| 1. |
- 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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| 2. |
- Samnegård, Ulrika, 1985-
(författare)
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The impact of forest on pest damage, pollinators and pollination services in an Ethiopian agricultural landscape
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The distribution of wild biodiversity in agroecosystems affect crop performance and yield in various ways. In this thesis I have studied the impact of wild biodiversity, in terms of trees and forest structures, on crop pests, pollinators and the pollination services provided in a heterogeneous landscape in southwestern Ethiopia. Coffee, Coffea arabica, is a forest shrub native to Ethiopia and is grown in most wooded areas in the landscape where I conducted my studies. Wild coffee is still found in remote parts of the forests in the landscape. For my first paper, I surveyed pest damage on coffee in coffee forest sites, where some sites were situated in continuous forest and some in isolated forest patches. I found the variation in pest damage frequency to mainly be among coffee plants within a site, rather than among sites, which indicates the importance of local processes. However, some pests were clearly connected to the forest habitat, such as the olive baboon.In my second study, I surveyed pollinators visiting coffee flowers across a gradient of shade-tree structures. I found the semi-wild honeybee to be the dominating flower visitor. The abundance of the honeybee was not related to shade-tree structures, but to amount of coffee flower resources in the site. On the other hand, other pollinators, which included other bee species and hoverflies, were positively affected by more shade trees in the site.In my third study I investigated how the forest cover affected local bee communities in the agricultural landscape. Moreover, I investigated if this relationship differed between the dry and rainy season. The distribution of food resources for bees changes between the seasons, which may affect the bees. Most trees, fruit trees and coffee, which are patchy resources, flowers in the dry season, whereas most herbs and annual crops, which are more evenly spread resources, flowers during the rainy season. I found a clear turnover in bee species composition between the dry and rainy season, with more mobile species in the dry season. Increased forest cover in the surrounding landscape had a positive impact on bee abundance and species richness. However, the impact did not change between seasons.In my fourth study I evaluated the pollination success and pollen limitation of a common oil crop in the landscape in relation to forest cover. I found severe pollen limitation across the landscape, which may be related to the observed low bee abundances. The pollen limitation was not related to surrounding forest cover.In conclusion, I have found the forest and wooded habitats to impact several mobile animals and pathogens in our study landscape, which in turn affect people. However, there is large complexity in nature and general relationships between forest structures and all crop related organisms may be unlikely to find. Various species are dependent on different resources, at different spatial scales and are interacting with several other species. To develop management strategies for increased pollination services, for reduced pest damage or for conservation in the landscape, more species-specific knowledge is needed.
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| 3. |
- Ayalew Nurihun, Biruk, 1983-
(författare)
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The relationship between climate, disease and coffee yield: optimizing management for smallholder farmers
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate change and diseases are threatening global crop production. Agroforestry systems, which are characterized by complex multispecies interactions, are considered to provide nature-based solutions for climate change mitigation and pest and disease regulation. Understanding the role of the abiotic environment and species interactions in shaping diseases and yield in agroforestry systems would enable us to develop effective ecologically-informed pest and disease management under a changing climate, support sustainable agricultural practices, and maximize the benefits gained from agroforestry systems. To gain such a comprehensive understanding of what shapes pest and disease levels and yield in agroforestry systems, we need to investigate how the interactions between agroforestry system components, such as trees, crops and their associated organisms, vary in space and time, and how they are influenced by abiotic factors in terms of pests and diseases and yield. In this thesis, my overarching goal was to understand how microclimate and management impact major coffee pests and diseases, their natural enemies, and coffee yield, as well as farmers’ perceptions of climate change and climate-mediated changes in disease dynamics and yield, with the aim of using these insights to optimize management decisions for smallholder farmers in southwestern Ethiopia. With this aim, I selected 58 sites along a gradient of management intensity, ranging from minimal management in the natural forest to moderate management in smallholder farms and intensive management in commercial plantations. As an approach, I combined observational and interview studies to examine i) the impact of shade tree species identity and canopy cover on coffee pests and diseases, ii) the effect of climate and management on coffee berry disease and yield, iii) the impact of climate on a host-hyperparasite interaction, and iv) farmers’ perceptions of climate change and climate-mediated changes in disease dynamics and yield. I found that tree identity affected the incidence and severity of coffee diseases, whereas insect pests were strongly affected by canopy cover, but in a species-specific way (I). Both climate and management affected coffee berry disease and yield. Importantly, the effect of climatic variables on disease and yield differed strongly between the developmental stages from flowering to ripening (II). In chapter (III), I found that the climatic niches of coffee leaf rust and its hyperparasite differed, with coffee leaf rust severity preferring high maximum temperatures, whereas the hyperparasite preferred cold nights. The interviews revealed that the majority of farmers perceived long-term changes in one or more aspects of the climate, and the majority of farmers perceived an increase in coffee leaf rust and a decrease in coffee berry disease. Climate data also supported farmers’ knowledge on climate-disease-yield relationships (IV). Taken together, my thesis advances our understanding of the relationship between climate and management of coffee pests, diseases and yield, and this may contribute to the development of ecologically-informed pest and disease management strategies for coffee production and other agroforestry crops.
