Hydrochorous Dispersal of Diaspores in a Reconnected Floodplain: Distribution Patterns and Potential for the Development of Floodplain Habitats

Aims River alterations reduce lateral connectivity between most rivers and their floodplains. This study aimed to characterize and compare the species composition of the established vegetation of a reconnected floodplain and the species composition of diaspores deposited during the first flooding after dike relocation as well as spatial patterns in the domains of the established vegetation and diaspore deposition. On this basis, benefits and challenges of the revitalization of alluvial floodplains and hydrochorous dispersal for the development of valuable floodplain habitats are discussed. Location Reconnected floodplain along the lower midsection of the Elbe River in Northern Germany. Methods We conducted vegetation surveys in the reconnected floodplain and sampled sediments containing deposited plant diaspores during the first flooding of the study site. Species richness and composition of the established vegetation and diaspore deposition were analyzed and compared in relation to floodplain morphology. Results Locations at low elevation and in proximity to flood channels received the highest input of sediments and diaspores. Such locations were also characterized by a higher diversity of floodplain characteristic species in the established vegetation as well as among the viable diaspores deposited during the first flooding. Deposited diaspores lacked species that could support the development of floodplain forests. Diaspore deposition mostly included species characteristic of pioneer and shoreline vegetation. Conclusions Unassisted floodplain forest development in the reconnected floodplain could be restrained by dispersal limitation due to insufficient presence of source populations with characteristic floodplain forest species. Apart from the lack of floodplain forest species, this study suggests that there are valuable synergies between revitalized flooding and disturbance dynamics that promote habitat heterogeneity and enhanced diaspore deposition, which can enrich respective areas with species characteristic of floodplain habitats. This applies especially to pioneer and shoreline vegetation, hygrophilous tall herbaceous vegetation, and wet meadow plant communities.