Pollen Loading Research Articles

Mechanistic understanding of perianth traits hindering pollination in Aristolochia contorta Bunge.

Insects are vital pollinators for angiosperms, playing a crucial role in their reproductive success and fruit production. Aristolochia contorta is a perennial herbaceous vine that occurs in fragmented populations across East Asia. One notable feature of this plant is its trap flower, which employs a unique mechanism to attract, trap, retain, and release insects, ensuring effective pollination. The presence of this trap flower significantly influences the pollination system of A. contorta. Field surveys and pollination experiments were conducted to understand the processes and effectiveness of its pollination mechanism. It was allogamous and was pollinated by the species from Ceratopogonidae. During the insect attraction stage, 11.57% of the flowers contained insects, primarily Ceratopogonidae spp. Most Ceratopogonidae spp. concentrated in few flowers, indicating that although overall attraction might be modest, specific flowers acted as significant focal points for gathering. Trichomes effectively trapped Ceratopogonidae spp. inside flower tubes. In the retention stage, 26.16% of Ceratopogonidae spp. were loaded with pollen grains, but only 7.91% of those exited the flowers in the release stage. The sticky texture of the perianth's internal cavity posed challenges during this release, leading to adhesion and clogging of the narrow perianth tube. Consequently, a significant portion of Ceratopogonidae spp. became trapped on the perianth wall and perished. This highlights that despite the significant energy and resources invested in flower development, the perianth contributes to the low pollination effectiveness. This study revealed additive factors with negative effects on pollination, including the densely clustered distribution of its pollinators within only a few flowers, insufficient pollen loading onto pollinators, hindered release of entrapped pollinators due to the perianth adhesive surface, and a high rate of defective pollen grains in A. contorta. These factors account for the observed phenomenon of low fruit set (7.7%) and contribute to the diminished rate of sexual reproduction in A. contorta populations. This might lead the species to heavily rely on asexual reproduction, which could potentially lead to gene erosion within populations. The implications of these findings extend to the ecological and conservation aspects, emphasizing the need to understand and conserve the unique pollination system of A. contorta.

Reproductive and pollination biology of the Critically Endangered endemic Campanula vardariana in Western Anatolia (Turkey)

Background and aims – Campanula vardariana (Campanulaceae) is a critically endangered endemic chasmophyte with a single population situated in the west of Turkey. Very little is known about the reproductive biology of C. vardariana and more information is needed to develop a sound conservation strategy for this endemic species.Material and methods – Floral traits such as flower morphology, nectar, and sugar concentration, as well as pollen viability and stigma receptivity were measured in different floral phases. We observed insect visitations to the flowers and identified pollinators. Additionally, we investigated the effect of cross and self-pollination on fruit and seed production.Key results – The flowers of C. vardariana are protandrous. The length of the styles, which were 8.74 mm during the pollen loading phase, reached 11.35 mm during the pollen presentation phase. The visitor observations made on the C. vardariana flowers revealed 11 visitor species from 5 families: 5 Halictidae, 3 Apidae, and one species each from Megachilidae, Colletidae, and Bombyliidae. Lasioglossum spp. touched the anthers and stigma using several parts of their bodies and were significant pollinators of C. vardariana. Under natural conditions, the mean number of seeds per fruit was around 60 after cross pollination, while no fruits were formed when pollinators were excluded.Conclusion – Campanula vardariana is entirely dependent on pollinators for its reproductive success, and bees, especially Halictidae and to a lesser extent Apidae, play an important role. Campanula vardariana is restricted to cracks in calcareous rocks and its population is threatened by goat overgrazing and mining activities (quarry formation). Since seed production is abundant in this population, anthropogenic activities currently form the biggest threat to its existence.

