Regional Estimates Of VEgetation Abundance From Large Sites Research Articles

High-resolution quantitative vegetation reconstruction in the North China Plain during the early-to-middle Holocene using the REVEALS model

Understanding the process and pattern of vegetation succession during the early-to-middle Holocene can yield valuable information for better predicting future vegetation evolution. In this study, we investigated the humidity evolution pattern in the North China Plain (NCP) during the early-to-middle Holocene by employing principal component analysis on 93 fossil spectra. Furthermore, by integrating the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model, we quantitatively reconstructed the process of vegetation succession and discussed vegetation response to climate change events. Our results indicate that the sample scores of the first principal component axis (PCA axis 1) exhibited a consistent negative bias, implying a gradual rise in regional humidity. The quantitatively reconstructed tree coverage was found to be lower than the uncorrected pollen proportions, while the coverage of herb plants showed a significant increase compared to their respective pollen percentages. In the early and middle Holocene, the vegetation of the NCP succeeded from meadow steppe (10,000 ∼ 8,100 cal yr B.P.) to meadow steppe with pine woodland patches (8,100 ∼ 7,100 cal yr B.P.), then to pine forest (7,100 ∼ 5,300 cal yr B.P.). The quantitatively reconstructed vegetation exhibited the most pronounced response to 8.2 ka climate event, with Asteraceae emerging as the dominant taxa. Furthermore, we conducted a comprehensive analysis of the impact of the 8.2 ka climate event on vegetation in northern China, identifying four distinct types of vegetation feedback: (1) negligible alterations in vegetation, (2) expansion of steppe or desert steppe, (3) proliferation of temperate tree species, and (4) augmentation of meadow steppe.

The challenge of comparing pollen-based quantitative vegetation reconstructions with outputs from vegetation models – a European perspective

Abstract. We compare Holocene tree cover changes in Europe derived from a transient Earth system model simulation (Max Planck Institute Earth System Model – MPI-ESM1.2, including the land surface and dynamic vegetation model JSBACH) with high-spatial-resolution time slice simulations performed in the dynamic vegetation model LPJ-GUESS (Lund–Potsdam–Jena General Ecosystem Simulator) and pollen-based quantitative reconstructions of tree cover based on the REVEALS (Regional Estimates of Vegetation Abundance from Large Sites) model. The dynamic vegetation models and REVEALS agree with respect to the general temporal trends in tree cover for most parts of Europe, with a large tree cover during the mid-Holocene and a substantially smaller tree cover closer to the present time. However, the decrease in tree cover in REVEALS starts much earlier than in the models, indicating much earlier anthropogenic deforestation than the prescribed land use in the models. While LPJ-GUESS generally overestimates tree cover compared to the reconstructions, MPI-ESM indicates lower percentages of tree cover than REVEALS, particularly in central Europe and the British Isles. A comparison of the simulated climate with chironomid-based climate reconstructions reveals that model–data mismatches in tree cover are in most cases not driven by biases in the climate. Instead, sensitivity experiments indicate that the model results strongly depend on the tuning of the models regarding natural disturbance regimes (e.g. fire and wind throw). The frequency and strength of disturbances are – like most of the parameters in the vegetation models – static and calibrated to modern conditions. However, these parameter values may not be valid for past climate and vegetation states totally different from today's. In particular, the mid-Holocene natural forests were probably more stable and less sensitive to disturbances than present-day forests that are heavily altered by human interventions. Our analysis highlights the fact that such model settings are inappropriate for paleo-simulations and complicate model–data comparisons with additional challenges. Moreover, our study suggests that land use is the main driver of forest decline in Europe during the mid-Holocene and late Holocene.

Middle to late Holocene plant cover variation in relation to climate, fire, and human activity in the Songnen grasslands of northeastern China.

