Importance of mowing and flood frequency in promoting species richness in restored floodplains

1. In recent years, European water management policies have promoted floodplain rehabilitation for flood mitigation purposes. This could provide opportunities for the restoration of valuable floodplain meadows. However, during restoration projects, it is essential to understand the effects of the measures undertaken. In this study, we focus on the interaction between flood frequency and mowing in determining species composition of temperate lowland floodplain meadows. We hypothesized that the interaction of regular flooding with annual mowing would result in higher species richness than annual mowing or regular flooding alone. 2. We compared the composition of annually mown and non-mown vegetation located in floodplain sites differing in flood frequencies. The presence of different plant growth forms and functional types was investigated in order to explain the mechanisms underlying the differences found. 3. Both flood frequency and mowing affected species composition. However, flood regime was less important than mowing regime. 4. Mowing was shown to strongly affect species composition by reducing productivity and competitiveness and offering opportunities for weak competitors. Annually mown sites harboured higher numbers of smaller species compared to non-mown sites which supported higher populations of tall graminoid species. CSR strategists (where C is competitiveness, S is stress-tolerance and R is ruderality) were most common in mown sites, demonstrating that mowing imposes a moderate degree of disturbance and nutrient stress. 5. Only the combination of frequent flooding with annual mowing clearly increased species richness. This can be attributed to the fact that mowing provides the necessary gaps for germination of flood imported seeds. 6. Synthesis and applications. Apart from focusing on the restoration of flood dynamics, managers should pay attention to the implementation and maintenance of extensive land management practices to ensure sustainable restoration results. Note that many European riparian sites have been abandoned during the last 20 years as a result of changes in policies and agricultural markets, yet annual disturbance and/or the creation of open vegetation gaps through annual mowing are necessary in order to maintain species-rich vegetations in these systems. The evaluation of possible administrative options bringing together the interests of farmers and conservationists is an important challenge in determining the restoration and preservation of these valuable floodplain habitats.