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Most localities of the critically endangered species Gagea bohemica (early star-of-Bethlehem) known in the Czech Republic were surveyed using the Braun-Blanquet approach. Based on formal definitions of the expert system for Czech non-forest vegetation, 69% of the 255 samples analysed were classified as already described pioneer plant communities on shallow soils. Samples unsorted by the expert system exhibit local or transient species composition. Ordination and multiple linear regression methods were used to study the effects of adjacent habitats and environmental conditions (altitude, Direct Potential Annual Radiation Index, herb layer cover and landcover) on species richness, the cover of G. bohemica, and the cover of nitrophytes. The geographical component (i.e. two distribution centres: one in Bohemia and one in Moravia) explained more variability in species composition than local environmental conditions or the effect of adjacent habitats. The local species pool significantly enriched the species composition of plots close to artificial and non-forested areas, less so in species-poor forested areas. However, close to areas transformed by humans, the vegetation was invaded by numerous ruderal species. The low variability in species composition of one of the most species-poor grassland communities in the Czech Republic could be associated with the relic character of its habitats. The different impacts of landscape structure on habitat diversity in Bohemia and Moravia may be a result of contrasting historical processes acting in different parts of the Czech landscape.