For future vegetation projections and conservation planning in grassland ecosystems, accurate estimates of past plant cover changes in grassland composition and their responses to the various driving factors are essential. This study quantitatively reconstructs the past regional plant cover in the Songnen grasslands (northeastern China) and explores the relative importance of climate, fire, and human activity on vegetation dynamics. For this purpose, the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model is applied to three pollen records from two areas, two in the center of the Songnen grasslands and one located in an area marginal to the grasslands. Results from the most reliable REVEALS scenarios show that from the mid-Holocene, steppe (mean cover 40.6%) and dry steppe (mean cover 54.2%) alternately dominated the central part of the Songnen grasslands while the marginal grasslands were mainly characterized by alternating broadleaved forests (mean cover 26.3%), coniferous forests (mean cover 41.9%) and dry steppes (mean cover 30.1%). By comparing the plant cover results with previous published regional climate, fire and human activity records, the results show that long term vegetation dynamics were mainly driven by East Asia Summer Monsoon (EASM) and the related precipitation variations, but was also affected by fire frequency and human activity. Moreover, vegetation evolution was sensitive to abrupt cooling events including the 4.2 ka BP and stacked ice-rafted debris (IRD) events; the change from steppe to dry steppe, for example, was driven by these abrupt climate changes. Fire events can alter the original vegetation stability allowing the vegetation to respond rapidly to climate changes while human activity merely has limited influence on vegetation changes.

Validation of relative pollen productivities for major tropical plant taxa: An empirical test using the REVEALS model in Hainan, China

The reliability of estimates of tropical lowland vegetation cover based on lacustrine pollen records has long been debated. Here, we assess the reliability of relative pollen productivity estimates (RPPs) obtained in tropical Hainan island using surface pollen assemblages from six reservoirs and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model. The resulting REVEALS estimates are compared to observations of vegetation coverin the studied region and pollen percentages. The REVEALS estimates for most tropical taxa including Poaceae, Moraceae, Euphorbiaceae, Mallotus/Macaranga, Castanopsis/Lithocarpus, were more similar to the observed vegetation cover than estimates based on simple pollen percentages, suggesting that the previously reported RPPs are reliable. The REVEALS estimates for some taxa (i.e. Rubiaceae and Anacardiaceae) are comparable to those based on pollen percentages, but RPPs for these taxa are difficult to evaluate. However, the pollen percentages for some taxa including Asteraceae and Papilionaceae agree better with the observed vegetation cover than the REVEALS corrections, implying either that there are problems with the corresponding RPPs or that there is bias in the observed vegetation data used for validation. We suggest that the reliability of the RPPs for plant taxa in tropical areas depends strongly on their abundance in the pollen and vegetation data: high abundance implies high reliability and vice versa. REVEALS cover estimates for groups of taxa consistently agreed well with observed vegetation cover, suggesting that the REVEALS model can be applied even in tropical regions if individual species are grouped, which may be useful when reconstructing historical landscape changes in tropical Asia.

The transformation of the forest steppe in the lower Danube Plain of southeastern Europe: 6000 years of vegetation and land use dynamics

