Theses and Dissertations at Montana State University (MSU)
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Item Impacts of forest mortality on streamflow in whitebark pine forests within the greater Yellowstone ecosystem(Montana State University - Bozeman, College of Letters & Science, 2024) Rautu, Teodora Stefana; Co-chairs, Graduate Committee: Brian V. Smithers and Danielle E. M. UlrichIncreasing forest mortality across the western U.S. raises concerns about its impact on streamflow. The hydrologic role of whitebark pine (Pinus albicaulis Engelm.) is of particular interest given its ongoing decline and prevalence at the upper treeline where precipitation is highest. Understanding the link between disturbed whitebark pine forests and streamflow is essential for better informing water resource management. In Chapter One, I investigated streamflow changes in two Wyoming whitebark pine watersheds: Upper Wind River (53% area affected by beetle outbreak) and Buffalo Fork (53% area affected by beetle outbreak and fire). Streamflow significantly increased post-beetle for Upper Wind River but did not significantly change post-disturbance for Buffalo Fork, attributed to the fire's limited spatial extent and post- beetle effects potentially occurring in the pre-disturbance period. In Chapter Two, I integrated Leaf Area Index into a hydrologic model to reflect changing canopy conditions and assessed water balance variables that drove the observed changes in streamflow in Chapter One. I found that an increase in annual precipitation primarily led to the increase in observed streamflow more so than forest mortality, and snowpack and snowmelt were consistent predictors of streamflow metrics. My findings suggest monitoring snow dynamics for accurate real-time and future streamflow forecasting. In Chapter Three, I used streamflow field data and the same hydrologic model to assess the impact of increasing tree mortality on streamflow within a whitebark pine- dominated watershed in Big Sky, Montana. After simulating mortality levels ranging from 0-90% for one year, tree mortality did not substantially impact streamflow until the 90% mortality level where annual flow and late summer flow substantially increased. Considering that mortality levels between 25-50% are more representative of whitebark pine mortality in one year, the lack of substantial impacts on snowpack and streamflow at the 25-50% mortality levels challenges the traditional assumption that whitebark pine mortality would lead to reduced snowpack and reduced late summer flow in open watersheds with 30% forest cover. Future studies should assess the multi-decade impacts of whitebark pine mortality on hydrologic processes and consider species differences in evapotranspiration as other subalpine species replace whitebark pine.Item Understanding the effects of floodplain shade on hyporheic and stream channel temperature cycles(Montana State University - Bozeman, College of Agriculture, 2024) Fogg, Sarah Kathleen; Chairperson, Graduate Committee: Geoffrey C. Poole; This is a manuscript style paper that includes co-authored chapters.River reaches with coarse-grained alluvial floodplains have a breadth of lateral interaction between the channel and surrounding landscape, yielding extensive riparian zones and high rates of gross water exchange between the channel and substrate (i.e., hyporheic exchange). The lateral hyporheic zone on floodplain rivers is often near the ground surface, allowing for heat exchange between the atmosphere, unsaturated sediments, and hyporheic zone. We hypothesized that floodplain shade overlying lateral hyporheic water influences the conductive heat flux through unsaturated sediments, thus influencing hyporheic temperatures and temperatures in associated stream channels. We conducted simulation modeling experiments to test the potential effects of floodplain shade on hyporheic and stream channel temperatures. We found that scenarios with floodplain shade led to cooler hyporheic and stream temperatures than scenarios lacking floodplain shade under a variety of realistic floodplain conditions. We conclude that floodplain forest shade is a novel consideration for riparian management on floodplain river reaches and may be crucial in managing and maintaining cold-water habitat into the future.Item Long-term environmental history of two low-elevation mixed-conifer forests, Mission Valley, Montana(Montana State University - Bozeman, College of Letters & Science, 2021) LaPierre, Kari Richard; Chairperson, Graduate Committee: David McWethyLow elevation mixed-conifer forests are widespread throughout the Northern Rocky Mountains, yet there are few long-term environmental histories from these structurally and compositionally heterogenous ecosystems. We reconstructed >10,000 