| 1. |
- Gaillard, Marie-José, 1953-, et al.
(author)
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Holocene land-cover reconstructions for studies on land cover-climate feedbacks
- 2010
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In: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 6, s. 483-499
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Journal article (peer-reviewed)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/landcover 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.
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| 2. |
- Hultberg, Tove, et al.
(author)
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Reconstruction of past landscape openness using the Landscape Reconstruction Algorithm (LRA) applied on three local pollen sites in a southern Swedish biodiversity hotspot
- 2015
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In: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 24:2, s. 253-266
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Journal article (peer-reviewed)abstract
- The Hornso-Allgunnen area in south-eastern Sweden has been known as a biodiversity hotspot for insects for about a century and is considered to host the most species-rich insect fauna in northern Europe. Several hypotheses for the causes behind this biodiversity have been put forward, but never tested for more than small parts of the area. We analyse here the possible role of the area's vegetation-cover history, in particular vegetation openness. We use pollen data from three sites in the Hornso-Allgunnen area and apply the recently developed Landscape Reconstruction Algorithm (LRA) for quantitative reconstruction of past vegetation abundance at the local spatial scale. The study suggests that the area was dominated by diverse, relatively open forest during at least the last 3,000 years. Several tree taxa, such as Pinus, Betula and Quercus that were all suggested to be important for the present diversity, have a long continuity at the local spatial scale and were common until recently. Small proportions of anthropogenic pollen indicators were found, suggesting small-scale agriculture, which however did not considerably affect the area's overall tree species composition. We propose that fire was the main cause for the open character of the area's wooded landscape during the Holocene and, indirectly, an important agent behind the high insect diversity. However, the richness of insects was (and is) most likely also favoured by the long continuity of Quercus, and by the warm and dry local climate. The LRA provides a more realistic estimate of the taxa composition as compared to pollen percentages alone, both for arboreal and non-arboreal taxa. The differences between pollen percentages and LRA-estimates of plant abundance can be important to consider when causes behind high modern diversity are interpreted from fossil pollen records. Our results demonstrate the benefits of using the LRA along with traditional pollen percentages.
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| 3. |
- Trondman, Anna-Kari, et al.
(author)
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Are pollen records from small sites appropriate for REVEALS model-based quantitative reconstructions of past regional vegetation? : An empirical test in southern Sweden
- 2016
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In: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 25:2, s. 131-151
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Trondman, Anna-Kari, et al.
(author)
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Pollen-based quantitative reconstructions of Holocene regional vegetation cover (plant-functional types and land-cover types) in Europe suitable for climate modelling
- 2015
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 21:2, s. 676-697
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Journal article (peer-reviewed)abstract
- We present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1 degrees x1 degrees spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.
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