Pollen Accumulation Research Articles

Comparing pollen spectra from modified Tauber traps and moss samples: examples from a selection of woodlands across Europe

This paper compares pollen spectra derived from modified Tauber traps and moss samples from a selection of woodland types from Bulgaria, the Czech Republic, Georgia, Greece, Poland, Switzerland and Wales. The study examines the representation of individual taxa in the two sampling media and aims to ascertain the duration of pollen deposition captured by a moss. The latter aim was pursued through the calculation of dissimilarity indexes to assess how many years of pollen deposited in a pollen trap yield percentage values that are most similar to those obtained from the moss. The results are broadly scattered; the majority of moss samples being most similar to several years of pollen deposition in the adjacent trap. For a selection of samples, a comparison of the pollen accumulation rate in pollen traps with the pollen concentration in the moss per unit surface indicates that the entrapment and/or preservation of individual pollen types in the moss differ from that in the pollen trap. A comparison of the proportion of different taxa in the moss with the pollen spectrum of 2 years of pollen deposition in the trap also revealed large differences. There is a tendency for bisaccate grains such as Pinus and Picea to have a higher representation in moss than in traps but there is considerable regional variation. The results indicate that pollen proportions from moss samples often represent the pollen deposition of one area over several years. However, bisaccate pollen grains tend to be over-represented in moss samples compared to both pollen traps and, potentially, lake sediments.

Estimating absolute pollen productivity for some European Tertiary-relict taxa

Tertiary-relict plants are survivors from the pre-Quaternary periods. Today, most European Tertiary relicts are confined to small, isolated stands distributed in the Mediterranean and Black Sea regions. In the past, however, the fossil record indicates that these species were probably distributed over large parts of the European continent and may have been important constituents of the vegetation. Little is known about their pollen representation, which limits our ability to reconstruct this past vegetation with any accuracy. This paper draws on the results of pollen trapping experiments in Bulgaria and Georgia, where relict stands of Aesculus hippocastanum, Cercis siliquastrum, Fagus orientalis, Juglans regia and Pterocarya fraxinifolia are still in existence. We compared average pollen accumulation rates (PAR) to vegetation data from around the trapping locations to derive estimates of absolute pollen productivity using various pollen dispersal functions. Composite dispersal functions that model pollen components carried above the vegetation canopy and falling as rain provided better relationships between PAR and plant abundance than functions that consider only a single component or the ‘trunk-space’ component carried under the canopy. A composite dispersal function with a simple model for regional pollen and the best overall correlation statistics gave the following estimates of absolute pollen productivity (grains cm−2 yr−1 with 1 SE intervals): Carpinus betulus 19,000–28,700; Fagus orientalis 15,600–20,400; Juglans regia 27,200–36,200; Pterocarya fraxinifolia 182,000–192,600; Quercus spp. 21,700–24,800; Tilia begoniifolia 51,600–68,300; and T. tomentosa 14,700–18,200. These estimates were applied to fossil data from the Black Sea coast to reconstruct palaeovegetation using absolute and relative methods.

Can we detect a west Norwegian tree line from modern samples of plant remains and pollen? Results from the DOORMAT project

In the DOORMAT (Direct Observation of Recent Macrofossils Across Treeline) project, the modern representation of local vegetation by pollen and plant remains (plant macrofossils) across a west Norwegian tree line, composed of Betula pubescens and Pinus sylvestris, has been studied over 2 years. The aim was to discover if the modern tree line could be detected and therefore how precisely past tree-line movements could be reconstructed and related to Holocene climate changes by using one proxy or a combination of both. Traps were placed in the vegetation from 663 to 1,120 m a.s.l., spanning the pine altitudinal species limit, the birch tree-line ecotone, and the vegetation zones up to the mid-alpine zone. Three traps were also set in the small lake Trettetjorn close to the modern tree line at 800 m a.s.l. Traps were emptied twice a year to sample both summer and winter seasons. Macrofossils represent their local vegetation well. However, tree Betula remains were trapped above the tree line and Pinus and Picea remains were recorded 1.0–1.5 km away from their sources, demonstrating considerable dispersal capacity. This shows that rare macrofossil remains do not necessarily represent the local presence of these trees. Aerial tree pollen deposition in traps at the upper limit of pine woodland and in the subalpine birch woodland was unexpectedly low, whereas pollen accumulation rates (PAR) were orders of magnitude higher in the lake traps. We hypothesise that the lake receives regional pollen rain washed in from its catchment by snow meltwater and that high values in traps are due to continuous suspension of pollen in the lake water during summer. The interpretation of tree-line changes from existing Holocene pollen and plant macrofossil data from Trettetjorn was supported and refined by the DOORMAT macrofossil data, but the modern pollen data were anomalous.

