| 31. |
- Dallmeyer, Anne, et al.
(författare)
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Holocene forest-cover changes in Europe - a comparison of dynamic vegetation model results and pollen-based REVEALS reconstructions
- 2023
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Ingår i: EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11206. - : European Geosciences Union (EGU).
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Konferensbidrag (refereegranskat)abstract
- We compare Holocene forest-cover changes in Europe derived from a transient MPI-ESM1.2 simulation with high spatial resolution time-slice simulations conducted in LPJ-GUESS and pollen-based quantitative reconstructions of forest cover based on the REVEALS model (pol-RVs). The dynamic vegetation models and pol-RVs agree with respect to the general temporal trends in forest cover for most parts of Europe, with a large forest cover during the mid-Holocene and substantially smaller forest cover closer to the present time. However, the age of the start of decrease in forest cover varies between regions, and is much older in the pol-RVs than in the models. The pol-RVs suggest much earlier anthropogenic deforestation than the prescribed land-use in the models starting 2000 years ago. While LPJ-GUESS generally overestimates forest cover compared to pol-RVs, MPI-ESM indicates lower percentages of forest cover than pol-RVs, particularly in Central Europe. A comparison of the simulated climate with chironomid-based climate reconstructions reveal that model-data mismatches in forest cover are in most cases not driven by biases in the climate. Instead, sensitivity experiments show that the model results strongly depend on the models tuning 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 during 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- and late-Holocene.
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| 32. |
- Dallmeyer, Anne, et al.
(författare)
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The challenge of comparing pollen-based quantitative vegetation reconstructions with outputs from vegetation models - a European perspective
- 2023
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Ingår i: Climate of the Past. - : Copernicus Publications. - 1814-9324 .- 1814-9332. ; 19:7, s. 1531-1557
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Tidskriftsartikel (refereegranskat)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.
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| 33. |
- Dearing, JA, et al.
(författare)
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Social-ecological systems in the Anthropocene : The need for integrating social and biophysical records at regional scales.
- 2015
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Ingår i: The Anthropocene Review. - : SAGE Publications. - 2053-0196 .- 2053-020X. ; 2:3, s. 220-246
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Tidskriftsartikel (refereegranskat)abstract
- Understanding social-ecological system dynamics is a major research priority for sustainable management of landscapes, ecosystems and resources. But the lack of multi-decadal records represents an important gap in information that hinders the development of the research agenda. Without improved information on the long-term and complex interactions between causal factors and responses, it will be difficult to answer key questions about trends, rates of change, tipping points, safe operating spaces and pre-impact conditions. Where available long-term monitored records are too short or lacking, palaeoenvironmental sciences may provide continuous multi-decadal records for an array of ecosystem states, processes and services. Combining these records with conventional sources of historical information from instrumental monitoring records, official statistics and enumerations, remote sensing, archival documents, cartography and archaeology produces an evolutionary framework for reconstructing integrated regional histories. We demonstrate the integrated approach with published case studies from Australia, China, Europe and North America.
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| 34. |
- Fontana, Sonia L., 1969-
(författare)
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Present and Past Coastal Dune Environments of South Buenos Aires Province, Argentina
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to describe present and past coastal dune environments in southern Buenos Aires Province, Argentina. The present vegetation of a dune system and its zonation are described on the basis of air photographs, physiognomy of the dune system and floristic composition. The vegetation was characterized by a large number of Poaceae and Asteraceae species. Five vegetation zones, based on floristic composition, were defined by cluster analysis. Pollen-vegetation comparison revealed that pollen assemblages differed considerably from the associated vegetation. Some of the major discrepancies were caused by large differences between pollen and vegetation proportion of Hyalis argentea and Discaria americana. However, the local vegetation was well represented in recent soil samples. Pollen traps recorded predominantly extralocal and regional pollen. A new species of ostracods was recovered from an interdunal lake. The species, a giant cypridid, was described and illustrated, and its geographical distribution and ecology were discussed. Two sediment sequences from the coastal intertidal zone and from a shallow freshwater lake were analysed for loss on ignition, calcareous microfossils (ostracods and foraminifers), macro remains and pollen. The coastal sequence was deposited between 7890 and 7630 cal. BP. Its pollen assemblages were typical for halophytic associations, with some psammophytic taxa also present in recent vegetation. The microfossils were representative of a littoral lagoon. The lake sequence comprised the last 3000 cal. BP. Pollen spectra indicated a relatively stable vegetation composition after the lake had been formed. Pollen assemblages reflected the present regional grassland vegetation with taxa characteristic for the surrounding dune communities. Human settlement was indicated in the pollen spectra by the presence of introduced taxa in the uppermost samples. The data presented provide a useful reference for the interpretation of fossil sequences from similar environments.
