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Emily Ulrich

Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Natural Resource Management

First Advisor

Lora Perkins


Invasive species cause substantial ecological, social, and economic impacts. In South Dakota, Bromus inermis (smooth brome) and Poa pratensis (Kentucky bluegrass) are substantial threats to remnant prairies by forming monotypic stands that are resistant to restoration while decreasing diversity and altering nutrient cycling. Understanding how invasion occurs is crucial to preventing invasion and restoring invaded areas. The focus of this study was to investigate two attributes (phenological niche separation and competitive ability) that may contribute to the invasiveness of smooth brome and Kentucky bluegrass. The objectives of my thesis were to: (1) determine if phenological niche separation exists between invasive and native species; and (2) quantify the competitive ability of smooth brome and Kentucky bluegrass. The first objective was achieved through a common garden experiment involving phenological observations of cool-season invasive and native species. The observations demonstrated that the invaders begin growth before the native species suggesting a phenological niche separation. Due to weather and predation factors future studies are needed to assess differences over the entire life cycle. The second objective was addressed with a competition experiment in a greenhouse. Performance (measured as final biomass) of a native grown with each invader was assessed by a relative interaction index (Rii) to evaluate the competitive ability of each invader. Three priority treatments (growth concurrently, invasive 21 days prior to native, native 21 days prior to invasive) were included to examine the effect of priority on competition. Priority treatments were significantly different from one another (F6,350=54.176, p<0.001), indicating that priority does have an influence on competition. In comparison to the invaders, the native had a strong competitive ability. Due to its strong competitive ability, these results suggest that the native could be an important species in the effort to prevent invasion or restore currently invaded areas.

Library of Congress Subject Headings

Smooth brome -- Phenology
Kentucky bluegrass -- Phenology
Grasses -- Great Plains
Plant competition
Invasive plants
Endemic plants


Includes bibliographical references (page 34-47)



Number of Pages



South Dakota State University


Copyright © 2014 Emily Ulrich. All rights reserved.