| Summary: | Species composition of a local habitat is a sample of regional species pool. Stress and disturbance define the environmental conditions and control the vegetation on the local scale. The variation of stress and disturbance inside a region control fluctuations in species richness and species composition. This thesis examines the effect of local stress and disturbance on the relationship between local and regional vascular plant species pools in arctic-alpine environment. The relationship is studied through beta-diversity, which measures the ratio of local and regional species richness. It tells how many times larger the regional species pool is compared to the local species pool. If stress, disturbance and biotic competition didn't limit the species dispersal at the local scale, there would be the same species composition in every habitat and no variance in beta-diversity. Stress level is studied through soil temperature, moisture and pH. Stress variables determine the resource shortage, which limits the primary production and species richness. Earth surface processes (ESP) are a major disturbance in a low-productive environment. ESPs modify physical conditions of a habitat, destroy vegetation and change the availability of resources. Stress and disturbance are distributed by local topography, which is measured with a mesotopographical index. The research was carried out by analyzing an environmental data, which was sampled in Finnish Lapland in 2011–2013. The data consists of 21 research grids that hold together 3360 research plots. A research grid is considered a region for which regional species richness was computed based on its plots' species pools. Beta-diversity was computed to every research plot as a ratio of regional and local species richness. The effect of environment on beta-diversity was studied through Spearman correlation coefficient and statistical modeling. Generalized linear models (GLM) were used to find out the best combination of stress variables in explaining the variation of beta-diversity ...
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