Abstract. Forest steppes are dynamic ecosystems, highly susceptible to changes in climate, disturbances and land use. Here we examine the Holocene history of the European forest steppe ecotone in the lower Danube Plain to better understand its sensitivity to climate fluctuations, fire and human impact, and the timing of its transition into a cultural forest steppe. We used multi-proxy analyses (pollen, n-alkanes, coprophilous fungi, charcoal and geochemistry) of a 6000-year sequence from Lake Oltina (southeastern Romania) combined with a REVEALS (Regional Estimates of Vegetation Abundance from Large Sites) model of quantitative vegetation cover. We found a greater tree cover, composed of xerothermic (Carpinus orientalis and Quercus) and temperate (Carpinus betulus, Tilia, Ulmus and Fraxinus) tree taxa, between 6000 and 2500 cal yr BP. Maximum tree cover (∼ 50 %), dominated by C. orientalis occurred between 4200 and 2500 cal yr BP at a time of wetter climatic conditions and moderate fire activity. Compared to other European forest steppe areas, the dominance of C. orientalis represents the most distinct feature of the woodland's composition at this time. Tree loss was underway by 2500 yr BP (Iron Age), with the REVEALS model indicating a fall to ∼ 20 % tree cover from the Late Holocene forest maximum, linked to clearance for agriculture, while climate conditions remained wet. Biomass burning increased markedly at 2500 cal yr BP, suggesting that fire was regularly used as a management tool until 1000 cal yr BP when woody vegetation became scarce. A sparse tree cover, with only weak signs of forest recovery, then became a permanent characteristic of the lower Danube Plain, highlighting more or less continuous anthropogenic pressure. The timing of anthropogenic ecosystem transformation here (2500 cal yr BP) falls between that in central-eastern (between 3700 and 3000 cal yr BP) and eastern (after 2000 cal yr BP) Europe. Our study is the first quantitative land cover estimate at the forest steppe ecotone in southeastern Europe spanning 6000 years. It provides critical empirical evidence that, at a broad spatial scale, the present-day forest steppe and woodlands reflect the potential natural vegetation in this region under current climate conditions. However, the extent of tree cover and its composition have been neither stable in time nor shaped solely by the climate. Consequently, vegetation change must be seen as dynamic and reflecting wider changes in environmental conditions including natural disturbances and human impact.

Relative pollen productivities of the major plant taxa of subtropical evergreen–deciduous mixed woodland in China

ABSTRACTQuantifying the relationship between pollen and vegetation is an essential step in the pollen‐based quantitative reconstruction of past vegetation cover. In this study, we use the Extended R‐Value (ERV) model and a modern dataset of pollen (collected from moss polsters) and related vegetation from 50 sites in the Daba Mountains (subtropical China) to (i) estimate the relevant source area of pollen (RSAP) of the moss samples and the relative pollen productivities (RPPs) of nine major plant taxa‐characteristic of the region, and (ii) evaluate the obtained RPPs. The RSAP estimates of moss polsters vary between 225 and 610 m depending on the ERV submodels and models of pollen dispersal and deposition used. The RPP estimates are different from values published in previous studies from temperate and subtropical China. This may be explained by differences in methodology, climate and vegetation (species composition and spatial distribution), of which vegetation is probably the most important factor. The ranking of the RPP estimates for the nine taxa is Pinus > Juglandaceae > D − Quercus (deciduous Quercus) > Poaceae > Rosaceae > Cyperaceae > Anacardiaceae > Castanea > Fabaceae. We use a ‘leave‐one‐out’ cross‐validation strategy and the Landscape Reconstruction Algorithm (LRA) for pollen‐based reconstruction of regional and local plant cover to evaluate the ERV model‐based RPP estimates. Both the REVEALS (Regional Estimates of VEgetation Abundance from Large Sites)‐based and the LOVE (LOcal Vegetation Estimates)‐based plant cover using the RPP estimates are closer to the modern vegetation composition than pollen percentages, thus confirming the applicability of the ERV model and the LRA approach in subtropical China.

Pollen-based quantitative land-cover reconstruction for northern Asia covering the last 40 ka cal BP

Abstract. We collected the available relative pollen productivity estimates (PPEs) for 27 major pollen taxa from Eurasia and applied them to estimate plant abundances during the last 40 ka cal BP (calibrated thousand years before present) using pollen counts from 203 fossil pollen records in northern Asia (north of 40∘ N). These pollen records were organized into 42 site groups and regional mean plant abundances calculated using the REVEALS (Regional Estimates of Vegetation Abundance from Large Sites) model. Time-series clustering, constrained hierarchical clustering, and detrended canonical correspondence analysis were performed to investigate the regional pattern, time, and strength of vegetation changes, respectively. Reconstructed regional plant functional type (PFT) components for each site group are generally consistent with modern vegetation in that vegetation changes within the regions are characterized by minor changes in the abundance of PFTs rather than by an increase in new PFTs, particularly during the Holocene. We argue that pollen-based REVEALS estimates of plant abundances should be a more reliable reflection of the vegetation as pollen may overestimate the turnover, particularly when a high pollen producer invades areas dominated by low pollen producers. Comparisons with vegetation-independent climate records show that climate change is the primary factor driving land-cover changes at broad spatial and temporal scales. Vegetation changes in certain regions or periods, however, could not be explained by direct climate change, e.g. inland Siberia, where a sharp increase in evergreen conifer tree abundance occurred at ca. 7–8 ka cal BP despite an unchanging climate, potentially reflecting their response to complex climate–permafrost–fire–vegetation interactions and thus a possible long-term lagged climate response.

