A 12 000-year record of environmental change in the Lomond Hills, Fife, Scotland: Vegetational and climatic variability

The Lomond Hills of Fife, an isolated upland area rising to over 500 m, provide an opportunity to investigate the effect of altitude on vegetation and climate in an area otherwise dominated by lower-lying land. The West Lomond site contains sediments of the Devensian Late-glacial period; they reveal a well-defined sequence of Bolling-Older Dryas-Allerod-Younger Dryas events, commencing ca. 12 190 radiocarbon years B.P. and a probable Amphi-Atlantic Oscillation between ca. 11 040 and 10 800 B.P. The Holocene record is constrained by low sediment input but does reveal a woodland presence at this altitude, dominated byBetula andCorylus. Size statistics forBetula pollen are presented and the implications of the vegetational and climatic record are discussed. The traditional view of a smooth progress towards more temperate conditions following the Younger Dryas is not supported; between 10 180 and 9120 B.P., three cooler periods are inferred, the earliest of which may belong to a terminal phase of the Younger Dryas. Comparative pollen ‘influx’ data strongly suggest thatQuercus,Ulmus andAlnus were not present locally. As a working hypothesis, it is suggested that the demise of woodland, from ca. 5950 B.P., was a result of exposure. Pollen indicative of human impact was probably derived from areas of lowland agricultural activity from ca. 5330 B.P. onwards.     

Vegetation and Climate Change during the Last Deglaciation in the Great Khingan Mountain,Northeastern China

The Great Khingan Mountain range, Northeast China, is located on the northern limit of modern East Asian Summer Monsoon (EASM) and thus highly sensitive to the extension of the EASM from glacial to interglacial modes. Here, we present a high-resolution pollen record covering the last glacial maximum and the early Holocene from a closed crater Lake Moon to reconstruct vegetation history during the glacial-interglacial transition and thus register the evolution of the EASM during the last deglaciation. The vegetation history has gone through distinct changes from subalpine meadow in the last glacial maximum to dry steppe dominated by Artemisia from 20.3 to 17.4 ka BP, subalpine meadow dominated by Cyperaceae and Artemisia between 17.4 and 14.4 ka BP, and forest steppe dominated by Betula and Artemisia after 14.4 ka BP. The pollen-based temperature index demonstrates a gradual warming trend started at around 20.3 ka BP with interruptions of several brief events. Two cold conditions occurred around at 17.2–16.6 ka BP and 12.8–11.8 ka BP, temporally correlating to the Henrich 1 and the Younger Dryas events respectively, 1and abrupt warming events occurred around at 14.4 ka BP and 11.8 ka BP, probably relevant to the beginning of the Bølling-Allerød stages and the Holocene. The pollen-based moisture proxy shows distinct drought condition during the last glacial maximum (20.3–18.0 ka BP) and the Younger Dryas. The climate history based on pollen record of Lake Moon suggests that the regional temperature variability was coherent with the classical climate in the North Atlantic, implying the dominance of the high latitude processes on the EASM evolution from the Last Glacial Maximum (LGM) to early Holocene. The local humidity variability was influenced by the EASM limitedly before the Bølling-Allerød warming, which is mainly controlled by the summer rainfall due to the EASM front covering the Northeast China after that.     

Upland vegetation in the north-west Iberian peninsula after the last glaciation: Forest history and deforestation dynamics

This paper presents the results of pollen analyses from organic sediments of seven cores (299 spectra) in a mountainous area of the north-west Iberian peninsula. The pollen diagrams, supported by seven¹⁴C dates, are used to construct a regional pollen sequence covering the main stages of vegetation dynamics, from the last phases of the Late-glacial until the present. During the Late-glacial Interstadial an important development of cryophilous forests (Betula andPinus) was recorded, although various mesophilous and thermophilous tree elements were also present. The Younger Dryas, palynologically clearly defined, is characterized by an important reduction in tree pollen percentages and the expansion of steppe formations (Poaceae andArtemisia). At the beginning of the Holocene, there was an expansion ofQuercus and a spread of other trees, which combined to give a vegetation cover of varied composition but dominated by mixed deciduous forests. Such forest formations prevailed in these mountains until 3000 years ago, when successive deforestation phases are recorded at various times as a result of increased farming activity. The results are compared with data from other mountainous areas in the northern Iberian peninsula and southern France.     

