| 1. |
- Hultberg, Tove, et al.
(författare)
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Ash dieback risks an extinction cascade
- 2020
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Ingår i: Biological Conservation. - : Elsevier BV. - 0006-3207 .- 1873-2917. ; 244
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale decline in populations of European ash (Fraxinus excelsior) are occurring throughout Europe due to the invasive fungus Hymenoscyphus fraxineus. This has grave ecological implications not only for ash trees, but also for the biodiversity supported by, and in some cases solely dependent on ash. Here we used data on the tree-species associations of biodiversity in Sweden, to predict extinction risks for ash-associated organisms, and the potential for combinations of other tree species to sustain ash-associated biodiversity. Of the 483 ash-associated species identified, 11% are exclusive to ash, and a further 23% prefer mainly ash. Notably, many ash-associated species are shared with wych elm (Ulmus glabra) which is similarly threatened by an invasive fungus. Considering the level of host association and the species' conservation status, 115 species were deemed at high risk of regional extinction. Using a mathematical optimization model we found that up to nine additional tree species would be needed to sustain all non-obligate ash dependent/preferring species in the absence of ash and elm. We discuss mitigation and adaption options to reduce the potential for an extinction cascade and conserve ash-associated biodiversity, but all pose unique challenges.
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| 4. |
- Hultberg, Tove, et al.
(författare)
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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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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 24:2, s. 253-266
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Hultberg, Tove, et al.
(författare)
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The late-Holocene decline of Tilia in relation to climate and human activities - pollen evidence from 42 sites in southern Sweden
- 2017
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Ingår i: Journal of Biogeography. - : Wiley. - 0305-0270 .- 1365-2699. ; 44:10, s. 2398-2409
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Tidskriftsartikel (refereegranskat)abstract
- Aim: The dominant role of Tilia in primeval forests of Scandinavia has long been recognized, but the timing and mechanisms for its decline have not been completely unravelled. A particular uncertainty involves the balance between climate and human activities as the drivers of the change. One reason for the uncertainty is the challenge in evaluating the past cover of the genus owing to its poorly dispersed pollen; another is that a multi-site study would be required to trace subregional differences. To overcome these obstacles, we here apply two different analytical methods to pollen data from 42 sites in two distinct vegetation zones of Sweden. Location: Temperate and hemi-boreal vegetation zones of southern Sweden. Methods: Generalized additive mixed models (GAMM) were used to model the development of Tilia and cereal pollen percentages over time. Twelve sites were used for reconstruction of local cover of Tilia using the landscape reconstruction algorithm (LRA). Results: Before 4000 cal. bp the Tilia mean pollen percentages were similar in the two vegetation zones. Thereafter, values in the hemi-boreal zone declined, with less Tilia since around 3000 cal. bp. In contrast, Tilia did not decrease in the temperate zone until this past millennium. The LRA application revealed that in some forests a large cover of Tilia remained considerably longer than has traditionally been estimated by pollen percentages alone. Main conclusions: By using a large coherent dataset we found significant differences in how the abundance and distribution of Tilia changed through time between two adjacent vegetation zones. We interpret the initial decline in the northern hemi-boreal zone to be driven by cooling climate, and the later decline in the southern temperate zone to be driven more by human land-use.
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| 6. |
- Hultberg, Tove
(författare)
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The long-term history of temperate broadleaves in southern Sweden
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Temperate broadleaves used to be abundant in the primeval forests in southern Sweden, yet today they cover only fractions of the forest land. Considering the present small area of the forest type, the habitat is of considerable interest for biodiversity, and knowledge about the history of temperate broadleaves is crucial for forest conservation and management. The main method used for studying past forest composition is pollen analysis, yet differences in pollen production and dispersal among taxa have hampered the estimation of historical cover of temperate broadleaves. By applying the Landscape Reconstruction Algorithm (LRA), a new model for translating pollen data into quantitative cover estimates, significantly improved understanding of the vegetation cover can be gained. The applications of the LRA to local and regional pollen data from southern Sweden carried out in this thesis show that in many areas, large cover of temperate broadleaves prevailed locally until rather recently, which is likely to be an important cause for the survival of the many threatened species associated with these tree taxa today, although in small and vulnerable populations. Many of our study sites showed no tendencies of local decline of temperate broadleaves until during the most recent 500 years, which is considerably later than in the region as a whole, as well as what has often been emphasized in other studies. For Tilia, the cover of which has confounded researchers since the introduction of pollen analysis, the decline in the southernmost parts of the country was not as early as commonly thought, but in general almost as recent as for many other temperate broadleaves. In this thesis it is also shown that in many presently protected biodiversity hotspots the forest composition changed radically during the last 500 years, and hence not even these hotspots can be claimed to have unbroken continuity back to ancient forests, or to be a reflection of "natural" forest in southern Sweden. Land use changes, such as forest clearance for agricultural purposes, as well as grazing and browsing by domestic animals are likely to have been important causes for this vegetation change.
