Relevant Source Area Of Pollen Research Articles

Relation between modern pollen rain, vegetation and climate in northern China: Implications for quantitative vegetation reconstruction in a steppe environment

Vegetation reconstructions from palaeoecological records depend on adequate understanding of relationships between modern pollen, vegetation and climate. A key parameter for quantitative vegetation reconstructions is the Relative Pollen Productivity (RPP). Differences in both environmental and methodological factors are known to alter the RPP estimated significantly, making it difficult to determine whether the underlying pollen productivity does actually vary, and if so, why. In this paper, we present the results of a replication study for the Bashang steppe region, a typical steppe area in northern China, carried out in 2013 and 2014. In each year, 30 surface samples were collected for pollen analysis, with accompanying vegetation survey using the “Crackles Bequest Project” methodology. Sampling designs differed slightly between the two years: in 2013, sites were located completely randomly, whilst in 2014 sampling locations were constrained to be within a few km of roads. There is a strong inter-annual variability in both the pollen and the vegetation spectra therefore in RPPs, and annual precipitation may be a key influence on these variations. The pollen assemblages in both years are dominated by herbaceous taxa such as Artemisia, Amaranthaceae, Poaceae, Asteraceae, Cyperaceae, Fabaceae and Allium. Artemisia and Amaranthaceae pollen are significantly over-represented for their vegetation abundance. Poaceae, Cyperaceae and Fabaceae seem to have under-represented pollen for vegetation with correspondingly lower RPPs. Asteraceae seems to be well-represented, with moderate RPPs and less annual variation. Estimated Relevant Source Area of Pollen (RSAP) ranges from 2000 to 3000m. Different sampling designs have an effect both on RSAP and RPPs and random sample selection may be the best strategy for obtaining robust estimates. Our results have implications for further pollen-vegetation relationship and quantitative vegetation reconstruction research in typical steppe areas and in other open habitats with strong inter-annual variation.

Testing quantitative pollen dispersal models in animal-pollinated vegetation mosaics: An example from temperate Tasmania, Australia

Reconstructing past vegetation abundance and land-cover changes through time has important implications in land management and climate modelling. To date palaeovegetation reconstructions in Australia have been limited to qualitative or semi-quantitative inferences from pollen data. Testing pollen dispersal models constitutes a crucial step in developing quantitative past vegetation and land cover reconstructions. Thus far, the application of quantitative pollen dispersal models has been restricted to regions dominated by wind-pollinated plants (e.g. Europe) and their performance in a landscape dominated by animal-pollinated plant taxa is still unexplored. Here we test, for the first time in Australia, two well-known pollen dispersal models to assess their performance in the wind- and animal-pollinated vegetation mosaics of western Tasmania. We focus on a mix of wind- (6 taxa) and animal- (7 taxa) pollinated species that comprise the most common pollen types and key representatives of the dominant vegetation formations. Pollen Productivity Estimates and Relevant Source Area of Pollen obtained using Lagrangian Stochastic turbulent simulations appear to be more realistic when compared to the results from the widely used Gaussian Plume Model.

Relative pollen productivity estimates for common taxa of the northern Siberian Arctic