A high-resolution marine palynological record from the central mainland coast of British Columbia, Canada: Evidence for a mid-late Holocene dry climate interval

Abstract Sediments collected in a 12-m long core (VEC02A04) obtained from Frederick Sound in the Seymour–Belize Inlet Complex of British Columbia were deposited between ca. 4540 cal. yr BP and ca. 1090 cal. yr BP in primarily dysoxic conditions. The sediments are characterized by alternating intervals of fine grained massive and laminated units. Laminated sediments consist of light-coloured diatom-rich layers deposited during summer and dark-coloured mineral-rich layers deposited during winter. Laminated sediments are most common in portions of the core deposited between ca. 2840 cal. yr BP and ca. 1820 cal. yr BP, and correspond to a decline in the relative abundance and pollen accumulation rate of Cupressaceae pollen between ca. 3190 cal. yr BP and ca. 2250 cal. yr BP. The preservation of laminated units and decline of Cupressaceae pollen at this time suggest that a drier and possibly cooler climate punctuated otherwise wet and temperate late Holocene conditions in the Seymour–Belize Inlet Complex. We correlate the occurrence of the mid-late Holocene dry climate interval documented in Frederick Sound to dynamics in the relative position and intensity of the Aleutian Low pressure system and suggest that climate change associated with dynamics of this semi-permanent air mass affected primary productivity and vegetation of the Seymour-Belize Inlet Complex.

Paleoclimatic implications of glacial and postglacial refugia for Pinus pumila in western Beringia

Palynological results from Julietta Lake currently provide the most direct evidence to support the existence of a glacial refugium for Pinus pumila in mountains of southwestern Beringia. Both percentages and accumulation rates indicate the evergreen shrub survived until at least ∼ 19,000 14C yr BP in the Upper Kolyma region. Percentage data suggest numbers dwindled into the late glaciation, whereas pollen accumulation rates point towards a more rapid demise shortly after ∼ 19,000 14C yr BP. Pinus pumila did not re-establish in any great numbers until ∼ 8100 14C yr BP, despite the local presence ∼ 9800 14C yr BP of Larix dahurica, which shares similar summer temperature requirements. The postglacial thermal maximum (in Beringia ∼ 11,000–9000 14C yr BP) provided Pinus pumila shrubs with equally harsh albeit different conditions for survival than those present during the LGM. Regional records indicate that in this time of maximum warmth Pinus pumila likely sheltered in a second, lower-elevation refugium. Paleoclimatic models and modern ecology suggest that shifts in the nature of seasonal transitions and not only seasonal extremes have played important roles in the history of Pinus pumila over the last ∼ 21,000 14C yr BP.

Vegetation response to glacial–interglacial climate variability near Lake Malawi in the southern African tropics

Pollen records from Lake Malawi, Africa spanning the last 135 kyr show substantial and abrupt vegetation response to multiple episodes of extreme aridity between 135 and 75 ka. Peaks in both the relative abundance and total production of Podocarpus pollen define the first two of these drought episodes. From 135 to 127 and again from 117 to 105 kyr BP, Podocarpus percentages remain above 16% with peak values as high as 38% indicating a period marked by a cool climate resulting in expansion of montane forest taxa to lower elevations. Marine palynological records from the Angola Margin and Congo Fan show similar peak Podocarpus percentages at this time (oxygen isotope stage 5d) indicating a similar climate across the African continent at this latitude. From 105 to 90 ka, continuing drought resulted in total pollen accumulation rates in Lake Malawi to fall to less than 300 grains/cm 2/yr of predominately grass pollen. This episode in African history was severe enough to cause the disappearance of pteridophytes and forest taxa such as Uapaca and Brachystegia as well as montane taxa ( Podocarpus, Olea spp. and Ericaceae) within the pollen source area of Lake Malawi. These taxa all remain nearly absent from the surrounding vegetation for the next 18,000 years. The resultant semi-desert vegetation would have been inhospitable for early humans living within or traveling through the Lake Malawi region. Increasing moisture following these arid intervals allowed expansion, creation and maintenance of a more diverse landscape vegetation mosaic around Lake Malawi including Zambezian miombo woodland, humid evergreen woodland and afromontane forests. The relative abundance of each fluctuated in response to either cooling (i.e. afromontane expansion from 60 to 56 ka) or moisture balance (i.e. increasing humid evergreen woodland between 75 and 65 ka). Notably there was no significant change in vegetation composition during the Last Glacial Maximum (LGM) (30–15 ka) as compared to the previous 20,000 years.

