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- Arnell, Matilda, 1987-
(författare)
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Distribution patterns of fleshy-fruited woody plants at local and regional scales
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fleshy-fruited woody plants share a long history with humans, providing us with food and wood material. Because of this relation, we have actively moved some of these plants across landscapes and continents. In Sweden, these species are often found in open and semi-open habitats such as forest edges, their fruits are most often dispersed by birds and their flowers are, with some exceptions, pollinated by insects. In this thesis my overall aim was to map and analyse distribution patterns of fleshy-fruited woody plants in Sweden to expand our knowledge on the mechanisms governing their distributions. First, I mapped a population of the early flowering, fleshy-fruited shrub Daphne mezereum (common mezeron, tibast) and surveyed the reproduction and fruit removal of all individuals (chapter I). My main aim was to investigate to what extent reproduction and fruit removal was affected by local distribution patterns. Secondly, I mapped local distribution patterns of fleshy-fruited woody species and analysed spatial associations between life stages and species (chapter II). My main aim was to relate these spatial associations to predictions of how bird dispersal would shape the local distribution patterns and the hypothesis that birds create ‘wild orchards’. Thirdly, I digitized historical maps and surveyed fleshy-fruited woody species along transects across landscapes (chapter III). My aim was to examine the hypothesis that these species accumulate in open and semi open habitats created by human land use. Fourthly, I estimated range filling of woody plants in Sweden at a 1 km2 resolution (chapter IV). My aim was to compare these estimates among species with different dispersal systems to understand the effect of dispersal on the occupancy of woody species at regional scales.I found the distribution patterns of these species to be affected by past and present land use, supporting the hypothesis that these plants accumulate in open habitats. Occurrences of species in this guild in todays’ forest are positively related to past human land use (chapter III) and the density of D. mezereum increases with decreasing distances to forest edges (chapter I). This accumulation may in part be explained by the positive effect of forest edges on reproduction and fruit removal (chapter I). I further found local distribution patterns of this guild and the individual species to be aggregated (chapter I and II), and spatial associations between saplings and reproductive individuals to support the ‘orchard’ hypothesis (chapter II). The aggregated pattern of fruit-bearing individuals was positively related to fruit removal whereas aggregated flowering individuals was negatively related to fruit set (chapter I). On the regional scale, I found these species to occupy climatically suitable areas, or fill their potential ranges, to a less extent that wind dispersed trees and shrubs (chapter IV), which may indicate dispersal limitation.In conclusion, the behaviour of birds and humans have shaped, and still shape the current distribution of fleshy-fruited trees and shrubs in Sweden, resulting in accumulation in open habitats and locally aggregated distribution patterns. Changing land-use practices and potential mismatches between fruit maturation and bird dispersal with a changing climate may thus result in even lower chances of these species to fill their potential ranges, due to habitat losses and dispersal limitations at local and regional scales.
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| 2. |
- Greiser, Caroline, 1987-
(författare)
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Microclimate at range margins : Consequences for boreal forest understory species
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A warmer climate will shift species distributional range margins poleward, but near-ground microclimates may modify these shifts. Cold-adapted northern species at their rear edge may survive locally in microrefugia with a colder microclimate, and warm-adapted southern species at their leading edge may colonize stepping stone habitats with a warmer microclimate. However, we do not always know if species ranges are limited by climate and which role microclimate variation plays in modifying range margins. This is especially true for lowland forests, where forest structure and composition have relatively large influences on near-ground microclimates.In this thesis, I explored patterns and drivers of forest microclimate at the southern margin of the boreal zone in central Sweden, where many northern and southern species meet. First, I measured, modelled and mapped near-ground temperatures across ca. 20 000 km2 of forested land (Paper I). Second, I tested if cold and warm microclimates favour northern and southern understory species, respectively. To answer this, I investigated the occurrence and performance patterns of understory vascular plants, bryophytes and lichens across microclimate gradients at the species’ northern or southern range margins (Paper II-IV). I performed both correlational analyses on natural populations and experimental testing with transplanted populations. Third, I derived recommendations and tools for biodiversity conservation and forest management (Paper I-IV).I found high spatial and temporal variation of forest microclimate, which was in the summer mainly linked to differences in forest density and in the cold season to terrain effects (Paper I). Cold and warm microclimates were occupied by natural edge populations of northern and southern species, respectively (Paper II and IV). However, in the transplant experiments with removed competition other factors were more important for the species performance. The southern herb appeared to cope well with the range of microclimate at its current northern range margin and instead seems to be limited by soil and light in northern conifer-dominated forests (Paper IV). The northern transplanted bryophytes and lichens showed no or a positive response to warmer temperature, but also to higher moisture, to more conifers in the overstory and to less gastropod grazing (Paper III). The results indicate that competition with southern species, herbivory, leaf litter and water scarcity might be more important than temperature as direct limiting factors at the species’ current southern range margin. To conclude, microclimate influences the occurrence and performance of range edge populations, but it likely does so indirectly via effects on water availability and biotic interactions.Forest management heavily modifies near-ground temperature and humidity and hence likely impacts the climate-driven range shifts of understory species. I call for considering these effects in conservation and management actions, e.g. by protecting valuable microclimates, moving from clear-cutting to selective logging, reducing forest fragmentation and drainage and favouring either broad-leaved or coniferous trees in the overstory - depending on the local conservation target (Paper I-IV). Climate-change induced biodiversity loss may thus be slowed down by responsible forest management that provides stepping stone habitats for advancing southern species as well as microrefugia for retreating northern species.
