The Z12 indicator “Diversity of Species Communities” monitors the development of species compositions in the various habitats and within individual regions. If uniform land uses and other processes were to cause the same species to expand nationwide, species numbers might increase on the small scale, but the result on the large scale would be homogenization, i.e. loss of diversity. Conversely, even species-poor locations can contribute to species diversity if they harbor species that do not occur anywhere else. Initial results indicate that plant species communities are indeed homogenizing not only in grasslands, but also in landscapes as a whole.

Comments

• Species communities in the Jura are almost as uniform as those found on the Central Plateau. Interestingly enough, the two regions tend to differ to a very considerable degree as regards mean butterfly diversities (cf. Z7 indicator “Species Diversity in Landscapes”). In other words, the Central Plateau is evenly species-poor, while the Jura is evenly species-rich.
• The difference between the Central Plateau and the Jura on the one hand and the Alps on the other hand is due to both natural causes and human land use. Because of their wider ranges of altitudes and their more marked reliefs, it is only natural that alpine regions be home to more diverse species communities than low-land regions. However, the uniformity of species communities on the Central Plateau and in the Jura has most likely also been brought about by the intensive land use these two regions are subjected to, which made local particularities disappear.
• The absolute indicator value computed for Switzerland overall (see Appendix 1) cannot be directly compared to the indicator values computed for its individual biogeographical regions. Since biogeographical regions are defined by standardized floral and faunal distribution patterns (Gonseth et al., 2001), the diversity of species communities is bound to increase when looking at the country as a whole.