Land Cover Reconstructions Research Articles

Changing with the times: From agricultural potential to spatially explicit reconstructions of past land use

Past land-use reconstructions are a key tool for studying long-term human ecodynamics and addressing pressing questions about the origins and evolutionary dynamics of the Anthropocene. In particular, agricultural landcover reconstructions are vital for understanding long-term human-environment dynamics. Most past agricultural land-use models, however, rely heavily on modelling assumptions, make limited use of known archaeological site locations to constrain or inform their estimates and tend to be limited to general estimates of percentages of plant types within catchments around pollen trapping lakes. The lack of information outside catchment areas and low spatial resolution even within catchments constrain the utility of these models. To address this problem, we propose a new approach that combines archaeological predictive modelling with pollen-based agricultural landcover reconstructions to produce more accurate, spatially explicit past landcover estimates. Here, we present the results of a case study deploying the new approach to produce improved past landcover maps for a region in the Western Taurus Mountains, southwestern Turkey. The study area surrounds Sagalassos, an antique urban centre with a regional settlement history encompassing nine millennia. We produced five archaeological predictive models for the study region using the ‘Locally Adaptive Models of Archaeological Potential’ (LAMAP) method spanning the Hellenistic through Late Ottoman period. We then combined those predictive surfaces with ‘Regional Estimates of VEgetation Abundance from Large Sites’ (REVEALS) pollen landcover reconstructions for the same periods based on pollen from sediment cores extracted from three catchments within the study area. Lastly, we compared the resulting hybrid landcover models to the archaeological record using data not used to make the predictions. We found that the hybrid landcover model aligned very well with the known extents of agricultural land-use from the study area. These results indicate that the proposed approach is a viable way to combine pollen-based landcover models with archaeological data and produce more accurate, empirically-based landcover reconstructions reflecting real human activity in the past.

Relationships Between Land Use and Terrestrial Organic Matter Transfer to the Baltic Sea Over the Last 500 Years

AbstractTerrestrial organic matter (OM) plays a key role in coastal organic carbon burial. However, few studies focus on the relationship between land use in the watershed and the transport of terrestrial OM to coasts from a long‐term perspective. In this study, we compared terrestrial OM deposition between an inlet of the Baltic Sea and an upstream lake within the same watershed over the last 500 years, using lignin biomarkers in the sediments. In combination with pollen‐based quantitative land cover reconstruction, we assessed the impacts of semicentennial‐scale changes in land use on terrestrial OM export. The results indicated that the concentration, composition, and degradation state of the lignin‐derived OM differed substantially between the two sites. The lake received larger amounts of lignin‐derived OM during periods of intensified agriculture, but the coastal site did not. The composition of lignin in the coastal sediment did not directly reflect variations in vegetation cover in the watershed. The reason could be that the OM was settled in the upstream basins. Furthermore, the terrestrial OM that did reach the coastal sediments was modified through degradation during the transport, and only the refractory component was deposited at the coast in a relatively unaltered form.

Did the Bronze Age deforestation of Europe affect its climate? A regional climate model study using pollen-based land cover reconstructions

Abstract. This paper studies the impact of land use and land cover change (LULCC) on the climate around 2500 years ago (2.5 ka), a period of rapid transitions across the European landscape. One global climate model was used to force two regional climate models (RCMs). The RCMs used two land cover descriptions. The first was from a dynamical vegetation model representing potential land cover, and the second was from a land cover description reconstructed from pollen data by statistical interpolation. The two different land covers enable us to study the impact of land cover on climate conditions. Since the difference in landscape openness between potential and reconstructed land cover is mostly due to LULCC, this can be taken as a measure of early anthropogenic effects on climate. Since the sensitivity to LULCC is dependent on the choice of climate model, we also use two RCMs. The results show that the simulated 2.5 ka climate was warmer than the simulated pre-industrial (PI, 1850 CE) climate. The largest differences are seen in northern Europe, where the 2.5 ka climate is 2–4 ∘C warmer than the PI period. In summer, the difference between the simulated 2.5 ka and PI climates is smaller (0–3 ∘C), with the smallest differences in southern Europe. Differences in seasonal precipitation are mostly within ±10 %. In parts of northern Europe, the 2.5 ka climate is up to 30 % wetter in winter than that of the PI climate. In summer there is a tendency for the 2.5 ka climate to be drier than the PI climate in the Mediterranean region. The results also suggest that LULCC at 2.5 ka impacted the climate in parts of Europe. Simulations including reconstructed LULCC (i.e. those using pollen-derived land cover descriptions) give up to 1 ∘C higher temperature in parts of northern Europe in winter and up to 1.5 ∘C warmer in southern Europe in summer than simulations with potential land cover. Although the results are model dependent, the relatively strong response implies that anthropogenic land cover changes that had occurred during the Neolithic and Bronze Age could have affected the European climate by 2.5 ka.

