Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Watershed Sciences

Committee Chair(s)

Karin Kettenring


Karin Kettenring


Kari E. Veblen


Timothy E. Walsworth


Wetlands provide important ecosystem services to society but are in danger across the globe partly due to the spread of invasive species (species that harm humans, the environment, or the economy). One species, Phragmites australis, is a widespread invader across the country, including in the wetlands of the Great Salt Lake and Utah Lake. Phragmites australis spreads widely and quickly outcompetes native species. In places where P. australis has already been removed, seeding wetlands helps block P. australis from returning. Native plants’ ability to prevent invasive species from entering the community is affected by many factors, but two that can be altered by restoration practitioners are density and diversity of seed mixtures. However, it has not been tested whether these two factors are stronger when combined. To address this knowledge gap, we conducted three experiments in greenhouse and field settings to determine factors that increase the ability to block invasion around the Great Salt Lake and Utah Lake. We looked at the effects of native species grown alone and in mixtures at two different native seeding densities when P. australis was present or absent. In a greenhouse setting, we found that native species identity was the most important factor determining native and P. australis growth in both native species monocultures and mixtures. The presence of P. australis also affected native growth and the ability to block P. australis, but depended on the native species tested. Finally, the high native seeding density increased native plant growth and decreased P. australis growth, with high performing species reaching these goals faster. In a field setting, we found that different, geographically close wetlands supported different plant communities but seeding treatments were mostly ineffective when extreme weather events occurred. Our findings suggest that, under ideal conditions, restoration practitioners should prioritize high performing species, consider that species will perform differently under different contexts (i.e. monocultures versus mixtures, P. australis present versus absent, different seeding densities), and seed at a high native seeding density. However, they also reflect the importance of bet-hedging as a strategy to ensure restoration success.



Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.