Weichselian interstadial pollen stratigraphy from Härjedalen,central Sweden

Weichselian interstadial vegetation history has been studied by means of pollen analysis of organic bearing fine-grained sediments at Dörrsvålen and Brovalltjärnen in a low mountain area in Härjedalen. The composition of the pollen flora suggests treeless vegetation consisting of shrubs and herbs. The interstadial vegetation consisted of Betula nana, Ericaceae, Juniperus and Salix spp. mixed with herbaceous plant communities including Gramineae, Cyperaceae, Caryophyllaceae, Saxifraga, Rumex/Oxyria and Polygonum. Betula and Pinus are represented by long distance-transported pollen. During the interstadial the climatic conditions seem to have been very harsh and continental as (cold) steppe plants reach high frequencies, e.g. Artemisia and Chenopodiaceae. The sediments are thought to have been deposited during an early Weichselian interstadial tentatively correlated with Tärendö in Norrbotten province, northern Sweden, and Odderade in Denmark and north-western Germany. Comparisons are made with other interstadial sites in central and northern Sweden, and in south-eastern Norway.     

A comparison of sedimentary DNA and pollen from lake sediments in recording vegetation composition at the Siberian treeline

Reliable information on past and present vegetation is important to project future changes, especially for rapidly transitioning areas such as the boreal treeline. To study past vegetation, pollen analysis is common, while current vegetation is usually assessed by field surveys. Application of detailed sedimentary DNA (sedDNA) records has the potential to enhance our understanding of vegetation changes, but studies systematically investigating the power of this proxy are rare to date. This study compares sedDNA metabarcoding and pollen records from surface sediments of 31 lakes along a north–south gradient of increasing forest cover in northern Siberia (Taymyr peninsula) with data from field surveys in the surroundings of the lakes. sedDNA metabarcoding recorded 114 plant taxa, about half of them to species level, while pollen analyses identified 43 taxa, both exceeding the 31 taxa found by vegetation field surveys. Increasing Larix percentages from north to south were consistently recorded by all three methods and principal component analyses based on percentage data of vegetation surveys and DNA sequences separated tundra from forested sites. Comparisons of the ordinations using procrustes and protest analyses show a significant fit among all compared pairs of records. Despite similarities of sedDNA and pollen records, certain idiosyncrasies, such as high percentages of Alnus and Betula in all pollen and high percentages of Salix in all sedDNA spectra, are observable. Our results from the tundra to single‐tree tundra transition zone show that sedDNA analyses perform better than pollen in recording site‐specific richness (i.e., presence/absence of taxa in the vicinity of the lake) and perform as well as pollen in tracing vegetation composition.     

Patterns in vegetation and sedimentation during the Weichselian Late-glacial in north-eastern Germany

