Recurrent drought amplifies drought impacts and increases seasonal synchrony in mountain grassland communities

Climate change increases the frequency and severity of drought events with strong repercussions on grassland ecosystems. While the effects of single drought events on ecosystem structure and functioning are well understood, it is largely unknown whether and how drought frequency modifies ecosystem responses to drought. Here, we assessed how the increase in frequency of severe, annual summer drought impacted grassland communities. We examined these effects in a species-rich sub-alpine mountain meadow with drought frequencies of one, three, and 13 years, compared to ambient conditions.
We found that high drought frequency increased seasonal plant community synchrony. This pattern was associated with a reduction in species richness, a shift in plant functional groups, a loss of early-seasonal plant species, and a constrained establishment of seedlings throughout the growing season. Additionally, these changes were accompanied by a decreased fraction of biomass as drought frequency increase..., , , # Data from: Recurrent drought amplifies drought impacts and increases seasonal synchrony in mountain grassland communities

[https://doi.org/10.5061/dryad.4tmpg4fmt](https://doi.org/10.5061/dryad.4tmpg4fmt)

## Description of the data and file structure

Four summer drought treatments were established in the enclosed area at the study site: a single year summer drought, three years of recurrent summer drought, 13 years of recurrent summer drought, and ambient conditions (n = 4, respectively). In total, 4 plots for ambient, single, three, and 13 years of drought frequency were installed four weeks before summer drought simulation in 2020, respectively. In all 16 plots, species composition and vegetation height (cm) were measured every two weeks from 22 May to 22 October 2020. Plant species composition was estimated by noting for each species present the number of modules and flowering stems. Seedling composition in the plots was counted separately every three weeks between the 23 June a...,