Preparation of a Yield Stress Pickering Emulsion Ink Stabilized by Naturally Occurring Bee Pollen Microparticles

Plant-based pollens have recently received significant attention in various fields owing to their numerous potential advantages including their unique architecture, mechanical strength, and high resistance to chemical attacks and biological degradation. In this study, we demonstrate viscoelastic Pickering emulsions of water and oil (trimethylolpropane trimethacrylate) stabilized by naturally occurring bee pollen microparticles. We systematically investigate the rheological properties of the pollen-stabilized emulsions with various pollen concentrations and water-to-oil ratios. It is observed that the emulsions prepared at a high pollen loading and an appropriate water-to-oil ratio show excellent shape retention and shear-thinning behaviors. The results suggest the possibility of utilizing pollen-stabilized Pickering emulsions for several applications including direct ink writing.

Significance of pollen assemblages for the vegetationcomposition of alpine shrub meadow in theQinghai-Tibetan Plateau, China

The Qinghai-Tibetan Plateau is a fragile, globally significant ecosystem which responds sensitively to global climate change and regional human activity. Modern observations show that the ecological environment of the Qinghai-Tibetan Plateau has changed substantially, with obvious regional differences in vegetation composition, since the 1980s. Studying the history of vegetation succession and changes in the spatial distribution of vegetation on the Qinghai-Tibetan Plateau can provide a scientific basis for accurate assessment and prediction of future changes. For this purpose, we selected Zeku Basin, in the northeastern Qinghai-Tibetan Plateau. The study area is open and flat and it belongs to the alpine and semi-humid climate zone with distinct seasonality. The annual average temperature ranges from −3−3°C, and the annual precipitation ranges from 400−700 mm and is concentrated during June-September. The regional vegetation in Zeku Basin includes alpine meadow and alpine shrub, which is mainly composed of herbs and shrubs tolerant of cold and humid conditions. The alpine meadow is dominated by Kobresia and Carex , accompanied by Compositae, Ranunculaceae, Poaceae and Potentilla , which are mainly distributed in basin areas and on the sunlit slopes of the mountains. The alpine shrubs are dominated by Potentilla fruticosa , with occasional Hippophae and Spiraea alpina , mostly distributed on the shaded slopes of the mountains. The extent of the study area was determined according to the degree of vegetation regionalization with reference to Google satellite imagery of Qinghai Province. 31 representative sites were selected within the study area, using the random layout method. At each site surface moss samples were collected and a vegetation inventory conducted. We analyzed the pollen composition of the surface samples and determined the characteristics of the pollen assemblages and the pollen source area in alpine shrub meadow. The principal results are as follows: (1) The pollen assemblages are dominated by Cyperaceae (29.75%), Aster (21.86%), Ranunculaceae (16.99%), Rosaceae (7.84%) and Poaceae (5.1%), which mainly originate from the vegetation within 40 km of the sites (the proportion of total pollen loading reached was 83%). There is the minor representation of the pollen of arboreal plants, such as Betula , Pinus and Picea , which was wind-transported over long distances. The vegetation composition varied substantially between different sites within distances of 0–100 m of each site, resulting in a poor relationship with the pollen assemblages. However, the pollen assemblages and the vegetation composition were more similar over the distance of 0–3 km from each site, suggesting that the regionally-homogenized vegetation has a better relationship with the pollen assemblages. (2) We suggest that the surface pollen assemblages from lakes in the Qinghai-Tibetan Plateau may be greatly affected by extra-regional pollen or intrazonal vegetation in the shrub meadow. High percentages of Artemisia and Chenopodiaceae in pollen assemblages do not reflect the coverage of these taxa in the corresponding regional vegetation. Therefore, within shrub meadow environments of the Qinghai-Tibetan Plateau, these taxa should be excluded from lake-sediment-based pollen studies of regional vegetation succession and climate change.