Relative pollen productivity estimates and changes in Holocene vegetation cover in the deciduous forest of southeastern Quebec, Canada

The Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model was used to quantify Holocene changes in vegetation cover in the deciduous forest of southeastern Quebec, Canada. The Extended R-Value (ERV) model was used to obtain relative pollen productivity estimates (PPEs) for eight tree taxa and to determine the relevant source area of pollen (RSAP) for lakes in this ecosystem. Modern vegetation was estimated using pollen data from 16 small (<0.5 km2) lakes and a species-level vegetation survey of southern Quebec. The RSAP was estimated to be within 1600 m of the lakes. Tsuga, Fagus, and Quercus were the most productive taxa, and Populus and Acer were the lowest. Reconstructed changes in absolute vegetation cover show a high abundance of Picea followed by Populus in the early Holocene. The reconstructed values for Populus suggest that it was widely distributed across the landscape. Abies and Acer were dominant on the landscape during the late to mid-Holocene, and an increase in Picea during the Neoglacial is more significant than in percentage diagrams. The REVEALS results provide estimates of land-cover change that are more realistic and informative than the use of pollen percentages alone.

Modern pollen–plant richness and diversity relationships exist along a vegetational gradient in southern Norway

The relationships between modern pollen and floristic plant richness, diversity and evenness are assessed using pollen assemblages and associated vegetation data from 52 lakes along an elevational and vegetational gradient in the Setesdal valley of south-central Norway. Various data transformations were applied to minimise bias in the vegetation and pollen datasets. Plant species were transformed to their pollen or spore equivalents to reduce taxonomic biases. Pollen counts were transformed using Andersen’s general pollen-representation values for northern European trees and shrubs and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model with pollen-productivity estimates (PPEs) appropriate for Setesdal to minimise pollen-representation bias. Pollen count-size bias (before or after transformation) was eliminated by rarefaction analysis based on bootstrap resampling. Richness and diversity were quantified using Hill numbers ( N0, N1, N2), and evenness was estimated as the ratios of N0, N1 and N2. Diversity partitioning was used to estimate β diversity. The strongest correlations between pollen and plant richness and diversity are with pollen counts transformed using Andersen’s representation values and rarefied to a common count size and with plants transformed to their pollen equivalents. However, if sites from the low-alpine zone are excluded where there are high values of far-transported tree pollen, the richness and diversity relationships are also statistically significant for untransformed pollen data and plants transformed into their pollen equivalents. The effects of data transformation on diversity partitioning and estimates of β diversity are explored. We demonstrate that there are statistically significant positive relationships between pollen and plant richness and diversity along the entire elevational gradient after transforming the datasets to minimise biases due to taxonomic differences, differential pollen representation, and pollen-count size, and similar significant positive relationships along the forested parts of the gradient (nemoral, boreonemoral, southern boreal, middle boreal) after transforming the datasets to minimise biases due to taxonomic differences and pollen-count size.