Aim To identify and interpret spatial patterns of vegetation and sedimentation during the Weichselian Late‐glacial. Location North‐eastern Germany and the adjacent fringe of north‐western Poland. Methods An inspection and comparison of palynological data from c. 150 sites. Results Open Vegetation phase I (Oldest Dryas = earlier part of the Meiendorf, 12,900–12,450 ¹⁴C bp ) and the Hippophaë phase (Bølling = later part of the Meiendorf; 12,450–12,000 bp ) were rather homogeneous palynologically in the study area. Open Vegetation phase II (Older Dryas; 12,000–11,900 bp ) is strongly recorded in the northern part of the study area with relatively thick sediments (suggesting severe soil erosion), but it can hardly be traced 200 km further to the south. This is attributed to sea buckthorn (Hippophaë) shrubs persisting longer in the south due to higher temperatures, to Betula forests expanding earlier under the influence of a more humid climate or to a generally denser vegetation independent of the behaviour of Hippophaë and Betula. During the late‐glacial Betula/Pinus forest phase (Allerød; 11,900–11,000 bp ), pine (Pinus) forests dominated in the southern regions, whereas birch (Betula) forests prevailed in the north. Open Vegetation phase III (Younger Dryas; 11,000–10,000 bp ) was characterized by heathlands in the northern regions with scattered birches and with sedimentation dominated by in‐washed silicates. In the south, pine parklands occurred with sedimentation dominated by local primary production which had markedly decreased after the previous warmer vegetation phase. Main conclusions The differences in vegetation and sedimentation during the open vegetation phases are attributed to a colder climate in the north than in the south, probably related to a climatic gradient between the ice‐free continental central Europe and the decaying Scandinavian ice sheet. The vegetation patterns during the late‐glacial Betula/Pinus forest phase are attributed to edaphic differences between the predominantly till plains in the northern part of the study area and the prevailing sandy outwash plains and Urstromtäler of the southern regions.     

A high-resolution Late-Glacial – Holocene pollen diagram from Pian di Gembro (Central Alps, Northern Italy)

The local and regional history of vegetation and climate, from the Late Glacial to the present, is represented in a new, high-resolution pollen diagram from Pian di Gembro (1350 m asl), ten ¹⁴C dates providing a reliable time control. An open pioneer vegetation dominated by Artemisia, Gramineae, and and Chenopodiaceae followed the retreat of the glaciers after the Last Glacial Maximum. Shrub vegetation with Juniperus, Alnus viridis, and Salix expanded soon after. Denser Betula-Pinus forests were present in Pian di Gembro around 12,320 B.P. Their extent was greatly reduced by the climatic cooling of the Younger Dryas, when open vegetation spread again. The beginning of the Holocene was marked by a considerable expansion in mixed oak taxa. Corylus immigrated to the site at 9,250 B.P. Picea and Abies expanded at 7,370 B.P., recording an abrupt change in the structure of the vegetational belts. A coeval climatic change is evidenced in the GRIP records and also detectable through oscillations of the timberline. Signs of human impact are present since late Atlantic, becoming more intense around 2,200 B.P. As pasture lands increased, Abies and Fagus slowly disappeared. The introduction of Castanea and Juglans is dated to Roman times, and Secale to the Middle Ages. Received February 4, 2002 / Accepted August 2, 2002     

Vegetation responses to rapid climatic changes during the last deglaciation 13,500–8,000?years ago on southwest And?ya, arctic Norway

The late-glacial vegetation development in northern Norway in response to climate changes during the Aller?d, Younger Dryas (YD), and the transition to the Holocene is poorly known. Here we present a high-resolution record of floral and vegetation changes at lake Lusvatnet, south-west And?ya, between 13500 and 8000 cal b.p. Plant macrofossil and pollen analyses were done on the same sediment core and the proxy records follow each other very closely. The core has also been analyzed using an ITRAX XRF scanner in order to check the sediment sequence for disturbances or hiatuses. The core has a good radiocarbon-based chronology. The Saksunarvatn tephra fits very well chronostratigraphically. During both the Aller?d and the Younger Dryas time-periods arctic vegetation prevailed, dominated by Salix polaris associated with many typically arctic herbs such as Saxifraga cespitosa, Saxifraga rivularis and Oxyria digyna. Both periods were cold and dry. Between 12450 and 12250 cal b.p. during the Younger Dryas chronozone, the assemblage changed, particularly in the increased abundance of Papaver sect. Scapiflora and other high-Arctic herbs, suggesting the development of polar desert vegetation mainly as a response to increased aridity. After 11520 cal b.p. a gradually warmer and more oceanic climate initiated a succession to dwarf-shrub vegetation and the establishment of Betula woodland after 1,000 years at c. 10520 cal b.p. The overall late-glacial aridity contrasts with oceanic conditions in southern Norway and is probably related to sea-ice extent.     

