Based on several hundred studies, Agroscope has estimated the impact of agricultural activities (e.g. number of cuts, application of various plant protection products, the presence of ecological structural elements such as stone walls) on these indicator-species groups. This impact is represented by the variable R, where R lies between 1 (activity has a clearly harmful impact on biodiversity) and 5 (activity promotes biodiversity). The score of the option Nopt is then calculated with the following formula for each indicator-species group:
In general, the larger Nopt, the higher the potential for biodiversity. Cmanagement lies between 0 and 10, and quantifies the importance of the activity for each indicator-species group. CHabitat also adopts values between 0 and 10, and takes into account the importance of habitat for each indicator-species group. The final score for an indicator-species group and for a particular crop or grassland (Nfin) is then calculated by averaging Nopt over all management measures. For amphibians, molluscs, spiders, ground beetles, butterflies and grasshoppers, Nfin is additionally calculated for species which are only found in a few selected biotopes (e.g. Red List species). A total of 17 indicators are calculated in this way for various indicator-species groups.
Next, the various Nfin are summarised into an overall biodiversity evaluation (BD points), with each Nfin being weighted. The more important an indicator-species group is as a feed basis for other species and the more species-rich the indicator-species group is in agricultural areas, the higher its weighting. BD points can then also be calculated on the entire-farm level instead of just per crop or grassland. Here, it is assumed that the impact of the respective BD points is proportional to the area.
The following example for butterflies on permanent grassland is intended to illustrate the method: A high number of cuts (intensive use) leads to a low R (R=1), since this has a negative effect on butterfly diversity. In addition, this low R is heavily weighted, since CHabitat and CManagement are relatively large: permanent grasslands are an important habitat for butterflies (CHabitat=7); moreover, the number of grass cuts has a major impact on butterflies (CManagement=7) compared to other management options. Butterflies are fairly important in the food chain, and exhibit high overall species richness. For this reason, the low R owing to the number of cuts also has a relatively strong effect on the calculation of the BD points.