Date of Award:

5-2023

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Committee Chair(s)

Kari E. Veblen

Committee

Kari E. Veblen

Committee

Mark W. Brunson

Committee

Thomas A. Monaco

Committee

Peter B. Adler

Committee

Eugene W. Schupp

Abstract

In the Intermountain West, rapid expansion of non-native grasses, primarily cheatgrass, has created a repeating cycle where cheatgrass easily ignites and after a fire, more cheatgrass establishes in the burned area, leading to more fire, and more cheatgrass. The primary method to prevent further fires is to plant grass and shrub seeds after a fire because they can deter cheatgrass from establishing and reduce the chance of fire. However, this approach does not always work. There is a need and interest in alternative ways to establish native grasses and forbs.

Sagebrush, the dominant shrub of lower-elevation regions of the Intermountain West, may act as a nurse plant: a plant that alters the environment around itself in a way that is beneficial to other plants. Capitalizing on the attributes that make sagebrush nurse plants, like shade and higher soil moisture, may help the establishment of grasses and forbs before a fire occurs, increasing the likelihood that cheatgrass will not dominate that system. While the area around nurse plants generally is thought of as a favorable place for grasses and forbs to grow, that may not always be the case. There may be minimal differences in the microenvironment between the canopy and interspace and there can be competition under the canopy between newly established plants and other vegetation that is already present.

I found that the sagebrush canopy influenced the survival of two native wildflower species, Munro’s globemallow and common yarrow, when they were transplanted as seedlings, but survival of two native transplanted grass species, bluebunch wheatgrass and squirreltail, was unaffected by the sagebrush canopy. However, when those same grasses were planted as seeds, if the seeds emerged, their emergence was highest near the canopy. Some of the attributes that make the canopy a “good” place for grasses and wildflowers to grow extend into the interspace, making the interspace potentially similarly “good.” I found that bluebunch wheatgrass and globemallow were shade tolerant and grew in ways that may allow them to be competitive under the canopy and persist in the interspaces, outside of what is generally considered a “good” nurse shrub microenvironment.

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