam Basin, formed part of a lake covering the western and central part of the Netherlands and extending for an unknown distance into the present North Sea. Annual layer counting shows that the lake drained after about a millennium, leaving shallow pools in the remaining depressions. The latter changed again into larger and deeper lakes including the Holland Lake during the rise of sea level in the early Eemian. Oxygen isotope values of the early lake sediments indicate an interglacial summer climate, but the nearness of dead-ice fields caused severe winters. The isotope record is furthermore characterized by the influx of large amounts of isotopically light water supplied by the river Rhine. A change to much colder conditions occurred simultaneously with the draining of the Holland Lake, as appears from oxygen isotope values and the sudden increase in non-arboreal pollen. This interval is correlated with the Kattegat Stadial and the sea-level standstill of Aladdins Cave on the Huon Peninsula of New Guinea. A short climate wiggle occurs at the end of this interval. The onset of the Eemian is marked by a rapid warming of ∼5°C which extends into local pollen-zone E3. Provided that our correlation of this cold interval with the sea-level standstill of Aladdins Cave is correct, the time interval between the earliest lake sediments in the Amsterdam Basin and the Eemian highstand took about 5–6 millennia.

Late Pliocene vegetation and climate of the Lake Baikal region, southern East Siberia, reconstructed from palynological data

Palynomorphs from a palaeomagnetically dated Late Pliocene sediment core (3.6–2.35 Ma) reflect highly variable climatic conditions and repeated expansion of steppe and boreo-alpine vegetation. Mixed coniferous forests ( Picea, Tsuga, Pinus) with associated broadleaved taxa ( Quercus, Corylus, Ulmus, Tilia) were affected by dry and cold intervals already between 3.48 and 3.39 Ma. Peak records of non-arboreal pollen types and spores, including subarctic-boreo-alpine Selaginella selaginoides, evidence advances of open vegetation, which can be correlated to glacial marine oxygen isotope stages. A cooling trend occurred from 3.15 Ma to 2.5 Ma, documented by cold–dry intervals and increased fluctuations of Picea and Pinus. Around 3–2.9 Ma the palaeoclimate variation pattern shifted towards cold–dry and warm–moist oscillations. Cooling strengthened after 2.89 Ma and severely restricted Tsuga development. Cool and oligotrophic limnic conditions are documented by abundant Gonyaulax dinoflagellate cysts in the interval 2.65–2.57 Ma. Due to decreasing precipitation extensive areas with open steppe and rock-steppe vegetation became permanently established after 2.62 Ma. Dry conditions became a dominant environmental factor in the Baikal region, coeval in time with the Red Clay–Loess shift in northern China. This climatic transition can be explained as a consequence of major intensification of Northern Hemisphere Glaciation around 2.75 Ma evidenced by marine records of ice-rafted debris.

A new Lateglacial chronostratigraphic tephra marker for the south-eastern Alps: The Neapolitan Yellow Tuff (NYT) in Längsee (Austria) in the context of a regional biostratigraphy and palaeoclimate

Längsee is a small meromictic lake in Carinthia, SE Alps, with partially varved Lateglacial sediments. The Längsee tephra correlates to the Neapolitan Yellow Tuff (NYT), an eruption from the Campanian Volcanic Province, Italy. This tephra provides a Lateglacial chronostratigraphic time marker from central Italy across the Adriatic Sea to the southeastern Alps. The Längsee tephra is discussed in the context of pollen, geochemical, and microstratigraphical data from a profundal sediment core from Längsee. The age of 14,120 cal yr BP for the NYT has been accepted from the Monticchio chronology. The timescale for the Lateglacial in the Längsee record is based on laminae counts and has been linked to calendar year ages using the NYT tephrachronological marker. Consequently, the mass expansion of Betula has been dated at 14,270 cal yr BP. The expansion of P. sylvestris started concurrent with the NYT, and about 180 yr later, at 13,940 cal yr BP, P. sylvestris forests were established. The Younger Dryas biozone at Längsee is characterized only by a slight increase in non-arboreal pollen and dominated by pine with visible variations only in pine pollen types. Differentiation of pine pollen types allowed the recognition of three minor fluctuations during the Lateglacial interstadial. Two of these oscillations tentatively have been correlated with the Aegelsee and Gerzensee oscillations in Switzerland as well as with vegetation changes in NW Germany.