Are pollen records from small sites appropriate for REVEALS model-based quantitative reconstructions of past regional vegetation? An empirical test in southern Sweden

In this paper we test the performance of the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model using pollen records from multiple small sites. We use Holocene pollen records from large and small sites in southern Sweden to identify what is/are the most significant variable(s) affecting the REVEALS-based reconstructions, i.e. type of site (lakes and/or bogs), number of sites, site size, site location in relation to vegetation zones, and/or distance between small sites and large sites. To achieve this objective we grouped the small sites according to (i) the two major modern vegetation zones of the study region, and (ii) the distance between the small sites and large lakes, i.e. small sites within 50, 100, 150, or 200 km of the large lakes. The REVEALS-based reconstructions were performed using 24 pollen taxa. Redundancy analysis was performed on the results from all REVEALS-model runs using the groups within (i) and (ii) separately, and on the results from all runs using the groups within (ii) together. The explanatory power and significance of the variables were identified using forward selection and Monte Carlo permutation tests. The results show that (a) although the REVEALS model was designed for pollen data from large lakes, it also performs well with pollen data from multiple small sites in reconstructing the percentage cover of groups of plant taxa (e.g. open land taxa, summer-green trees, evergreen trees) or individual plant taxa; however, in the case of this study area, the reconstruction of the percentage cover of Calluna vulgaris, Cyperaceae, and Betula may be problematic when using small bogs; (b) standard errors of multiple small-site REVEALS estimates will generally be larger than those obtained using pollen records from large lakes, and they will decrease with increasing size of pollen counts and increasing number of small sites; (c) small lakes are better to use than small bogs if the total number of small sites is low; and (d) the size of small sites and the distance between them do not play a major role, but the distance between the small sites and landscape/vegetation boundaries is a determinant factor for the accuracy of the vegetation reconstructions.

From pollen percentage to regional vegetation cover — A new insight into cultural landscape development in western Norway

The REVEALS (Regional Estimates of VEgetation Abundance from Large Sites) model was applied to a pollen dataset from a large lake in western Norway to reconstruct the vegetation cover throughout the last c. 11,400years. The reconstructions, based on 18 common taxa, show development of a forested landscape until c. 5600calyr BP, followed by several phases of opening and reforestation, probably connected to variation in the intensity and type of human impact. From c. 5600calyr BP (Early Neolithic) to c. 3200calyr BP (Early Bronze Age), a general increase in openness takes place, with increased deforestation c. 4300 and 4000calyr BP. More extensive forest clearances are seen at 2750calyr BP (Late Bronze Age) and 1800calyr BP (Roman Iron Age). Reforestation is recognised at c. 5400, 4100, 3600, 2900, 1900, 1200, 700 and 300calyr BP. Calluna is present in the vegetation both in the Mesolithic and the Neolithic, and heathland expansion is inferred to take place in the Late Bronze Age, with further expansion c. 1800 and 950calyr BP, probably reflecting increased use of outfield resources at the expense of grasslands. Forest disturbance and grazing are inferred to have taken place from 5600calyr BP, and communities comparable to historical time periods have existed from 2750calyr BP. An expansion in the area used for cereal cultivation probably took place in the Roman Iron Age. In the last century, from c. 1920, an expansion of conifers takes place, and Picea shows a strong increase during the last twenty years. Changes in both forest composition and land-cover are more clearly reflected with the REVEALS model than from the pollen percentage diagram, and the probability of presence of taxa within the region is demonstrated. REVEALS modelling combined with archaeological data is recommended as an approach to gain increased knowledge about land-cover changes through time.

From landscape description to quantification: A new generation of reconstructions provides new perspectives on Holocene regional landscapes of SE Sweden

The development since the beginning of the 20th century of the pollen-analytical theory and method as a palaeoecological tool for describing landscape development is outlined with reference to southern Scandinavia. Numerical methods applied since the 1980s are discussed. The aim of this paper is to provide a new perspective on the landscape development and human impact during the Holocene by applying the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model to the pollen records from the reference site Lake Färskesjön in SE Sweden. The model was applied both to a previously published record (core 1956, entire Holocene until ad 1600) and a newly collected dataset (core 2013, the last 3000 years). The comparison between the REVEALS estimates of vegetation cover and historical landscape maps indicate that traditional, uncorrected pollen percentages significantly underestimate the degree of landscape openness created by long-term farming and pasturing, but that the degree of underestimation varies over time, depending on the species composition of both the forest and the open-land communities. The REVEALS reconstructions are also a useful tool for the quantification of past land-use changes that may have affected the nutrient loading to the Baltic Sea.

