README.txt

AUTHOR: Reto Schmucki

FILE NAME: EU27_grassland_indicator_value.csv

FORMAT: csv

TITLE: EU Grassland Butterfly Index 1991-2023 (GBI values)

DATE COMPUTED: 15/05/2025

SUMMARY: GBI data used to produce figure 5, "The Grassland Butterfly Indicator for the EU27 countries from 1991 to 2023", in Van Swaay et al. (2025). The Grassland Butterfly Indicator (GBI) corresponds to a time series of annual indices that aggregate the multi-BMS index (EU27) for 17 species. In the same way that we combined the index across BMS in step 3, we calculated the geometric mean for each year, assigning the same weight to each species. For species with shorter time series, the first year of the series was set to the value of the indicator in that year. If values were missing within or at the end of the time series, the value of the last non-missing index was used. Using this approach, we can calculate a single time series of multiple species indices, with annual values corresponding to the grassland butterfly index. From these annual indices, we produced a smoothed time series corresponding to the grassland butterfly indicator. The smoothed indicator was created using LOESS smoothing with a span of 0.75 and a degree of 2 (Soldaat et al. 2017). For details, see Van Swaay et al. (2025), https://doi.org/10.5281/zenodo.16281872. 


CONTENT: The data contain the GBI time series for 33 years, presented in seven columns and 34 rows, including headers.

COLUMN HEADING:
1. year: The year (1991-2023)rfly Index
2. indicator: The value of the annual Grassland Butterfly Index
3. ind_gam0: The smoothed value (LOESS: span=0.75, degree=2) of the annual Grassland Butterfly Index
4. SMOOTH: The rescaled smoothed value (ind_gam0) starting at 100 in the first year of the time series, where the first year is 1991.
5. NSPECIES: The number of species of the 17 grassland butterfly species that contributed to the annual index in a given year.
6. LOWsmooth1: Lower bound of the 90% confidence interval around the SMOOTH (GBI), see details of the non-parametric bootstrap method in Van Swaay et al. (2025), page 33.
7. UPPsmooth1: Upper bound of the 90% confidence interval around the SMOOTH (GBI), see details of the non-parametric bootstrap method in Van Swaay et al. (2025), page 33.


CITATION: Van Swaay C.A.M., Schmucki R., Roy D.B., Dennis E.B., Collins S., Fox R., Kolev Z.D., Sevilleja C.G., Warren M.S., Whitfield A., Wynhoff I., Arnberg H.J.H., Balalaikins M., Barea-Azcón J.M., Boe A.M.B., Bonelli S., Botham M.S., Bourn N.A.D., Cancela J.P., Caritg R., Dapporto L., Ducry A., Dušej G., de Flores M., Dopagne C., Escobés R., Eskildsen A.E., Fric Z.F., Fernández-García J.M., Fontaine B., Glogovčan P., Gohli J., Gracianteparaluceta A., Grill A., Harpke A., Harrower C., Heliölä J.K., Høye T.T., Judge M., Kati V., Krenn H.W., Kühn E., Kuussaari M., Lang A., Lehner D., Lysaght L., Maes D., McGowan D., Melero Y., Mestdagh X., Middlebrook I., Monasterio Y., Monteiro E., Montes A., Munguira M.L., Musche M., Olivares F.J., Ozden O., Pladevall C., Pavličko A., Pettersson L.B., Rákosy L., Roth T., Rüdisser J., Šašić M., Scalercio S., Schönwälder M., Settele J., Sielezniew I., Sielezniew M., Sobczyk-Moran G., Stefanescu C., Švitra G., Svabadfalvi A., Tiitsaar A., Titeux N., Tzirkalli E., Tzortzakaki O., Ubach-Permanyer A., Vičiuvienė E., Vray S., Zografou K. (2025). EU Grassland Butterfly Index 1991-2023 Technical report. Butterfly Conservation Europe & EMBRACE/eBMS (www.butterfly-monitoring.net) & Vlinderstichting report VS2025.014. https://doi.org/10.5281/zenodo.16281872