Floristic evolution of nutrient-poor grasslands in the Alps.

The nutrient-poor, semi-natural grasslands of the Swiss Alps are amongst the most species-rich habitats in Europe. To investigate changes over 25 years in the diversity and floristic composition of these plant communities, we repeated a total of 151 phytosociological releves, originally recorded between 1975 and 1985 in Chateau-d'Oex, Grindelwald, Tujetsch und Sent. In this second survey, our results showed that the grasslands still remained very diverse. On average, we counted 52 to 60 species per plot (25-100 m(2)) according to region and compared to the original survey there was even an increase in three of four regions of between 2 and I I species. The plant communities included a high proportion of nutrient-poor grassland habitat specialists (NPG-species) some of which are protected in Switzerland; this Substantiates their particular nature conservation value. However the proportion of these species significantly declined over the last 25 years (-4% to -12%) while species typical of fertile grasslands and ubiquitous species increased. The increase in mean nutrient indicator values (+0,07 to +0,24 units) indicates that the floristic shifts were most probably due to a nutrient accumulation in these habitats. The NPG-species were only maintained in unfertilized meadows managed as ecological compensation areas (ECA) whereas there was a significant decline in all other types of land use (meadows converted to sheep pastures, cattle pastures, meadows not managed as ECA and slightly fertilized ECA meadows). To maintain the high conservation value of nutrient-poor grasslands in the Alps, it is important to support low-intensity management, especially mowing, and to prevent further eutrophication.