Pollen fillers for reinforcing and strengthening of epoxy composites

Pollen grains have the potential to be effective plant-based biorenewable fillers in polymer matrices due to their high modulus, strength, chemical stability, and unique nanoscale architectures. In this work, we present evidence for the effectiveness of pollen as a reinforcing filler in epoxy matrices, characterized as a function of pollen loading and surface treatment. Composites prepared with unmodified native defatted ragweed pollen (D) displayed decreased mechanical properties and increasing glass transition temperatures (Tg) with increasing pollen loading. A soft interphase was observed to form around native pollen that is likely due to incompletely cured epoxy, resulting in decreased mechanical properties. However, pollen treated via a common base-acid (BA) surface preparation was a load-bearing, toughening filler in epoxy composites, displaying simultaneously increased tensile strength (by 47%) and strain at break (by 70%), improving interfacial morphology (absence of soft interphase), and increasing Tg at 10 wt% pollen loading. Elastic modulus improves by 14% with 10 wt% BA pollen loading, and fitting of the modulus with the Halpin-Tsai and Counto models results in an estimated pollen exine modulus of 8 GPa, the first reported pollen modulus measurement from composite studies. Improvements in mechanical properties in BA pollen versus D pollen likely result due to crosslinks with the epoxy matrix due to the presence of protic functional groups (hydroxyls or carboxyls) on the BA surface. BA-treated ragweed pollen shows promise as a toughening filler for imparting higher strength to polymers without increasing mass.

Maps From Mud—Using the Multiple Scenario Approach to Reconstruct Land Cover Dynamics From Pollen Records: A Case Study of Two Neolithic Landscapes

Pollen records contain a wide range of information about past land cover, but translation from the pollen diagram to other formats remains a challenge. In this paper, we present LandPolFlow, a software package enabling Multiple Scenario Approach (MSA) based land cover reconstruction from pollen records for specific landscapes. It has two components: a basic Geographic Information System which takes grids of landscape constraints (e.g. topography, geology) and generates possible 'scenarios' of past land cover using a combination of probabilistic and deterministic placement rules to distribute defined plant communities within the landscape, and a pollen dispersal and deposition model which simulates pollen loading at specified points within each scenario and compares that statistically with actual pollen assemblages from the same location. Goodness of fit statistics from multiple pollen site locations are used to identify which scenarios are likely reconstructions of past land cover. We apply this approach to two case studies of Neolithisation in Britain, the first from the Somerset Levels and the second from Mainland, Orkney. Both landscapes contain significant evidence of Neolithic activity, but present contrasting contexts. In Somerset, wet-preserved Neolithic remains such as trackways are abundant, but little dry land settlement archaeology is known, and the pre-Neolithic landscape was extensively wooded. In Orkney, the Neolithic archaeology includes domestic and monumental stone-built structures forming a UNESCO World Heritage Site, and the pre-Neolithic landscape was largely treeless. Existing pollen records were collated from both landscapes and correlated within a new age model framework (presented elsewhere). This allowed pollen data to be grouped into 200 year periods, or “timeslices”, for reconstruction of land cover through time using the MSA. Reconstruction suggests that subtle but clear and persistent impacts of Neolithisation on land cover occurred in both landscapes, with no reduction in impact during periods when archaeological records suggest lower activity levels. By applying the methodology to specific landscapes, we critically evaluate the strengths and weaknesses and identify potential remedies, which we then expand into consideration of how simulation can be incorporated into palynological research practice. We argue that the MSA deserves a place within the palynologist’s standard tool kit.

Nectaries in fly-deceptive pitcher-trap blossoms of Aristolochia

The flowers of the eight Aristolochia species studied in this paper (A. arborea, A. clematitis, A. gigantea, A. grandiflora, A. rotunda, A. salvadorensis, A. sempervirens, A. tricaudata) represent three different pollinator deceit cases in this genus: brood site mimic in carrion-fly and fungus-gnat blossoms and food source mimic. In any case, all of them have nectaries on the inner wall of the kettle which provide a small quantity of nectar. As regards the histology, two different types of nectaries can be discerned: the trichomatous type and the so-called nectarioles (termed by Vogel, 1998). The latter type, characterized by clusters of independent and isolated glandular units, is reported for the first time in the kettles of Aristolochia, namely in A. arborea, A. salvadorensis and A. tricaudata.The nectar production in the kettles of the investigated species is regarded as food ensuring survival of the imprisoned pollinators during captivity. Additionally, the location of the nectaries on the inner kettle wall can be interpreted as an adaptation directing the trapped flies to the exit after pollination and fresh pollen loading.