Combining Agent-Based Modelling and Geographical Information Systems to Create a New Approach for Modelling Movement Dynamics: A Case Study of Mesolithic Orkney

AbstractThe earliest Holocene occupation of Orkney is still poorly understood. This pilot study explores the use of multi-factorial landscape and land-cover reconstruction to form a baseline physical environment for the assessment of Mesolithic movement and potential site suitability. A geographic information systems (GIS) approach to landscape reconstruction through proxy use allows for an analogue of Mesolithic land cover and extent to be generated and used to predict the potential for Mesolithic site/material remains. The integration of agent-based modelling introduces a novel investigation of pathways in the landscape, divined not with a fixed destination but with a programmed least-cost movement behaviour to extrude “natural corridors” of movement from the study area. Utilising the base physical characteristics of the natural environment, without introducing complex sociopolitical or economic drivers for movement promotes the use of a complex physical environment as a necessary consideration as baseline for all studies of mobility and movement. This approach also intends to present a platform to develop more universal or widely applicable models capable of providing a relevant baseline landscape for the rapid assessment and investigation of the archaeological potential of an area. Developing or understanding the role of a robust landscape permits the appropriate assessment of project utility, scale, and layering and integration of more complex input factors.

Holocene deforestation history of NE Belgium: An evaluation of pollen- and population-based approaches for reconstructing land cover

Several methods to reconstruct past land cover are available which can be roughly divided into approaches based on pollen data and approaches based on (estimates of) historical human population. In this study, the REVEALS model and non-metric multidimensional scaling (NMDS) are applied to pollen sequences obtained from multiple alluvial floodplains located in the sandy and loamy regions of northeastern Belgium, thereby obtaining the first regional (semi-)quantitative estimates of Holocene landscape openness for this area. These estimates are subsequently compared to the two most widely-used scenarios for anthropogenic land cover change (ALCC): KK10 and HYDE.In contrast with the two population-based ALCC scenarios, the pollen-based reconstructions are well in agreement and indicate considerable variability in past land cover, not only between the two regions but even between the individual catchments. This agreement implies that NMDS could serve as an alternative approach to provide insight in large amounts of pollen data in case not all required model parameters are available to run the REVEALS model. Moreover, NMDS can provide a better understanding of which taxa are related to a particular type of landscape. Taking into account such insights in the interpretation of the REVEALS model output might help to pinpoint the onset of significant human impact on the landscape more precisely. Given that alluvial sites often experienced early anthropogenic impact, including pollen data obtained from alluvial sites could not only improve the spatial coverage and accuracy of current pollen-based land cover reconstructions but could also improve our understanding of human transformation of the landscape, which can in turn contribute to an improvement of the ALCC scenarios.

Spatial and temporal patterns of upland vegetation over the last 200 years in the northern pyrenees: Example from the Bassiès valley, Ariège, France

