LOCAL EXTINCTIONS OF PLANTS IN REMNANTS OF EXTENSIVELY USED CALCAREOUS GRASSLANDS 1950-1985

Over the last few decades changes in land use have caused a drastic de cline 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 lo cal 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 sensitiv ity to nutrient availability. We considered the possibility that speci es 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 betwe en records taken at defined misplacement distances at two sites indepe ndent of life form and habitat specificity of a species and mainly con fined from 1950-1985 and for which new and old records existed from si milar positions. In 1950, 1181 local populations of 185 species were r ecorded in these sites, yet in the new records 462 (39%) populations w ere 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 spec ies with a short life cycle (p < 0.05), and for species with high habi tat specificity (p < 0.05). Local extinctions did not depend on specie s sensitivity to nutrient availability. When recordings of species wit h an abundance of 0.1% were omitted because of potential pseudo-turnov er, the results remained unchanged. Fragmentation and isolation of nut rient-poor calcareous grassland in the Swiss Jura mountains has progre ssed to such a degree that many plants of these habitats are going loc ally extinct, even in intact remnants.