Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Small mammal diversity and abundance in Douglas fir old growth forests(Montana State University - Bozeman, College of Letters & Science, 1992) Cramer, Patricia CatherineItem Acid and enzymatic hydrolysis of autohydrolyzed lignocellulosic substrates(Montana State University - Bozeman, College of Engineering, 1987) Lamar, David AllenItem Effects of Douglas fir establishment in southwestern Montana mountain big sagebrush communities(Montana State University - Bozeman, College of Agriculture, 1998) Grove, Adam JayItem Breeding bird communities in mature and old-growth Douglas-fir forests in southwest Montana(Montana State University - Bozeman, College of Letters & Science, 1997) Sparks, James RobertItem 20th Century forest-grassland ecotone shift and effects of livestock herbivory(Montana State University - Bozeman, College of Agriculture, 2005) Sankey, Temuulen Tsagaan; Chairperson, Graduate Committee: Cliff Montagne.I studied 20th Century lower forest-grassland ecotone shift in the Centennial Valley in southwestern Montana, USA and the Darhad Valley in northern Mongolia and investigated the effects of livestock herbivory on ecotone dynamics. A total of 525 aspen (Populus tremuloides) and 1,703 Douglas-fir (Pseudotsuga menziesii) trees were cored and 10,168 seedlings were counted at five sites along the ecotone in the Centennial Valley. A total of 2,968 Siberian larch (Larix sibirica) were cored and 4,709 seedlings were counted at five ecotones in the Darhad Valley. Tree-age distribution was constructed to determine 20th Century tree establishment. Tree age and location within the ecotone were correlated to describe the process of ecotone shift into the adjacent grassland. To examine livestock herbivory effects on ecotone shift, the number of new trees was correlated with ten different levels of cattle grazing intensity during the last 60 years in the Centennial Valley and with five different grazing regimes during the last 80 years in the Darhad Valley. Three different types of ecotone shift into the adjacent grassland were documented: forest boundary shift, densification, and fairy ring establishment. No evidence of ecotone shift upslope towards the forest was found. Grazing intensity had a complex relationship with tree encroachment. Aspen and Douglas-fir tree encroachment was low at medium levels of grazing intensity, but aspen establishment was higher at low and high grazing levels and Douglas-fir establishment was higher at low grazing levels. Siberian larch tree encroachment was higher at low and high grazing intensities by sheep and cattle, but it was lower at low and medium grazing levels by goat-sheep and goatsheep- cattle mixes. My results implied that grazing can both facilitate and inhibit tree encroachment. I propose a model of grazing effects on tree encroachment that integrates both inhibition and facilitation effects of grazing disturbance. I also propose a conceptual model of lower forest-grassland ecotone shift and a conceptual model of ecotone shift and livestock herbivory effects. My models suggest that grazing can be used as a tool to maintain the equilibrium between forest and grassland vegetation and to increase or decrease forest expansion.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.