Quantitative estimates of past vegetation with a clearly defined spatial scale are a critical step to better understand the patterns and processes of changes in vegetation and land-cover over time and space. However, such estimates are difficult to obtain from pollen data due to their lack of spatial dimension and the inter-taxonomic differences in pollen production, dispersal, and deposition mechanisms. This study assesses the potential of the Landscape Reconstruction Algorithm (LRA) to reconstruct the spatial and temporal patterns of upland vegetation in the Bassiès Valley, northern Pyrenees over the last 200 years, a period characterised by a decline of traditional pastoral activities. We used well-dated pollen records from eight bogs and ponds and vegetation and land-cover data within a 1-km radius from each site to evaluate the LRA-based reconstruction of local land-cover. The LRA approach was then used to reconstruct the 200-year history of local land-cover dynamics at 10 to 20-year intervals around each site in relation to land-abandonment. Our study shows that in addition to allowing long-term reconstruction, LRA estimates (1) are more sensitive to vegetation composition changes over time and space compared to historical land-cover maps and pollen percentages, and (2) improve the reconstruction of past local vegetation compared to pollen percentages alone. The LRA results reveal site-specific land-cover trajectories within the small-sized study area over 200 years. Some sites exhibit changes in land-cover composition with heathland and tree cover increase (ESC, EM), while others are found to be more stable, dominated 1) exclusively by heathland (LEG, W1652), 2) heathland with intermediate proportions of grassland (FOUZ, SIG), or 3) exclusively by grassland (OT). This land-cover composition variability over space and time may be related both to local topography and past grazing activity. The quantification of past vegetation dynamics provides opportunities for bridging the gap between researchers, policy makers and practitioners, and should be taken into account to further investigate the effect of long-term grazing activities on the past and modern plant and landscape diversity.

Two thousand years of Landscape—Human interactions at a coastal peninsula in Norway revealed through pollen analysis, shoreline reconstruction, and radiocarbon dates from archaeological sites

Human impact on long-term vegetation and biodiversity changes is often discussed on a general level, connecting palynological data to archaeological time periods. In the present paper we present environmental change during the last 2,400 years on a coastal peninsula in Norway using pollen data from three sites: one lake and two bogs, in addition to 621 radiocarbon dates and in-context pollen samples from archaeological sites. Locally, a close relationship between palynological richness reflecting high landscape, habitat and floristic diversity, and the summed probability distribution of radiocarbon dates was found. During the settlement period 400 BCE–550 CE, concordant with maximum number of dates from archaeological contexts, a mosaic landscape containing infields and outfields developed. Cereals were cultivated and animals were grazing in heathlands that could provide both summer grazing and winter fodder. Additionally, seashores and wetlands were used for grazing. Settlement recession from 350 CE and abandonment following the 536 CE climate event, resulted in vegetation successions toward reforestation, abandonment of arable fields, and marshes turning into ombrotrophic peat. At the same time the distance to the sea, and to species rich shoreline meadows, continued to increase due to continuous postglacial land uplift in a flat landscape. A new increase in the summed probability distribution 900–1250 CE, is reflected in expansion of outfield pastures, heathlands in particular, a management that continued up into modern time. The local development is supported by the results on a regional scale, indicating overall climatic and social causes for observed vegetation changes. Both palynological richness and pollen-based landcover reconstructions indicate reforestation and less habitat diversity in the sixth century. On a regional scale, reforestation in the fifteenth century following the late medieval crises, is more pronounced than on the local scale, although both reflect exploitation of outfield resources.

Land cover reconstruction in Northwest China since 6 ka BP: Preliminary application of a new strategy

The mid-Holocene is generally regarded as a relatively warm period, and therefore reconstructing land cover change from the mid-Holocene onwards may help predict future changes under warming scenarios. In this study, we used a new strategy which combines the REVEALS model with modern analogue technique (MAT) to achieve a land cover reconstruction since 6 ka BP for Northwest (NW) China. The REVEALS results are more consistent with our general understanding of pollen-vegetation relationships in NW China than the pollen percentage data. However, although the model has potential for future applications, further quantitative testing is needed. Modern calibration sets can provide modern “analogues” for most of the fossil samples, but the numbers of modern samples from areas with a low vegetation cover are limited, which may lead to over- or underestimation of the results, despite the overall small prediction error. Our land cover results show that, since ∼6 ka BP, the vegetation cover in mountains areas was significantly greater than at lower elevations, with the threshold cover value of 45%. At lower elevations, the vegetation cover gradually decreased from east to west. Elevation differences and the distance from the sea may be the main reasons for the differences. The mountains were dominated by steppe, meadow/meadow steppe, and forest, while the lower elevations were dominated by desert and desert steppe, with generally only small changes in vegetation type, reflecting the long-term arid climatic background of the region. However, since ∼6 ka BP there were several differences in the pattern of dry-wet climate shifts across the study region. The vegetation in most areas indicates a trend towards wetter conditions, or no significant trend, except for sites G1 and G3 which show an aridification trend.

