Theses and Dissertations at Montana State University (MSU)
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Item Spatial and temporal dynamics of conifer expansion in southwest Montana(Montana State University - Bozeman, College of Agriculture, 2022) Haygood, Nathaniel Paul; Chairperson, Graduate Committee: Craig Carr; This is a manuscript style paper that includes co-authored chapters.Since the mid-19th century, pinyon-juniper woodlands in western North America have experienced an expansion in range and density and a corresponding degradation in the provision of ecological goods and services including forage production, watershed function, biological diversity, and habitat values. While this is well-documented in other systems, there is little information characterizing shifts in tree range and abundance within the northern extent of these juniper and pine woodlands. The purpose of this research project was twofold: 1) identify and improve understanding of Rocky Mountain juniper and limber pine age distribution and compare these data to other systems, and 2) evaluate understory dynamics along the gradient of woodland development to assess impacts to understory species composition and abundance, as tree densities and range increase. We aged 278 trees across 38 plots in southwest Montana. We recorded soil moisture throughout the growing season (May-July), aspect, elevation, soil texture, herbaceous production and diversity, and tree density and canopy cover from 2019-2021. Greater than 95% of all trees were under 100 years old and the oldest tree (juniper) was 247 years old. Across the study site, limber pine was younger than Rocky Mountain juniper and appeared to prefer different sites. Maximum and mean juniper age was higher on dry sites with high sand content and lower on moist sites with low sand content in the top 15cm of the soil profile. Understory shrub and cool-season perennial grass cover was negatively influenced by heavy tree canopy cover on southwest to southeast aspects. The results from this study indicate 1) limber pine and Rocky Mountain juniper generally occupy different sites, 2) juniper and pine stand age is lower on north facing aspects with coarse soils and higher soil moisture content in late spring and early summer. Currently, increasing conifer dominance on north facing aspects appears to minimally impact cool-season perennial grass cover and production. Comparatively, increasing conifer dominance on south facing slopes may reduce cool-season perennial grass and shrub cover and production. We recommend the inclusion of these findings, as land managers seek to sustain delivery of necessary ecological goods and services.Item Red squirrel (Tamiasciurus hudsonicus) midden site selection and the influence of conifer species compositions on midden occurrence in the Cooke City Basin of Montana(Montana State University - Bozeman, College of Agriculture, 2017) Elkins, Eric Kyle; Chairperson, Graduate Committee: Bok SowellThroughout the Greater Yellowstone Ecosystem (GYE), whitebark pine (WBP: Pinus albicaulis) seeds serve as an important fall food source for threatened Yellowstone grizzly bears (Ursus arctos). Grizzly bears depend on red squirrel (Tamiasciurus hudsonicus) midden sites to obtain WBP seeds. In light of recent WBP population declines, managers are concerned about the negative effects that loss of WBP may have on grizzly bears. Therefore, managing WBP for grizzly bears is facilitated by understanding red squirrel habitat requirements and identifying areas that are most likely to contain middens. Previous studies indicate that red squirrel middens are most prevalent in subalpine mixed conifer forests with interspersed WBP, but a critical gap remains in identifying a conifer species composition that is ideal for midden sites. We studied red squirrel habitat selection in the Cooke City Basin (CCB) of Montana to identify variables associated with midden sites and midden area. We also examined conifer species compositions to identify a composition where middens are most likely to occur. Habitat variables, midden counts, and midden area measurements were collected in 810, 30 meter diameter circular plots equally spaced along 27 transect lines in the CCB. General linear mixed models (GLMM) were used to assess variables associated with red squirrel midden site selection, and linear mixed models (LMM) were used to assess variables associated with midden area. Results of the GLMM indicated that red squirrel midden occurrence probability is positively associated with the amount of hillshade (light) and canopy cover in a conifer stand. Additionally, midden occurrence increased as the percent WBP in a stand increased up to 44 percent, but decreased thereafter. Results of the LMM indicated that midden area is positively associated with total canopy cover. We identified that a conifer species composition of approximately 44 percent WBP and a 56 percent mixture of subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii) is ideal for midden sites. We concluded that managing for areas within subalpine zone mixed conifer forests containing similar compositions should be a priority to ensure availability of prime habitat for midden sites and associated WBP seeds for grizzly bears.