Holocene changes in vegetation composition in northern Europe: why quantitative pollen-based vegetation reconstructions matter

We present pollen-based reconstructions of the spatio-temporal dynamics of northern European regional vegetation abundance through the Holocene. We apply the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model using fossil pollen records from eighteen sites within five modern biomes in the region. The eighteen sites are classified into four time-trajectory types on the basis of principal components analysis of both the REVEALS-based vegetation estimates (RVs) and the pollen percentage (PPs). The four trajectory types are more clearly separated for RVs than PPs. Further, the timing of major Holocene shifts, rates of compositional change, and diversity indices (turnover and evenness) differ between RVs and PPs. The differences are due to the reduction by REVEALS of biases in fossil pollen assemblages caused by different basin size, and inter-taxonomic differences in pollen productivity and dispersal properties. For example, in comparison to the PPs, the RVs show an earlier increase in Corylus and Ulmus in the early-Holocene and a more pronounced increase in grassland and deforested areas since the mid-Holocene. The results suggest that the influence of deforestation and agricultural activities on plant composition and abundance from Neolithic times was stronger than previously inferred from PPs. Relative to PPs, RVs show a more rapid compositional change, a largest decrease in turnover, and less variable evenness in most of northern Europe since 5200 cal yr BP. All these changes are primarily related to the strong impact of human activities on the vegetation. This study demonstrates that RV-based estimates of diversity indices, timing of shifts, and rates of change in reconstructed vegetation provide new insights into the timing and magnitude of major human disturbance on Holocene regional vegetation, features that are critical in the assessment of human impact on vegetation, land-cover, biodiversity, and climate in the past.

The Holocene vegetation cover of Britain and Ireland: overcoming problems of scale and discerning patterns of openness

The vegetation of Europe has undergone substantial changes during the course of the Holocene epoch, resulting from range expansion of plants following climate amelioration, competition between taxa and disturbance through anthropogenic activities. Much of the detail of this pattern is understood from decades of pollen analytical work across Europe, and this understanding has been used to address questions relating to vegetation-climate feedback, biogeography and human impact. Recent advances in modelling the relationship between pollen and vegetation now make it possible to transform pollen proportions into estimates of vegetation cover at both regional and local spatial scales, using the Landscape Reconstruction Algorithm (LRA), i.e. the REVEALS (Regional Estimates of VEgetation Abundance from Large Sites) and the LOVE (LOcal VEgetation) models. This paper presents the compilation and analysis of 73 pollen stratigraphies from the British Isles, to assess the application of the LRA and describe the pattern of landscape/woodland openness (i.e. the cover of low herb and bushy vegetation) through the Holocene. The results show that multiple small sites can be used as an effective replacement for a single large site for the reconstruction of regional vegetation cover. The REVEALS vegetation estimates imply that the British Isles had a greater degree of landscape/woodland openness at the regional scale than areas on the European mainland. There is considerable spatial bias in the British Isles dataset towards wetland areas and uplands, which may explain higher estimates of landscape openness compared with Europe. Where multiple estimates of regional vegetation are available from within the same region inter-regional differences are greater than intra-regional differences, supporting the use of the REVEALS model to the estimation of regional vegetation from pollen data.

The impact of land-use change on floristic diversity at regional scale in southern Sweden 600 BC–AD 2008