Arctic shrub colonization lagged peak postglacial warmth: Molecular evidence in lake sediment from Arctic Canada

Arctic shrubification is an observable consequence of climate change, already resulting in ecological shifts and global‐scale climate feedbacks including changes in land surface albedo and enhanced evapotranspiration. However, the rate at which shrubs can colonize previously glaciated terrain in a warming world is largely unknown. Reconstructions of past vegetation dynamics in conjunction with climate records can provide critical insights into shrubification rates and controls on plant migration, but paleoenvironmental reconstructions based on pollen may be biased by the influx of exotic pollen to tundra settings. Here, we reconstruct past plant communities using sedimentary ancient DNA (sedaDNA), which has a more local source area than pollen. We additionally reconstruct past temperature variability using bacterial cell membrane lipids (branched glycerol dialkyl glycerol tetraethers) and an aquatic productivity indicator (biogenic silica) to evaluate the relative timing of postglacial ecological and climate changes at a lake on southern Baffin Island, Arctic Canada. The sedaDNA record tightly constrains the colonization of dwarf birch (Betula, a thermophilous shrub) to 5.9 ± 0.1 ka, ~3 ka after local deglaciation as determined by cosmogenic ¹⁰Be moraine dating and >2 ka later than Betula pollen is recorded in nearby lake sediment. We then assess the paleovegetation history within the context of summer temperature and find that paleotemperatures were highest prior to 6.3 ka, followed by cooling in the centuries preceding Betula establishment. Together, these molecular proxies reveal that Betula colonization lagged peak summer temperatures, suggesting that inefficient dispersal, rather than climate, may have limited Arctic shrub migration in this region. In addition, these data suggest that pollen‐based climate reconstructions from high latitudes, which rely heavily on the presence and abundance of pollen from thermophilous taxa like Betula, can be compromised by both exotic pollen fluxes and vegetation migration lags.     

A survey of modern pollen and vegetation along a south–north transect in Mongolia

Aim This modern pollen‐rain study documents the spatial and quantitative relationships between modern pollen and vegetation in Mongolia, and explores the potential for using this relationship in palaeoclimatic reconstructions. Location East‐central Mongolia. Methods We collected 104 pollen surface samples along a south–north transect across five vegetation zones in Mongolia. Discriminant analysis was used to classify the modern pollen spectra into five pollen assemblages corresponding to the five vegetation zones. Hierarchical cluster analysis was used to divide the main pollen taxa into two major groups and seven subgroups representing the dry and moist vegetation types and the main vegetation communities within them. Results Each vegetation zone along the transect can be characterized by a distinctive modern pollen assemblage as follows: (1) desert zone: Chenopodiaceae–Zygophyllaceae–Nitraria–Poaceae pollen assemblage; (2) desert‐steppe zone: Poaceae–Chenopodiaceae pollen assemblage; (3) steppe zone: Artemisia–Aster‐type–Poaceae–Pinus Haploxylon‐type pollen assemblage; (4) forest‐steppe zone: Pinus Haploxylon‐type–Picea–Artemisia–Betula, montane forb/shrub and pteridophyte pollen assemblage; and (5) mountain taiga zone: Pinus Haploxylon‐type–Picea–Poaceae–Cyperaceae, montane forb/shrub and Pteridophyte pollen assemblage. Main conclusions Based on the ratio between the major pollen taxon groups and subgroups, we propose two pollen–climate indices that represent the precipitation and temperature conditions in the study region. When plotted along our south–north transect, the moisture indices (M) and temperature indices (T) mimic the regional gradients of precipitation and temperature across Mongolia very closely. These pollen–climate indices can be used for palaeoclimatic reconstruction based on fossil pollen data.     

