Vegetation changes in semi-natural meadows with unchanged management in southern Sweden, 1965-1990

Vegetation records from 1963-66 and 1990 were compared in eight semi-permanent plots from continuously managed, semi-natural hay-meadows from five sites in southern Sweden to find out whether changes in plant communities could be detected in these grasslands over a period of ca. 25 years in spite of unchanged management. It was found that species richness, ct-diversity and species frequency distribution remained fairly constant over the period, while there was considerable species turnover. However, it was also found that the total cover of vascular plants increased as well as the proportion of graminoids, both in cover and in species number, with a corresponding decrease of forbs. The number of species favoured by mowing also decreased as well as the number of typical grassland species. The detected changes are interpreted partly as effects of increased loads of atmospheric nitrogen deposition, and partly related to small changes in management intensity (changed frequency of mowing and/or aftermath grazing). It is possible that the significant land use changes in adjacent areas resulting in large landscape changes (increase of forests and woodlands) might have negatively influenced the interchange of grassland species, leading to an increase in the number of non-typical grassland species in the meadows. (C) 2000 Editions scientifiques et medicales Elsevier SAS.