European pollen-based REVEALS land-cover reconstructions for the Holocene: methodology, mapping and potentials

Abstract. Quantitative reconstructions of past land cover are necessary to determine the processes involved in climate–human–land-cover interactions. We present the first temporally continuous and most spatially extensive pollen-based land-cover reconstruction for Europe over the Holocene (last 11 700 cal yr BP). We describe how vegetation cover has been quantified from pollen records at a 1∘ × 1∘ spatial scale using the “Regional Estimates of VEgetation Abundance from Large Sites” (REVEALS) model. REVEALS calculates estimates of past regional vegetation cover in proportions or percentages. REVEALS has been applied to 1128 pollen records across Europe and part of the eastern Mediterranean–Black Sea–Caspian corridor (30–75∘ N, 25∘ W–50∘ E) to reconstruct the percentage cover of 31 plant taxa assigned to 12 plant functional types (PFTs) and 3 land-cover types (LCTs). A new synthesis of relative pollen productivities (RPPs) for European plant taxa was performed for this reconstruction. It includes multiple RPP values (≥2 values) for 39 taxa and single values for 15 taxa (total of 54 taxa). To illustrate this, we present distribution maps for five taxa (Calluna vulgaris, Cerealia type (t)., Picea abies, deciduous Quercus t. and evergreen Quercus t.) and three land-cover types (open land, OL; evergreen trees, ETs; and summer-green trees, STs) for eight selected time windows. The reliability of the REVEALS reconstructions and issues related to the interpretation of the results in terms of landscape openness and human-induced vegetation change are discussed. This is followed by a review of the current use of this reconstruction and its future potential utility and development. REVEALS data quality are primarily determined by pollen count data (pollen count and sample, pollen identification, and chronology) and site type and number (lake or bog, large or small, one site vs. multiple sites) used for REVEALS analysis (for each grid cell). A large number of sites with high-quality pollen count data will produce more reliable land-cover estimates with lower standard errors compared to a low number of sites with lower-quality pollen count data. The REVEALS data presented here can be downloaded from https://doi.org/10.1594/PANGAEA.937075 (Fyfe et al., 2022).

Pollen-based temporal-spatial land cover reconstruction in North China for the last 6,000 years

Based on 74 fossil pollen records and relative pollen productivity estimates for 29 plant taxa, we produced a quantitative reconstruction of regional vegetation change in North China over the past 6,000 years, using the combined MAT-REVEALS approach. The results include the spatial dynamics of the five main land cover types (Pinus, coniferous trees excluding Pinus, deciduous trees, grassland and bare ground) for three time slices: 6 ka, 3 ka and 0.05 ka. From 6 ka to the present, the total vegetation cover decreased from 64% to 61% (i.e., bare ground increased from 36% to 39%), mainly because of decreases in the cover of deciduous trees (from 19% to 14%). At the same time, the cover of coniferous trees increased (from 10% to 14%), and that of herb plants was largely unchanged (from 34% to 33%). The vegetation cover was greater at high latitudes and altitudes than at lower latitudes and in lowland areas. On the regional scale, temperate coniferous forest with Larix and Betula was dominant in the Greater Khingan Mountains, while in the Changbai Mountains, deciduous forest (decreasing from 72% to 56%) gradually transitioned to coniferous-deciduous mixed forest (Pinus and coniferous trees increased from 1% to 18%). The deciduous forest was dominated by Quercus, Betula and Pinus and occurred mainly in the warm temperate mountains of North China, where the vegetation cover was relatively high before 3 ka (>70%), before decreasing substantially to 55% at 0.05 ka. Grassland with Artemisia and Poaceae was the main land cover type in the North China Plain and in the temperate steppe region where forest vegetation was relatively sparse. The spatial dynamics of the land cover types appear to have been affected by climate change; climatic cooling in the second half of the Holocene led to the southward migration of coniferous trees. At the same time, human activities were likely the cause of the reduction of the regional vegetation cover, especially the tree cover.

Do Local Habitat Conditions Affect Estimates of Relative Pollen Productivity and Source Area in Heathlands?