Response of tundra ecosystem in southwestern Alaska to Younger-Dryas climatic oscillation

Climatic warming during the last glacial–interglacial transition (LGIT) was punctuated by reversals to glacial‐like conditions. Palaeorecords of ecosystem change can help document the geographical extent of these events and improve our understanding of biotic sensitivity to climatic forcing. To reconstruct ecosystem and climatic variations during the LGIT, we analyzed lake sediments from southwestern Alaska for fossil pollen assemblages, biogenic‐silica content (BSiO₂%), and organic‐carbon content (OC%). Betula shrub tundra replaced herb tundra as the dominant vegetation of the region around 13 600 cal BP (cal BP: ¹⁴C calibrated calendar years before present), as inferred from an increase of Betula pollen percentages from << 5% to >> 20% with associated decreases in Cyperaceae, Poaceae, and Artemisia. At c. 13 000 cal BP, a decrease of Betula pollen from 28 to << 5% suggests that shrub tundra reverted to herb tundra. Shrub tundra replaced herb tundra to resume as the dominant vegetation at 11 600 cal BP. Higher OC% and BSiO₂% values suggest more stable soils and higher aquatic productivity during shrub‐tundra periods than during herb‐tundra periods, although pollen changes lagged behind changes in the biogeochemical indicators before c. 13 000 cal BP. Comparison of our palaeoecological data with the ice‐core dδ¹⁸O record from Greenland reveals strikingly similar patterns from the onset through the termination of the Younger Dryas (YD). This similarity supports the hypothesis that, as in the North Atlantic region, pronounced YD climatic oscillations occurred in the North Pacific region. The rapidity and magnitude of ecological changes at the termination of the YD are consistent with greenhouse experiments and historic photographs demonstrating tundra sensitivity to climatic forcing.     

Modern pollen assemblages from Reasi (Jammu and Kashmir), India: a tool for interpreting fossil pollen records

Twenty five surface samples/moss cushions were collected for palynological analysis from open areas of Reasi District, Jammu and Kashmir (India). These samples were used to investigate the relationships between extant vegetation and modern pollen spectra, which serve as modern analogue for the reliable ecological interpretation of fossil pollen records. The present vegetation in the region comprises tropical dry deciduous forests and subtropical pine forests with scattered stands of oak. The pollen analysis reveals that Pinus sp. (average 69% in the pollen assemblages), amongst the conifers, dominates the pollen rain, which can be attributed to its high pollen productivity and exceptional pollen dispersal efficiency. Cedrus sp. and Podocarpus sp. pollen contribute with an average of 16 and 5% to the total pollen rain. Other conifers such as Picea sp., Abies sp., Juniperus sp. and Tsuga sp., as well as broad-leaved taxa such as Quercus sp., Alnus sp., Betula sp., Carpinus sp., Corylus sp., Juglans sp., Ulmus sp., Salix sp., Elaeocarpus sp., Mallotus sp. and Aesculus sp., have lower averages of 1 to 4.5% in the total pollen rain which could be either due to their poor pollen dispersal efficiency or to the poor preservation in the samples. Tubuliflorae (average 25%), Poaceae (average 6.26%), Cerealia and other crop plants (average 7.68%) are other prominent taxa in the pollen rain. The nearly complete absence of members of tropical dry deciduous forests in the pollen spectra likely is due to the fact that most species in this vegetation type are not wind pollinated.     

