Local extinctions of plants in remnants of extensively used calcareous grasslands 1950-1985

Populationen und ihre Dynamik Over the last few decades changes in land use have caused a drastic decline in the area of extensively used calcareous grasslands in central Europe. The persistence of many vulnerable plant species now depends on relict populations. We use phytosociological records from nutrient-poor calcareous grasslands in the Swiss Jura mountains to study local extinctions of plants from 1950-1985. We tested whether the risk of local extinction is higher in small populations, higher for plants with a short life cycle than for those with a longer life cycle, higher for specialist plant species, and higher for species with a high sensitivity to nutrient availability. We considered the possibility that species could have been missing in the new records without actually having gone extinct, if new and old phytosociological records were not taken at the same position (pseudo-turnover). We found pseudo-turnover between records taken at defined misplacement distances at two sites independent of life form and habitat specificity of a species and mainly confined from 1950-1985 and for which new and old records existed from similar positions. In 1950, 1181 local populations of 185 species were recorded in these sites, yet in the new records 462 (39%) populations were no longer present. Whereas the frequency of habitat specialist per site decreased (p > 0.05), the frequency of generalists increased (p > 0.01), leaving the total number of species per site unchanged. Local extinction was more likely for small populations (p > 0.01), for species with a short life cycle (p > 0.05), and for species with high habitat specificity (p > 0.05). Local extinctions did not depend on species sensitivity to nutrient availability. When recordings of species with an abundance of 0.1% were omitted because of potential pseudo-turnover, the results remained unchanged. Fragmentation and isolation of nutrient-poor calcareous grassland in the Swiss Jura mountains has progressed to such a degree that many plants of these habitats are going locally extinct, even in intact remnants.