A near‐annual palaeohydrological study based on testate amoebae from a sub‐alpine mire: surface wetness and the role of climate during the instrumental period

AbstractWe present the first testate amoeba‐based palaeohydrological reconstruction from the Swiss Alps, and the first depth to the water table (DWT) calibration dataset for this region. Compared to existing models, our new calibration dataset performs well (RMSEP = 4.88), despite the length of the water table gradient covered (53 cm). The present‐day topography and vegetation of the study mire Mauntschas suggest that it is partly ombrotrophic (large Sphagnum fuscum hummocks, one of which was the coring site) but mostly under the minerotrophic influence of springs in the mire and runoff from the surrounding area. Ombrotrophic Sphagnum fuscum hummocks developed at the sampling site only during the last 50 years, when testate amoebae indicate a shift towards dry and/or acid conditions. Prior to AD 1950 the water table was much higher, suggesting that the influence of the mineral‐rich water prevented the development of ombrotrophic hummocks. The reconstructed DWT correlated with Pinus cembra pollen accumulation rates, suggesting that testate amoebae living on the mire and P. cembra growing outside of it partly respond to the same factor(s). Finally, temperature trends from the nearby meteorological station paralleled trends in reconstructed DWT. However, contrary to other studies made on raised bogs of northwestern Europe, the highest correlation was observed for winter temperature, despite the fact that testate amoebae would more logically respond to moisture conditions during the growing season. The observed correlation with winter temperature might reflect a control of winter severity on surface moisture during at least the first part of the growing season, through snow melt and soil frost phenomena influencing run‐off. More ecohydrological work on sub‐alpine mires is needed to understand the relationships between climate, testate amoebae and peatland development. Copyright © 2009 John Wiley & Sons, Ltd.

Absolute pollen productivity and pollen–vegetation relationships in northern Finland

AbstractPollen productivity is one of the most critical parameters for pollen–vegetation relationships, and thus for vegetation reconstruction, in either pollen percentages or pollen accumulation rates. We obtain absolute pollen productivity of three major tree types in northern Finland: pine (Pinus sylvestris), spruce (Picea abies) and birch (Betula pubescens ssp. pubescens and B. pubescens ssp. czerepanovii treated as one taxon). Long‐term monitoring records of pollen traps from 15 sites (duration: 5–23 years) and tree volume estimates within a 14 km radius of each trap were compared to estimate pollen productivity (grains m−3 a−1) of these trees using a regression method. The slope of the linear relationship between pollen loading and distance‐weighted plant abundance represents pollen productivity. Estimated productivities of pollen (×108 grains m−3 a−1) for pine, spruce and birch are 128.7 (SE 31.5), 341.9 (SE 81.3) and 411.4 (SE 307.7), respectively. The birch estimate (P > 0.05) is not as good as the others and should be used with caution. Pollen productivities of pine, spruce and birch in northern Finland are, in general, comparable to those of congeneric species in other regions of Europe and Japan. Although the year‐to‐year variations are significant, our volume‐based estimates of pollen productivity for pine and spruce will be essential for quantitative reconstruction of vegetation in the region. Copyright © 2009 John Wiley & Sons, Ltd.