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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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| 5. |
- Dahlberg, C. Johan, 1978-
(författare)
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The role of microclimate for the performance and distribution of forest plants
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microclimatic gradients may have large influence on individual vital rates and population growth rates of species, and limit their distributions. Therefore, I focused on the influence of microclimate on individual performance and distribution of species. Further, I examined differences in how microclimate affect species with contrasting distributions or different ecophysiological traits, and populations within species. More specifically, I investigated the performance of northern and southern distributed forest bryophytes that were transplanted across microclimatic gradients, and the timing of vegetative and reproductive development among northern, marginal and more southern populations of a forest herb in a common garden. Also, I compared the landscape and continental distributions across forest bryophytes and vascular plants and, thus, their distribution limiting factors at different spatial scales. Lastly, I examined the population dynamics across microclimatic gradients of transplants from northern and southern populations of a forest moss. The effects of microclimatic conditions on performance differed among bryophytes with contrasting distributions. There were no clear differences between northern and southern populations in the timing of development of a forest herb or in the population dynamics of a moss. However, within each region there was a differentiation of the forest herb populations, related to variation in local climatic conditions and in the south also to proportion of deciduous trees. The continental distributions of species were reflected in their landscape distributions and vice versa, in terms of their occurrence optima for climatic variables. The variation in landscape climatic optima was, however, larger than predicted, which limit the precision for predictions of microrefugia. Probably, the distributions of vascular plants were more affected by temperature than the distributions of bryophytes. Bryophytes are sensitive to moisture conditions, which was demonstrated by a correlation between evaporation and the population growth rate of a forest moss. We might be able to predict species’ landscape scale distributions by linking microclimatic conditions to their population growth rates, via their vital rates, and infer larger scale distribution patterns.
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| 6. |
- Hailu, Beyene Zewdie, 1983-
(författare)
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Fungal disease dynamics, genetic variation and biodiversity-yield relationships : — a study along a gradient of coffee management in southwestern Ethiopia
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intensification of agricultural systems is a major threat to the associated biodiversity and could also affect the dynamics of pests and pathogens. One such system that is currently under an intensification trajectory is the production of Arabica coffee. In this thesis, I studied the relationships between fungal diseases and their natural enemies, the genetic variation in coffee, coffee yield and associated biodiversity along a coffee management gradient in southwestern Ethiopia.The specific goals of this thesis were to investigate variation in fungal diseases on coffee and their natural enemies along a gradient of management (I, II), how genetic variation in coffee among sites relate to variation in incidence of the fungal diseases (III), and to investigate the trade-offs in biodiversity-yield relationships along the gradient of coffee management (IV). To answer these questions, I selected 60 sites along a gradient of management that ranged from coffee naturally growing in only little disturbed forests to intensively managed plantations. I used both observational studies and molecular approaches.In paper I, I examined if the severity of the four major fungal diseases on coffee varied along the gradient and assessed the main drivers of variation in disease severity. I found that two of the fungal diseases were more severe in the intensively managed coffee sites, while the other two were more severe in the less intensively managed sites. Altitude was the main driver for the diseases, but related in a different way to the different diseases. In paper II, I examined the temporal dynamics in coffee leaf rust-hyperparasite interaction, the biocontrol potential of the hyperparasite and environmental drivers for the two species for three consecutive years during the dry and wet seasons. I found that the rust was more common during the dry season and in managed sites while the hyperparasite was common during the wet season and in sites that were less managed. My results also revealed that higher hyperparasite incidence during the wet season resulted in a lower growth rate of the rust during the subsequent dry season. In paper III, I investigated if genetic composition and diversity of coffee sites relate to the incidence of the fungal diseases assessed. I found that genetic composition of the coffee stands was linked to the incidence of the four fungal diseases, but genetic diversity among the coffee sites did not relate to the incidence of the diseases. In paper IV, I examined biodiversity-yield trade-offs and shape of the relationships between biodiversity and yield along the gradient of management. I found a steep, concave shape initial decline in biodiversity values as coffee yield increased to a certain level, after which a further increase in yield did not have much effect on biodiversity values.In conclusion, I found different drivers for the different diseases and for the parasite-hyperparasite interaction. It is difficult to achieve a single management approach that can suit the different pathogen species investigated. High genetic diversity among coffee sites did not reduce disease pressure. While the more complex, less managed sites provide high biodiversity values, and could potentially serve as habitats for natural pest control and in situ conservation for coffee genetic diversity, the yield gap compared to more intensively managed sites was very high. To optimize coffee management and conservation of biodiversity in these landscapes, there is a need to develop strategies whereby the smallholder farmers who depend on coffee and the forest as the main source of livelihood can benefit through for example coffee certification schemes that can pay premium prices for biodiversity-friendly coffee management.
