Seed bank responses to wetland restoration: Do restored wetlands resemble reference conditions following sediment removal?

Sedimentation and alterations of natural hydroperiods from watershed cultivation have affected most depressional wetlands in the Great Plains. This can result in altered plant community structure through changes in water availability and depth as well as burial of seed banks. The vegetation and seed banks of 15 wetlands were sampled within the Rainwater Basin Region of Nebraska. Our objectives were to: (1) compare wetland seed bank communities among wetlands with different watershed land uses (reference, restored and impacted by watershed cultivation); (2) determine the available seed bank following sediment removal and establish if wetland zonation occurs in the deeper sediment layer of pre-scraped agricultural wetlands; and (3) determine the similarity between extant vegetation and the seed banks for each wetland land use treatment. There were no significant differences in seed bank species richness and the number and composition of annual, perennial, native, or exotic species among reference, restored, and agricultural playas. Restored wetlands had a greater number of upland species germinate from the surface soil seed bank compared to reference and agricultural playas. Availability of seeds after 30 cm of soil was removed (to simulate available seed bank if the wetland was to be restored) in crop land use wetlands was low (2–52 seeds/wetland) making determination of wetland zonation difficult. There was no difference in the similarity between the seed bank and extant vegetation among the three land use treatments. Sediment removal appears to be successful in removing weedy and exotic species from the seed bank; however, the seed bank is not the primary source for playa wetland revegetation. Restored and reference wetlands have similar seed bank community characteristics (i.e., richness) however, each wetland land use treatment was associated with differing plant species and plant guilds.

► Restored and reference wetland seed banks are dominated by differing plant guilds.
► Restored wetland seed banks are dominated by mudflat annuals.
► Sediment removal leaves little seed for recolonization.
► Sediment removal successfully removes weedy and exotic species from the seed bank.
► Reseeding of restored wetlands is most likely needed to regain the species found at reference sites.