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| 7. |
- Lindbladh, Matts, et al.
(författare)
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From broadleaves to spruce - the borealization of southern Sweden
- 2014
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Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 29, s. 686-696
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Tidskriftsartikel (refereegranskat)abstract
- Mixed or broadleaf forests were once common in many regions of Northern Europe, whereas today conifers often dominate. The aim of the study was to investigate the spatial and temporal patterns and processes which underlie this transition to Picea abies dominance in southern Sweden. We use recently developed paleoecological methods to determine long-term changes in the relative abundance of tree species, and digitalized National Forest Inventory (NFI) databases to assess more recent changes in the spatial coverage of Picea throughout the region. The novel combination of the two databases reveals that Picea became a widespread and abundant species in many parts of southern Sweden around 1000 years ago. After a brief decline in abundance starting around 500 years ago, NFI data indicate a rapid increase in the volume of Picea between 1920 and 1950, prior to the large-scale introduction of Picea-dominated plantation forests. The available evidence suggests that abandonment of forest grazing and slash-and-burn cultivation, as well as selection cutting benefited the natural establishment and growth of Picea during the first half of the twentieth century. Hence, prior to the impacts of industrialized forestry that began in the 1950s, other processes were already favouring increased Picea abundance.
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| 8. |
- Lindbladh, Matts, et al.
(författare)
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Halland's forests during the last 300 years: a review of Malmstrom (1939)
- 2011
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Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 26, s. 81-90
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Forskningsöversikt (refereegranskat)abstract
- Carl Malmstrom's historical forest maps of the province of Halland, in south-western Sweden, were published over 70 years ago, but are still important to science and conservation. They show the transformation of a seventeenth century landscape of temperate broadleaves to a landscape dominated by open land and heather (Calluna vulgaris) in the nineteenth century, and to a landscape of coniferous forest plantations in the twentieth century. This article summarizes and reviews the original research, first published in Swedish in 1939. Malmstrom concludes that the large changes to forest abundance and composition over the last 300 years were predominantly the product of human endeavours. The most important causal factors behind the decrease in forest area until the mid-nineteenth century were the incentives to increase arable land and meadows, the grazing and burning of Calluna heaths, and logging for timber, fencing and firewood. The subsequent increase in forest abundance after this period were due to agricultural improvements, the cessation of heather burning and active reforestation. Malmstrom had a relatively holistic view of the ecosystem for his time, yet his perspective remains that of an early twentieth century silviculturalist as he did not put his observations into the context of conservation or landscape ecology. Despite acknowledging that beech forest is the natural vegetation for the area, he still concludes that coniferous plantations have won full domiciliary rights. Recent research has confirmed Malmstrom's views on the patterns and processes that characterized changes in land use and forest composition in the province of Halland, although there has been some question as to the onaturalnesso of seventeenth century beech forests.
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| 9. |
- Trondman, Anna-Kari, et al.
(författare)
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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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Ingår i: Vegetation History and Archaeobotany. - : Springer Science and Business Media LLC. - 0939-6314 .- 1617-6278. ; 25:2, s. 131-151
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Tidskriftsartikel (refereegranskat)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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| 10. |
- Trondman, Anna-Kari, et al.
(författare)
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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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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 21:2, s. 676-697
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Tidskriftsartikel (refereegranskat)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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