Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Relationship between intensity of livestock grazing and trout biomass in headwaters of east front Rocky Mountain streams, Montana(Montana State University - Bozeman, College of Letters & Science, 2016) Gilham, Andrew Terrence; Chairperson, Graduate Committee: Alexander V. ZaleLivestock grazing is the most common land-use practice in the western United States. Riparian and stream habitats are particularly susceptible to effects of poorly-managed livestock grazing. About 80% of stream and riparian habitats in the western United States are thought to have been damaged by livestock grazing, but because grazing usually pre-dated assessments of fish populations and stream habitats, before and after comparisons are impossible. The spatial and temporal complexity of livestock grazing make it difficult to isolate its effects on instream habitat and channel morphology characteristics. Moreover, instream habitat and channel morphology are also influenced by inherent watershed characteristics (i.e., basin area, gradient, discharge). I assessed the effects of livestock grazing on 25 separate 150-m long sample sites (1400 to 1585 m in elevation) within ten headwater basins along the northeastern Rocky Mountain Front in north-central Montana. I used scat counts as an index of relative grazing intensity to assess the effects of livestock grazing on channel morphology characteristics, stream substrate, instream cover, and trout biomass. To my knowledge, this effort is the first to quantify livestock grazing intensity using scat counts to assess grazing effects on trout biomass. I assessed potential effects that grazing intensity had on habitat condition and fish biomass using linear mixed models, which also accounted for watershed and sample site effects. I found that the proportion of fine sediment in the streambed increased as the number of scats increased (P < 0.001), but the area of undercut banks declined as scat counts increased (P < 0.001). Estimated trout biomass declined as number of scats increased, even when I accounted random effects of stream and year in a linear mixed-effect model (P = 0.009). My results corroborate previous findings that livestock grazing along stream channels may reduce trout biomass, but unlike previous studies I actually quantified grazing intensity using scat counts. Since increased livestock grazing intensities were related to increased levels of fine sediments in streambeds and smaller areas of undercut streambanks, I suggest that these factors may be related to why increased livestock grazing reduced trout biomass.Item The effects of timing of grazing on plant and arthropod communities in grasslands of southwest Montana(Montana State University - Bozeman, College of Letters & Science, 2013) Davis, Stacy Christine; Co-chairpersons, Graduate Committee: Laura Burkle and Wyatt F. CrossGrassland plants have co-evolved with native ungulate grazers for millions of years, but over the last 100 years there has been a shift towards grazing by domestic livestock in North America. Many of the grazing-induced changes in plant and arthropod communities depend on how the grazing regime is implemented. Timing of grazing is one component of the grazing regime that is less well understood than grazing intensity and type of grazer, but is predicted to have important implications for plant and higher trophic level responses. The purpose of this study was to experimentally assess how timing of grazing affected plant and arthropod communities in high-elevation grasslands of southwest Montana. We designed a 2-year field experiment that manipulated cattle grazing by implementing two grazing initiation dates, one beginning in mid-June and the other in mid-July. We compared plant (biomass and height) and arthropod characteristics (density and biomass of orders) across two years that differed in cumulative precipitation. Grazing reduced total plant biomass, forb biomass, and plant height with little to no recovery regardless of timing of grazing. The density of the most dominant arthropod order, Hemiptera, was reduced in both grazing treatments. By comparing end of season plant responses to grazing, we found that total plant biomass was unaffected in the drier year while forb biomass was unaffected in the wetter year. Many end of season arthropod responses were reduced by grazing in both study years. Although both grazing treatments reduced many plant and arthropod characteristics, grazing earlier in the growing season may impact higher trophic levels that are reliant on the presence of forbs and Hemiptera earlier in the growing season. These results have important implications for meeting conservation grazing objectives and for how timing of grazing may influence food availability for grassland-associated avian species of concern, in particular, smaller passerines.