Relative Pollen Productivity is an essential parameter for quantitative reconstruction of past land cover from pollen records, but published studies have produced a range of different values for the same taxa. Heathland habitats have limited plant diversity and strong spatial patterning, therefore are useful case studies to investigate aspects of pollen dispersal and deposition, but the estimated spatial area “sensed” by pollen records in these habitats also varies widely between studies. In this study, we estimate pollen productivity from two different microhabitats in a heathland ecosystem in order to investigate the role of local environmental conditions in any observed differences. Vegetation survey was carried out using the Crackles Bequest Project method, pollen assemblages from moss samples counted using standard methods, and relative pollen productivity and estimated source area derived using Extended R-Value analysis. Analysis of the data suggests that at least two pollen source areas exist at the sites studied, reflecting scales of landscape organisation. Microhabitat does not appear to have a marked effect on estimates of Relative Pollen Productivity in this heathland system. This study confirms earlier findings that the estimates obtained for some taxa from heathlands are substantially different than those from agricultural landscapes, especially Poaceae. The findings suggest that the factors controlling Relative Pollen Productivity are still not fully understood, and that differences between locations may reflect real, habitat-led differences. Further investigation of this parameter, which is central to reconstruction of past land cover from pollen records whether overtly incorporated via an algebraic model or less explicitly present via ecological narrative, biomisation or modern analog approaches, is clearly necessary.

The potential of REVEALS-based vegetation reconstructions using pollen records from alluvial floodplains

The two-step Landscape Reconstruction Algorithm—comprising the models REVEALS and LOVE—translates fossil pollen assemblages into quantitative reconstructions of past vegetation cover. The REVEALS model has been applied to lakes and bogs of varied sizes, but application to records from alluvial sites is currently lacking and could further extend these reconstructions to areas where lakes and bogs are absent. In addition, since alluvial sites are often located in areas that experienced early anthropogenic impact, such data will provide more insight into land cover change in the context of agricultural development. In this paper, we test the performance of the REVEALS model using pollen records from multiple alluvial sites obtained from the floodplains of the Belgian Dijle catchment. The modelled vegetation cover is compared to the observed vegetation cover based on a historical land cover map of ca. ad 1775 (ca. 175 cal bp). The discrepancy between the modelled and the observed regional vegetation cover is relatively small and can largely be explained by local differences in land cover surrounding the sites, based on the results of the LOVE model. This study concludes that the LRA approach accurately reconstructs the regional vegetation cover of the river catchment based on pollen obtained from alluvial floodplains, and shows that it is able to reflect major local differences in land cover as well. Including pollen data obtained from alluvial floodplains could lead to a substantial increase in spatial coverage of future LRA-based land cover reconstructions.

Reconstruction of Residential Land Cover and Spatial Analysis of Population in Bursa Region (Turkey) in the Mid-Nineteenth Century

The historic reconstruction of residential land cover is of significance to uncover the human-environment relationship and its changing dynamics. Taking into account the historical census data and cadastral maps of seven villages, this study generated residential land cover maps for the Bursa Region in the 1850s using a model based on natural constraints, land zoning, socio-economic factors and residential suitability. Two different historical reconstructions were generated; one based on a high density residential model and another based on a low density model. The simulated landcover information was used as an ancillary data to redistribute aggregated census counts to fine scale raster cells. Two different statistical models were developed; one based on probability maps and the other applying regression models including Ordinary Least Squares (OLS) and Geographically Weighted Regression (GWR) models. The regression models were validated with historical census data of the 1840s. From regression models, socio-economic and physical characteristics, accessibility and natural amenities showed significant impacts on the distribution of population. Model validation analysis revealed that GWR is more accurate than OLS models. The generated residential land cover and gridded population datasets can provide a basis for the historical study of population and land use.