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| 35. |
- Fyfe, Ralph M., et al.
(författare)
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The Holocene vegetation cover of Britain and Ireland : overcoming problems of scale and discerning patterns of openness
- 2013
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 73, s. 132-148
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Tidskriftsartikel (refereegranskat)abstract
- 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. (C) 2013 Elsevier Ltd. All rights reserved.
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| 36. |
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| 37. |
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| 38. |
- Gaillard, Marie-Jose, et al.
(författare)
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A late Holocene record of land-use history, soil erosion, lake trophy and lake-level fluctuations at Bjäresjösjön (South Sweden) changes in southern Sweden
- 1991
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Ingår i: Journal of Paleolimnology. - 0921-2728 .- 1573-0417. ; 6, s. 51-81
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Tidskriftsartikel (refereegranskat)abstract
- Land-use history, soil ersosion, lake trophy and lake-level fluctuations during the last 3000 years werereconstructed through a multidisciplinary palaeolimnological study (pollen, plant macrofossils, diatoms,physical and chemical analysis, magnetic measurements and radiometric methods) of a small eutrophiclake in southern Sweden (Bj~resjOsjOn, Scania). There are striking responses in diatom, chemical,sediment yield and magnetic records to land-use changes documented by pollen analysis or historicalsources, and to lake-level changes identified from sedimentary changes. Our multidisciplinary approachassists interpretation of the processes controlling long-term changes and separation of the effects ofdifferent factors (land-use changes, lake-level fluctuations) on individual biostratigraphical records.Climate has controlled processes in the lake indirectly, through lake-level fluctuations, from the LateBronze Age to the Viking Age (700 BC-AD 800). Since the Viking Age, land-use controlled most of thechanges observed in the lake's development and soil erosion processes. Major changes in lake developmentoccurred during the last 200 years, due to a drastic increase in soil erosion and water eutrophicationduring a period of agricultural modernization.
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| 39. |
- Gaillard, Marie-Jose, et al.
(författare)
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A multidisciplinary study of Lake Bjäresjö (S Sweden): land-use history, soil erosion, lake trophy and lake-level fluctuations during the last 3000 years
- 1991
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Ingår i: Hydrobiologia. - 0018-8158 .- 1573-5117. ; 214, s. 107-114
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Tidskriftsartikel (refereegranskat)abstract
- The lake Bjaresjosjon, Southern Scania, Southern Sweden, was studied in the context of the project 'The cultural landscape of the past 6000 years in Southern Sweden'. Pollen, plant macrofossils, diatoms, physical and chemical analysis, magnetic measurements and radiometric methods (Pb-210, C-14) have been used to study palaeoecological changes, i.e. climate, land use, lake trophy and soil erosion during the past 3000 years. This multidisciplinary study shows striking responses of diatom communities, physical and chemical characteristics, sediment yields and magnetic parameters to land-use changes and lake-level fluctuations. Moreover, the latter are closely related to the settlement history at the site, inferred from archaeological records and historical sources. Before 650 AD, the limnological development was affected mainly by lake-level fluctuations, but partly also by human impact (extensive forest clearings and dominant pastoral farming). With the expansion of arable farming (around 650 AD), human impact on the landscape was the major factor influencing soil erosion processes in the catchment and limnological changes in the lake.
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| 40. |
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