Semester of Graduation

Summer 2023

Degree

Master of Renewable Natural Resources (SRNR)

Department

Department of Renewable Natural Resources

Document Type

Thesis

Abstract

Arid wetlands are diverse systems that provide habitat for a variety of flora and fauna, including stopover and breeding habitat for migratory birds. In the western United States, these wetlands support a network of stopover sites on the Pacific Flyway, and due primarily to wetland loss and alterations, these areas are becoming more isolated. Malheur Lake is a shallow endorheic lake in eastern Oregon that supported a robust emergent marsh throughout most of the 20th century. However, following large scale flooding in the 1980s, emergent vegetation was extirpated and has only reestablished in small patches. Our objective was to identify factors limiting vegetation establishment using a plant succession approach. We sought to answer three broad questions: (1) is the seedbank present and viable? (2) are conditions conducive for germination and survival of seedlings? and (3) how does a reduction in herbivory and wind-wave action affect existing vegetation growth? Utilizing a greenhouse experiment, we found that the seedbank is viable and contains the two most historically common robust emergents: Hardstem bulrush (Schoenoplectus acutus) and broadleaf cattail (Typha latifolia). Seedlings of these species emerged at 94% and 80% of our seedbank samples in 2021 and 2022, respectively. In 2021, hardstem bulrush was detected at all field germination plots, broadleaf cattail was detected at 55% of plots, and alkali bulrush (Bolboschoenus maritimus) was detected at 55% of plots. In 2022, hardstem bulrush was detected at all plots, broadleaf cattail was detected at 5% of plots, and alkali bulrush was detected at 27% of plots. We recorded peak germination counts in mid to late July for both years followed by a decline that likely corresponded with drying soil. We also tested how a reduction of wind-wave action and herbivory affected vegetation expansion using exclosures. The results of this study indicate that vegetation establishment at Malheur Lake is not limited by seedbank presence, and a combination of abiotic and biotic factors including soil moisture and herbivory may be limiting establishment of seedlings depending on lake conditions.

Date

5-15-2023

Committee Chair

King, Sammy L.

DOI

10.31390/gradschool_theses.5788

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