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Item Influences of elk browse on aspen stand structure and landbirds at the National Elk Refuge, Jackson Hole, Wyoming(Montana State University - Bozeman, Graduate School, 2015) Edwards, Jennifer Lindsay; Chairperson, Graduate Committee: Peggy Taylor.Aspen stands in the Rocky Mountains are hot spots of biodiversity meeting the habitat needs of many species, including wintering ungulates. Ungulates have the potential to alter habitat composition and structure via browsing, especially near areas of concentrated use associated with winter feedgrounds. The National Elk Refuge, established in Jackson, Wyoming in 1912, has provided supplemental winter feed for elk during all but nine winters since its establishment. I conducted the current study to assess aspen stand structure, estimate the likelihood of aspen recruitment given current browse levels, and examine if existing bird communities are reflective of aspen stand structure. I sampled 27 aspen stands at varying distances from feedgrounds during June 2014. I quantified aspen structure using five height class categories along 10 x 40 m belt transects. Twenty trees in height range of elk browse (i.e., 50-150 cm) were selected and measured within each belt to determine the Live-Dead Index, a quantification of browse intensity. I conducted two rounds of bird point counts to assess bird community composition in relation to aspen stand structure. My results indicated current browse levels were largely precluding aspen recruitment. LD Index values indicated 89% of 27 stands sampled in the National Elk Refuge were experiencing high browse intensity and aspen < or = 150 cm were being browsed back to ground level. A relationship between distance to feedgrounds and LD Index was not present, possibly resulting from intensive browsing throughout the refuge. In addition, bird communities were responding to the altered aspen stand structure. For example, Yellow Warblers were strong indicators of stands that had experienced recent aspen recruitment (i.e. greater mid-story canopy and structure). White-breasted Nuthatches were an indicator of a bird community group associated with larger aspen stands. Based on the current lack of recruitment on the refuge, large exclosures surrounding targeted aspen stands are recommended to protect juvenile aspen until they grow out of the browse zone.Item Understanding the role of biophysical setting in aspen persistence(Montana State University - Bozeman, College of Letters & Science, 2003) Brown, Kathryn; Chairperson, Graduate Committee: Andrew HansenItem The effect of Fomes igniarius on Populus tremuloides in the Gallatin National Forest of Montana(Montana State University - Bozeman, College of Agriculture, 1941) Kelly, Marvin F.Item Effects of beaver reintroduction and ungulate browsing on aspen recovery in the Eagle Creek drainage of the northern Yellowstone winter range(Montana State University - Bozeman, College of Agriculture, 2013) Runyon, Molly Jean; Chairperson, Graduate Committee: Bok SowellUngulate browsing and lack of overstory disturbance have historically prevented aspen regeneration on the Northern Yellowstone Winter Range (NYWR). Aspen clones regenerate if sprouts are produced that grow into recruitment stems (>2 m tall) and replace the mature overstory. Beaver were reintroduced to the Eagle Creek drainage on the NYWR in 1991 in an attempt to facilitate recovery of riparian aspen communities by removing aspen overstory and increasing sprouting. However, intense ungulate browsing, primarily from the Northern Yellowstone elk herd, was preventing aspen recruitment in Eagle Creek in 2005. Wolf predation has contributed to a 56% decrease in this elk herd from 2005 to 2012. I investigated the effects of beaver reintroduction and ungulate herbivory on aspen recovery in the Eagle Creek drainage in 2012. Aerial photos taken of Eagle Creek in 1990, 2005, and 2011 showed that although beaver activity stimulated aspen sprouting, the mature overstory of many aspen stands has not been replaced 21 years after beaver reintroduction (p>0.05). Sprouting and recruitment were investigated using 4-m radius circular vegetation plots (n=31) established in aspen stands throughout Eagle Creek in 1997 and monitored annually until 2012. Beaver activity stimulated increased sprouting in 71% of these plots, and 77% of the plots had > or = 1 recruitment stem in 2012. Prolonged flooding and high browsing levels contributed to lack of recruitment in 23% of the plots (p<0.05). In 2012, 75% of the paired plots associated with aspen exclosures had unfenced aspen stems with an average stem height > or = 2 m. Recent increases in aspen recruitment in Eagle Creek indicate that aspen communities are regenerating. This is likely the result of decreased browsing pressure on aspen saplings from 2005 to 2012. These findings are consistent with the predictions of a density-mediated trophic cascade following wolf reintroduction.Item 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 Aspen response to prescribed fire in Southwest Montana(Montana State University - Bozeman, College of Agriculture, 2008) Durham, Daniel Avery; Chairperson, Graduate Committee: Clayton B. Marlow.A collaborative effort by the BLM, MAES and MFWP, the Whitetail Watershed Restoration Project used prescribed fire in 2005 and 2006 to address aspen decline, conifer encroachment and altered hydrologic function in a forested watershed within Jefferson County, MT. As part of this effort quaking aspen response to fire was evaluated in two sub-drainages of the Whitetail Basin three years after treatment. Unburned stands were first surveyed to determine whether regeneration was occurring and to measure the distribution of aspen stems by size class. This information was then compared to stem response in burned stands. Big game and cattle impacts on aspen sucker height and density were measured using a