Document Type

Thesis - Open Access

Award Date

2026

Degree Name

Master of Science (MS)

Department / School

Natural Resource Management

First Advisor

Lora Perkins

Abstract

Native grasslands and restoration sites in the Northern Great Plains face pressure from invasive cool-season grass species, such as smooth brome (Bromus inermis) and cheatgrass (Bromus tectorum). Native cool-season grass species may compete in the same niche as the invaders and provide resistance to invasion of existing or restored grasslands. Green needlegrass (Nassella viridula) and junegrass (Koeleria macrantha) were evaluated in this study for competitive effect and priority effect against invasive bromes to inform management decisions. Greenhouse studies were conducted to evaluate competitive ability of the two native species as well as how priority influences competition. In my first chapter, each invasive brome was grown alone from seed, with a single species native neighbor, and with the combination of both native species as neighbors to evaluate competitive ability. Priority treatments included native first invasive first and simultaneous, with 14 days used as the timing of priority. Aboveground biomass and relative interaction index (RII) were used as response variables to determine competitive ability and influence of priority. Junegrass demonstrated a significant competitive effect against smooth brome in both the native first and concurrent priority treatments. Green needlegrass also had significant competitive effect against smooth brome in both the native first and concurrent priority treatments. The combination of native species also showed similar results. When competing with cheatgrass, native species priority effect was determined to be more significant at reducing biomass than individual species’ competitive ability. My second chapter evaluated how smooth brome rhizomes interacted with the same native species grown from seed. Smooth brome was grown alone, with a single species native neighbor, and with the combination of both native species as neighbors to evaluate competitive ability. Smooth brome active rhizomes were identified and transplanted into pots. Priority treatments included native first invasive first and concurrent, with 14 days used as the timing of priority. Aboveground biomass and relative interaction index (RII) were used as response variables to determine competitive ability and influence of priority. Junegrass demonstrated the strongest competitive effect against smooth brome in concurrent and native first treatments. Green needlegrass also showed competitive effect against smooth brome in the native first treatment. The combination of species did not perform as well as individual species in this experiment but still demonstrated competitive effect against smooth brome in invasive first and native first treatments.

Publisher

South Dakota State University

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Rights Statement

In Copyright