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| 7. |
- Koelemeijer, Irena A., 1994-
(författare)
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Effects of drought on boreal forest understory species
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Extreme climatic events, such as droughts, can have large effects on biodiversity. Drought effects in forest understories are variable over small spatial scales and can be exacerbated, or buffered, by the local vegetation structure, distance to forest edges, hydrology, and soil characteristics. Boreal forest landscapes are intensively managed, which affects several of these factors and many boreal forest species are confined to small forest fragments in an otherwise managed landscape. In this thesis, I investigated how summer drought affects different taxa in spruce-dominated forest understories, including vascular plants, bryophytes, lichens and fungi. I assessed if drought sensitivity can be linked to taxonomic group and species traits, and how drought effects vary over space and time. I conducted both observational studies, after the drought in 2018, and experimental studies in which I used rainout shelters to exclude all precipitation for 45 days. First, I examined if spatial variation in the 2018 drought was correlated with old-growth forest affiliated species richness and community composition, and tested if drought effects on understory species were stronger in edge exposed forest patches (chapter I). I also investigated how the 2018 drought affected the depth and magnitude of microclimatic edge effects, using the annual growth of an understory moss (chapter II). Second, I assessed how the experimental drought affected the performance of transplanted understory plants (chapter III) and soil fungal communities in terms of biomass, community composition and sporocarp production (chapter IV), and investigated how spatial variation in canopy cover, soil moisture and soil nutrients modified responses to drought (chapter III and IV). Finally, I suggest tools to optimize forest management and biodiversity conservation in a changing climate with a higher drought prevalence (chapter I – IV).My results indicate that summer droughts can have significant impacts on forest understory species, both above and belowground, and that these impacts vary across landscapes. The groups that correlated most strongly with spatial variation in the 2018 drought were cyanolichens, epiphytes on high-pH bark, and species on logs and boulders (chapter I). After the experimental drought, particularly bryophytes, and the orchid Goodyera repens, experienced long-lasting negative effects on growth and reproduction (chapter III). Belowground, the experimental drought negatively affected species richness of saprotrophic fungi in the phylum Basidiomycota and ectomycorrhizal fungi with extensive and hydrophobic extramatrical mycelia (chapter IV). My results suggest that understory species are more vulnerable to extreme drought in edge exposed forest patches (chapter I), and edge effects were twice as strong during the 2018 drought compared to regular years (chapter II). Within forest patches, higher canopy cover and soil moisture levels reduced negative drought responses to some extent (chapter II, III, IV). In order to maintain the conservational value of small forest remnants in future climates with a higher frequency of droughts, the amount of edge habitat surrounding these forest patches needs to be reduced. This can be achieved by adding buffer zones with high shade levels or by moving away from clearcutting as the dominant harvesting practice. Furthermore, minimizing canopy opening and restoring hydrological networks can buffer drought impacts on understory species.
