Bet Hedging to Aid Seed-Based Wetland Restoration Under Hydrologic Extremes

Abstract

Reestablishing native plant communities following invasive species management is a common restoration goal for wetland managers. Although passive recolonization is occasionally sufficient, often, active revegetation through seeding is required. However, the outcomes of seeding likely differ by site (due to varying environmental conditions) and the composition of the seed mix. We evaluated the effects of both passive recolonization and seeding treatments (varying density and diversity of natives) on wetland plant community cover and composition at two sites in the Great Salt Lake Watershed, USA, over two years. We found that passive recolonization was insufficient to increase native plant cover at one location and limit invasive species' cover at either location. Furthermore, different emergent wetland restoration sites, despite geographic proximity, had different plant community outcomes, likely due to distinct site environmental conditions. We also found that the effects of the seeding treatments appeared to be overwhelmed by water depth due to two extreme weather events (severe drought in year 1 and prolonged flooding in year 2). However, these events provided an opportunity to observe the recovery potential of the different functional groups and identify three species of restoration interest (Bolboschoenus maritimus, Schoenoplectus acutus, and Distichlis spicata) that were able to survive the extreme conditions during both growing seasons at one site. These findings underscore the importance of not relying on passive recolonization and instead using bet-hedging strategies (e.g., seeding diverse mixes with species with a range of hydrologic tolerances) to overcome hydrologic extremes, conditions likely to become more common with climate change and ever-increasing upstream water diversions.