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| 2. |
- Borg, Christina, 1970-
(författare)
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Structural Growth in Mountain Birch, Betula pubescens ssp. czerepanovii
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, I have studied long shoot performance in the monoecious, deciduous tree Betula pubescens ssp. czerepanovii. In field studies and a common garden experiment, I have a) studied how environmental variations affect the performance of long shoots in mountain birch, and b) described the relationship between long shoot performance and characteristics of the parent long shoot.I have shown that difference in long shoot performance to some extent can be explained by environmental variables such as temperature, precipitation and global radiation the current and previous summer, annual soil and air temperatures, and the length of growing season. For example, a low summer temperature the previous summer had a negative effect on a majority of long shoot characteristics. Variation in shoot characteristics was of the same magnitude along the regional east-western gradient as along the local altitudinal gradient. Variation among individual trees was of the same magnitude as variation among years. Further, long shoot performance was affected by the parent shoot characteristics and reflects that primordia of different organs are formed in the previous summer. On several occasions, freezing damage to mountain birch has been observed on Mt Njulla in northernmost Sweden. Following such damage, fewer but larger leaves emerge. Damages were compensated for with increased number of buds on long shoots produced the same year and one year after damage. Moreover, there were more new long shoots born on short shoots among damaged trees. Dormant buds and short shoots fulfil important functions in a fluctuating environment and as an adaptation to recurring damages of different origin and severity.Differences in the performance among mountain birch saplings grown in a common-garden at Abisko could to a large degree be explained by their origin. Further, saplings from Sweden and from Iceland responded differently to defoliation, and fertilization did not alter the responses to defoliation.
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| 4. |
- Carlsson, Bengt Å., et al.
(författare)
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Alpine and subalpine vegetation
- 1999
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Ingår i: Swedish plant geography. - Uppsala : Svenska växtgeografiska sällskapet. - 9172100842 ; , s. 75-89
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Bokkapitel (refereegranskat)
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| 5. |
- Eriksson, Åsa, 1964-
(författare)
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Recruitment and distribution patterns of plants in Swedish semi-natural grasslands
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Semi-natural pastures with different histories of management are nowadays the main remnants of the traditional agrarian landscape in southern Sweden. The aims of this thesis were to investigate the importance of features of the present-day landscape and its management history for species distribution and abundance patterns in Swedish semi-natural pastures, with a particular focus on factors affecting recruitment processes. Seedling recruitment in these semi-natural pastures was enhanced by disturbances, with the largest advantage for small-seeded species. The majority of species in semi-natural pastures have small seeds that germinate in the autumn. Seedlings seem to recruit mainly from the local species-pool, with 83 % of the recruited species found in the vegetation, whereas 44 % of the recruited species were found in the seed bank. Plant species diversity and distribution patterns are influenced by management history. In the study of distribution patterns of Thymus serpyllum I found that T. serpyllum populations were associated with Iron Age remnants, indicating that T. serpyllum is dependent on human activities, both for dispersal and for the maintenance of established populations. The highest species diversity was found in pastures with a long continuous management regime, whereas no significant species-area relationship could be detected in the present-day landscape. The highest arbuscular mycorrhizal colonization was also found in pastures with a long continuous management regime. The explanation for this patterns is probably that long continuous management is associated with an increasing likelihood of successful dispersal of plant species as well as of fungal species. Thus, historical distribution of pasture areas and their management history may be more important than the present-day distribution. The effects of the dramatic changes of the cultural landscape during this century, with fragmentation of the landscape and changing management, will work on other time scales. The fact that most species in semi-natural pastures are long-lived perennial species, implies that changes in species composition will be slow. Plantago media was found to have an overall negative population growth rate and a restricted dispersal ability, and this may be viewed as a first step towards visible changes. Dispersal limitation seems to be important in the present-day landscape, with T. serpyllum and P. media as examples of both local and regional dispersal limitation. The lack of area-relationship may also be an effect of "self-similarity" of grasslands. Indeed, I found that the majority of species (61%) in Swedish semi-natural pastures were recorded at the smallest spatial scale (0.01m2), and that the area sampled at this scale comprised only 1.25 % of the area examined. This indicates a small-scale structuring of diversity in these pastures.
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| 6. |
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| 7. |
- Hedenas, Henrik, et al.
(författare)
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Changes Versus Homeostasis in Alpine and Sub-Alpine Vegetation Over Three Decades in the Sub-Arctic
- 2012
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Ingår i: Ambio. - : Springer Verlag (Germany). - 0044-7447 .- 1654-7209. ; 41, s. 187-196
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Tidskriftsartikel (refereegranskat)abstract
- Plant species distributions are expected to shift and diversity is expected to decline as a result of global climate change, particularly in the Arctic where climate warming is amplified. We have recorded the changes in richness and abundance of vascular plants at Abisko, sub-Arctic Sweden, by re-sampling five studies consisting of seven datasets; one in the mountain birch forest and six at open sites. The oldest study was initiated in 1977–1979 and the latest in 1992. Total species number increased at all sites except for the birch forest site where richness decreased. We found no general pattern in how composition of vascular plants has changed over time. Three species, Calamagrostis lapponica, Carex vaginata and Salix reticulata, showed an overall increase in cover/frequency, while two Equisetum taxa decreased. Instead, we showed that the magnitude and direction of changes in species richness and composition differ among sites.
