title: Seed Ecology and Regeneration Processes to Inform Seed-Based Wetland Restoration
Creators: name: Tarsa, Emily E.
Publisher: name: Utah State University
Year: 2022

description: Wetlands provide immense value to wildlife and humans but have been degrading rapidly around the world. One major challenge is the loss of native plant species in wetlands, which limits the ability of wetlands to function as they should. Restoring wetlands requires a combination of removing the cause of degradation (such as invasive plant species) and, in many cases, actively returning native plants to the site especially via seeding. Further, early plant life stages are the most vulnerable for plants and is often the time in which sown species die and fail to establish. Thus, understanding how and why seeds die or survive across species and environmental conditions can provide guidance for seed-based wetland restoration. Here, we sought to answer these important knowledge gaps through a series of greenhouse and lab experiments. First, we sought to answer what native sowing rate was needed to maximize native plant performance across a gradient of invasive species seed density, environmental conditions, and timing of seed addition. Separately, we performed a lab and growth chamber experiment in which we measured important characteristics about seeds and seedlings (grown in different environmental conditions) to better understand (and ultimately predict) why some species do well and in what conditions that can occur. Finally, in a separate greenhouse experiment, we grew native and invasive wetland plants for eight-weeks and tracked whether seeds germinated, survived, or died in order to quantify plant transitions through these early life stages. We also assessed ‘end-of-season’ percent cover and the rate of clonal production to gauge how early stages of plant growth contributes to invasion resistance. We found native plant establishment increased with higher native sowing densities, especially when native seeds were sown early in the season. However, the biggest driver in plant community composition following seeding was the density of invasive Phragmites australis seeds in the soil. Low water levels yielded higher native plant performance and more effectively suppressed P. australis growth. We also identified characteristics of seeds and seedlings that explained their germination and early growth patterns—species that had light seeds with thin seed coats and shallow seed dormancy had faster time to germination and higher growth rates, while species with heavy seeds had thick seed coats, deep seed dormancy, slower germination, and higher resource allocation to plant structures. Finally, we found that high-water levels enhanced the probability of seed germination, and that high temperatures lead to higher clonal development in seedlings. Overall, Phragmites australis was a superior performer is early life stages, but Distichlis spicata performed well due to high germination probabilities and Eleocharis palustris performed well due to extensive clonal production. As seed-based wetland restoration becomes increasingly necessary, the findings from this dissertation provide guidance on which native species should be used, where seeds should be sourced, and what environmental conditions should be targeted to maximize native plant establishment and restore wetland functions.