Evaluation of restoration success in alluvial grasslands under contrasting flooding regimes

Along the northern Upper Rhine, Germany, large-scaled restoration attempts aiming at the recovery of species-rich alluvial meadows from ex-arable fields were evaluated. We analysed floristic composition, soil nutrient status and biomass production of old and newly established meadows with respect to their position in both, the recent functional flood-plain and the fossil flood-plain compartment which is protected from flooding by a dyke. It is hypothesised that restoration in terms of species-enrichment will be more successful in the functional floodplain due to the input of propagules in the course of flooding events.Generally, we found great floristic differences between old and new meadows, independent of their position in the floodplain. After 15-20 years of restoration management, the floristic structure of new meadows was still dominated by sown grasses and a high proportion of ruderal and arable species, whereas target species of flood-meadows largely failed to establish in both compartments. Old and new meadows differed only slightly in the environmental variables, while measured significant differences in plant available phosphorus and biomass yield were revealed between floodplain compartments.The results indicated a minor effect of edaphic site conditions on the low restoration success and limited dispersal and recruitment were revealed to be the main constraints for restoration. We found no evidence that species enrichment is enhanced in the functional floodplain via the input of diaspores by flooding. Our results strongly suggest that dispersal limitation of target species is unlikely to be overcome merely by the restoration of more natural flooding conditions.