Abstract. This study explores the relationship between land-use and floristic diversity between 600 BC and AD 2008 in the uplands of southern Sweden. We use fossil pollen assemblages and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model to quantitatively reconstruct land cover at a regional scale. Floristic richness and evenness are estimated using palynological richness and REVEALS-based evenness, respectively. We focus on the period AD 350 to 750 to investigate the impact of an inferred, short-lived (< 200 yr) period of land-use expansion and subsequent land abandonment on vegetation composition and floristic diversity. The observed vegetation response is compared to that recorded during the transition from traditional to modern land-use management at the end of the 19th century. Our results suggest that agricultural land use was most widespread between AD 350 and 1850, which correlates broadly with high values of palynological richness. REVEALS-based evenness was highest between AD 500 and 1600 which indicates a more equal cover among taxa during this time interval. Palynological richness increased during the inferred land-use expansion after AD 350 and decreased during the subsequent regression AD 550–750, while REVEALS-based evenness increased throughout this period. The values of palynological richness during the last few decades are within the range observed during the last 1650 yr. However, REVEALS-based evenness shows much lower values during the last century compared to the previous ca. 2600 yr, which indicates that the composition of present-day vegetation is unusual in a millennial perspective. Our results show that regional scale changes in land use have had clear impacts on floristic diversity in southern Sweden, with a vegetation response time of less than 20 to 50 yr. We show the importance of traditional land use to attain high biodiversity and suggest that ecosystem management should include a regional landscape perspective.

Pollen-based biome reconstruction to the mid-Holocene transition in Sahel and Sahara: first palynological results of a lacustrine record from the Mega-Lake Chad

We present pollen-based reconstructions of the spatio-temporal dynamics of northern European regional vegetation abundance through the Holocene. We apply the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model using fossil pollen records from eighteen sites within five modern biomes in the region. The eighteen sites are classified into four time-trajectory types on the basis of principal components analysis of both the REVEALS-based vegetation estimates (RVs) and the pollen percentage (PPs). The four trajectory types are more clearly separated for RVs than PPs. Further, the timing of major Holocene shifts, rates of compositional change, and diversity indices (turnover and evenness) differ between RVs and PPs. The differences are due to the reduction by REVEALS of biases in fossil pollen assemblages caused by different basin size, and inter-taxonomic differences in pollen productivity and dispersal properties. For example, in comparison to the PPs, the RVs show an earlier increase in Corylus and Ulmus in the early-Holocene and a more pronounced increase in grassland and deforested areas since the mid-Holocene. The results suggest that the influence of deforestation and agricultural activities on plant composition and abundance from Neolithic times was stronger than previously inferred from PPs. Relative to PPs, RVs show a more rapid compositional change, a largest decrease in turnover, and less variable evenness in most of northern Europe since 5200 cal yr BP. All these changes are primarily related to the strong impact of human activities on the vegetation. This study demonstrates that RV-based estimates of diversity indices, timing of shifts, and rates of change in reconstructed vegetation provide new insights into the timing and magnitude of major human disturbance on Holocene regional vegetation, features that are critical in the assessment of human impact on vegetation, land-cover, biodiversity, and climate in the past.

Quantitative reconstructions of changes in regional openness in north-central Europe reveal new insights into old questions

By applying the recently developed model REVEALS (Regional Estimates of VEgetation Abundance from Large Sites) (Sugita, 2007) to pollen data from a large number of sites across Northern Germany and Denmark, we construct maps of regional patterns in landscape openness and in cover abundance of key plant taxa in the cultural landscape of north-central Europe for selected time slices in the Holocene.The results indicate that the pattern of landscape openness across the regions of northern Germany and Denmark prior to the introduction of agriculture was affected by soil conditions and degree of continentality. The 8.2 ka climate event did not lead to a general decrease in tree cover, although some changes in species composition were observed. The early phases of agriculture also had little effect on landscape openness at the regional scale, but later human impact lead to large scale deforestation and development of arable areas, grasslands and of heathlands in the north-western part of the region. The timing and degree of deforestation, and the weight between arable and grazing areas varied in space, partly due to differences in natural conditions, partly due to differences in cultural impact.

