Populationsgrösse und Gefährdung von Magerwiesen-Pflanzen im Nordwestschweizer Jura

Abstract

During the last decades the area of extensively used calcareous grasslands has drastically declined in the Jura mountains of NW Switzerland. Remnants have become small and isolated. In 1997 we recorded the local occurrence of 14 endangered plant species on 44 remnants of calcareous grassland and the frequency distribution of population size in a sample of 221 populations. One third of the populations had a population size with less than 10, two thirds with less than 100 flowering individuals. For nine of the recorded species population size increased significantly with remnant area. Between 1997 and 1998 we observed considerable fluctuations in population size. We conclude that many local populations are at a high risk of extinction as a consequence of small population size due to area reduction and fragmentation.