Nectar vs. pollen loading affects the tradeoff between flight stability and maneuverability in bumblebees

Bumblebee foragers spend a significant portion of their lives transporting nectar and pollen, often carrying loads equivalent to more than half their body mass. Whereas nectar is stored in the abdomen near the bee's center of mass, pollen is carried on the hind legs, farther from the center of mass. We examine how load position changes the rotational moment of inertia in bumblebees and whether this affects their flight maneuverability and/or stability. We applied simulated pollen or nectar loads of equal mass to Bombus impatiens bumblebees and examined flight performance in a wind tunnel under three conditions: flight in unsteady flow, tracking an oscillating flower in smooth flow, and flower tracking in unsteady flow. Using an inertial model, we estimated that carrying a load on the legs rather than in the abdomen increases a bee's moment of inertia about the roll and yaw axes but not the pitch axis. Consistent with these predictions, we found that bees carrying a load on their legs displayed slower rotations about their roll and yaw axes, regardless of whether these rotations were driven by external perturbations or self-initiated steering maneuvers. This allowed pollen-loaded bees to maintain a more stable body orientation and higher median flight speed in unsteady flow but reduced their performance when tracking a moving flower, supporting the concept of a tradeoff between stability and maneuverability. These results demonstrate that the types of resources collected by bees affect their flight performance and energetics and suggest that wind conditions may influence resource selection.

Ovarian Control of Nectar Collection in the Honey Bee (Apis mellifera)

Honey bees are a model system for the study of division of labor. Worker bees demonstrate a foraging division of labor (DOL) by biasing collection towards carbohydrates (nectar) or protein (pollen). The Reproductive ground-plan hypothesis of Amdam et al. proposes that foraging DOL is regulated by the networks that controlled foraging behavior during the reproductive life cycle of honey bee ancestors. Here we test a proposed mechanism through which the ovary of the facultatively sterile worker impacts foraging bias. The proposed mechanism suggests that the ovary has a regulatory effect on sucrose sensitivity, and sucrose sensitivity impacts nectar loading. We tested this mechanism by measuring worker ovary size (ovariole number), sucrose sensitivity, and sucrose solution load size collected from a rate-controlled artificial feeder. We found a significant interaction between ovariole number and sucrose sensitivity on sucrose solution load size when using low concentration nectar. This supports our proposed mechanism. As nectar and pollen loading are not independent, a mechanism impacting nectar load size would also impact pollen load size.

Flower morphology, nectar traits and pollinators of Cerinthe major (Boraginaceae-Lithospermeae)

In April and May 2010, a natural population of Cerinthe major (Boraginaceae-Lithospermeae) was investigated with regard to: floral morphology, phenology, sexual receptivity during anthesis, the production of nectar and its sugar and amino acid content. The pollinator array of this species was also investigated. Cerinthe major has showy, pentamerous, hermaphroditic flowers with a deep yellow corolla tube arranged on numerous scorpioid inflorescences. Nectar and pollen are the main floral rewards for pollinators. The arrangement of stamens limits access to nectar and promotes pollen loading onto pollinator bodies as they force their way towards the source of nectar. By limiting the direct exposure of nectar to the environment, the corolla tube and the arrangement of anther filaments seemingly protect nectar from evaporation resulting from high temperatures and low relative humidity during flower anthesis. The green, annular nectary located at the base of the ovary lobes is composed of a very thin epidermis enclosing a dense mass of parenchyma. The epidermis lacks stomata, and the thin cuticle has an irregular surface. The parenchyma cells do not store starch during the pre-secretory stage, suggesting that immediate photosynthesis is the most likely source of nectar carbohydrates. Generally, anthesis lasts 4–5 days; the gynoecium becomes fully receptive on the second day and this is synchronous with anther dehiscence. Since nectar production begins during the bud stage, a substantial volume is available for flower visitors at anthesis. Nectar production decreases drastically in senescent flowers and, if not consumed, the nectar can be re-absorbed. Analysis of sugars revealed a sucrose-dominant nectar (sucrose=93.18±1.35%). Proline, GABA, taurine, leucine, citrulline and alanine were the main amino acids present and are probably implicated in pollinator flight performance.The bees Bombus hortorum, Anthophora sp. and Eucera sp. were constant and frequent visitors of C. major flowers. Moreover, the manner in which they interacted with the flower in order to obtain nectar and pollen loads was sufficient evidence for their role as pollinators. Their different foraging behaviours suggest that each species may promote differences in pollen flow both within and among individuals of the population.

