High-elevation ecosystems will experience increasing periods of above-average warmth and altered precipitation changes because of climate change. This causes uncertainties for community properties such as productivity and biodiversity. Increasing temperature may increase productivity by increasing growing season length and metabolic rate or decrease productivity by causing drought stress. Competitive outcomes between species may change with altered climatic conditions, causing shifts in community composition. This study investigates the resistance of aboveground biomass and plant community composition of montane and alpine grassland ecosystems to abruptly altered temperature and precipitation conditions. Intact plant-soil communities were translocated downslope spanning an elevational gradient of 2,090 m in the European Alps. We hypothesize that increasing temperature leads to (1) increased aboveground biomass in the absence of precipitation deficits, (2) decreased species richness, and (3) shifts in plant community composition. After one year of exposure to their new environment, aboveground biomass changes appeared to be dependent on precipitation regimes, whereas species richness declined consistently with changed climatic conditions. No deterministic shift in community composition was found. Abrupt changes in climatic conditions can lead to rapid responses of community properties, indicating that these high-elevation communities may have low initial resistance to future heat waves and droughts.

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Questions Habitat islands are often characterized by the presence of more or less sharp boundaries to adjacent matrix habitats. However, knowledge on boundaries of natural habitat islands is scarce, especially regarding patterns of beta diversity and its two underlying components: species turnover and nestedness. We therefore aim to quantify the effects of fine‐scaled and sharp boundaries of quartz islands (quartz gravel‐covered soils) on the different components of plant beta diversity and how they are linked to different soil environmental drivers. Location Knersvlakte, Western Cape, South Africa. Methods We sampled plant species richness in 56 fine‐scale transects of 6 m × 1 m plots across eight different boundary types (four quartz island to matrix, four between habitats on quartz islands). Soil depth and chemistry (pH, electrical conductivity) were analyzed for each 1 m2 plot. Differences in the two beta diversity components (turnover and nestedness) for each boundary type were tested by t tests. We used linear models to test relationships between species and environmental dissimilarity. Results All boundary types showed high beta diversity. Species turnover was the prevailing component for six boundary types, the nestedness component was only important for two boundary types. We found a significant linear increase of species dissimilarity with increasing dissimilarity in soil pH and distinct plant communities for the habitat types, but no significant increase for electrical conductivity or soil depth. Conclusions The spatial distinctiveness of the quartz islands leads to sharp boundaries, which result in high beta diversity, mainly through species turnover. This reflects the high levels of diversification and adaptation of the local plant communities. Nestedness occurred at two boundaries to the matrix, indicating that the latter does not necessarily represent an impermeable boundary for all species of the respective ecosystem. Studying diversity patterns across boundaries contributes to the question of applicability of island biogeography theory to habitat islands.