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Sökning: L773:0939 6314 OR L773:1617 6278

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  • Ammann, Birgitta, et al. (författare)
  • The potential of stomata analysis inconifers to estimate presence of conifer trees: examples from the Alps
  • 2014
  • Ingår i: Vegetation History and Archaeobotany. - 0939-6314 .- 1617-6278. ; 23:3, s. 249-264
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>To estimate whether or not a plant taxon found in the fossil record was locally present may be difficult if only pollen is analyzed. Plant macrofossils, in contrast, provide a clear indication of a taxon’s local presence, although in some lake sediments or peats, macrofossils may be rare or degraded. For conifers, the stomata found on pollen slides are derived from needles and thus provide a valuable proxy for local presence and they can be identified to genus level. From previously published studies, a transect across the Alps based on 13 sites is presented. For basal samples in sandy silt above the till with high pollen values of <em>Pinus</em>, for example, we may distinguish pine pollen from distant sources (samples with no stomata), from reworked pollen (samples with stomata present). The first apparent local presence of most conifer genera based on stomata often but not always occurs together with the phase of rapid pollen increase (rational limit). An exception is <em>Larix</em>, with its annual deposition of needles and heavy poorly dispersed pollen, for it often shows the first stomata earlier, at the empirical pollen limit. The decline and potential local extinction of a conifer can sometimes be shown in the stomata record. The decline may have been caused by climatic change, competition, or human impact. In situations where conifers form the timberline, the stomata record may indicate timberline fluctuations. In the discussion of immigration or migration of taxa we advocate the use of the cautious term “apparent local presence” to include some uncertainties. Absence of a taxon is impossible to prove.</p>
  • Berglund, B.E., et al. (författare)
  • Long-term changes in floristic diversity in southern Sweden – palynological richness, vegetation dynamics and land-use.
  • 2008
  • Ingår i: Vegetation History and Archaeobotany. - 0939-6314 .- 1617-6278. ; 17:5, s. 573-583
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The rarefaction technique is applied to two Holocene pollen sequences (covering the last 12,000 calendar years) from two lakes in southern Sweden. One represents an open agricultural landscape, the other a partly wooded and less cultivated landscape. The inferred palynological richness is interpreted as an approximate measure of floristic diversity at the landscape scale. The overall trend is an increased diversity from the mid-Holocene to the Modern period, which is linked to a parallel rise in human impact. The pattern is similar for the two sites with peaks corresponding to archaeological periods characterised by deforestation and expanding settlement and agriculture. The highest diversity was reached during the Medieval period, about A.D. 1,000-1,400. Declining diversity during the last 200 years characterises the agrarian landscape. These results confirm, for southern Scandinavia, the "intermediate disturbance" hypothesis for biodiversity at the landscape scale and on millennial to century time scales. They have implications for landscape management in modern nature conservation that has the purpose of maintaining and promoting biodiversity.</p>
  • Bigler, Christian, et al. (författare)
  • Holocene environmental history of Lake Vuolep Njakajaure (AbiskoNational Park, northern Sweden) reconstructed using biologicalproxy indicators
  • 2006
  • Ingår i: Vegetation History and Archaeobotany. - 0939-6314 .- 1617-6278. ; 15:4, s. 309-320
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract  Holocene environmental and climatic changes are reconstructed using analyses of biological proxies in lake sediments from Vuolep Njakajaure, a lake located near the altitudinal treeline in northern Sweden (68°20′ N, 18°47′ E). We analysed biological proxy indicators from both aquatic and terrestrial ecosystems, including diatoms, pollen and chironomid head capsules, in order to reconstruct regional Holocene climate and the development of the lake and its catchment. During the early Holocene and after 2500 cal b.p., <em>Fragilaria</em> taxa dominated the diatom assemblages, whereas planktonic <em>Cyclotella</em> taxa prevailed during the major part of the Holocene (7800–2300 cal b.p.), indicating the importance of the pelagic habitat for diatom assemblage composition. The planktonic diatoms appeared at the same time as <em>Alnus</em> became established in the catchment, probably altering nutrient availability and catchment stability. The pollen record is dominated by mountain birch (<em>Betula pubescens</em> ssp. <em>tortuosa</em>) pollen throughout the Holocene, but high percentage abundances of Scots pine (<em>Pinus sylvestris</em>) pollen suggest the presence of a mixed pine-birch forest during the mid-Holocene (6800–2300 cal b.p.). Head capsules of Tanytarsini and <em>Psectrocladius</em> dominated the chironomid assemblage composition throughout the Holocene, in combination with <em>Corynocera ambigua</em> after 2300 cal b.p. A quantitative, diatom-based reconstruction of mean July air temperature indicated a relatively cold temperature during the early Holocene (9000–8000 cal b.p.) and after ca. 2300 cal b.p., whereas the mid-Holocene period is characterised by stable and warm temperatures. The overall patterns of Holocene climate and environmental conditions are similarly described by all biological proxy-indicators, suggesting relatively warm conditions during the mid-Holocene (ca. 7800–2300 cal b.p.), with a subsequent colder climate after 2300 cal b.p. However, the onset and magnitude of the inferred changes differ slightly among the proxies, illustrating different responses to lake development phases, land-uplift, and climate forcing (e.g., insolation patterns) during the Holocene in northern Sweden.