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.

The use of modelling and simulation approach in reconstructing past landscapes from fossil pollen data: a review and results from the POLLANDCAL network

Information on past land cover in terms of absolute areas of different landscape units (forest, open land, pasture land, cultivated land, etc.) at local to regional scales is needed to test hypotheses and answer questions related to climate change (e.g. feedbacks effects of land-cover change), archaeological research, and nature conservancy (e.g. management strategy). The palaeoecological technique best suited to achieve quantitative reconstruction of past vegetation is pollen analysis. A simulation approach developed by Sugita (the computer model POLLSCAPE) which uses models based on the theory of pollen analysis is presented together with examples of application. POLLSCAPE has been adopted as the central tool for POLLANDCAL (POLlen/LANdscape CALibration), an international research network focusing on this topic. The theory behind models of the pollen–vegetation relationship and POLLSCAPE is reviewed. The two model outputs which receive greatest attention in this paper are the relevant source area of pollen (RSAP) and pollen loading in mires and lakes. Six examples of application of POLLSCAPE are presented, each of which explores a possible use of the POLLANDCAL tools and a means of validating or evaluating the models with empirical data. The landscape and vegetation factors influencing the size of the RSAP, the importance of pollen productivity estimates (PPEs) for the model outputs, the detection of small and rare patches of plant taxa in pollen records, and quantitative reconstructions of past vegetation and landscapes are discussed on the basis of these examples. The simulation approach is seen to be useful both for exploring different vegetation/landscape scenarios and for refuting hypotheses.

Pollen productivity estimates from the forest—tundra ecotone in west-central Sweden: implications for vegetation reconstruction at the limits of the boreal forest

Successful reconstruction of vegetation from fossil pollen data in the arctic and alpine tundra, and at the forest—tundra ecotone, is hampered by low pollen production of the major taxa in these environments and the likely dominance of the background pollen component. New approaches to the quantification of vegetation from pollen data (the REVEALS and LOVE models) rely on quantification of background and local pollen by applying models of pollen dispersal and deposition to modern pollen— vegetation survey work. To date, research within this emerging area has focused on lowland environments. This paper presents pollen productivity estimates (PPEs) from the forest—tundra ecotone derived from west central Sweden, discusses the relevant source area of pollen (RSAP) in this environment and estimates the background pollen contribution. The results suggest that the RSAP for moss polsters at the forest—tundra ecotone is c. 500 m, and that PPEs for the major forest tundra ecotone taxa show significant differences compared with previous studies from southern Sweden. Proximity to range limits (controlled by climatic factors) appears to be the main factor causing generally lower pollen production; however, individual taxa respond in different ways, depending on differences in growth behaviour, reproductive strategy and the species and subspecies that represent the pollen taxa. The background pollen component was dominated by arboreal taxa, and contributed c. 60% of the total pollen loading. Graminoids dominated the local component. The PPEs presented here are to date the most appropriate parameters to use for quantification of vegetation at the tundra treeline; however, the data demonstrate that caution needs to be exercised with regards to selection of appropriate PPEs for accurate quantification of taxa at their ecological range.