Pollen productivity estimates strongly depend on assumed pollen dispersal II: Extending the ERV model

Pollen productivity estimates (PPEs) are a key parameter for quantitative land-cover reconstructions from pollen data. PPEs are commonly estimated using modern pollen-vegetation data sets and the extended R-value (ERV) model. Prominent discrepancies in the existing studies question the reliability of the approach. We here propose an implementation of the ERV model in the R environment for statistical computing, which allows for simplified application and testing. Using simulated pollen-vegetation data sets, we explore sensitivity of ERV application to (1) number of sites, (2) vegetation structure, (3) basin size, (4) noise in the data, and (5) dispersal model selection. The simulations show that noise in the (pollen) data and dispersal model selection are critical factors in ERV application. Pollen count errors imply prominent PPE errors mainly for taxa with low counts, usually low pollen producers. Applied with an unsuited dispersal model, ERV tends to produce wrong PPEs for additional taxa. In a comparison of the still widely applied Prentice model and a Lagrangian stochastic model (LSM), errors are highest for taxa with high and low fall speed of pollen. The errors reflect the too high influence of fall speed in the Prentice model. ERV studies often use local scale pollen data from for example, moss polsters. Describing pollen dispersal on his local scale is particularly complex due to a range of disturbing factors, including differential release height. Considering the importance of the dispersal model in the approach, and the very large uncertainties in dispersal on short distance, we advise to carry out ERV studies with pollen data from open areas or basins that lack local pollen deposition of the taxa of interest.

Modern pollen-vegetation relationships in the Taihang Mountains: Towards the quantitative reconstruction of land-cover changes in the North China Plain

Pollen-based land cover reconstructions are important for understanding the history of regional environmental responses to natural and anthropogenic factors, and for managing the ecological environment. The vegetation in the mountain landscape of North China has been significantly influenced by human activities, and evaluating the pollen-vegetation relationship for the region is important for reconstructing anthropogenic land-cover changes in the North China Plain. In this study, 35 sampling sites were randomly selected in representative vegetation zones of the Taihang Mountains in North China. Based on a detailed vegetation survey (field work combined with the analysis of remote sensing images), we evaluated the pollen-vegetation relationships in the area. In addition, the relevant pollen source area (RSAP) of the sampling sites and the relative pollen productivity (RPP) of the major plant taxa were estimated using ERV (Extended R-Value) models. The results show that the pollen spectra in the Taihang Mountains reliably reflect the vegetation landscape of different altitudinal zones. The estimated RSAP in the Taihang Mountains is ~ 600 m. Using Poaceae as a reference taxon (RPP = 1), the RPPs of the dominant plant taxa in the Taihang Mountains can be ordered as follows: Pinus > Hippophae > Caryophyllaceae > Betula > Quercus > Rhododendron > Artemisia > Asteraceae > Cyperaceae. Our results suggest the importance and complexity of RPP estimates in the Taihang Mountains, and provide valuable implications for improving the accuracy of reconstructions of land-cover changes in the North China Plain.

Quantitative reconstruction of vegetation cover from modern pollen rain in the Cerrado biome of Brazil

Fossil pollen assemblages are an important tool to reconstruct vegetation variability at centennial and millennial-scales. However, in the Cerrado biome of Brazil, the influence of the local vegetation, the heterogeneity of the landscape and the accuracy of pollen identification leads to a wide margin of error in interpretation. In this study, we present a method of quantitative reconstruction of past vegetation cover (forest, savanna, and grassland) that accounts for these different aspects. Our method is based on analysis of 47 surface samples collected in the southern Cerrado biome (east-central Brazil). First, we defined criteria that can be used to identify the local ecosystem (lake, marsh, palm swamp, or gallery forest) represented by the pollen assemblages. The pollen assemblages were then compared to data extracted from vegetation maps, resulting in the assessment of three pollen score equations related to each of the vegetation types (forest, savanna, and grassland). Based on these scores, we developed linear regression models that can be used to reconstruct the proportion of each type of land cover from pollen assemblages. We compared the results obtained for three different areas (respectively with 300 m, 500 m, and 1 km radius) to evaluate the size of the pollen source area for the Cerrado sites. We apply our models to two fossil pollen records to illustrate their use and application. Our method for the quantitative reconstruction of past land cover in the Cerrado biome is a new tool to investigate climate drivers and the long-term effects of fire in this Neotropical savanna.