Modern pollen–vegetation relationships in subarctic southern Greenland and the interpretation of fossil pollen data from the Norse landnám

Aim The objective of this paper is to explore the relationships that exist between vegetation and modern pollen rain in the open, largely treeless landscape of subarctic Greenland. The implications of these results for the interpretation of fossil pollen assemblages from the time of the Norse landnám are then examined. Location The study area is the sheep farming district of Qassiarsuk in the subarctic, subcontinental vegetational and climatic zone of southern Greenland (61° N, 45° W). Between c.ad 1000–1500 this region was contained within the Norse Eastern Settlement. Methods Detrended Correspondence Analysis (DCA) of harmonized plant–pollen data sets is used to compare plant cover in 64 vegetation quadrats with pollen assemblages obtained from moss polsters at matching locations. Presence/absence data are also used to calculate indices of association, over‐ and under‐representation for pollen types. Results Good correspondence between paired vegetation–pollen samples occurs in many cases, particularly in locations where Salix glauca–Betula glandulosa dwarf shrub heath is dominant, and across herbaceous field boundaries and meadows. Pollen samples are found to be poor at reflecting actual ground cover where ericales or Juniperus communis are the locally dominant shrubs. Dominant or ubiquitous taxa within this landscape (Betula, Salix and Poaceae) are found to be over‐represented in pollen assemblages, as are several of the ‘weeds’ generally accepted as introduced by the Norse settlers. Main conclusions Due to their over‐representation in the pollen rain, many of the Norse apophytes and introductions (e.g. Rumex acetosa and R. acetosella) traditionally used to infer human activity in Greenland should be particularly sensitive indicators for landnám, allowing early detection of Norse activity in fossil assemblages. Pteridophyte spores are found to be disassociated with the ground cover of ferns and clubmosses, but are over‐represented in pollen assemblages, indicating extra‐local or regional sources and long residence times in soil/sediment profiles for these microfossils. A pollen record for Hordeum‐type registered in close proximity to a field containing barley suggests that summer temperatures under the current climatic regime are, at least on occasion, sufficient to allow flowering.     

Plant survival in Iceland during periods of glaciation?

Aim The paper addresses the classical question of possible plant survival in Iceland during the last glacial period in the light of a palaeobotanical record from northern Iceland, spanning the period 11,300–9000 BP , including the Younger Dryas stadial. We review the Late Cenozoic fossil plant record, the past debate on glacial plant refugia in Iceland, and the evidence for ice-free areas during the Weichselian. Location The investigated lake sediment record comes from Lake Torfadalsvatn, which is situated in the northwestern part of the Skagi peninsula in northern Iceland. Methods The sediment chronology was constructed from the cccurrence of the Vedde Ash and the Saksunarvatn ash, two well-dated Icelandic tephras, together with the results from five AMS and conventional radiocarbon dates performed on bulk sediment samples. The vegetational reconstruction was based on detailed pollen analysis of the sediment sequence. Results The pollen analysis revealed that many of the taxa present in the area prior to the Younger Dryas stadial continued to produce pollen during that cold event. The more or less immediate reappearance of a few other pollen taxa at the Younger Dryas-Preboreal boundary suggests that these plants also survived, even if they did not produce sufficient pollen to be recorded during the Younger Dryas stadial. Main conclusions We conclude that the relatively high plant diversity found in high Arctic areas and present-day nunataks in Iceland and Greenland, together with the fact that many plant species were able to survive the Younger Dryas stadial on the Skagi peninsula, suggest that species with high tolerance for climate fluctuations also survived the whole Weichselian in Iceland. This conclusion is supported by recent palaeoclimatic data from ice-cores and deep-sea sediments, indicating that Icelandic climate during the last glacial was only occasionally slightly colder than during the Younger Dryas stadial.     

Vegetation and climate changes during the last 21 000 years in S.W. Africa based on a marine pollen record

