Effects of different mowing regimes on seedling recruitment in alluvial grasslands

The availability of suitable microsites for seedling recruitment is of high importance for the successful restoration and maintenance of species diversity in semi-natural grassland communities. In this context, disturbances imposed by management are known to have a strong impact on microsite quality. We investigated the effects of different mowing regimes on seedling recruitment of six typical flood-meadow herbs in seed addition experiments in two alluvial grasslands with different flooding regimes. One study site was situated in the functional floodplain and the other one in the fossil floodplain, which is protected against direct flooding by a dyke and only submerged by ascending groundwater. Treatments included three different mowing regimes: (i) mowing in September, (ii) mowing in June, (iii) mowing in May and August. Seedling recruitment was monitored over 2 years. In both studied meadows a low percentage of final establishment (< 4%) occurred, suggesting a lack of suitable microsites in the sward. Particularly, germination of the small-seeded Inula salicina largely failed while the large-seeded Iris spuria showed the highest number of germinated seeds. The applied mowing regimes affected recruitment of individual flood-meadow species differently. A positive effect of mowing twice in May and August could only be found for Serratuta tinctoria. Thus, flexible mowing regimes that vary among years are probably most useful to ensure seedling recruitment of a broad variety of flood-meadow species. (c) 2005 Geseltschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.