The Effects of Seed Mix Composition, Sowing Density, and Seedling Survival on Plant Community Reassembly in Great Salt Lake Wetlands

Wetlands are known for their valuable benefits (e.g., providing habitat, improving water quality, lessening the negative impacts of drought and flooding). Invasive wetland plant species are species that cause harm to ecosystems, the economy, or human health, and replace native wetland plant communities. The revegetation of native plants may be one way to improve wetlands that have been impacted by invasive species. In Great Salt Lake (Utah, USA) wetlands, the invasive, non-native grass Phragmites australis (common reed) reduces the quality and quantity of habitat for both wildlife and humans (e.g., birdwatchers, waterfowl hunters). Even when P. australisis greatly reduced, native plant communities slowly, or never return. In wetland restoration, best practices for the selection of seed mixes and sowing densities are limited. We conducted greenhouse and field experiments to investigate the effects of different seed mixes and sowing densities on wetland plant communities. We found that in general, higher sowing densities of 5,813 and 9,690 pure live seed per square meter had higher native plant cover compared to the unseeded plots and a more commonly applied seeding rate of 1,938 pure live seed per square meter. However, higher sowing densities did not always reduce invasive plant cover in our experiments. To better understand how native wetland plant species grow from seed, we studied germination, seedling emergence, and survival. We observed poor performance of many of the wetland species we studied, providing more evidence that higher sowing densities are likely needed in restoration. Two native species, Distichlis spicata (saltgrass) and Bidens cernua (nodding beggartick), performed well across experiments. Including these species into restoration seed mixes may be one way to improve revegetation outcomes. This research informs best practices for increasing native plant establishment and improving important habitat in Utah and the Intermountain West.