Monitoring fluvial pollen transport, its relationship to catchment vegetation and implications for palaeoenvironmental studies

Despite being the most important source of pollen and spore input into most lakes and near-shore marine sediments, we know very little about fluvial (waterborne) pollen and spore transport. This paper presents the results of a dedicated monitoring programme conducted over 2 years and at a catchment scale in South West England. The land use of the nine sub-catchments monitored was determined using Landsat Thematic Data. At two stations, pollen and spore sampling through storm hydrographs was undertaken whilst at the other 7 sub-catchments only peak flow samples were collected. Samples were also collected from re-suspended bed material, riverbanks and at low flows. Airborne pollen flux was monitored using modified Tauber traps. The results support previous research illustrating how the vast majority of fluvial pollen and spores are transported during floods (in this case 91%) and that the main control on waterborne pollen and spore assemblages is the catchment vegetation. However, strong seasonal effects are shown as well as the importance of distinctive sources, such as the riparian input, bed re-suspension and overland flow into drains and tributaries. Fine sediment in river pools appears to act as a selective store of damaged cereal-type pollen grains in arable catchments and this can reduce the inherent underestimate of arable land from pollen diagrams with a high fluvial input and increase the visibility of early agriculture. In order to simulate the likely result of a flood-dominated influx to a small lake scenario, modelling was undertaken whereby different sub-catchments were substituted in order to represent changes in catchment vegetation under a constant hydrological regime. The results show the dampened response of land use groups to catchment land use change, and the frequent occurrence of anomalous single-level peaks due to seasonal flushes from specific near-stream vegetation types. Both these features are commonly seen in lake pollen diagrams. Fluvial pollen and spore loading is dependant upon discharge and so concentrations in laminated or varved sediments could be regarded as a proxy for flood magnitude. The implications for this study on the interpretation of lake and near-shore marine pollen and spore diagrams are discussed and it is argued that a more quantitative approach to waterborne pollen could improve the estimation of land use from lakes in the temperate zone.

A step further towards quantitative reconstruction of past vegetation in Fennoscandian boreal forests: Pollen productivity estimates for six dominant taxa

Pollen productivity estimates (PPE) are needed for producing quantitative reconstructions of the past landscapes by means of modelling. This study aims to provide estimates of relative pollen productivity for the two main tree species ( Pinus sylvestris L. and Betula sp .), for Cyperaceae and Gramineae, and the dominant dwarf shrubs ( Empetrum, Vaccinium sp .) of northern boreal forest vegetation in Finnish Lapland. A set of 24 moss samples were collected and their pollen content analysed, and detailed vegetation analyses were carried out within a 10.5 m radius around the samples. Vegetation further away, up to 10 km from the sites, was analysed from the Finnish Land Survey data. Vegetation proportions were calculated from the remotely sensed data using the program PolFlow, and distance weighting was applied using the program ERV_v6. The distance weighted vegetation data from the field survey and the Land Survey data were combined, and analysed with the pollen data using the ERV model. The resulting PPEs were evaluated by simulating pollen loadings with the POLLSCAPE model for an independent set of eight moss samples from the same area, using the obtained PPEs. The estimated pollen loadings and the observed pollen loadings were compared using paired samples t-tests. The PPEs obtained for the two major tree species are in keeping with expectations: PPE for Pinus is 8.4 (reference taxon Gramineae = 1) and for Betula 4.6. For Cyperaceae (0.002), Empetrum (0.07), and Vaccinium (0.01) the PPEs are very low and, according to paired samples t-test of the predicted and actual pollen loading, not reliable for Cyperaceae and Gramineae. The radius of the relevant source area of pollen (RSAP) is estimated to be ca. 1000 m. The pollen productivity estimates of the species, especially Pinus and Betula, are different in the northern boreal forest than in previously studied areas, such as southern Sweden. This has great implications for quantitative interpretations of fossil pollen records from the region.