The role of human disturbance in Late Holocene vegetation changes on Kullaberg, southern Sweden

A pollen record from a small peatland located on Kullaberg in northwestern Skane, southern Sweden, revealed that grazing pressure might have been the major disturbance agent controlling the vegetation, at least from ca. 1500 B. C. until the latter part of the nineteenth century. The pollen data also indicate a step-by-step increase in grazing pressure, expressed as a marked increase in non-arboreal pollen representation at ca. 1500 B. C., A. D. 650 and A. D. 1650. The increase at A. D. 650 probably indicates a more regular and intensive use of the area, resulting in a forest structure that was much more open than earlier, together with an expansion of Fagus, which rapidly replaced Quercus as the local forest dominant. At about this time the first patches of heath vegetation originated, but they probably only covered a small part of Kullaberg. Larger areas with an intensively grazed Calluna heath, as shown by eighteenth century maps, probably evolved around ca. A. D. 1650, when much of Kullaberg seems to have been deliberately deforested.

Palynological study of the drilled sediments from the Kathmandu Basin and its palaeoclimatic and sedimentological significance

Palynological study of a series of slimes obtained from a 284-m-long drill well in the Kathmandu Basin revealed palaeoclimatic records and deposition al environmental changes in the Kathmandu Valley during the last 2.5 myr. The slimes consist of fluvio-deltaic and lacustrine sediments comprising 218 m long muddy beds and 66.3 m of sandy beds. As a result of palynological study on the 189 pieces of slime, a total 43 types of fossil pollen and spores were identified. They comprise arboreal pollen of one family and 20 genera, non-arboreal pollen of 10 families and 10 genera and spores. In the pollen diagram, Quercus and Cyclobalanopsis are predominant, with frequencies exceeding 70%. Pinus, Alnus and Gramineae are the next dominant taxa. Three fossil pollen zones, which reflect major climatic change, were discriminated: Zone I indicates a cool climate from ca. 2.5 to 2.1 Ma; Zone II shows a warm and relatively dry climate without remarkable fluctuation from ca. 2.1 to 1.0 Ma; and Zone III is characterized by seven cycles of warm-and-wet and cold-and-dry climate from 1.0 Ma to present, which reflect the repetition of glacial and interglacial periods. The last cold maximum at 11 m depth seems to correspond to the last glacial age around 20 kyr B.P.
 The sedimentation rate of the drill-well was estimated from an approximate age-depth plot based on approximate ages inferred by comparison between the palaeoclimatic curve drawn by pollen analysis and δ18O curve obtained from planktonic foraminifers of deep-sea sediments in the Indian Ocean. Consequently, the average sedimentation rate of the uppermost part from 115 m to 11 m in depth is estimated at 104 mm/kyr.

Pollen influx into Tauber traps in Estonia in 1997–1998

Modern pollen trapping data, obtained in the years 1997 and 1998 from 32 modified Tauber traps in different landscape regions of Estonia, are discussed. Preliminary analyses have revealed great variability of pollen influx values. The influx of arboreal pollen (AP) in 1998 was in general three to four times higher than in 1997. In both years, Betula and Alnus pollen dominated, accounting for up to 70% of total AP. The share of non-arboreal pollen (NAP) was much higher in pollen traps than in samples from lake and bog sediments and this reflects the influence of very local vegetation. Cerealia-type pollen influx values are closely correlated with the distance of the study site from the nearest field and also show the existence of some background values in the atmosphere.

Modern pollen samples from alpine vegetation on the Tibetan Plateau

Abstract A set of 316 modern surface pollen samples, sampling all the alpine vegetation types that occur on the Tibetan Plateau, has been compiled and analysed. Between 82 and 92% of the pollen present in these samples is derived from only 28 major taxa. These 28 taxa include examples of both tree (AP) and herb (NAP) pollen types. Most of the modern surface pollen samples accurately reflect the composition of the modern vegetation in the sampling region. However, airborne dust‐trap pollen samples do not provide a reliable assessment of the modern vegetation. Dust‐trap samples contain much higher percentages of tree pollen than non‐dust‐trap samples, and many of the taxa present are exotic. In the extremely windy environments of the Tibetan Plateau, contamination of dust‐trap samples by long‐distance transport of exotic pollen is a serious problem. The most characteristic vegetation types present on the Tibetan Plateau are alpine meadows, steppe and desert. Non‐arboreal pollen (NAP) therefore dominates the pollen samples in most regions. Percentages of arboreal pollen (AP) are high in samples from the southern and eastern Tibetan Plateau, where alpine forests are an important component of the vegetation. The relative importance of forest and non‐forest vegetation across the Plateau clearly follows climatic gradients: forests occur on the southern and eastern margins of the Plateau, supported by the penetration of moisture‐bearing airmasses associated with the Indian and Pacific summer monsoons; open, treeless vegetation is dominant in the interior and northern margins of the Plateau, far from these moisture sources. The different types of non‐forest vegetation are characterized by different modern pollen assemblages. Thus, alpine deserts are characterized by high percentages of Chenopodiaceae and Artemisia, with Ephedra and Nitraria. Alpine meadows are characterized by high percentages of Cyperaceae and Artemisia, with Ranunculaceae and Polygonaceae. Alpine steppe is characterized by high abundances of Artemisia, with Compositae, Cruciferae and Chenopodiaceae. Although Artemisia is a common component of all non‐forest vegetation types on the Tibetan Plateau, the presence of other taxa makes it possible to discriminate between the different vegetation types. The good agreement between modern vegetation and modern surface pollen samples across the Tibetan Plateau provides a measure of the reliability of using pollen data to reconstruct past vegetation patterns in non‐forested areas.

