| 1. |
- Serge, M. A., et al.
(författare)
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Testing the Effect of Relative Pollen Productivity on the REVEALS Model : A Validated Reconstruction of Europe-Wide Holocene Vegetation
- 2023
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Ingår i: Land. - : MDPI. - 2073-445X. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- Reliable quantitative vegetation reconstructions for Europe during the Holocene are crucial to improving our understanding of landscape dynamics, making it possible to assess the past effects of environmental variables and land-use change on ecosystems and biodiversity, and mitigating their effects in the future. We present here the most spatially extensive and temporally continuous pollen-based reconstructions of plant cover in Europe (at a spatial resolution of 1 degrees x 1 degrees) over the Holocene (last 11.7 ka BP) using the 'Regional Estimates of VEgetation Abundance from Large Sites' (REVEALS) model. This study has three main aims. First, to present the most accurate and reliable generation of REVEALS reconstructions across Europe so far. This has been achieved by including a larger number of pollen records compared to former analyses, in particular from the Mediterranean area. Second, to discuss methodological issues in the quantification of past land cover by using alternative datasets of relative pollen productivities (RPPs), one of the key input parameters of REVEALS, to test model sensitivity. Finally, to validate our reconstructions with the global forest change dataset. The results suggest that the RPPs.st1 (31 taxa) dataset is best suited to producing regional vegetation cover estimates for Europe. These reconstructions offer a long-term perspective providing unique possibilities to explore spatial-temporal changes in past land cover and biodiversity.
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| 2. |
- Sim, Thomas G., et al.
(författare)
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Regional variability in peatland burning at mid-to high-latitudes during the Holocene
- 2023
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Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 305
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Tidskriftsartikel (refereegranskat)abstract
- Northern peatlands store globally-important amounts of carbon in the form of partly decomposed plant detritus. Drying associated with climate and land-use change may lead to increased fire frequency and severity in peatlands and the rapid loss of carbon to the atmosphere. However, our understanding of the patterns and drivers of peatland burning on an appropriate decadal to millennial timescale relies heavily on individual site-based reconstructions. For the first time, we synthesise peatland macrocharcoal re-cords from across North America, Europe, and Patagonia to reveal regional variation in peatland burning during the Holocene. We used an existing database of proximal sedimentary charcoal to represent regional burning trends in the wider landscape for each region. Long-term trends in peatland burning appear to be largely climate driven, with human activities likely having an increasing influence in the late Holocene. Warmer conditions during the Holocene Thermal Maximum (similar to 9e6 cal. ka BP) were associated with greater peatland burning in North America's Atlantic coast, southern Scandinavia and the Baltics, and Patagonia. Since the Little Ice Age, peatland burning has declined across North America and in some areas of Europe. This decline is mirrored by a decrease in wider landscape burning in some, but not all sub-regions, linked to fire-suppression policies, and landscape fragmentation caused by agricultural expansion. Peatlands demonstrate lower susceptibility to burning than the wider landscape in several instances, probably because of autogenic processes that maintain high levels of near-surface wetness even during drought. Nonetheless, widespread drying and degradation of peatlands, particularly in Europe, has likely increased their vulnerability to burning in recent centuries. Consequently, peatland restoration efforts are important to mitigate the risk of peatland fire under a changing climate. Finally, we make recommendations for future research to improve our understanding of the controls on peatland fires.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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| 4. |
- Björkman, Leif, et al.
