Date of Award:

5-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Karin M. Kettenring

Committee

Karin M. Kettenring

Committee

Erin N. Rivers

Committee

Thomas A. Monaco

Abstract

Reestablishing native plant communities in degraded habitats through seeding or planting ("revegetation") is a necessary step to restore ecosystems and their functions (e.g., supporting biodiversity, nutrient cycling, etc.). Globally, wetlands have suffered high rates of degradation and also experience numerous invasions. Invasive species are those that cause environmental, economic, or societal harm. Phragmites australis is a widespread invasive species that outcompetes native plants and reduces habitat diversity. Reestablishing native plant communities can limit P. australis invasion, yet effective methods to do so remain somewhat untested in wetlands. Additionally, stressful environmental conditions can increase plant mortality in revegetation efforts. In semi-arid wetlands, hydrology and salinity are two key environmental stressors that affect plant survival. However, their combined impacts on native and invasive plants are unclear. In field and controlled-setting (e.g., greenhouse) experiments, we tested the effectiveness of varied revegetation approaches in the context of P. australis reinvasion and environmental stressors to inform wetland restoration in the Great Salt Lake (GSL) Watershed. In GSL wetlands, we introduced two native mixes with distinct growth habits (grass-like vs. broad-leaved), varied the method of introduction (seed vs. seedling), and varied the order of seed and seedling introduction. However, treatments had no effect on total native or invasive cover due to extreme drought followed by prolonged flooding. As environmental conditions shifted from drought to flooding, there were community shifts from drought-tolerant to flood-tolerant species, highlighting the importance of including native species with differing environmental tolerances in revegetation mixes. In a 6-week greenhouse and 7-week mesocosm experiment, we tested the effects of seed mix, water level, salinity, and P. australis presence on plant community outcomes. We found that forbs (i.e., broad-leaved species) were generally resistant to P. australis presence and reduced invasion. Additionally, mixes created with diverging species' environmental tolerances were negatively affected by stressful environmental conditions but still limited P. australis growth in all conditions. Overall, our findings support designing revegetation mixes with diverging environmental tolerances to withstand broad environmental conditions and incorporating high-performing forbs to maximize invasion resistance. However, additional strategies will still be necessary to achieve restoration goals due to increasing environmental extremes.

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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.

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