Diatom, Pollen, and Chemical Evidence of Postglacial Climatic Change at Big Lake, South-Central British Columbia, Canada

Postglacial climatic conditions were inferred from cores taken from Big Lake in southern British Columbia. Low concentrations of nonarboreal pollen and pigments near the base of the core suggest that initial conditions were cool. Increases in both aquatic and terrestrial production suggest warmer and moister conditions until ∼8500 cal yr B.P. Hyposaline diatom assemblages, increases in nonarboreal pollen, and increased concentrations of pigments suggest the onset of arid conditions from ∼8500 to ∼7500 cal yr B.P. Slightly less arid conditions are inferred from ∼7500 until ∼6660 cal yr B.P. based on the diatoms, small increases and greater variability in biogenic silica and pigments, and higher percentages of arboreal pollen. At ∼6600 cal yr B.P., changes in diatoms, pigments, biogenic silica, and organic matter suggest that Big Lake became fresh, deep, and eutrophic until ∼3600 cal yr B.P., when water levels and nutrients decreased slightly. Our paleoclimatic inferences are similar to pollen-based studies until ∼6600 cal yr B.P. However, unlike these studies, our multiple lines of evidence from Big Lake imply large changes in effective moisture since 6000 cal yr B.P.

Modern pollen and stomate deposition in lake surface sediments from across the treeline on the Kola Peninsula, Russia

We sampled and analyzed surface sediments from 31 lakes along a latitudinal transect crossing the coniferous treeline on the Kola Peninsula, Russia. The major vegetation zones along the transect were tundra, birch-forest tundra, pine-forest tundra, and forest. The results indicate that the major vegetation types in our study area have distinct pollen spectra. Sum-of-squares cluster analysis and principal components analysis (PCA) groupings of pollen sites correspond to the major vegetation zones. PCA ordination of taxa indicates that the first axis separates taxa typical of the forest zone ( Pinus, Picea) from taxa typical of tundra and forest-tundra zones (Polypodiaceae, Ericaceae, and Betula). The current position of the coniferous treeline, defined in our region by Pinus sylvestris, occurs roughly where Pinus pollen values reach 35% or greater. Arboreal pollen (AP)/non-arboreal pollen (NAP) ratios were calculated for each site and plotted against geographic distance along the transect. AP/NAP ratios of 7 or greater are found within pine-forest tundra and forest vegetation zones. Pinus stomates (dispersed stomatal guard cells) are absent from sites north of the coniferous treeline and all but two samples from the forested sites contain stomates. Stomate concentrations among the samples are highly variable and range from 10 to 458 per ml and positively correlate with the changing Pinus pollen values.

Comparison of intradiurnal variation of airborne pollen in Mar del Plata (Argentina). Part I. Non-arboreal pollen

Intradiurnal variation of non-arboreal pollen (NAP) aredescribed in relation to the associated weather using the data obtainedwith a Burkard trap in Mar del Plata city, for a three year data set(1988, 1992 and 1995). The daily pattern of concentration was quitehomogeneous during the years analysed except for 1995, when it showed avariation due to the change of position of the station. Qualitativecomposition of the NAP airborne pollen was mainly represented byPoaceae, Plantago and Cyperaceae during the three years. The daily trendshowed high concentrations during daylight hours, when instability andconvective movements prevail, and low concentrations in the night, whenmeteorological conditions favour the development of a stable stratifiedlayer.