Pollen dispersal and deposition characteristics of Abies alba, Fagus sylvatica and Pinus sylvestris, Roztocze region (SE Poland)

Pinus sylvestris L., Abies alba Mill. and Fagus sylvatica L.—the significant forest forming tree species in Europe are important for palaeoecological interpretations based on the results of pollen analysis of fossil deposits. The potential pollen loading for Pinus sylvestris, Abies alba and Fagus sylvatica was modelled using simulated and actual vegetation maps, measured fall-speed values and pollen productivity estimates from the literature. The influx of fir pollen drops sharply with distance from the pollen source due to the high fall speed and moderate pollen productivity. The vast majority of Abies alba pollen is deposited within less than 50 m of the sampling site and a major proportion within 100 m. For beech the corresponding numbers would be 300 and 1,800 m, and for pine 1,000 and 4,500 m. The observed mean pollen accumulation rate (PAR) values for Pinus and Fagus were ca. 5,800 and 1,100 grains cm−2 year−1, respectively. In the case of Abies, the mean annual PAR for the whole region is ca. 700 grains cm−2 year−1. In SE Poland the regional signal is represented by PARs of Abies alba 1,000 grains cm−2 year−1, >2,000 grains cm−2 year−1 and >3,500 grains cm−2 year−1 respectively.

Invasion of Norway spruce (Picea abies) and the rise of the boreal ecosystem in Fennoscandia

Summary 1. Norway spruce ( Picea abies ), one of the dominant tree species in Eurasia, has spread slowly westward in northern Europe, invading eastern Finland about 6500 calibrated years ago (cal. years BP), eastern central Sweden about 2700 cal. years BP and southern Norway about 1000 cal. years BP. Its spread is the most recent and best constrained invasion of a main tree species in northern Europe and allows an assessment of colonization patterns and associated competitive replacement processes. 2. We analysed five selected high-resolution pollen accumulation rate (PAR) -records along a 700-km long transect in the direction of P. abies invasion from eastern Finland to central Sweden across the present P. abies - and Pinus sylvestris- dominated southern boreal zone. 3. Our results show that the P. abies population increased in size from the time of the initial expansion to levels comparable with the modern in 100‐550 years. At each site P. abies invaded a dense, intact Pinus ‐ Betula ‐ Alnus forest, mixed with temperate deciduous taxa, particularly Tilia cordata and Corylus avellana . The resident mixed forest provided no or weak resistance to the colonization of P. abies , and the variable population growth rate was therefore not caused by compositional differences in the resident forest but by other, possibly local edaphic factors. 4. Of the taxa that formed the resident forest, T . cordata responded most strongly to the invasion of P. abies . This suggests that the mid-Holocene T. cordata population decline was not directly climateinduced but resulted from competitive replacement due to overlapping ecological niches with P. abies , a stronger competitor. 5. Synthesis . The rise to dominance of P. abies was caused not only by its rapid population growth but by associated competitive suppression of other taxa, leading to a major ecosystem change from a mixed conifer-deciduous forest to the modern P. abies - and P. sylvestris -dominated boreal conifer forest in central Fennoscandia. This competitive suppression by P. abies is still reflected in the scattered occurrence and generally weak performance of T. cordata in the boreal zone of Europe and may influence its distribution and abundance patterns under predicted future climate scenarios.

A late Quaternary paleotemperature record from Hanging Lake, northern Yukon Territory, eastern Beringia

The late Quaternary paleoclimate of eastern Beringia has primarily been studied by drawing qualitative inferences from vegetation shifts. To quantitatively reconstruct summer temperatures, we analyzed lake sediments for fossil chironomids, and additionally we analyzed the sediments for fossil pollen and organic carbon content. A comparison with the δ 18O record from Greenland indicates that the general climatic development of the region throughout the last glaciation–Holocene transition differed from that of the North Atlantic region. Between ∼ 17 and 15 ka, mean July air temperature was on average 5°C colder than modern, albeit a period of near-modern temperature at ∼ 16.5 ka. Total pollen accumulation rates ranged between ∼ 180 and 1200 grains cm − 2 yr − 1 . At ∼ 15 ka, approximately coeval with the Bølling interstadial, temperatures again reached modern values. At ∼ 14 ka, nearly 1000 yr after warming began, Betula pollen percentages increased substantially and mark the transition to shrub-dominated pollen contributors. Chironomid-based inferences suggest no evidence of the Younger Dryas stade and only subtle evidence of an early Holocene thermal maximum, as temperatures from ∼ 15 ka to the late Holocene were relatively stable. The most recognizable climatic oscillation of the Holocene occurred from ∼ 4.5 to 2 ka.