Pollen productivity estimates (PPE) are used to quantitatively reconstruct variations in vegetation within a specific distance of the sampled pollen archive. Here, for the first time, PPEs from Siberia are presented. The study area (Khatanga region, Krasnoyarsk territory, Russia) is located in the Siberian Sub-arctic where Larix is the sole forest-line forming tree taxon. Pollen spectra from two different sedimentary environments, namely terrestrial mosses (n=16) and lakes (n=15, median radius~100m) and their surrounding vegetation were investigated to extract PPEs. Our results indicate some differences in pollen spectra between moss and lake pollen. Larix and Cyperaceae for example obtained higher representation in the lacustrine than in terrestrial moss samples. This highlights that in calibration studies, modern and fossil datasets should use archives of similar sedimentary origin. Results of an Extended R-Value model were applied to assess the relevant source area of pollen (RSAP) and to calculate the PPEs for both datasets. As expected, the RSAP of the moss samples was very small (about 10m) compared to the lacustrine samples (about 25km). Calculation of PPEs for the six most common taxa yielded generally similar results for both datasets. Relative to Poaceae (reference taxon, PPE=1) Betula nana-type (PPEmoss: 1.8, PPElake: 1.8) and Alnus fruticosa-type (PPEmoss:6.4, PPElake:2.9) were overrepresented while Cyperaceae (PPEmoss:0.5, PPElake:0.1), Ericaceae (PPEmoss: 0.3, PPElake<0.01), Salix (PPEmoss:0.03, PPElake<00.1) and Larix (PPEmoss: <0.01, PPElake:0.2) were under-represented in the pollen spectra compared to the vegetation in the RSAP. The estimation for the dominant tree in the region, Larix gmelinii, is the first published result for this species, but needs to be considered very preliminary. The inferred sequence from over- to under-representation is mostly consistent with results from Europe; however, the absolute values show some differences. Gathering vegetation data was limited by the remoteness of our study area and a lack of high-resolute satellite imagery and vegetation maps. Our estimate may serve as a first reference to strengthen future vegetation reconstructions in this climate-sensitive region.

Pollen production estimates (PPEs) and fall speeds for major tree taxa and relevant source areas of pollen (RSAP) in Changbai Mountain, northeastern China

For model-based quantitative reconstructions of past vegetation cover on the scale of landscapes, pollen productivity estimates (PPEs) are key input parameters. In this study, we employed a random sampling strategy to collect moss polsters at 20 sites in Changbai Mountain, northeastern China. A detailed vegetation survey within 1000-m radius around each sampling point was carried out and digitized vegetation maps were used for vegetation data compilation. A forest map at the scale of 1:25,000 was used to extract information about vegetation for the area between 1000 and 5000m from each sampling point. Using the ERV (Extended R-Value) model, pollen productivity was estimated for Larix, Pinus, Juglans, Ulmus, Tilia, Betula and Fraxinus relative to Quercus. Estimates of pollen fall speeds for the eight taxa as well as the relevant source area of pollen (RSAP) were also obtained. Three different ERV sub-models were tested against the data. The sub-model 3 produced the best goodness of fit and the PPE values calculated with this sub-model show that Betula (5.04), Pinus (3.11), Juglans (1.94) and Ulmus (1.40) are high pollen producers with higher PPEs than Quercus while Fraxinus (0.76), Larix (0.30), Tilia (0.16) are low pollen producers compared to Quercus. The high pollen producers are all anemophilous species, while low pollen producing plants include both entomophilous, such as Fraxinus, Tilia and anemophilous species such as Larix. The estimated RSAP for the eight tree pollen taxa is about 2000–2500m.

Relative pollen productivities of typical steppe species in northern China and their potential in past vegetation reconstruction

The Relative Pollen Productivities (RPPs) of common steppe species are estimated using Extended R-value (ERV) model based on pollen analysis and vegetation survey of 30 surface soil samples from typical steppe area of northern China. Artemisia, Chenopodiaceae, Poaceae, Cyperaceae, and Asteraceae are the dominant pollen types in pollen assemblages, reflecting the typical steppe communities well. The five dominant pollen types and six common types (Thalictrum, Iridaceae, Potentilla, Ephedra, Brassicaceae, and Ulmus) have strong wind transport abilities; the estimated Relevant Source Area of Pollen (RSAP) is ca. 1000 m when the sediment basin radius is set at 0.5 m. Ulmus, Artemisia, Brassicaceae, Chenopodiaceae, and Thalictrum have relative high RPPs; Poaceae, Cyperaceae, Potentilla, and Ephedra pollen have moderate RPPs; Asteraceae and Iridaceae have low RPPs. The reliability test of RPPs revealed that most of the RPPs are reliable in past vegetation reconstruction. However, the RPPs of Asteraceae and Iridaceae are obviously underestimated, and those of Poaceae, Chenopodiaceae, and Ephedra are either slightly underestimated or slightly overestimated, suggesting that those RPPs should be considered with caution. These RPPs were applied to estimating plant abundances for two fossil pollen spectra (from the Lake Bayanchagan and Lake Haoluku) covering the Holocene in typical steppe area, using the “Regional Estimates of Vegetation Abundance from Large Sites” (REVEALS) model. The RPPs-based vegetation reconstruction revealed that meadow-steppe dominated by Poaceae, Cyperaceae, and Artemisia plants flourished in this area before 6500-5600 cal yr BP, and then was replaced by present typical steppe.

