Theses and Dissertations at Montana State University (MSU)
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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 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 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).