| Summary: | Ecosystems today are under increasing pressure from a rapidly changing climate, changes in land-use, habitat fragmentation and degradation and increasing anthropogenic disturbance. Studying drivers of biodiversity patterns is of increasing importance for understanding the dynamics of communities and their reactions and adaptation to changes in the future. Climate change is predicted to be most dramatic in mountainous areas, influencing shifts in vegetation patterns, which have already been observed. Vegetation in cliff outcrops is highly distinct from surrounding vegetation, and commonly contains many rare species, including a high proportion of endemics. Despite this, cliffs are not well represented by ecological studies. This thesis is based on field studies investigating some aspects of processes shaping biodi-versity patterns in plant communities in terms of species distribution, composition and diversity. Patterns of diversity were related to environmental and spatial factors, human distur-bance and biotic interactions. The investigated plant communities were cliffs and surrounding matrix vegetation at a subarctic alpine tundra site and cliff ecosystems in south-west Sweden. Vegetation at the investigated sites were surveyed along with estimations of environmental variables and analyzed to identify the drivers of observed diversity patterns. At the subarctic alpine study site, results show that cliff habitats are highly important for landscape diversity. They contained many species specialized for this habitat, which cannot persist in the surrounding landscape. Bryophytes and lichens contained species more distinctly affiliated to the cliff habitats compared to vascular plants. At the same subarctic alpine site, the cushion plant Silene acaulis was shown to act as a nurse plant in cold-stressed environments, enhancing local biodiversity at higher elevation in the Scandes. At the investigated cliff sites in south-west Sweden, distribution of bryophytes specialized for cliff environments was indicated to be ...
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