Calibrating Vegetation Cover and Grassland Pollen Assemblages in the Flint Hills of Kansas, USA

Grassland cover and composition respond to climate and have undoubtedly changed during the Holocene, but quantitative reconstructions from fossil pollen have been vague about spatial scale and taxon-specific cover. Here, we estimate the relevant source area of pollen for sedimentary basins approximately 50 m in radius, and we report pollen productivity estimates for 12 plant taxa in the tallgrass prairies of central North America. Both relevant source area of pollen and pollen productivity estimates were calculated via the Extended R-Value Model. To obtain these estimates, we collected and quantified the pollen found in surface sediment samples from 24 ponds across the study area. Vegetation was surveyed in the field in a 100 m radius around each pond, and vegetation maps from the Kansas Gap Analysis Project (GAP) were used to a radius of 2 km. Pollen fall speeds were calculated according to Stoke’s Law. Pollen assemblages from basins approximately 50 m in radius have a relevant source area of 1060 m in this grassland landscape. Pollen productivity estimates range from 0.02 to over 30 among the 12 taxa: Artemisia, Ambrosia, Asteraceae, Chenopodiaceae, Cornus, Fabaceae, Juniperus, Maclura, Poaceae, Populus, Quercus, and Salix. Woody taxa generally have higher pollen productivity than herbaceous taxa (except for Chenopodiaceae and Ambrosia).

Estimates of relative pollen productivity (RPP) for selected taxa from southern Greenland: A pragmatic solution

This paper presents the reanalysis of a modern surface sample pollen–vegetation dataset from southern Greenland aimed at extracting estimates of relative pollen productivity (RPP). RPP is a key parameter required in order to use models of pollen dispersal and deposition for hypothesis-testing and quantitative reconstruction of past vegetation cover from pollen assemblages. The data were originally collected for ordination analysis, but as sample points were located in relatively homogenous stands of representative vegetation it was possible to reprocess the vegetation data into a suitable format for obtaining initial estimates of RPP using the extended R-value approach. Although it is not possible to accurately estimate the relevant source area of pollen (RSAP) and thus obtain the best available estimates of RPP, preliminary estimates of RPP relative to Poaceae were obtainable for 17 pollen types.

The interpretation of Holocene pollen assemblages from coastal lowlands: differentiating natural and anth-ropogenic causal processes and the problems of equifinality