An eight-year record of pollen deposition in the Pieria mountains (N. Greece) and its significance for interpreting fossil pollen assemblages

Modern pollen deposition in the Pieria mountains, North Greece, is monitored by means of six modified Tauber traps (P1–P6). The traps are placed on an altitudinal transect from 1200 m to 2000 m a.s.l and cover a range of landscapes from forests composed of Pinus sylvestris and/or P. nigra to open sub-alpine communities with dwarf shrubs, mostly Juniperus communis ssp. nana. Since October 1996 the contents of the traps have been collected on an annual base. An eight-year series (1996–2003) of pollen deposition data, expressed as both pollen accumulation rates (PAR) and pollen percentages, is presented. The eight year average PARs reflect the vegetation within the immediate catchment area of each trap. The pollen assemblage at sites P1 and P2, which are placed at and above the treeline, respectively, signal this transitional zone through having low tree and high shrub PARs. Pine is the dominant tree species of the vegetation throughout the forested part of the transect and, as a result, trap to trap variations in its PAR define the magnitude of the total tree PAR. Other tree species, such as Quercus, contribute to the background pollen loading or, like Abies, are known to have relatively low pollen productivity. Although the PARs of Fagus are very low, due to the relationship between the location of beech forests and the topography of the Pieria mountains, two peaks in 1998 and 2001 are in keeping with the three-year cycle of mast observed in Greek beech forests. The occurrence of Castanea pollen is seen to be dependent on the dominant wind direction at the time of flowering. Juniper is the major constituent of the shrub vegetation especially near and above the treeline so, like pine, its PARs shape the trap to trap fluctuations of the total shrub PAR. A comparison of the percentage pollen values between traps P3 and P6 and the surface samples of two previously analysed cores shows the usefulness of the pollen trap results in interpreting the vegetation represented by the fossil pollen assemblages: pollen deposition monitored at different elevations is a good key for tracing past altitudinal changes in the treeline from the fossil record.

Integrated palaeoecological and historical data in the service of fine‐resolution land use and ecological change assessment during the last 1000 years in Rõuge, southern Estonia

AbstractAims Our aim is to reconstruct decadal scale development of historical landscapes during the last 1000 years by means of fossil pollen analysis of annually laminated lake sediments, and detailed historical maps and documents.Location Lake Rõuge Tõugjärv (Estonia), a small lake with annually laminated lake sediments situated in a dense prehistoric setting.Methods The chronology of the palaeodata is based on the annual laminations supported by AMS 14C and 210Pb dating and 137Cs, 241Am, and spheroidal carbonaceous particle marker horizons. The time‐scale and resolution allows fine sampling (the pollen samples generally comprise 3.5 years) and vegetation change reconstruction. Relevant source area of pollen (RSAP) of the lake was estimated, and the statistical zonation, rate of change, palynological richness, and DCA and PCA ordinations were generated on the basis of the pollen data. The historical calibration data set (maps, numerical information on population, domestic stock, farmland division, etc.) is based on archival material preserved in the Estonian Historical Archives.Results The topmost part (0–180 cm) of the sediment column of Lake Rõuge Tõugjärv, covering the last 1000 years, is visibly laminated carbonaceous gyttja. The varve chronology extends from ad 2000 to ad 1339, with a cumulative ± 9‐year error estimate. Beyond this the chronology is extrapolated using the 14C date and varve age–depth estimations. The simulation of the RSAP of Lake Tõugjärv shows that the major portion of the pollen loading originating from local vegetation is derived from plants growing within 2000 m of the sampling site. The pollen record divides into five statistically significant subgroups, which fall on the PCA plot into three clusters reflecting the general openness–closedness of the landscape. During the period between ad 1000 and 1200 (RT 1) the Rõuge area was generally wooded with birch, spruce and pine forests. The advancement of extensive farming gradually opened up the landscape between ad 1200 and 1650 (RT 2 and RT 3). The maximum openness of the landscape was reached between ad 1650 and 1875 (RT 4), with the most open period in the late eighteenth century. Historical maps from 1684 and 1870–99 and available quantitative data on population, domestic stock, farmland division, etc. show the same trend. The pollen data covering the last 125 years, and maps from 1935 and 1995, show the reduction of arable land in RSAP of the lake under investigation and the reduction of open land to an extent comparable with the end of the seventeenth century.Main conclusions The formation and development of the cultural landscape at Rõuge over the last 1000 years is characterized by rapid changes in floristic richness and rates of vegetation change attributed to certain historic processes in the RSAP. Five phases of landscape and social development are clearly distinguished during the last 1000 years. The decadal scale vegetation response to human‐induced forcing agrees with historical maps and documents and could be used for past landscapes prior to the period with solid historical data.

