Shifts in mollusc traits following floodplain reconnection: testing the response of functional diversity components

Restoration of ecosystems can mitigate the global loss of biodiversity and provide essential ecological functions and services. Although traitcomposition and functional diversity (FD) are important tools in assessing recovery processes, very few restoration projects use them to evaluate restoration success. Consequently, little is known about traitand FD trajectories following restoration measures. Here, we tested the effect of dyke-slotting to reconnect a floodplainon the traitresponse of mollusc communities over 6 years, based on a random stratified sampling design (plots within areas) with before and after control impact. Traitcharacteristics included flood resistance, drought resistance and resilience from which community-weighted mean traitvalues were derived. FD and its components (alpha, beta, gamma) were calculated with Rao's quadratic entropy. Flood duration in the restored area increased from 4–13 to 6–17 weeks/year after reconnection, similarly to the reference area (4–10 to 6–14 weeks). Hence, the re-connection by dyke-slotting had no substantial effect on flood duration (due to seepage water). Despite that, dyke-slotting triggered weak but significant shifts in the traitcompositions of the restored floodplainmollusc communities. Traitsreflecting species’ resilience, crushing resistance and drought resistance increased in abundance, while traitscharacteristically found in more stable habitats decreased (e.g. cross-fertilisation, diet specialisation). Overall, traitcomposition of the restored area progressively moved to that found in the active floodplain. While there were some significant temporal changes in FD within areas (reference, restored), there were no significant effects of dyke-slotting on any of the FD indices. The incorporation of spatiotemporal dynamics of FD and traitcomposition may facilitate the evaluation of restoration trajectories, especially when different components (hierarchical FD configuration, single traitdistributions) are considered together. Such complementary approaches could be integrated in future restoration monitoring programs.