Vegetation reconstructions from palaeoecological records depend on adequate understanding of relationships between modern pollen, vegetation and climate. A key parameter for quantitative vegetation reconstructions is the Relative Pollen Productivity (RPP). Differences in both environmental and methodological factors are known to alter the RPP estimated significantly, making it difficult to determine whether the underlying pollen productivity does actually vary, and if so, why. In this paper, we present the results of a replication study for the Bashang steppe region, a typical steppe area in northern China, carried out in 2013 and 2014. In each year, 30 surface samples were collected for pollen analysis, with accompanying vegetation survey using the “Crackles Bequest Project” methodology. Sampling designs differed slightly between the two years: in 2013, sites were located completely randomly, whilst in 2014 sampling locations were constrained to be within a few km of roads. There is a strong inter-annual variability in both the pollen and the vegetation spectra therefore in RPPs, and annual precipitation may be a key influence on these variations. The pollen assemblages in both years are dominated by herbaceous taxa such as Artemisia, Amaranthaceae, Poaceae, Asteraceae, Cyperaceae, Fabaceae and Allium. Artemisia and Amaranthaceae pollen are significantly over-represented for their vegetation abundance. Poaceae, Cyperaceae and Fabaceae seem to have under-represented pollen for vegetation with correspondingly lower RPPs. Asteraceae seems to be well-represented, with moderate RPPs and less annual variation. Estimated Relevant Source Area of Pollen (RSAP) ranges from 2000 to 3000 m. Different sampling designs have an effect both on RSAP and RPPs and random sample selection may be the best strategy for obtaining robust estimates. Our results have implications for further pollen-vegetation relationship and quantitative vegetation reconstruction research in typical steppe areas and in other open habitats with strong inter-annual variation.

Relative pollen productivity estimates for herbaceous taxa in the Hulunbeier steppe, Inner Mongolia

We estimated relative pollen productivity estimates (PPE), key parameters for the quantitative interpretation of pollen data, for 13 taxa using modern pollen assemblages from 54 sites and recent vegetation data. Vegetation mapping in the area covered a minimum radius of 2 km around each sampling site. Vegetation data were weighted by the Prentice model, i.e. weighting by distance and by the dispersal–deposition parameters of different pollen types. PPE values were calculated by three submodels of the Extended R-value model. ERV 1 produced the best goodness of fit. The PPEs for Urtica and Sambucus nigra are published here for the first time, and the PPE for the Chenopodiaceae represents the first estimate for Europe. Values for the other ten taxa (Poaceae, Pinus, Salix, Fraxinus, Quercus, Tilia, Artemisia, Plantago lanceolata, Alnus and Cerealia) are comparable with or fall within the ranges of values published in previous studies. Herb taxa produce ca 3–11 times more pollen than the Poaceae. Herbs produce even more pollen than trees, whose production is 1–6 times higher than that of the Poaceae. The lowest pollen producers are the Cerealia, producing 20 times less pollen than the Poaceae. Our estimate of the relevant source area of pollen (RSAP) of 1050 m is relatively high compared to other studies in semi-open landscapes. This is possibly caused by the uneven pattern of some taxa in the vegetation mosaic (Pinus, P. lanceolata, Salix and Alnus). The distance of 1100 m, at which all taxa are present around each site, is similar to the RSAP distance (1050 m).

Evaluating the effect of flowering age and forest structure on pollen productivity estimates

Pollen productivity estimates (PPEs) are indispensable prerequisites for quantitative vegetation reconstructions. Estimates from different European regions show a large variability and it is uncertain whether this reflects regional differences in climate and soil or is brought about by different assessments of vegetation abundance. Forests represent a particular problem as they consist of several layers of vegetation and many tree species only start producing pollen after they have attained ages of several decades. Here we used detailed forest inventory data from north-eastern Germany to investigate the effect of flowering age and understory trees on PPEs. Pollen counts were obtained from 49 small to medium sized lakes chosen to represent the different forest types in the region. Surface samples from lakes within a closed forest of Fagus yielded disproportionate amounts of Fagus pollen, increasing its PPE and the variability of all other estimates. These samples were removed from further analysis but indicate a high trunk-space component that is not considered in the Prentice–Sugita pollen dispersal and deposition model. Results of the restricted dataset show important differences in PPEs based on the consideration of flowering age and understory position. The effect is largest for slow growing and/or late flowering trees like Fagus and Carpinus while it is minimal for species that flower early in their development like Betula and Alnus. The large relevant source area of pollen (RSAP) of 7 km obtained in this study is consistent with the landscape structure of the region.