A high resolution marine pollen record from site GeoB1023, west of the northern Namib desert provides data on vegetation and climate change for the last 21 ka at an average resolution of 185 y. Pollen and spores are mainly delivered to the site by the Cunene river and by surface and mid-tropospheric wind systems. The main pollen source areas are located between 13°S and 21°S, which includes the northern Namib desert and semi-desert, the Angola-northern Namibian highland, and the north-western Kalahari. The pollen spectra reflect environmental changes in the region. The last glacial maximum (LGM) was characterised by colder and more arid conditions than at present, when a vegetation with temperate elements such as Asteroideae, Ericaceae, and Restionaceae grew north of 21°S. At 17.5 ka cal. B.P., an amelioration both in temperature and humidity terminated the LGM but, in the northern Kalahari, mean annual rainfall in the interval 17.5-14.4 ka cal. B.P. was probably 100–150 mm lower than at present (400–500 mm/y). The Late-glacial to early Holocene transition includes two arid periods, i.e. 14.4–12.5 and 10.9–9.3 ka cal. B.P. The last part of the former period may be correlated with the Younger Dryas. The warmest and most humid period in the Holocene occurred between 6.3 and 4.8 ka cal. B.P. During the last 2000 years, human impact, as reflected by indications of deforestation, enhanced burning and overgrazing, progressively intensified.     

Exploitation of Local,Drifted and Imported Wood by the Vikings on the Faroe Islands

Summary

Two hundred wood samples have been examined from the Viking settlement at Argisbrekka on Eysturoydated to AD 770–1015. They fall into three categories:-1. local wood: Juniperus. Betula pubescens Ehrh., Corylus, Salix and heathland dwarf shrubs; 2. driftwood: Picea, Larix and Pinus section strobus; and 3. imported wood: Quercus, Pinus section sylvestris, Alnus and Fraxinus. The local tree vegetation was over-exploited and Betula became extinct in the course of the Viking Age. Driftwood, mainly of Siberian origin, seems to be the most important tree resource and was used for houses and utensils. Imported wood probably mostly comprised ships and finished products made in Scandinavia. The detection of tree Betula growth between 2,460 BC and AD 770 is a new contribution to the vegetational history of the Faroe Islands.     

Temporal and spatial changes of vegetation cover on the Chinese Loess Plateau through the last glacial cycle: evidence from spore-pollen records

To reconstruct the palaeovegetation cover of the Chinese Loess Plateau over different time intervals of the last glacial–interglacial cycle, the spore-pollen representation of loess-soil samples in six loess sections along a north–south transect is analyzed and previously published pollen data reviewed. Results show that the temporal changes in the vegetation cover of the Plateau are controlled essentially by the history of the East-Asian summer monsoon; there is a general pattern that the pollen components indicating relatively humid climatic conditions are better represented during interglacial and interstadial periods than during glacial and stadial periods. The herbaceous pollen concentrations show a general increase from south to north with the decrease of monsoonal precipitation over the Loess Plateau. Through the last 130 ka or so, the main body of the Loess Plateau has been covered by an Artemisia-dominated grassland vegetation, suggesting that future rehabilitation of the landscape that aims for soil–water preservation on the Loess Plateau should focus on the planting of herbs.     

Representation of tundra vegetation by pollen in lake sediments of northern Alaska

Aim To understand better the representation of arctic tundra vegetation by pollen data, we analysed pollen assemblages and pollen accumulation rates (PARs) in the surface sediments of lakes. Location Modern sediment samples were collected from seventy‐eight lakes located in the Arctic Foothills and Arctic Coastal Plain regions of northern Alaska. Methods For seventy of the lakes, we analysed pollen and spores in the upper 2 cm of the sediment and calculated the relative abundance of each taxon (pollen percentages). For eleven of the lakes, we used ²¹⁰Pb analysis to determine sediment accumulation rates, and analysed pollen in the upper 10–15 cm of the sediment to estimate modern PARs. Using a detailed land‐cover map of northern Alaska, we assigned each study site to one of five tundra types: moist dwarf‐shrub tussock‐graminoid tundra (DST), moist graminoid prostrate‐shrub tundra (PST) (coastal and inland types), low‐shrub tundra (LST) and wet graminoid tundra (WGT). Results Mapped pollen percentages and multivariate comparison of the pollen data using discriminant analysis show that pollen assemblages vary along the main north–south vegetational and climatic gradients. On the Arctic Coastal Plain where climate is cold and dry, graminoid‐dominated PST and WGT sites were characterized by high percentages of Cyperaceae and Poaceae pollen. In the Arctic Foothills where climate is warmer and wetter, shrub‐dominated DST, PST and LST were characterized by high percentages of Alnus and Betula pollen. Small‐scale variations in tundra vegetation related to edaphic variability are also represented by the pollen data. Discriminant analysis demonstrated that DST sites could be distinguished from foothills PST sites based on their higher percentages of Ericales and Rubus chamaemorus pollen, and coastal PST sites could be distinguished from WGT sites based on their higher percentages of Artemisia. PARs appear to reflect variations in overall vegetation cover, although the small number of samples limits our understanding of these patterns. For coastal sites, PARs were higher for PST than WGT, whereas in the Arctic Foothills, PARs were highest in LST, intermediate in DST, and lowest in PST. Main conclusion Modern pollen data from northern Alaska reflect patterns of tundra vegetation related to both regional‐scale climatic gradients and landscape‐scale edaphic heterogeneity.     