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| 8. |
- Lemessa, Debissa, 1973-
(författare)
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Pests and pest controlling organisms across tropical agroecological landscapes in relation to forest and tree-cover
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A major challenge in agroecosystems is how to manage the systems so that it reduces crop pests and enhances natural pest control. This thesis investigates patterns of crop pests and top-down effects of birds and arthropod predators in relation to land-use composition across spatial scales. In paper (I) I examined the crop distribution and land-use types in relation to the crop raiding patterns in 15 transectsin sites close to and far from forests along with a questionnaire survey at household level. I found severe crop raiding close to forests, but it had no impact on crop composition growing between the two sites. In paper (II) I examined the effect of forest and tree cover, at local and landscape scales, on the abundance of arthropod predators by collecting specimens from 40 home gardens. My result showed higher abundance of arthropod predators when either the home garden or the surroundings had a high tree-cover, compared to when tree-cover at both scales was similarly either high or low. In paper (III) I investigated the effect of excluding birds and arthropod predators on leaf damage on rape seed in 26 home gardens. I found stronger top-down impacts from arthropod predators on crop pests in tree-poor gardens than in tree-rich gardens. There was no effect of birds. In paper (IV) I explored the effect of landscape complexity on bird and arthropod predation using plasticine caterpillars in 36 home gardens across landscapes. The rate of arthropod predation on caterpillars was higher in simple than in complex landscapes. The rate of bird predation did not vary between complex and simple landscapes. In simple landscapes, arthropod predation was higher than that of birds. The overall results suggest that simplified gardens/landscapes still have enough habitat heterogeneity to support arthropod predators for the significant top-down controlling effect on crop pests. However, I did not find clear effect of complexityon the top-down effect of birds.
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| 9. |
- Lönnell, Niklas, 1969-
(författare)
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Dispersal of bryophytes across landscapes
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dispersal, especially long-distance dispersal, is an important component in many disciplines within biology. Many species are passively dispersed by wind, not least spore-dispersed organisms.In this thesis I investigated the dispersal capacity of bryophytes by studying the colonization patterns from local scales (100 m) to landscape scales (20 km). The dispersal distances were measured from a known source (up to 600 m away) or inferred from a connectivity measure (1–20 km). I introduced acidic clay to measure the colonization rates over one season of a pioneer moss, Discelium nudum (I–III). I also investigated which vascular plants and bryophytes that had colonized limed mires approximately 20–30 years after the first disturbance (IV).Discelium effectively colonized new disturbed substrates over one season. Most spores were deposited up to 50 meters from a source but the relationship between local colonization rates and connectivity increased with distance up to 20 km (I–III). Also calcicolous wetland bryophyte species were good colonizers over similar distances, while vascular plants in the same environment colonized less frequently. Common bryophytes that produce spores frequently were more effective colonizers, while no effect of spore size was detected (IV). A mechanistic model that take into account meteorological parameters to simulate the trajectories for spores of Discelium nudum fitted rather well to the observed colonization pattern, especially if spore release thresholds in wind variation and humidity were accounted for (III).This thesis conclude that bryophytes in open habitats can disperse effectively across landscapes given that the regional spore source is large enough (i.e. are common in the region and produce spores abundantly). For spore-dispersed organisms in open landscapes I suggest that it is often the colonization phase and not the transport that is the main bottle-neck for maintaining populations across landscapes.
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| 10. |
- Schmalholz, Martin, 1981-
(författare)
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Resistance and recolonization of bryophyte assemblages following disturbances : - detecting patterns and exploring mechanisms
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Disturbances are ubiquitous features of most northern forest ecosystems. The subsequent response of plant assemblages on both short (resistance or not) and long term (recolonization or not) will depend on a number of factors operating at several spatial scales. In boreal forest ecosystems, bryophyte assemblages are a conspicuous and species rich group of plants for which these processes are poorly understood. Using a combination of experimental and observational approaches this thesis explores these questions for closed-canopy bryophyte assemblages in relation to a) microtopography (both for the initial and long-term response), b) environmental constrains during post-logging succession and c) disturbance type. My results clearly show that the shade and shelter provided by microtopographic surface structures can increase survival rates of bryophytes following clear-cut logging by decreasing mortality from microclimatic stress and mechanical disturbance. Following clear-cutting, the recovery of forest floor and dead wood living bryophytes seems to be a relatively steady and progressive process without any major bottleneck episodes in the young or semi-mature forest stages with much of the pre-disturbance composition recovered after 50 years. Although boulders were found to increase the initial survival on clear-cuts and hence increase disturbance resistance, we found no evidence that boulders influenced the subsequent recolonization process. Lastly, strong compositional dissimilarities were found in young forests (40 years) following clear-cut logging, wildfire and insect outbreak, indicating divergent trajectories to occur following different disturbances. Hence, early seral stages of forest ecosystems regenerating after natural disturbances seem to compliment young managed forests in maintaining landscape level diversity.
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