Relative pollen productivity estimates in the modern agricultural landscape of Central Bohemia (Czech Republic)

We estimated relative pollen productivity estimates (PPE), key parameters for the quantitative interpretation of pollen data, for 13 taxa using modern pollen assemblages from 54 sites and recent vegetation data. Vegetation mapping in the area covered a minimum radius of 2km around each sampling site. Vegetation data were weighted by the Prentice model, i.e. weighting by distance and by the dispersal–deposition parameters of different pollen types. PPE values were calculated by three submodels of the Extended R-value model. ERV 1 produced the best goodness of fit. The PPEs for Urtica and Sambucus nigra are published here for the first time, and the PPE for the Chenopodiaceae represents the first estimate for Europe. Values for the other ten taxa (Poaceae, Pinus, Salix, Fraxinus, Quercus, Tilia, Artemisia, Plantago lanceolata, Alnus and Cerealia) are comparable with or fall within the ranges of values published in previous studies. Herb taxa produce ca 3–11 times more pollen than the Poaceae. Herbs produce even more pollen than trees, whose production is 1–6 times higher than that of the Poaceae. The lowest pollen producers are the Cerealia, producing 20 times less pollen than the Poaceae. Our estimate of the relevant source area of pollen (RSAP) of 1050m is relatively high compared to other studies in semi-open landscapes. This is possibly caused by the uneven pattern of some taxa in the vegetation mosaic (Pinus, P. lanceolata, Salix and Alnus). The distance of 1100m, at which all taxa are present around each site, is similar to the RSAP distance (1050m).

The role of landscape structure in determining palynological and floristic richness

The associations between floristic and palynological richness and landscape structure were studied based on modern pollen–vegetation data from a patchy cultural landscape in southern Estonia (northern temperate vegetation zone). Nine study sites (small lakes and their surrounding vegetation) represent land cover gradient from closed forest to semi-open vegetation. Floristic richness (number of species) and floristic richness of pollen types (number of pollen-equivalent taxa) were used to describe the vegetation within the radius of 250 m from the pollen sampling sites. Palynological richness was calculated to describe the modern pollen samples diversity. Landscape structure was estimated on the basis of landscape openness and three landscape diversity measures: richness of community patches, Simpson evenness of community patches and Simpson diversity of community patches. To study the effect of the spatial scale of landscapes on the vegetation–landscape and pollen–landscape associations, landscape structure was estimated within eight radii (250–2,000 m) around each lake. The results showed that landscape openness was the most important determinant of both floristic richness and palynological richness in southern Estonia and that landscape diversity estimated by Simpson diversity index was also significantly associated with the richness estimates. Floristic and palynological richness were significantly positively correlated with landscape structure within the radii greater than 1,000 m from the pollen sampling sites, which is similar to the estimated Relevant Source Area of Pollen in southern Estonia. We conclude that within one floristic or climatic region, palynological richness gives reliable estimates about the variation in floristic richness and landscape structure; however, caution must be taken when comparing pollen-inferred vegetation diversities from different regions or when interpreting fossil pollen records from times with highly different vegetation associations.

362 Estimating relevant source area of pollen and relative pollen productivity in the Hakkoda Mountains, northeastern Japan

362 Estimating relevant source area of pollen and relative pollen productivity in the Hakkoda Mountains, northeastern Japan

Estimating pollen productivity and relevant source area of pollen using lake sediments in Norway: How does lake size variation affect the estimates?

