The response of hydrophyte growth forms and plant strategies to river restoration

Evaluating ecological responses to restoration is important for assessing the success of river restorations. We evaluated the response of species richness and diversity of aquatic macrophyte (hydrophyte, instream aquatic plant) growth forms and strategies (Grime’s CSR strategies; C competitive, S stress tolerant, R ruderal) in 10 small- and 10 large-scale river restoration projects in nine European countries. Restoration had no effect on total richness and diversity but significant effects if specific growth forms and plant strategies were considered. Results indicated that restoration caused an increase in the richness and diversity of submerged and a decrease in the proportion of competitive species. Responses were especially pronounced in relatively small widening projects in gravel-bed mountain rivers but not in relatively large restoration projects in sand-bed lowland rivers. Moreover, flow restoration increased the richness and diversity of floating-leaved species. In rivers with a high proportion of wetlands and waterbodies in the catchment, restoration increased the abundance of competitive plants. These results highlight that river and catchment properties need to be considered when evaluating river restoration projects. We suggest hydrophyte growth forms and plant strategies as suitable response variables to assess the effect of river restoration projects.