The identification of wingless Betula fruits in Weichselian sediments in the Gross Todtshorn borehole (Lower Saxony, Germany) – the occurrence of Betula humilis Schrank.

Betula fruits lacking their wings were recovered from the Gross Todtshorn borehole, Germany, covering the late Eemian interglacial, the Early Weichselian, and the Weichselian pleniglacial. In order to identify them, a data-set of seven size and shape variables was made from modern fruits of B. pubescens, B. pendula, B. nana, and B. humilis. These measurements were summarised by principal components analysis (PCA). The 140 measured fossil fruit-bodies were positioned passively on the PCA plot and identified by comparison with the dimensional envelopes of the modern species. Tree birches (B. pendula, B. pubescens) occurred in the Eemian and Early Weichselian interstadials, but not thereafter.B. nana was widespread during the intervening stadials and the Oerel interstadial. B. humilis occurred throughout the sequence, coexisting with tree birches in the Early Weichselian and with B. nana in the stadials. It usually grew on mire surfaces, in contrast to B. nana which mainly grew on mineral substrates. However, B. nana grew on peat with B. humilis in the pleniglacial Oerel interstadial, suggesting a more continental climate with cold winters. A modern analogue could be near the Ural mountains. B. humilis is presently rare in central Europe, but during the Weichselian it was well established in northern Germany. The PCA has enabled specific determination of the wingless Betula fruits, leading to vegetational and climatic reconstructions and contributing to the previously poorly known historical biogeography of Betula humilis. Received June 14, 2000 / Accepted January 2, 2001     

The lateglacial vegetation and radiocarbon dating of Lake Trilistnika, Rila Mountains (Bulgaria)

Pollen analysis, supplemented by 5 ¹⁴C dates, was carried out on the lateglacial section (160 cm) of a core retrieved from the glacial Lake Trilistnika (2216 m) in the northwestern Rila Mountains (Bulgaria). The reconstruction of the lateglacial vegetation history is linked for the first time to a chronological framework for the time window 13000–10000 b.p. The delimitation of an interstadial/stadial cycle, analogous with the Bølling/Allerød-Younger Dryas from Western Europe, is based on important changes in the pollen stratigraphy. Mountain-steppe vegetation composed of Artemisia, Chenopodiaceae, Poaceae and other cold-resistant herbs, with isolated stands of Pinus and Juniperus-Ephedra shrubland, dominated the landscape after the ice-retreat. Interstadial conditions were established before 12815±130 b.p. The spread of tree vegetation at lower elevation as a response to the climate improvement was confined to the time interval 12110±95–11140±75 b.p. The Younger Dryas stadial is characterised by a re-advance of the mountain-steppe vegetation. The results are compared with other sites of lateglacial age from the high mountains (Rila, northern Pirin, western Rhodopes) in southern Bulgaria.