This study aims to estimate relative pollen productivity (PPEs) of major pollen types and the relevant source area of pollen (RSAP) in a semi-open landscape in western Norway. Extended R-value (ERV) models are used to analyse a data set consisting of surface pollen assemblages from 34 lakes and vegetation survey around each site. Ordination techniques indicate relatively short gradients (&lt;2.3 SD) both in the vegetation and pollen data sets. The lake sizes vary from 0.4 ha to 19.0 ha (mean=5.7 ha, sd=4.3 ha) but follow a normal distribution – a departure from the assumption of the ERV models that the lake size should be constant among sites. Simulations demonstrate that, if the sizes of circular-shaped lakes follow a normal distribution, the ERV model-based methods provide the expected PPE and RSAP values using a standardized lake radius. If the distribution is highly skewed or equally random around the mean, the results are not reliable. We apply the analytical strategy implied from the simulations to obtain relative PPEs and the RSAP in western Norway. PPEs for ten taxa ( Alnus, Fagus, Picea, Pinus, Quercus, Juniperus, Salix, Calluna, Cyperaceae, Rumex) relative to Poaceae are comparable with some of those previously obtained in different parts of Europe, indicating that there are general patterns of high and low pollen producers that will be useful for reconstruction purposes. The RSAP estimate is the area within a radius of 900–1100 m. This study demonstrates the importance of careful evaluation of the extent to which the departures from the model assumptions affect the outcomes from the ERV model-based analysis.

Reassessment of Holocene vegetation change on the upper Tibetan Plateau using the pollen-based REVEALS model

Previous studies based on fossil pollen data have reported significant changes in vegetation on the alpine Tibetan Plateau during the Holocene. However, since the relative proportions of fossil pollen taxa are largely influenced by individual pollen productivities and the dispersal characteristics, such inferences on vegetation have the potential to be considerably biased. We therefore examined the modern pollen–vegetation relationships for four common pollen species on the Tibetan Plateau, using Extended R-value (ERV) models. Assuming an average radius of 100 m for the sampled lakes, we estimated the relevant source area of pollen (RSAP) to be 2200 m (which represents the distance from the lake). Using Poaceae as the reference taxa (Pollen Productivity Estimate, PPE = 1), ERV Submodel 2 derived relative high PPEs for the steppe and desert taxa: 2.079 ± 0.432 for Artemisia and 5.379 ± 1.077 for Chenopodiaceae. Low PPEs were estimated for the Cyperaceae (1.036 ± 0.012), whose plants are characteristic of the alpine Kobresia meadows. Applying these PPEs to four fossil pollen sequences since the Late Glacial, the plant abundances on the central and north-eastern Tibetan Plateau were quantified using the “Regional Estimates of Vegetation Abundance from Large Sites” (REVEALS) model. The proportions of Artemisia and Chenopodiaceae were greatly reduced compared to their original pollen percentages in the reconstructed vegetation, owing to their high productivities and their dispersal characteristics, while Cyperaceae showed a relative increase in the vegetation reconstruction. The reconstructed vegetation assemblages of the four pollen sequence sites always yielded smaller compositional species turnovers than suggested by the pollen spectra, as revealed by Detrended Canonical Correspondence Analyses (DCCA) of the Holocene sections. The strength of the previously reported vegetation changes may therefore have been overestimated, which indicates the importance of taking into account pollen–vegetation relationships when discussing the potential drivers (such as climate, land use, atmospheric CO 2 concentrations) and implications (such as for land surface–climate feedbacks, carbon storage, and biodiversity) of vegetation change.

Relative pollen productivity estimates of major anemophilous taxa and relevant source area of pollen in a cultural landscape of the hemi-boreal forest zone (Estonia)