  • Broström, Anna, et al. (författare)
  • Pollen productivity estimates of key European plant taxa for quantitative reconstruction of past vegetation : a review
  • 2008
  • Ingår i: Vegetation History and Archaeobotany. - 0939-6314 .- 1617-6278. ; 17:5, s. 461-478
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Information on the spatial distribution of past vegetation on local, regional and global scales is increasingly used within climate modelling, nature conservancy and archaeology. It is possible to obtain such information from fossil pollen records in lakes and bogs using the landscape reconstruction algorithm (LRA) and its two models, REVEALS and LOVE. These models assume that reliable pollen productivity estimates (PPEs) are available for the plant taxa involved in the quantitative reconstructions of past vegetation, and that PPEs are constant through time. This paper presents and discusses the PPEs for 15 tree and 18 herb taxa obtained in nine study areas of Europe. Observed differences in PPEs between regions may be explained by methodological issues and environmental variables, of which climate and related factors such as reproduction strategies and growth forms appear to be the most important. An evaluation of the PPEs at hand so far suggests that they can be used in modelling applications and quantitative reconstructions of past vegetation, provided that consideration of past environmental variability within the region is used to inform selection of PPEs, and bearing in mind that PPEs might have changed through time as a response to climate change. Application of a range of possible PPEs will allow a better evaluation of the results.</p>
  • Ekblom, Anneli, et al. (författare)
  • Land use history and resource utilisation from A.D. 400to the present, at Chibuene, southern Mozambique
  • 2014
  • Ingår i: Vegetation History and Archaeobotany. - 0939-6314 .- 1617-6278. ; 23:1, s. 15-32
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>This paper discusses changing patterns of resource utilisation over time in the locality of Chibuene, Vilankulos, situated on the coastal plain of southern Mozambique. The macroscopic charcoal, bone and shellassemblages from archaeological excavations are presented and discussed against the off-site palaeoecological records from pollen, fungal spores and microscopic charcoal. The Chibuene landscape has experienced four phases of land use and resource utilisation that have interacted with changes in the environment. Phase 1 (A.D. 400–900), forest savanna mosaic, low intensity cattle herding and cultivation, trade of resources for domestic use. Phase 2 (A.D. 900–1400), forest savanna mosaic, high intensity/extensive cultivation and cattle herding. Phase 3 (A.D. 1400–1800), savanna woodland and progressive decrease in forests owing to droughts. Decline of agricultural activities and higher reliance on marine resources. Possible trade of resources with the interior. Phase 4 (A.D. 1800–1900), open savanna with few forest patches. Warfare and social unrest. Collapse of trade with the interior. Decline in marine resources and wildlife. Loss of cattle herds. Expansion of agriculture locally and introduction of New World crops and clearing of <em>Brachystegia</em> trees. The study shows the importance of combining different environmental resources for elucidating how land use and natural variability have changed over time.</p>
  • Felde, Vivian A., et al. (författare)
  • Compositional turnover and variation in Eemian pollen sequences in Europe
  • 2020
  • Ingår i: Vegetation History and Archaeobotany. - 0939-6314 .- 1617-6278. ; 29:1, s. 101-109
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The Eemian interglacial represents a natural experiment on how past vegetation with negligible human impact responded to amplified temperature changes compared to the Holocene. Here, we assemble 47 carefully selected Eemian pollen sequences from Europe to explore geographical patterns of (1) total compositional turnover and total variation for each sequence and (2) stratigraphical turnover between samples within each sequence using detrended canonical correspondence analysis, multivariate regression trees, and principal curves. Our synthesis shows that turnover and variation are highest in central Europe (47-55 degrees N), low in southern Europe (south of 45 degrees N), and lowest in the north (above 60 degrees N). These results provide a basis for developing hypotheses about causes of vegetation change during the Eemian and their possible drivers.</p>
  • Gaillard, Marie-Jose, et al. (författare)
  • The use of modelling and simulation approach in reconstructing past landscapes from fossil pollen data: a review and results from the POLLANDCAL network
  • 2008
  • Ingår i: Vegetation History and Archaeobotany. - 0939-6314 .- 1617-6278. ; 17:5, s. 419-443
  • Forskningsöversikt (refereegranskat)abstract
    • <p>Information on past land cover in terms of absolute areas of different landscape units (forest, open land, pasture land, cultivated land, etc.) at local to regional scales is needed to test hypotheses and answer questions related to climate change (e.g. feedbacks effects of land-cover change), archaeological research, and nature conservancy (e.g. management strategy). The palaeoecological technique best suited to achieve quantitative reconstruction of past vegetation is pollen analysis. A simulation approach developed by Sugita (the computer model POLLSCAPE) which uses models based on the theory of pollen analysis is presented together with examples of application. POLLSCAPE has been adopted as the central tool for POLLANDCAL (POLlen/LANdscape CALibration), an international research network focusing on this topic. The theory behind models of the pollen-vegetation relationship and POLLSCAPE is reviewed. The two model outputs which receive greatest attention in this paper are the relevant source area of pollen (RSAP) and pollen loading in mires and lakes. Six examples of application of POLLSCAPE are presented, each of which explores a possible use of the POLLANDCAL tools and a means of validating or evaluating the models with empirical data. The landscape and vegetation factors influencing the size of the RSAP, the importance of pollen productivity estimates (PPEs) for the model outputs, the detection of small and rare patches of plant taxa in pollen records, and quantitative reconstructions of past vegetation and landscapes are discussed on the basis of these examples. The simulation approach is seen to be useful both for exploring different vegetation/landscape scenarios and for refuting hypotheses.</p>
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