22 July 2013 (EEA) – The European Grassland Butterfly Indicator is built from European species trends. In this chapter, we give an overview of the trends of grassland butterflies in Europe and the EU.
First, we calculate the trend in each country and for each species separately. Figure 3.1 shows four of the national trends for the Wall Brown (Lasiommata megera). The European trend is calculated for this species by combining all the national trends. In Annex 2, the method is described in greater detail. The results show that this butterfly declined, especially in the early 1990s, and was more or less stable on a low level after that. In the EU, eight species show a decline and five are stable. Two species show an increase and for two species the trend is uncertain (Table 3.1). In Europe, eight species are declining and two are stable. One species shows an increase and the trend for the remaining species is uncertain (Table 3.2).
3 Species trends
Note: Note that the starting year for the left graph (see also Map 1.1) for each scheme is different. All indexes are set to 100 for the first year of a scheme.
When interpreting the species trends it is important to take account of various points.
- The coverage of the species' populations and thus the representativeness of the data may be lower at the beginning of the time series (see also the note for Map 1.1). As more countries join in, the indices improve in accuracy each year.
- Large year‑to‑year fluctuations or a low number of transects can cause large standard errors, leading to uncertain European or EU trends.
- In almost half of the EU Member States, and even more non‑EU countries, there is no BMS yet. The trends shown only represent the countries in Map 1.1. However, because they are based on a wide geographic range of countries, we believe that they are reasonably representative of the EU as a whole.