Estimates of relevant source area of pollen (RSAP) and relative pollen productivity (PPE) are critical parameters for quantitative reconstructions of past vegetation and land cover. This study provides estimates for PPE relative to Poaceae for ten taxa, characterizing the cultural landscape of south Estonia and the RSAP for 40 lakes with an average radius of approximately 100 m (22–274 m, average 101 m) in the region. We evaluate the effects on those estimates of various combinations of factors, such as the analytical methods (i.e. three Extended R value (ERV) sub-models), the distance-weighting methods used to determine plant abundance, and alternative classification schemes of vegetation and land cover data around study sites. Different combinations of ERV sub-models and distance-weighting methods lead to estimates of RSAP varying between 1500 m and 2000 m. The differences in the estimated RSAP are strongly related to the patch size of the vegetation data. According to ERV sub-model 1, which shows the highest log-likelihood among the three sub-models, most of the taxa have PPE that are higher ( Picea, Pinus, Quercus), slightly higher ( Salix, Artemisia, Filipendula) or similar ( Betula, Cerealia, Cypreraceae) to that of Poaceae. The three ERV sub-models produce only slightly different PPE. However, the selection of distance-weighting method for vegetation has considerable influence on the PPE values. The inverse distance-weighting methods, which do not consider inter-taxonomic differences in pollen dispersal, tend to underestimate PPE for taxa with heavy pollen grains and overestimate PPE for taxa with light pollen grains, compared to the results obtained using other methods that consider taxon specific pollen-dispersal. General land-cover data, based on the classification scheme similar to the CORINE (COoRdination of Information on the Environment) database, could be used for estimating the RSAP and PPE, although some potential problems remain when the classification is too simplified and consolidated.

Testing the Landscape Reconstruction Algorithm for spatially explicit reconstruction of vegetation in northern Michigan and Wisconsin

The Landscape Reconstruction Algorithm (LRA) overcomes some of the fundamental problems in pollen analysis for quantitative reconstruction of vegetation. LRA first uses the REVEALS model to estimate regional vegetation using pollen data from large sites and then the LOVE model to estimate vegetation composition within the relevant source area of pollen (RSAP) at small sites by subtracting the background pollen estimated from the regional vegetation composition. This study tests LRA using training data from forest hollows in northern Michigan (35 sites) and northwestern Wisconsin (43 sites). In northern Michigan, surface pollen from 152-ha and 332-ha lakes is used for REVEALS. Because of the lack of pollen data from large lakes in northwestern Wisconsin, we use pollen from 21 hollows randomly selected from the 43 sites for REVEALS. RSAP indirectly estimated by LRA is comparable to the expected value in each region. A regression analysis and permutation test validate that the LRA-based vegetation reconstruction is significantly more accurate than pollen percentages alone in both regions. Even though the site selection in northwestern Wisconsin is not ideal, the results are robust. The LRA is a significant step forward in quantitative reconstruction of vegetation.

Effect of vegetation data collection strategies on estimates of relevant source area of pollen (RSAP) and relative pollen productivity estimates (relative PPE) for non-arboreal taxa

Thirteen surface moss samples were collected for pollen analysis from an area of heathland in western Norway. Vegetation composition at different distances around the sampling locations was measured using three different survey methods; rooted frequency within a sub-divided 1 m × 1 m quadrat, visual estimates of cover within a 1 m × 1 m quadrat and a modified form of the ‘circle-walking method’. Extended R-value analysis was used to explore the pollen–vegetation relationships for five main taxa, Calluna vulgaris, Vaccinium-type, Cyperaceae, Poaceae and Potentilla-type. The estimates of relevant source area of pollen obtained were similar regardless of the vegetation survey method. Values obtained were always under 4 m. However, estimates of relative pollen productivity and the background pollen component (proportion of pollen coming from vegetation growing beyond the relevant source area of pollen) differ markedly depending on the method of vegetation survey chosen. This has important implications for the quantitative reconstruction of past vegetation cover.

Estimating the Relevant Source Area of Pollen in the past cultural landscapes of southern Sweden — A forward modelling approach

