Factors influencing the seed source and sink functions of a floodplain nature reserve in the Netherlands

Question How do species traits and abiotic factors influence the extent of hydrochorous dispersal into and out of a small floodplain area along a free-flowing river in The Netherlands? Location The Kappersbult nature reserve (53 degrees 07'28 ' N, 6 degrees 37'14 ' E), which is a floodplain along the Dutch River Drentsche Aa. Methods Seeds transported by the river were collected in fine mesh nets for 24 consecutive hours once or twice a week for 1 year, upstream and downstream of the studied floodplain. Data on the captured seeds were related to species traits and abiotic factors and species composition in the floodplain. Results The floodplain functioned both as a seed source and sink. High levels of river water seemed to promote seed transport to or from the floodplain. Seeds of riverbank species occurred significantly more often in the river water than expected. Net source species had significantly higher seed production, taller stature and higher seed buoyancy, but lower site elevation than net sink species. Seed weight was significantly higher for sink species than for other species. Conclusion Our study found that inundation, and therefore more natural river water management, is a prerequisite for seed transport to and from a floodplain. The restoration of target floodplain vegetation may be successful for common species that produce many seeds and grow in proximity to the river. Consequently, it is expected that the probability of restoring vegetation types that occur further from the river, such as wet grasslands, by hydrochorous dispersal is low