Pollen/climate calibration based on a near‐annual peat sequence from the Swiss Alps

AbstractThe objective of this study was to develop a high‐resolution pollen‐based climate inference model (using ‘calibration in time’) for the mire Mauntschas (SE Swiss Alps, 1818 m above sea level). We focused on 11 types of pollen and spores (referred to as pollen for simplicity) for which we produced 150 year (a) time series of accumulation rates and percentages. Dating of these series was based on 29 14C dates from pure Sphagnum, spheroidal carbonaceous particles, larch bud moth events, and an age–depth model that took into account probabilities of calibrated 14C ages, the degree of curvature of the age–depth line and changes in concentrations of all major pollen types. Time resolution was 1–5 a. We first smoothed the series using a 3 a triangular filter, thus removing time‐resolution dependent changes in variability, and minimising effects of potential dating uncertainties. Using redundancy analysis, we then studied the simultaneous response of the selected pollen to 288 different combinations of monthly temperature or precipitation data measured at Sils Maria (1798 m above sea level), located 9 km from Mauntschas. From AD 1954 to 2002, mean May–August air temperature from the same year explained most (18.1%) of the variation in pollen accumulation rates. The amount of explained variation dropped to 9.9% after detrending all data with a 50 a high‐pass filter, which possibly removed non‐climatic trends. Temperature explained more variation among PAR than among pollen percentages; however, during the verification period (AD 1864–1953) the former were potentially affected by dating uncertainties and could not be used. For developing a pollen‐based temperature inference model, we tested ordinary least squares regression, time series regression, ridge regression, principal components regression, and partial least squares regression. During the well‐dated calibration period (AD 1954–2002), ordinary least squares regression based on percentages of six pollen types turned out to be the most parsimonious model, having a cross‐validated root mean square error of prediction of 0.23°C for mean April–November temperature. A comparison of reconstructed with measured temperature from Sils Maria during the verification period showed that the model best reflected long‐term (at least decadal‐scale) temperature changes. Copyright © 2009 John Wiley & Sons, Ltd.

Free‐shape 14C age–depth modelling of an intensively dated modern peat profile

AbstractThe paper presents a new algorithm for finding the best‐fit age–depth model of a peat profile dated with 14C. This algorithm of free‐shape modelling is useful when the age–depth curve is wiggly and difficult to approximate by a simple mathematical function. The performance of the free‐shape algorithm is illustrated with the example of the MA2 peat profile from Mauntschas mire, using 29 radiocarbon dates spanning the last 1300 a, and where the age–depth curve revealed a relatively complicated shape.The best‐fit age–depth model searched for is a curve maximising the ‘Fit quality’, defined as a combination of fit of 14C dates to the radiocarbon calibration curve, general smoothness of the age–depth line, and similarity of relative changes in the modelled sediment accumulation rates to those suggested by independent data. The algorithm of free‐shape age–depth modelling searched for a reasonable equilibrium or compromise between the conditions above. Uncertainty of the free‐shape model was assessed with a Monte Carlo Markov chain built from large number of age–depth lines accepted with probabilities dependent on the ‘fit quality’ defined as above.Parallel fluctuations in concentrations of most pollen taxa in MA2 strongly suggest a complicated shape of the age–depth curve, which is supported in the upper part of the profile by the record of spheroidal carbonaceous particles, and in some levels also by the 14C dates. A modification of total pollen concentrations was therefore used as a quantitative indicator of relative changes of the peat accumulation rate. The use of pollen concentrations improved the fit of the 14C dates in several cases.Application of the final age–depth model to the pollen data resulted in a diagram of pollen accumulation which allows interpretation in ecological terms, whereas age–depth models that did not use pollen concentrations led to problematic and confusing results. The obtained age–depth model is therefore accepted as a good approximation of the actual conditions. Copyright © 2009 John Wiley & Sons, Ltd.

