Elevation‐Dependent Changes in Biodiversity: Plant Community Shifts in Swiss Grasslands Over the Last Two Decades

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Questions Grassland ecosystems are subject to anthropogenic changes in land use and in climatic and further environmental conditions. In Switzerland, land‐use intensification has led to diversity loss and shifts in the composition of plant communities at low elevations, while higher‐elevation grasslands have been less impacted. However, recent studies have pointed to potential land‐use intensification even at higher elevations, in addition to ongoing changes in temperature, precipitation and nitrogen deposition. Here we investigate how vegetation changed at different elevations in the last 20 years and how this related to environmental and land‐use changes. Location Switzerland's grasslands. Methods We analysed monitoring data from Swiss grasslands collected on plots on a grid sampling over the whole country over the last 20 years across an elevation range from 212 to 2724 m a.s.l. We assessed the magnitude and drivers of changes in plant species richness and mean ecological indicator values for nutrients, which relate to changes in land use, and we assessed the shift in winners and loser species, that is, species gained and lost per plot. Results We found contrasting diversity changes across the elevation range in the last 20 years. Contrary to expectations, both species richness and mean nutrient indicator values were relatively stable at intermediate to high elevations. At low elevations, we even observed increasing species richness, which correlated with decreasing mean nutrient indicator values. However, we could not explain the vegetation changes with changes in environmental conditions. Conclusions These results point to a positive tendency for habitat conservation at lower elevations, which coincides with federal biodiversity‐promoting measures. However, we also found shifts in community composition indicating increasing thermophilisation and drought tolerance of the vegetation. It is therefore crucial to further enhance biodiversity measures in lowland grasslands, and to develop mitigation strategies for the consequences of vegetation changes driven by drought and higher temperatures across all elevations in Switzerland.