Impacts of long-term land use on terrestrial organic matter input to lakes based on lignin phenols in sediment records from a Swedish forest lake

Organic carbon burial in lake sediments plays an important role in the global carbon cycle, and is heavily affected by the terrestrial organic matter input. However, few studies have focused on long-term changes in terrestrial organic matter input to lakes in response to land-use changes. The aim of this study was to assess variations in sedimentary terrestrial organic matter over the last 1000 years based on lignin biomarker records from two sediment cores from Lake Skottenesjön, southwestern Sweden. In combination with pollen-based quantitative land cover reconstruction, we investigated the impacts of centennial-scale land-use changes on terrestrial organic matter input to lake sediments. The results show that human activities in the catchment had significant impacts on terrestrial organic export by modifying the vegetation cover. Intensified use of the forest in the 18th and 19th centuries led to enhanced soil erosion, and increased terrestrial organic matter input to the lake. Although farmland expanded between the 12th and the middle of 14th century, no significant change in terrestrial organic matter input was observed at that time. Much higher export of terrestrial organic and minerogenic matter to the lake was observed during the period of modern forestry in the 20th century as compared to previous periods of minor forest disturbance, such as 11th century. The changes in the vegetation cover in the catchment considerably modified the composition of terrestrial organic matter deposited in the lake sediments, which is reflected by the composition of lignin phenols. This study demonstrates that the combination of lignin phenols analysis and pollen-based quantitative land cover reconstruction is a useful approach for investigating long-term changes in terrestrial organic matter delivery to lake ecosystems.

Spatially Continuous Land-Cover Reconstructions Through the Holocene in Southern Sweden

Climate change and human activities influence the development of ecosystems, with human demand of ecosystem services altering both land use and land cover. Fossil pollen records provide time series of vegetation characteristics, and the aim of this study was to create spatially continuous reconstructions of land cover through the Holocene in southern Sweden. The Landscape Reconstruction Algorithm (LRA) was applied to obtain quantitative reconstructions of pollen-based vegetation cover at local scales, accounting for pollen production, dispersal, and deposition mechanisms. Pollen-based local vegetation estimates were produced from 41 fossil pollen records available for the region. A comparison of 17 interpolation methods was made and evaluated by comparing with current land cover. Simple kriging with cokriging using elevation was selected to interpolate the local characteristics of past land cover, to generate more detailed reconstructions of trends and degree of variability in time and space than previous studies based on pollen data representing the regional scale. Since the Mesolithic, two main processes have acted to reshape the land cover of southern Sweden, originally mostly covered by broad-leaved forests. The natural distribution limit of coniferous forest has moved southward during periods with colder climate and retracted northward during warmer periods, and human expansion in the area and agrotechnological developments has led to a gradually more open landscape, reaching maximum openness at the beginning of the 20th century. The recent intensification of agriculture has led to abandonment of less fertile agricultural fields and afforestation with conifer forest.

Holocene vegetation changes in the transition zone between subtropical and temperate ecosystems in Eastern Central China

The Qinling Mountain Range represents the current transition zone between the temperate and subtropical ecosystems of Eastern Central China. Climate changes have certainly affected the vegetation composition to the north and south of this mountain range in different ways. Here, we reconstruct past regional land-cover changes by applying the REVEALS model to pollen records from the temperate, temperate–subtropical transition, and subtropical vegetation zones (Tianchi Lake, Daye Lake, and the Dajiuhu wetland, respectively). The location of sites in the mountains can complicate the interpretation of pollen results owing to the complexity of the landscape. Herein, we have therefore tested the effect of using different model inputs for land-cover reconstructions. Based on the best options, we found that regional vegetation changes were mainly controlled by the general climate trend. Both temperate and subtropical trees developed when the climate conditions were warm and moist during the mid-Holocene. The later period is characterised by cooler and drier climate conditions that result in an increase in open land, specifically from 2200 calendar years before present (cal yr BP). This landscape openness tendency has been amplified by the spread and intensification of land use (e.g., deforestation to develop farming) over the last few millennia and centuries. The vegetation at the current transition between the temperate and subtropical ecosystems of Eastern Central China has been mainly influenced by, and is still dependent on the climate; however, the impact of land use on vegetation seems to have been greater and more intense earlier in the temperate zone than in the subtropical zone.

Comment on : Pollen-based reconstruction of Holocene land-cover in mountain regions: Evaluation of the landscape reconstruction algorithm in the Vicdessos valley, northern Pyrenees, France

Comment on : Pollen-based reconstruction of Holocene land-cover in mountain regions: Evaluation of the landscape reconstruction algorithm in the Vicdessos valley, northern Pyrenees, France