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| 8. |
- Hedenås, Henrik, et al.
(författare)
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Changes Versus Homeostasis in Alpine and Sub-Alpine Vegetation Over Three Decades in the Sub-Arctic
- 2012
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 41:Suppl 3, s. 187-196
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Tidskriftsartikel (refereegranskat)abstract
- Plant species distributions are expected to shift and diversity is expected to decline as a result of global climate change, particularly in the Arctic where climate warming is amplified. We have recorded the changes in richness and abundance of vascular plants at Abisko, sub-Arctic Sweden, by re-sampling five studies consisting of seven datasets; one in the mountain birch forest and six at open sites. The oldest study was initiated in 1977-1979 and the latest in 1992. Total species number increased at all sites except for the birch forest site where richness decreased. We found no general pattern in how composition of vascular plants has changed over time. Three species, Calamagrostis lapponica, Carex vaginata and Salix reticulata, showed an overall increase in cover/frequency, while two Equisetum taxa decreased. Instead, we showed that the magnitude and direction of changes in species richness and composition differ among sites.
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| 9. |
- Hytteborn, Håkan, et al.
(författare)
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Century-long tree population dynamics in a deciduous forest stand in central Sweden
- 2017
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 28:5, s. 1057-1069
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Tidskriftsartikel (refereegranskat)abstract
- Question: We quantify tree dynamics over a century of free development in a small broadleaved forest dominated by Fraxinus excelsior and Ulmus glabra. What are the internal and external factors driving the changes, and how predictable are they? What were the time scale and effects of the spread of Dutch elm disease (DED)? Location: Vårdsätra, eastern central Sweden.Methods: The survival, growth and recruitment of all trees (≥ 12 cm in girth) were monitored in 1912, 1967, 1988 and 2013 (more often for a part of the forest). Woody species in the field and shrub layers were surveyed in permanent plots in 1976 and 2012. We used transition matrix models to project changes in population sizes and species composition within the century and for 2050.Results: The results indicate that the forest was in a successional development during the first period. The species composition had stabilised by 1967, except for an expansion of Acer platanoides and the drastic effect of DED that struck the forest around 2000. It took only a decade to kill virtually all large elms in the forest, leading to strong decrease in stem density and basal area. The evidence for effects of DED is still weak, but there has been an increase in saplings, notably of Fraxinus, Prunus padus, Ulmus, and of shoots of Corylus avellana. Several species that are abundant in the vicinity and as seeds fail to establish (Picea abies, Betula spp., Quercus robur, Populus tremula). Projections for 2050 based on the third period (1988-2013) are probably unrealistic since also Fraxinus may disappear because of the recent arrival of the ash dieback.Conclusions: Slow dynamics in forests that could follow from climate change will locally probably be overruled by unforeseen catastrophes, such as invasions by forest pathogens. These initiate changes with long lag phases difficult to quantify. Still, a dense deciduous forest can resist invasion of colonist species and of regionally dominant conifers; the reason being unfavourable conditions for establishment rather than dispersal limitation
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| 10. |
- Hytteborn, Håkan, et al.
(författare)
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Spatial heterogeneity ensures long-term stability in vegetation and Fritillaria meleagris flowering in Uppsala Kungsäng, a semi-natural meadow
- 2023
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 18:3
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Tidskriftsartikel (refereegranskat)abstract
- Semi-natural grasslands are becoming increasingly rare, and their vegetation may be affected by environmental changes and altered management. At Kungsängen Nature Reserve, a wet to mesic semi-natural meadow near Uppsala, Sweden, we analysed long-term changes in the vegetation using data from 1940, 1982, 1995 and 2016. We also analysed the spatial and temporal dynamics in the Fritillaria meleagris population based on countings of flowering individuals in 1938, 1981–1988 and 2016–2021. Between 1940 and 1982 the wet part of the meadow became wetter, which led to an increased cover of Carex acuta and pushed the main area of flowering of F. meleagris up towards the mesic part. Annual variation in the flowering propensity of F. meleagris (in May) was affected by temperature and precipitation in the phenological phases of growth and bud initiation (June in the previous year), shoot development (September in the previous year) and initiation of flowering (March–April). However, the response to weather was in opposite directions in the wet and mesic parts of the meadow, and the flowering population showed large year-to-year variation but no long-term trend. Variation in management (poorly documented) led to changes in different parts of the meadow, but the overall composition of the vegetation, species richness and diversity changed little after 1982. Species richness and species composition of the meadow vegetation, and the long-term stability of the F. meleagris population are maintained by the variation in wetness, highlighting the importance of spatial heterogeneity as an insurance against biodiversity loss in semi-natural grasslands and nature reserves generally.
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