Date of Award:

5-2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Ecology

Committee Chair(s)

Kari E. Veblen

Committee

Kari E. Veblen

Committee

Thomas A. Monaco

Committee

Eugene W. Schupp

Abstract

In the western United States, thousands of acres of degraded rangelands are dominated by aggressive invasive species such as cheatgrass (Bromus tectorum), and are seeded by managers with native plants in an attempt to restore species diversity, wildlife habitat, and ecosystem services. There are many options for obtaining seeds of native plants; for instance, they can be collected from the region where restoration is to occur, or they may be purchased through commercial producers. For a given plant species, managers may also select seeds from unique subspecies, cultivars, and populations. Genetic differentiation among these within-species groups can not only affect their growth form and trait expression, but also how well these groups are able to compete with invasive species.

I assessed how within-species groups of a commonly-seeded native bunchgrass, squirreltail (Elymus elymoides), differed in their response to competition from cheatgrass. I specifically looked at differences among representatives of: 1) three squirreltail subspecies, 2) wild-collected vs. commercially-available squirreltail seed, and 3) eighteen distinct squirreltail populations. I hypothesized that there would be variation among all representatives of these three within-species groups. I also hypothesized that squirreltail seeds collected from areas that are heavily invaded with cheatgrass will have higher tolerance of competition, resulting from their opportunity to locally adapt to the competitor. Finally, I assessed whether plant traits could predict the response of squirreltail to competition from cheatgrass; my hypothesis was that plants which partitioned a greater portion of their biomass to roots would better tolerate competition.

To test these hypotheses, I performed a greenhouse study in which I grew squirreltail plants both alone and with cheatgrass, and created an index of how much squirreltail biomass was lost due to competition. I found that there was variation in response to competition among subspecies, but no variation among populations, and no variation between wild and commercial seeds. Contrary to my hypotheses, populations from cheatgrass-invaded areas were no different in their response to competition than those from un-invaded areas, suggesting that local adaptation is not occurring. Finally, although several growth traits were good predictors of competitive response, the plants which were less affected by competition partitioned more biomass to leaves, not to roots as I had expected; this finding suggested that light was the primary limiting resource for seedlings in this competition experiment. By confirming variation among squirreltail subspecies in their ability to tolerate competition, and by linking growth traits to competitive tolerance, this work provides information to restoration practitioners who must choose among seed sources for revegetation of invaded rangelands, and to native plant breeders aiming to create improved native plant varieties by selecting for traits associated with higher establishment success in invasion-prone areas.

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