Pinus and Betula pollen accumulation rates from the northern boreal forest as a record of interannual variation in July temperature

AbstractFossil Pinus and Betula pollen accumulation rates (PARs, grains cm−2 a−1) from a peat profile in Nellim, northern Finland, were compared to a 20‐year annually resolved record of monitored pollen deposition data of both taxa from 2.5 km away, in order to determine the boundaries in the fossil pollen record. The smoothing inherent in the fossil PAR data is about 5 years compared with the annually monitored PARs but, while year‐to‐year variation in PARs is lost, the overall trend is retained. The fossil PARs were then calibrated with the appropriately smoothed temperature record for northern Finland. Betula pollen accumulation rates are much lower in the fossil record compared to the monitored ones. The correlation between fossil Betula PARs and July mean temperatures is much higher than the correlation between fossil Pinus PARs and temperature, probably because the subspecies Betula pubescens ssp. pubescens is at its northern limit in the area. The temperature signal in this dataset was disturbed during the period when the forests in the area were heavily cut and when regenerating trees were reaching maturity. Copyright © 2009 John Wiley & Sons, Ltd.

Conifer pollen abundance provides a proxy for summer temperature: evidence from the latitudinal forest limit in Finland

AbstractA 23‐year record of pollen deposition (pollen accumulation rates: PARs) indicates that pollen production of the two most common northern boreal conifers – pine and spruce – varies dramatically from year to year and that high and low pollen years show consistency over the whole of northern Lapland. Testing for a calibration between the annual PARs of these two trees and a whole range of meteorological parameters reveals that the highest correlation is between pollen quantity and summer temperature centred around July of the year before pollen emission. Critical mean July temperature limits for the flowering of Pinus and Picea are 12°C and 13°C, respectively. This strong and region‐wide relationship suggests that fossil Pinus and Picea PARs could be used as a proxy for summer temperature. Results are illustrated as maps showing the relationship between forest limits and July temperature and between PARs and the correlation coefficient with July temperature. It is noticeable, however, that although the climate signal is strong at the forest limit of the taxon in question, it is often weaker in the centre of its ecological range. This has implications when interpreting fossil pollen records. Temperature calibrations will vary spatially as the position of the forest limit changes. Copyright © 2009 John Wiley & Sons, Ltd.

FLORAL SYNDROME AND BREEDING SYSTEM OF LOBELIA CHINENSIS, A PERENNIAL HERB WITH STAMEN FUSION

Aims Lobelia chinensis (Campanulaceae), a perennial herbaceous creeper that grows mainly on riverbanks or wet farmland in central and southern China, is characterized by stamen fusion. The anthers of its five stamens are fused tightly into a tube in which the stigma and style are packed, and the filaments are also fused at the upper parts, forming a column-like structure surrounding the pis-til. The objective was to elucidate the adaptive significance of this growth pattern, the floral syndrome and breeding system using anatomical analyses, pollination surveys and bag experiments. Methods Flowers were observed at different developmental stages to determine the growth patterns of each floral part, especially morphologies of sexual organs, dichogamy and numbers of pollen grains and ovules, and their possible changes in spatial position and morphology. Pollination surveys were conducted to find the primary floral visitors. Bag experiments were conducted to determine self-compatibility, autogamy and apomixy. These studies would reveal the breeding system. Important findings Flower diameter was 1cm. The lower parts of perianth were fused into an open tube. The stigma and style were enclosed in the anther tube and the united parts of filaments. The flower was protandrous, and the pollen grains were released into the anther tube and dropped on the stigma surface. Growth of the style sent the stigma out of the anther tube 1 or 2 days after opening and then it became receptive. The main floral visitors were ants, hoverflies and flies. The pollen-ovule ratio (P/O) was 100, suggesting facultative autogamy, but the outcrossing index suggested the breeding system is outcrossing with partial self-compatibility and a pollinator is needed. Bag experiments indicated no apomixy and no spontaneous autogamy, but self-compatibility. The species largely outcrossed but suffered pollen limitation in field. The low P/O in this stamen-fused species might be due to the higher siring probability of individual pollen grains resulting from the accumulation and collective pollination of pollen, a similar mechanism to pollen aggregation such as pollinia, tetrads and viscin threads. The correlation of stamen fusion with perianth tube, dichogamy and low pollen-ovule ratio in this and other anther-fused species suggested that these floral traits probably formed a floral syndrome adaptive for small pollinators.

