Theses and Dissertations at Montana State University (MSU)
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Item An ecological study of creeping juniper (Juniperus horizontalis Moench.) in Montana(Montana State University - Bozeman, College of Letters & Science, 1978) Miller, John GageItem A study of the comparative value of Juniperus scopulorum and Juniperus virginiana as understock for four juniper clones(Montana State University - Bozeman, College of Agriculture, 1959) Van Sloun, Neil J.Item The influence of Douglas-fir and Rocky Mountain juniper on Wyoming and mountain big sagebrush cover in Southwest Montana(Montana State University - Bozeman, College of Agriculture, 2010) Kitchen, Karen Ann; Chairperson, Graduate Committee: Bok Sowell.Expansion of conifers into sagebrush steppe is a management concern, since conifers reduce sagebrush cover for wildlife. The primary objective of this research was to examine the relationship between the conifers, Douglas-fir (Pseudotsuga menziesii) and Rocky Mountain juniper (Juniperus scopulorum), and two subspecies of big sagebrush, Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis) and mountain big sagebrush (Artemisia tridentata spp. vaseyana), in southwest Montana using a best-fit model. A secondary objective was to determine whether either of the two conifer species have a greater influence on sagebrush cover. Percent cover of both conifers and sagebrush was recorded at 40 Wyoming and 40 mountain big sagebrush plots at each of three study sites in southwest Montana (n = 240). The best-fit model utilizes the terms site, sagebrush subspecies, the square root of conifer cover, and site by sagebrush subspecies as the independent variables, with the square root of sagebrush cover as the dependent variable. The model (the square root of sagebrush cover = a i - 0.401 x the square root of conifer cover; r ² = 0.61) found a negative relationship between conifer cover and sagebrush cover and indicates that there is no difference between the two sagebrush subspecies and across all three sites in the study area. The best-fit model was validated within the 95 % confidence interval at all three study sites. Validation trials with data from three sites outside the study area were successful for one site, suggesting that the model is better suited to lower elevation, less productive sites. There was no difference in the influence of Douglas-fir or Rocky Mountain juniper cover on live sagebrush cover, indicating that sagebrush responds similarly to competition from both species. Controlling both conifers may increase sagebrush cover slightly, but responses will be small due to low levels of initial sagebrush cover. If maintenance of sagebrush cover is desired, conifer control should be initiated before conifer cover reaches 10 %, since the rate of sagebrush decline is highest at low levels of conifer cover. However, conifer control is not recommended because both conifers and sagebrush are important components of big game winter range.Item Factors influencing big sagebrush cover in Southwest Montana(Montana State University - Bozeman, College of Agriculture, 2010) Mendelsohn, Brittany Jennifer; Chairperson, Graduate Committee: Bok Sowell.The sagebrush steppe provides important habitat to many wildlife species. Conifer expansion of Douglas-fir and Rocky Mountain juniper into this area is a growing concern. Currently management focuses on the removal of Rocky Mountain juniper. The primary objective of this study was to determine the relationship between live sagebrush cover and aspect, slope, elevation, soil texture, soil depth and rock outcroppings. The second objective was to compare Douglas-fir and Rocky Mountain juniper's canopy areas at comparable ages. Percent cover of shrubs and conifers as well as the abiotic factors were recorded at forty Wyoming and forty mountain big sagebrush plots at each of three study sites in southwest Montana (Pipestone, Elkhorn, and Whitetail) (n = 240). The best-fit model utilizes the terms site, sagebrush subspecies, square root of conifer cover and site by sagebrush subspecies as the independent variables, with square roots of sagebrush cover as the dependent variable. The model found that abiotic factors had no correlation (p>0.05) with live sagebrush cover, but conifer cover had a negative effect on sagebrush cover. Equations were developed to predict canopy area of Douglas-fir and Rocky Mountain juniper thru time. Our findings suggest conifers should not be removed to increase sagebrush cover due to low response of sagebrush cover. Douglas-fir is the dominant conifer on these sites and has three times more canopy than Rocky Mountain juniper at similar ages (p<0.001). Rocky Mountain juniper is generally thought to have higher food and cover values for deer and elk and upland game birds compared to Douglas-fir (Gunderson 1990, Kufeld 1973). Therefore, the current practice of removing Rocky Mountain juniper to increase sagebrush cover should not be continued.