Butterfly resurvey data from Swiss Alpine grasslands, 2002–2004 and 2023–2025

This dataset accompanies Hempel et al., 2026, Biological Conservation, 2026 "Limitations of agri-environment schemes — Diversity loss and thermophilization of butterfly communities in mountain grasslands despite two decades of conservation management."
The data comprise butterfly observations from 30 grassland sites in two Swiss Alpine regions (Grindelwald and Tujetsch), collected during an initial survey in 2002–2004 and a resurvey in 2023–2025. All sites were continuously managed under either extensive (16 sites) or intensive (14 sites) management throughout the 20-year interval.

Files
butterfly_observations_individual.csv — Butterfly observations after individual-level taxonomic imputation, used for abundance and community composition analyses in the manuscript. Each unidentified individual was probabilistically assigned to a species based on the relative abundances of confirmed species within the same higher taxonomic unit. Each row corresponds to a single butterfly individual.

butterfly_observations_record.csv — Butterfly observations after record-level (conservative) taxonomic imputation, used for species richness analyses. All individuals of a higher taxonomic unit observed at a given visit were collectively assigned to a single species, to avoid inflating richness estimates. Each row preserves the original record structure with the imputed species name.

plot_metadata.csv — Plot-level metadata for the 30 study sites, including region, management classification, elevation, and slope aspect (northness).

Notes on imputation: The imputation procedure used the full pool of observations to compute relative abundances, prior to the subsetting step that selected the four standardised visits per site–year for analysis.

Column key
yearID: Sampling year (2002–2004 or 2023–2025)
region: Study region: Grindelwald or Tujetsch
plotID: Site identifier
roundID: Visit number within the sampling season
Name_original: Field-recorded species name
Name_std: Standardised species name
Name_imputed: Species name after imputation (used for analyses)
abundance: Number of individuals
management: Management classification: extensive or intensive
Elevation_100: Elevation in 100-m units
northness: Slope aspect transformed to northness (−1 = south, +1 = north)