Modelling pollen sedimentation in Danish lakes at c.ad 1800: an attempt to validate the POLLSCAPE model

AbstractAims To validate the POLLSCAPE simulation model of pollen dispersal and deposition, and evaluate the effect of factors such as pollen productivity, wind speed and regional plant abundance, using a data set of ad 1800 pollen assemblages and historical land cover data.Location Denmark.Methods ad 1800 land cover from historical maps is digitized for 2000 m radii around 30 Danish lakes (3.5–33 ha). The simulation model POLLSCAPE is used to predict sedimentary pollen assemblages in the lakes from the plant abundance data inferred from these maps, with different model parameter settings for wind speed, pollen productivity, regional pollen loading, etc. The model predictions are compared with observed ad 1800 pollen assemblages from the lake sediment records. Furthermore, pollen productivity is estimated from the ad 1800 pollen and vegetation data using the Extended R‐value model.Results Generally the model reproduces the patterns in the observed pollen assemblages, and for most pollen types there are significant correlations between observed and predicted pollen proportions. The pollen proportions predicted by the POLLSCAPE model are sensitive to the pollen productivity estimates used, the regional background pollen loading and average wind speed. There is a difference in background pollen loading between eastern and western Denmark, especially of Calluna pollen. The fit between predicted and observed pollen assemblages is best at wind speeds around 2.5 m s−1, and decreases rapidly at lower wind speeds. The pollen productivity estimates from the ad 1800 data set are comparable with estimates from moss polsters in modern analogues of traditional cultural landscapes in Sweden and Norway.Main conclusions The POLLSCAPE model reproduces the patterns in the observed pollen assemblages from the lakes well, considering the uncertainty in the historical plant abundance data. This study indicates that the simulation model can be a useful tool for investigating relationships between vegetation and pollen composition, but also that the simulated pollen proportions are sensitive to the pollen productivity estimates, the regional background and to wind speed.

OPENLAND3: a computer program to estimate plant abundance around pollen sampling sites from vegetation maps: a necessary step for calculation of pollen productivity estimates

OPENLAND3 belongs to a suite of computer programs included in the POLLSCAPE simulation model. These programs make it possible to calculate estimates of pollen loadings in lake basins or bogs using vegetation data. OPENLAND3, written in Visual Basic 6, is designed to produce appropriate vegetation data files from vegetation maps stored in a Geographical Information System. It calculates percentage cover of plant taxa in concentric circles at increasing distances from a central point, using either real digitised maps or hypothetical maps (simulated landscape designs). Such data are necessary for simulation of pollen dispersal and deposition, and for calculation of pollen productivity estimates and relevant source area of pollen using specific mathematical models developed by palynologists, such as the Prentice-Sugita model. OPENLAND3 also produces output files needed to run RS-OPEN, another program included in POLLSCAPE, in order to obtain estimates of pollen loadings in lakes or bogs. The rationale of OPENLAND3, the algorithm used, and a modification of RS-OPEN (RS-OPEN2) are described. A test of the programme capability using a detailed vegetation map from southern Sweden shows that simulations using OPENLAND3 produce coherent results. Pollen loading for species characterized by high pollen productivity is higher than for species with low pollen productivity. Altering the wind speed has also a significant effect on pollen loading. As wind speed increases, the proportions of the light pollen decrease, while the heavy pollen types increase, which is what empirical data suggest, and what the model predicts in earlier studies.