(författare)
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Late-Glacial and Holocene forest dynamics at Steregoiu in the Gutaiului Mountains, Northwest Romania
- 2003
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Ingår i: Review of Palaeobotany and Palynology. - 0034-6667 .- 1879-0615. ; 124:1-2, s. 79-79
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Tidskriftsartikel (refereegranskat)abstract
- Pollen analyses and AMS C-14 measurements were performed on lacustrine sediments and peat deposits from the former crater lake Steregoiu in a mid-altitude area in the Gutaiului Mountains in NW Romania in order to provide a detailed reconstruction of the vegetational development of the area during the Late-Glacial and Holocene. The bottom sediments are siliciclastic and were deposited probably during the Full Glacial, which is characterised by open patchy vegetation consisting of a mosaic of shrubs, herbs, and ungrown grounds. Around 14 700 cal yr BP an open Pinus-Betula forest expanded, at the same time as organic-rich lake sediments started to be deposited. This change was likely a response to the first deglacial warming phase at the beginning of the Boiling period, or GI-1e, in the GRIP event stratigraphy. Between 13 750 and 12 950 cal yr BP an open forest dominated by Betula, Picea, Pinus, and Ulmus developed in the area. The forest composition implies rather warm climatic conditions, which may correspond to the Allerod, or GI-1c-GI-1a. Around 12950 cal yr BP the forest retracted, and at 12600 cal yr BP open patchy vegetation became re-established. These changes imply a return to significantly colder conditions, which may correspond to the Younger Dryas, or GS-1. At 11500 cal yr BP Betula, Pinus, and Alnus quickly responded to the temperature rise, characterising the beginning of the Holocene. Within a few hundred years, around 11300 cal yr BP, Ulmus and Picea became re-established and a mixed forest type expanded. Quercus, Tilia, and Fraxinus likely arrived at around 10 750 cal yr BP, and from about this time Betula, and Pinus started to diminish. Around 10 500 cal yr BP a dense mixed forest dominated by Ulmus, Picea, Quercus, Tilia, and Fraxinus had developed in the area. Corylus probably became locally established around 10 500 cal yr BP, but it did not expand until 10 200 cal yr BP. Tilia and Fraxinus were locally important until 8600 cal yr BP, when Picea gained renewed importance and the lake became completely overgrown. Picea was probably an important constituent in the carr forest at the site as well as in the upland forest. Around 4800 cal yr BP Fagus and Carpinus became important in the local stand, apparently without any major disturbance of the forest. Until around 3400 cal yr BP the forest was highly diverse, but when Fagus eventually expanded, Ulmus, Tilia, Picea, and Corylus diminished. From about 2200 cal yr BP onwards Fagus has been the local forest dominant, but some Quercus and Carpinus individuals have been present as well. Pollen evidence for human influence on the local vegetation is comparatively scant. The area may have been used for forest grazing from about 1050 cal yr BP, but the grazing pressure was probably low until ca. 300 cal yr BP. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 5. |
- Björkman, Leif, et al.
(författare)
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Lateglacial and early Holocene vegetation development in the Gutaiului Mountains, northwestern Romania
- 2002
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Ingår i: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 21:8-9, s. 1039-1059
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Tidskriftsartikel (refereegranskat)abstract
- Pollen analyses and AMS C-14 measurements were performed on lacustrine sediments and peat sequences from two former crater lakes (Preluca Tiganului, Steregoiu) situated in the Gutaiului Mountains in northwestern Romania, in order to reconstruct the vegetation development during the Lateglacial and Early Holocene. Before c. 14,700 cal. years BP (GS-2) open vegetation with shrubs (Salix, Juniperus), grasses and herbs (e.g. Artemisia and Chenopodiaceae) prevailed in the area. Around c. 14,700 cal. years BP and coinciding with the beginning of GI-le, Pinus expanded, and patchy vegetation with scattered Pinus stands developed. The last 100 years of GI-le (14,150-14,050 cal. years BP) were characterised by an increase in Pinus and Betula and an expansion of open forest communities. This development was shortly interrupted between 14,050 and 13,800 cal. years BP (likely corresponding to the cold phase GI-ld), when the tree cover became reduced and open vegetation with scattered Pinus individuals became frequent. The period with a significant expansion of Betula and Picea and the formation of an open forest (including Pinus and Omits), which took place between 13,800 and c. 12,950 cal. years BP, is tentatively correlated with GI-lc-a. A renewed reduction in tree cover (decrease of Picea and Betula, disappearance of Ulms) started at similar to 12,950 cal. years BP and at 12,600 cal. years BP forest stands were rapidly replaced by open vegetation communities with low shrubs (Salix, Juniperus), grasses and herbs (e.g. Artemisia and Chenopodiaceae). The period between 12,900 and 11,500 is correlated with the cold phase GS-1. At 11,500 cal. years BP, most likely as a response to the warmer climatic conditions at the beginning of the Holocene, an expansion of Betula and Alnus and, slightly later, also of Ulmus can be observed. Between 11,500 and 11,250 cal. years BP, open forests with Betula, Pinus and Ulmus were widespread in the area. At 11,250 cal. years BP dense forests dominated by Ulmus replaced the open forest type. Around 10,700cal. years BP Quercus, Tilia and Fraxinus expanded strongly, and Acer and Corylus became established. Mixed deciduous forest with Picea dominated the upland vegetation between 10,700 and 10, 150 cal. years BP. At 10,150 cal. years BP Corylus increased significantly and between 10,150 and 8500 cal. years BP, dense mixed deciduous forests with Picea and Corylus were abundant in the area. Climatic fluctuations seem to have been the driving force behind vegetation changes during the Lateglacial period, while the forest development during the Early Holocene was mainly driven by migrational and successional processes.