series of 3-part ungulate exclosures in a sub-sample of burned stands. Regeneration was occurring in only1 of 40 unburned stands suggesting aspen was declining in this area. Sucker density increased dramatically in the burned stands after three years increasing the likelihood for regeneration. Within the first three years post-fire big game and the combination of big game and cattle did not affect sucker density in the burned stands. Although sucker height was significantly less in plots used by ungulates we did not feel it was enough to prevent regeneration. This assertion was supported by sufficient annual growth rates and the recruitment of individual regeneration stems into stands outside of protected plots. While it appears fire has increased the potential for aspen regeneration in the Whitetail Basin, early growth rates have allowed for some individual stem to surpass browse height to date, suggesting future monitoring will be necessary to learn if the current recruitment levels are sufficient to regenerate the majority of stands.Item Quaking aspen (Populus tremuloides) ecology on forest service lands north of Yellowstone National Park(Montana State University - Bozeman, College of Agriculture, 2007) Kimble, David Stuart; Chairperson, Graduate Committee: Bok Sowell.The primary objective of this study was to determine if quaking aspen (Populus tremuloides) density and recruitment changed on the Gallatin National Forest north of Yellowstone National Park from 1991 to 2006. Three-hundred sixteen aspen stands were surveyed on the 560 km² study area. Secondary objectives were to determine if aspen density and recruitment were influenced by elk (Cervus elaphus) browsing, conifer establishment, and cattle (Bos spp.) grazing. A 202.3 m² circular plot was established within each stand. All aspen stems within each plot were categorized into size classes: sprouts (< 1 m), saplings (1-2 m), recruitment stems (> 2 m and < 5 cm diameter at breast height), and mature stems (> 2 m and > 5 cm diameter at breast height). Recruitment stems and mature stems have grown above the height at which elk generally browse. Recruitment stems have attained this height in the past 10-15 years.Item Evaluating aspen responses to changes in elk abundance, distribution and behavior following wolf reestablishment in West-Central Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2011) Shafer, Timothy Lee; Chairperson, Graduate Committee: David RobertsThe reintroduction of wolves to Yellowstone National Park (YNP) in the mid-1990's has created a unique natural experiment for the investigation of trophic cascades operating at large spatial scales and involving large terrestrial mammals. Wolves have been directly linked to changes in elk density/behavior and have been hypothesized to be the driving force behind observed changes in woody plant growth in the system. The primary objectives of this study were to investigate the occurrence of a trophic cascade among wolves, elk and aspen in an area of YNP where elk abundance and distribution changed dramatically as a direct result of wolf reestablishment in the system. In Chapter 2, I determined the distribution and demographic characteristics of aspen in the Madison headwaters study area (MHSA) and identified the environmental attributes associated with its distribution on the landscape. Additionally, I evaluated the morphology, productivity, and persistence of aspen in both clonal and seedling-established. In Chapter 3, I established a climate-growth relationship for aspen to investigate the occurrence of a shift in productivity related to climate coincident with the timing of wolf reestablishment. I used standard dendrochronology techniques to investigate growth trends and identified which climate variables are most important to aspen productivity in this region. Additionally, I established the timing of historic aspen recruitment in the MHSA using age of mature trees. In Chapter 4, I investigated a trophic cascade among wolves, elk and aspen. I reconstructed historical browse conditions for aspen to look for a shift in browse regimes that occurred concurrently with the changes in elk abundance/distribution by performing a dendrochronological analysis of aspen architectural morphology. I also evaluated plant height, productivity, and longevity of aspen where elk densities had declined dramatically in order to capture the expected growth response. I used ANOVA's and multiple comparison procedures to evaluate browse conditions and aspen growth among sites where elk densities have declined dramatically and those where elk densities have remained relatively constant.Item Restoring aspen riparian stands with beaver on the northern Yellowstone winter range(Montana State University - Bozeman, College of Agriculture, 2007) McColley, Samuel David; Chairperson, Graduate Committee: Bok F. Sowell.Aspen (Populus tremuloides) on the Gardiner Ranger District, Gallatin National Forest, have declined over the last half-century. In an attempt to reverse this trend, beaver (Castor canadensis) were reintroduced in Eagle Creek in 1991. Beaver promote aspen suckering through their dam and lodge building activities. In 2005, I assessed the long-term effects of beaver on aspen stands and the associated riparian area in the Eagle Creek Drainage. Aerial photographs taken in 1990 and 2005 were used to compare changes in riparian area vegetation where beaver were reintroduced. Aspen canopy cover decreased (P<0.05) from 43% to 25% on Eagle Creek (29 ha) between 1990 and 2005. Willow (Salix spp.) cover increased (P<0.05) from 10% to 14% and alder (Alnus incana) cover and water surface area doubled during the same period. Aspen recovery was estimated by comparing vegetative changes among control sites with <10% beaver use (n = 5), active beaver sites (n = 6), sites abandoned for 1-3 years (n = 7), sites abandoned for 4-6 years (n = 4), and sites abandoned for 7-11 years (n = 5).