Occurrence of rare and protected plant species related to species richness in calcareous xerothermic grassland

Occurrence of rare and protected plant species is regarded as a strong argument for creating a protected area. It is therefore especially important to know whether rare and protected species are reliable indicators of abundance of other, more common, unprotected species. We analysed co-occurrence of protected and rare species with other xerothermic plant species in calcareous xeric grassland in Western Poland. In the years 2005-2006, on 62 plots (25 m[^2] each) we identified vascular plants on a 60 km[^2] area in the Odra R. Valley and its smaller tributaries valleys. Legally protected species appeared not to be better indicators of xerothermic species richness than non-protected species. The rarest species (Anthericum liliago L., Carex supina Willd. ex Wahlenb. and Stipa borysthenica Klokov ex Prok.) were significantly less useful indicators of xerothermic species richness than other rare and common species. These results let us conclude that designing a network of protected areas on the basis of rare and protected species may result that some common species, biodiversity hotspots or well developed phytocenoses will be ignored.