In this paper, we estimate the Relevant Source Area of Pollen (RSAP) in past hypothetical landscapes of the Middle and Late Holocene in southern Sweden, in order to explore the possible effects of past changes in vegetation composition, openness and structure in terms of patch size and spatial distribution. The RSAP of small basins (bogs or lakes) in the past has to be estimated if quantitative reconstruction of past vegetation at the local spatial scale is to be achieved using Sugita's Landscape Reconstruction Algorithm (LRA). In this study we apply a forward modelling approach to estimate past RSAP using the computer simulation model HUMPOL. The landscape designs are based on past landscape maps produced using a combination of palaeobotanical, archaeological and historical data, and the area's geology and soil characteristics. Four time windows characterised by different landscape/land-use were selected, i.e. Early Neolithic, Late Bronze Age, Viking Age, and Middle Ages. We found that RSAP estimates for hypothetical past landscapes in Skåne differ by ca. 600 m to 1200 m between the selected time periods, whatever the size of the basin (lake or bog, 25–250 m radius). The most probable explanation for the differences in RSAP between time slices is variable patch size and spatial distribution of patches in the landscape. The RSAPs vary between ca. 1200 and 2300 m for small basins (25 m and 70 m radius), and between ca. 2000 and 3000 m for larger basins (250 m radius). These values are within the range of earlier estimates of modern and past RSAPs for southern Scandinavia obtained using simulated or empirical data. These results suggest that, given the type of setting of that region in terms of taxa composition and traditional land-use, the RSAP for small-size lakes (25–250 m radius) will generally be in the range ca. 1200–3000 m. The forward modelling approach is found to be useful to assess the possible effects on RSAP of changes in vegetation/landscape characteristics between different periods of the past. Moreover, comparison of RSAP estimates obtained using both the forward and backward modelling approaches will be important to identify the most credible RSAP estimates for the past.

Relevant Source Area of Pollen in patchy cultural landscapes and signals of anthropogenic landscape disturbance in the pollen record: A simulation approach

Using the HUMPOL simulation computer model we explored the effects of various factors characteristic of mosaic cultural landscapes on the Relevant Source Area of Pollen (RSAP sensu Sugita) of small lakes (50 m radius), and the representation of NAP and human-impact pollen indicators in small lakes. The following aspects were tested: 1) effect of variations in the spatial distribution of taxa/patches and species diversity on RSAP, 2) effect of changes in the proportion of landscape openness and size of openings on the RSAP and the pollen signal, and 3) the value of low-abundance anthropogenic indicator species to detect openness in the landscape. Moreover, we examined a methodological aspect of the MOSAIC computer program, i.e. the variability in RSAP due to inherent variations between replicates of random landscape simulation scripts using the program MOSAIC. We found differences in the RSAP estimates between runs using replicates of the same landscape created in the program MOSAIC. Such differences need to be taken into account when interpreting results involving the use of MOSAIC replicates. The simulations suggest that, if the model assumptions are valid, the RSAP is sensitive to vegetation structure in terms of patch size, and taxa/patch diversity and spatial distribution, whatever the properties of the taxa modelled. The longer the distance from each sampling site to get a sufficient cover of all taxa within the landscape, the larger the RSAP. If the spatial distribution of patches is very uneven and/or some taxa/patches are characterised by low frequencies in the randomized landscape, this distance will become longer. Further analysis of the results and new modelling experiments are necessary to provide better means for testing the presented hypothesis on the effect of spatial vegetation/landscape evenness on RSAP. The simulations indicate that, in hypothetical mosaic tree/herb landscapes including common NW European taxa of traditional cultural landscapes, RSAP estimates are relatively robust, i.e. will seldom be smaller than 1000 m and larger than 2500 m in radius in the case of 50 m radius lakes. NAP percentage is not a reliable “measure” of landscape openness. A NAP percentage value may represent a large range of openness percentage cover depending on the size and spatial distribution of the openness patches. Common pollen indicators of human impact and landscape openness will be represented in a pollen assemblage from small lakes when the landscape is relatively open (≥ 30%) and a minimum of 300–1000 grains is counted. Findings of pollen indicators of human impact may not be as reliable indicators of land use within the RSAP as has sometimes been assumed, especially when human activity is small scale. Moreover, it is important to realize that a small number of grains may indicate relatively large overall openness cover in the landscape, especially if the open areas consist of few large clearings rather than many small clearings.