Date of Award:

10-2017

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Ecology

Advisor/Chair:

Kari E. Veblen

Co-Advisor/Chair:

Thomas A. Monaco

Abstract

Overabundance of shrubs poses a major threat to semiarid ecosystems due to degraded understory vegetation. Previous efforts suggest a need for greater understanding of which management practices work best to improve these ecosystems. I sought to develop a better understanding of how the relative performance of commonly seeded species is influenced by three sagebrush removal techniques.

I calculated effect sizes for cover and frequency to estimate relative changes in abundance of 15 common plant species seeded at 63 restoration sites throughout Utah. Shrubs were reduced by fire or mechanical treatment. Effect sizes were assessed using meta-analysis techniques for two post-treatment timeframes. Introduced grasses and shrubs had greater increases in cover and frequency following treatment, respectively. The introduced shrub Bassia prostrata experienced the largest increases in abundance following treatments. Forb abundance was highest when treated with fire. Over the long term the fire treatment resulted in greater increases for four of the seven grass species. Large increases in perennial grasses over time suggest that seeding efforts contributed to enhancing understory herbaceous conditions. My results provide new insights regarding the interactive effects of species and shrub-reduction treatments.

Secondly, I evaluated emergence patterns of six commonly seeded restoration species in soils collected from Wyoming big sagebrush (A. t. ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) and mountain big sagebrush (A. t. ssp. vaseyana [Rydb.] Beetle) plant communities. I developed a novel experimental design that regularly wetted soils to field capacity and allowed them to naturally dry by evaporation, which resulted in distinct differences in the duration of wet-dry cycles. Results showed that inherent differences in soil texture and organic matter between vaseyana and wyomingensis soils translated into fundamental differences in soil water holding capacity. Although species collectively exhibited greater emergence in vaseyana soils than wyomingensis soil, patterns were vastly different among species and differences between soils became more pronounced under low soil water for two of the test species. I concluded that the manner in which soils and water uniquely influenced emergence patterns provide new insights in species suitability for restoration sites and how inherent soil differences may constrain seeding success.

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