Calibrated pollen accumulation rates as a basis for quantitative tree biomass reconstructions

Recent investigations show that the pollen accumulation rate (PAR) of the common tree taxa is directly related to the biomass and, by inference, to the population size of the taxa around the study site. Fossil PAR records preserved in lakes provide therefore a potential proxy for quantitative biomass and population reconstructions. We use the high-resolution PAR records obtained from two accurately dated lake sediment cores in Finland to generate quantitative Holocene biomass records for Pinus, Picea and Betula, the most common tree taxa of the European Boreal forest. PAR values were calibrated to biomass values by comparing the modern PAR values with the modern biomass values and assuming a linear relationship between the past PAR and biomass values. The obtained PAR and biomass values and trends are remarkably coherent between the two records. Pinus has a stable Holocene biomass size and its modern biomass, about 20 t/ha, corresponds with the natural Pinus biomass in the study regions. In contrast, Picea immigrated from the East during the mid Holocene, had a maximum biomass, 50—60 t/ha, at 3500—1000 cal. yr BP, and declined strongly during the last 1500—1000 years as a result of increased human activity and related rise of fire frequency. Thus, the modern Picea biomass in the study regions, about 22 t/ha, is only 35—40% of the natural Picea biomass. The results of this pilot study demonstrate the potential of the calibrated PAR data in quantitative biomass and population reconstructions. Such reconstructions can provide fresh insights into the structure of past plant communities and, when combined with records reflecting palaeoclimates, natural disturbances, and human activity, can help to disentangle the long-term importance of different enviromental drivers to changes in plants populations and ecosystems.

Development of the late glacial Baltic basin and the succession of vegetation cover as revealed at Palaeolake Haljala, northern Estonia

The 4.5 m thick Haljala sequence in North Estonia was studied to provide information on palaeoenvironmental changes between 13 800 and 11 300 cal yr BP. Late glacial environmental history of North Estonia was reconstructed using AMS-dated pollen record, sediment composition, plant macrofossils, and ostracods. The obtained data show environmental fluctuations that are linked to the climate shifts of the Last Termination in the North Atlantic region. Decrease in the arboreal pollen accumulation rate around 13 700-13 600 and 13 300-13 100 cal yr BP refers to short deterioration of climate within the Allerod Interstadial and has been correlated with the cooling of the Greenland Interstadial GI-1c and GI-1b events, respectively. Between 13 100 and 12 850 cal yr BP the pollen accumulation rate of trees, shrubs, and herb as well as organic matter increased, indicating short-term climate amelioration and establishment of pine-birch woods. This change has been correlated with the GI-1a event. Climate deterioration during the Younger Dryas (GS-1) was inferred from the reduction of tree pollen and flourishing of cold-tolerant species, such as Artemisia, Chenopodiaceae, and Cyperaceae. New data show that ice cover of the Pandivere Upland started to perish already about 13 800 cal yr BP.

Estimating pollen diversity from pollen accumulation rates: a method to assess taxonomic richness in the landscape

A new method is presented to estimate pollen diversity on the basis of pollen-accumulation rates, rather than on a constant count of pollen as is traditional. Accumulation-based estimates of pollen diversity can be interpreted in terms of taxonomic richness on the landscape. The traditionally used constant-count estimates, on the other hand, reflect the evenness in the vegetation much more than its taxonomic richness, but they reflect this in a distorted way because of the real but mostly unknown differences in pollen productivity among plant taxa. Pollen-accumulation rates might also be used to estimate turnover of plant species from pollen assemblages. Differences in pollen productivity among plant taxa also have effects on various other data-summarizing techniques, including estimates of rates of change.

Pollen accumulation rates as a tool for detecting land-use changes in a sparsely settled boreal forest

A peat profile from the village of Nellim in northern Finnish Lapland was analysed at a near-annual resolution in order to test to what degree of accuracy the land-use history of the village could be reconstructed on the basis of organic microfossils. The profile was first AMS 14C dated and a robust chronology constructed to enable near-annual sampling. A set of 47 contiguous samples were treated and counted to produce a pollen accumulation rate diagram (PAR, grains cm−2 year−1). PARs enabled a better distinction of the fine-scale human induced changes in the pollen assemblages than the classical percentage representation because real changes in each pollen taxon could be followed. Changes in the accumulation rate of pine pollen reflect regional changes in forest-use in Lapland and both local events and regional logging activity could be distinguished. Local within-mire changes were deduced from the peat stratigraphy and the testate amoebae. The limitations for using PARs seem to be connected to the physiology of the plants and the taphonomy of the different pollen types and this must be taken into account when making interpretations.