Graduate Thesis Or Dissertation

 

Grazing Effects on Fuels and Plant Community Characteristics across Three Community Types in Wyoming Big Sagebrush Steppe Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cz30q207k

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  • Livestock grazing is the prominent land use in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) steppe and has been present since the late 1800’s. There have been calls to remove livestock grazing from rangelands as historic grazing practices resulted in the degradation of some native plant communities and wildlife habitat. However, the distinction between historic grazing and moderate contemporary grazing practices is often not made. Contemporary grazing differs greatly from historic grazing because grazing frequency, intensity, and season of use are managed, and periodic adjustments are made to maintain ecological integrity. Contemporary grazing may be an ecologically responsible land use compared to historic grazing, but there’s still information lacking on its effects on different plant community types found within Wyoming big sagebrush steppe. Intact, degraded, and exotic annual grass dominated sites are three common community types found in Wyoming big sagebrush steppe that have experienced long-term contemporary grazing. As there have been calls to remove contemporary grazing, it is important for land managers to understand the implications of removing contemporary grazing as it may affect plant community characteristics and fuels differently. The effect of grazing exclusion on fuel characteristics was evaluated among three common Wyoming big sagebrush community types: intact, degraded, and exotic annual grass types. In this study, a randomized block design within each community type, repeated over two years, was utilized to determine the effects of contemporary grazing exclusion on fuel characteristics. In each community type, five long-term (+10 yrs.) grazing exclosures were established with grazed and ungrazed treatments at each site. Grazing altered fuel characteristics in a manner that decreased wildfire probability, intensity, and severity in each community type. Effects of contemporary grazing on several fuel characteristics varied among community types, suggesting that fuel management plans should distinguish community types across grazing allotments as the effect of grazing on fuels may vary. Also, as community type and year consistently had significant effects on differences found in fuel characteristics, the spatial and temporal variation across Wyoming big sagebrush steppe should be considered when utilizing contemporary grazing to manage fuels. In addition to evaluating fuel characteristics, a study on plant community characteristics was also evaluated to determine if the removal of contemporary grazing affects intact plant communities and promotes plant community recovery in degraded and exotic annual grass invaded sites. Plant community characteristics were collected in the same sites and treatments as in the fuels study. Only two plant community characteristics were influenced by the interaction between grazing treatment and community type, suggesting that the effects the contemporary grazing exclusion may vary slightly by community type. As there were very few differences between the grazed areas and grazing exclosures, it is likely that contemporary grazing exclusion may not affect intact communities nor promote recovery of degraded and exotic annual grass communities. In the exotic annual grass sites, because there were negligible differences in annual grass abundance between the grazed and ungrazed areas, heavier grazing pressure could be warranted to reduce exotic annual grasses depending on management goals. Variables that consistently explained differences in plant community characteristics were community type and year, indicating that spatial and temporal variation had an effect on plant communities and may better explain differences in plant community composition and diversity than the exclusion of contemporary grazing.
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