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| 6. |
- Feurdean, A., et al.
(författare)
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Late Quaternary palaeocological and paleoclimatological reconstruction in the Gutaiului Mountains, NW Romania
- 2004
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 19:8, s. 809-827
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Tidskriftsartikel (refereegranskat)abstract
- Macrofossil, pollen, lithostratigraphy, mineral magnetic measurements (SIRM and magnetic susceptibility), loss-on-ignition, and AMS radiocarbon dating on sediments from two former crater lakes, situated at moderate altitudes in the Gutaiului Mountains of northwest Romania, allow reconstruction of Late Quaternary climate and environment. Shrubs and herbs with steppe and montane affinities along with stands of Betula and Pinus, colonised the surroundings of the sites prior to 14 700 cal. yr BP and the inferred climatic conditions were cold and dry. The gradual transition to open Pinus-Betula forests, slightly higher lake water temperatures, and higher lake productivity, indicate more stable environmental conditions between 14 700 and 14 100 cal. yr BP. This development was interrupted by cooler and drier climatic conditions between 14 100 and 13 800 cal. yr BP, as inferred from a reduction of open forests to patches, or stands, of Pinus, Betula, Larix, Salix and Populus. The expansion of a denser boreal forest, dominated by Picea, but including Pinus, Larix, Betula, Salix, and Ulmus started at 13 800 cal. yr BP, although the forest density seems to have been reduced between 13 400 and 13 200 cal. yr BP. Air temperature and moisture availability gradually increased, but a change towards drier conditions is seen at 13 400 cal. yr BP. A distinct decrease in temperature and humidity between 12 900 and 11 500 cal. yr BP led to a return of open vegetation, with patches of Betula, Larix, Salix, Pinus and Alnus and individuals of Picea. Macrofossils and pollen of aquatic plants indicate rising lake water temperatures and increased aquatic productivity already by ca. 11 800 cal. yr BP, 300 years earlier than documented by the terrestrial plant communities. At the onset of the Holocene, 11 500 cal. yr BP, forests dominated by Betula, Pinus and Larix expanded and were followed by dense Ulmus forests with Picea, Betula and Pinus at 11 250 cal. yr BP. Larix pollen was not found, but macrofossil evidence indicates that Larix was an important forest constituent at the onset of the Holocene. Moister conditions were followed by a dry period starting about 10 600 cal. yr BP, which was more pronounced between 8600 and 8200 cal. yr BP, as inferred from aquatic macrofossils. The maximum expansion of Tilia, Quercus, Fraxinus and Acer between 10 700 and 8600 cal. yr BP may reflect a more continental climate. A drier and/or cooler climate could have been responsible for the late expansion (10 300 cal. yr BP) and late maximum (9300 cal. yr BP) of Corylus. Increased water stress, and possibly cooler conditions around 8600 cal. yr BP, may have caused a reduction of Ulmus, Tilia, Quercus and Fraxinus. After 8200 cal. yr BP moisture increased and the forests included Picea, Tilia, Quercus and Fraxinus.
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