Floristic diversity in the transition from traditional to modern land-use in southern Sweden a.d. 1800–2008

We aim to provide a long-term ecological analysis of land-use and floristic diversity in the transition from traditional to modern land-use management in the time a.d. 1800–2008 in southern Sweden. We use the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model to quantify land-cover changes on a regional scale at 20-year intervals, based on the fossil pollen record. Floristic richness and evenness are estimated using palynological richness and the Shannon index applied to the REVEALS output, respectively. We identified a transition period of 60 years between 1880 and 1940 when the total tree cover increased and the tree composition changed from deciduous to coniferous dominance. Within the shrinking area of open land, arable land taxa expanded, while the number and coverage of herbs in the remaining grasslands decreased. The succession from open grasslands to more tree-covered habitats initially favoured palynological richness, which reached its highest values during the first 40 years of the transition period. The highest REVEALS-based evenness was recorded in the time of traditional land-use and at the beginning of the transition period, reflecting higher habitat diversity at these time intervals. Our results support a more dynamic ecosystem management that changes between traditional land-use and phases of succession (<40 years) to promote floristic diversity. We have developed and applied a palaeoecological methodology that contributes realistic estimates to be used in ecosystem management.

Holocene land-cover reconstructions for studies on land cover-climate feedbacks

Abstract. The major objectives of this paper are: (1) to review the pros and cons of the scenarios of past anthropogenic land cover change (ALCC) developed during the last ten years, (2) to discuss issues related to pollen-based reconstruction of the past land-cover and introduce a new method, REVEALS (Regional Estimates of VEgetation Abundance from Large Sites), to infer long-term records of past land-cover from pollen data, (3) to present a new project (LANDCLIM: LAND cover – CLIMate interactions in NW Europe during the Holocene) currently underway, and show preliminary results of REVEALS reconstructions of the regional land-cover in the Czech Republic for five selected time windows of the Holocene, and (4) to discuss the implications and future directions in climate and vegetation/land-cover modeling, and in the assessment of the effects of human-induced changes in land-cover on the regional climate through altered feedbacks. The existing ALCC scenarios show large discrepancies between them, and few cover time periods older than AD 800. When these scenarios are used to assess the impact of human land-use on climate, contrasting results are obtained. It emphasizes the need for methods such as the REVEALS model-based land-cover reconstructions. They might help to fine-tune descriptions of past land-cover and lead to a better understanding of how long-term changes in ALCC might have influenced climate. The REVEALS model is demonstrated to provide better estimates of the regional vegetation/land-cover changes than the traditional use of pollen percentages. This will achieve a robust assessment of land cover at regional- to continental-spatial scale throughout the Holocene. We present maps of REVEALS estimates for the percentage cover of 10 plant functional types (PFTs) at 200 BP and 6000 BP, and of the two open-land PFTs "grassland" and "agricultural land" at five time-windows from 6000 BP to recent time. The LANDCLIM results are expected to provide crucial data to reassess ALCC estimates for a better understanding of the land suface-atmosphere interactions.

Theory of quantitative reconstruction of vegetation II: all you need is LOVE

This paper describes the LOVE (LOcal Vegetation Estimates) model for estimating local vegetation composition within the relevant source area of pollen. This model quantifies and then subtracts background pollen (ie, pollen coming from beyond the relevant source area) in order to arrive at a quantitative reconstruction of local vegetation. Parameters required for LOVE applications are pollen counts from target sites, the relevant source area of pollen of these sites, pollen productivity estimates and regional vegetation composition within 104 -105 km2. Regional vegetation composition is obtained using fossil pollen from large sites (≥102 ha) with the REVEALS (Regional Estimates of VEgetation Abundance from Large Sites) model, the first step of the Landscape Reconstruction Algorithm (LRA) specifically designed for LOVE applications. POLLSCAPE simulations demonstrate that (1) regional vegetation composition can be used to predict background pollen at and beyond the relevant source area of pollen for given-sized basins, (2) LOVE with the LRA framework provides a robust and accurate estimate of local vegetation composition much better than vegetation reconstruction using pollen percentages alone and (3) although the relevant source area of pollen is difficult to estimate particularly in past landscapes, a proposed method using backward modelling of LOVE is effective to estimate the relevant source area in landscapes of unknown vegetation patchiness and heterogeneity. Thus, the LRA will also be useful to estimate indirectly changes in spatial structure of past vegetation and landscape caused by natural and anthropogenic forcing.