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| 3. |
- Nuppenau, Jan-Niklas, 1989-
(författare)
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Thriving in extremes : Local adaptation of grasses (Poaceae) to geothermally heated soils on a subarctic island
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Temperature is one of the most decisive parameters when it comes to determining characteristics and distributions of life worldwide. For plants, as sessile organisms, it is particularly important to be able to deal with the temperatures they are exposed to at a given location. To understand evolutionary processes in plants, it is therefore crucial to gain knowledge about how plants deal with extreme temperatures and respond to changes in temperature. Such knowledge is especially needed given the ongoing rise in temperature under climate change. However, investigations in natural systems on how plants cope with opposing temperature extremes and the effect of long term heating are scarce. In Iceland, a subarctic island in the North Atlantic, a limited number of plant species grow on geothermally heated soils and non-heated soils alike. This constitutes a fascinating natural laboratory for studying local adaptations to opposing temperature extremes and especially constant warming. In my thesis, I investigated responses to geothermal heating in three grass species: Agrostis stolonifera and Agrostis vinealis, which are among the few vascular plants growing on the most heated soils, and Festuca rubra, which grows on moderately heated soils.First, I reconstructed phylogenetic relationships among Icelandic populations of A. stolonifera and A. vinealis and accessions across both species distribution ranges (Paper I). For A. stolonifera, but not for A. vinealis, I found a distinct geothermal lineage, which is not the closest relative of non-thermal populations. In a subsequent test of thermal tolerance for the geothermal lineage of A. stolonifera, I found no difference in survival following cold treatment, but geothermal plants survived exposure to higher temperatures. However, geothermal plants overall performed worse at colder conditions, which indicates a trade-off between heat tolerance and performance at colder temperatures (Paper II). Comparing survival ability and flowering phenology of the geothermal and non-thermal lineages of A. stolonifera in an overwintering experiment, I found no differences in survival rates but delayed flowering in geothermal A. stolonifera (Paper III). I additionally compared winter survival ability and phenology among several geothermal and non-thermal populations of F. rubra, as well as between northern and southern Swedish populations. I found no difference between geothermal and non-thermal populations of F. rubra but delayed flowering and higher performance in the northern Swedish population (Paper IV).The different findings for different species and temperature conditions emphasize the complexities of plant evolutionary responses to elevated temperatures. Whether a species adapts to elevated temperatures seems to depend not only on the level of maximum temperature rise, but also on species’ evolutionary histories, and on winter conditions. The found trade-off between heat tolerance and performance at optimal conditions suggests that adapting to extreme heat may limit viability under cooler conditions. These findings highlight the peculiarities of geothermal ecosystems, their value for studying thermal tolerances and provide a framework for future work on thermal adaptations of geothermal grasses.
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| 4. |
- Christiansen, Ditte Marie, 1990-
(författare)
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Responses of boreal forest understory plant communities to climate and forestry
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A warming climate is altering species distributions and community compositions. To understand and predict changes in species distributions to climate change, we often use species occurrences together with large-scale regional climate data. This can be problematic for several reasons. Species living near the ground experience small-scale spatial variation in temperatures, i.e., microclimate, that are influenced by topography and vegetation and can therefore deviate a lot from regional temperatures. Further, climate often affects species indirectly via species interactions, and such interactions can also change with climate. And last, species may respond slower than climate changes. Ignoring these aspects can complicate our understanding of species-climate relationships.In this thesis, I examined how microclimate and changes in microclimate due to forest management impact performances, interactions, and distributions of plant species in boreal forest understory communities. First, I quantified the importance of microclimate for species performances and distributions. Specifically, I compared the effects of spring temperatures measured on local and regional scales on the population dynamics of a southern forest herb (I). I also tested how small-scale spatial microclimate variation contributed to the regional co-existence of northern and southern understory plant species (II). Second, I examined the role of species interactions in driving abundance patterns of two moss species with different temperature niches across their Swedish ranges by transplanting them separately and together across a climate gradient (III). Lastly, I investigated how understory plant communities respond to changes in microclimate caused by forest management (IV), and how past microclimates influence current patterns of species occurrence, abundance, and reproduction (II).I found that local spring temperatures had a significant effect on the population dynamics of the southern forest herb that could not be detected using regional spring temperatures (I). Spatial variation in microclimate explained the regional co-existence of two northern and two southern species, where the northern species were favoured by cold microclimates and the southern species by warm microclimates (II). In the transplant experiment (III), I found that climate-mediated competition can override the direct effects of climate and limit abundances across ranges. Lastly, I found that microclimate changes caused by forest management activities had a large effect on understory communities (IV), and that current abundances of northern and southern species were partly explained by past microclimate (II).Overall, I demonstrated that, to understand how species (particularly understory plants) respond to climate, we need to replace the standard use of regional climate data with locally measured climate data or down-scaled gridded climate data that account for variation in topography as well as vegetation. To predict how species will respond to climate change, we also need to include species interactions and how these interactions change with a changing climate. Finally, changes in microclimate following changes in forest structure have large effects on understory species. The last finding is important to consider when studying changes in understory communities in a climate context and could be used to mitigate climate effects on forest biodiversity.
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