Invasive species are a global environmental challenge that have contributed to degradation of wetland ecosystems. Phragmites australis is of particular concern in wetlands, particularly in the Great Salt Lake wetlands of the U.S. Intermountain West, as it rapidly outcompetes native species that provide important ecosystem functions. While seed-based restoration is a promising restoration strategy following P. australis control, recruitment following seeding is often unpredictable and largely unsuccessful. Seed sowing density is an important consideration, though few guidelines exist for optimal seeding density in wetland restoration. Furthermore, competitive exclusion of invaders depends not only on initial seeding density, but also the composition (i.e. functional roles/traits) of native species and environmental conditions. To address these context-dependencies, we conducted two mesocosm experiments investigating: 1) the influence of P. australis density and the density of a mix of diverse native species on recruitment, and 2) the effect of water and nutrient availability on competitive interactions. For experiment 1, mesocosms were sown with P. australis seeds at three densities and a native seed mix at four densities. We found that higher native seeding densities resulted in increased native biomass, but only when P. australis propagule pressure was greatly reduced. In the second experiment, we identified the species and sowing densities that were better able to exclude P. australis across a range of environmental conditions. Taken together, these results provide a better understanding of the context dependency of competitive interactions in wetland restoration, which can be used to maximize wetland restoration outcomes with limited seed supplies.
Audio/Video, Conference Presentation, SER2019
Pre-approved for CECs under SER's CERP program
Society for Ecological Restoration