years of vegetation change, fire activity, and human presence (e.g., pollen, charcoal, biomarkers) for two closed-basin lakes in mixed-conifer forests in the Mission Valley, western Montana. Environmental reconstructions highlight periods of pronounced changes in climate, vegetation, and fire activity. The late glacial period (>18,000-11,000 cal yr. BP) was characterized by post-glacial warming, generally wet conditions, establishment of mixed-conifer forests and infrequent fires. Following an abrupt, short-lived return to Juniper/Douglas fir parkland associated with the Younger Dryas (~12,900-11,500 cal yr. BP), warming temperatures during the early Holocene (11,000-6,000 cal yr. BP) promoted the expansion of open parkland/grasslands and frequent fire activity until cooler summers and warm, wet winters facilitated the development of modern-day closed mixed-conifer forests. Organic biomarker analyses indicate human presence within the Rainbow Lake watershed for millennia c. 7,000-3,000 cal yr. BP. Regional fire frequency increased during this period at Rainbow Lake, suggesting a possible increased role of human influence.Item Climate-fire-vegetation dynamics in the Greater Yellowstone Ecosystem: recent trends and future projections in a changing climate(Montana State University - Bozeman, College of Letters & Science, 2020) Emmett, Kristen Dawn; Co-chairs, Graduate Committee: Benjamin Poulter and David Roberts; Katherine M. Renwick and Benjamin Poulter were co-authors of the article, 'Disdentangling climate and disturbance effects on regional vegetation greening trends' in the journal 'Ecosystems' which is contained within this dissertation.; Katherine M. Renwick and Benjamin Poulter were co-authors of the article, 'Adapting a dynamic vegetation model for regional biomass, plant biogeography, and fire modeling in the western U.S.: evaluating LPJ-GUESSLMFIRECF' submitted to the journal 'Ecological modelling' which is contained within this dissertation.; Benjamin Poulter was a co-author of the article, 'Processed-based modeling approaches for climate-vegetation-fire feedbacks in the Greater Yellowstone Ecosystem' which is contained within this dissertation.Climate change threatens to change forested ecosystems and wildfire characteristics across the globe. For the Greater Yellowstone Ecosystem (GYE), under future warming temperatures, wildfire activity is expected to increase and the suitable habitat for many dominant tree species is expected to shrink. Previous studies predict large high severity fires to occur more frequently, potentially so frequent that forests are unable to grow old enough to produce seeds and self-regenerate. Studies of suitable climate spaces show that previously habitable areas may become too warm or dry to support common GYE trees. The first goal of this dissertation was to use vegetation images from satellites to detect recent changes in forest productivity in the GYE, and then determine the relative importance of recent climate and disturbance observations in explaining these changes. We found that areas with detected increases in plant growth, or 'greening' trends, were associated with forested areas regenerating after wildfire. Detected decreases in plant growth, or 'browning' trends, were associated with areas that had recently burned. Historically dry areas with recent increases in precipitation were associated with greening trends. Warming of 0-2 °C was associated with greening trends, while greater increases in temperature (>2 °C) were correlated with browning trends. The key take-away is although forests in the GYE are usually considered temperature limited, changes in precipitation may be more important than previously thought. The second goal of this dissertation was to adapt a global vegetation computer model for regional applications to simulate forests and wildfire dynamics, ultimately to run simulations under future climate conditions to predict how forest extent and composition may change. Life history characteristics and climate limitations were aquired for the dominant GYE plant types to dictate their establishment, growth, competition, and mortality in the new model. Before running future simulations, it is required to evaluate how well the model represents current conditions. Adding new equations that calculate the initiation, spread, and effects of crown fires was required to reproduce recent vegetation abundance, distribution of plant types, and fire activity in the GYE. Methods, expected results, and implications of running future simulations are described in Chapter 4.Item Linking plant and soil nutrient dynamics in temperate and tropical montane forests(Montana State University - Bozeman, College of Letters & Science, 2018) Qubain, Claire Anne; Chairperson, Graduate Committee: David Roberts; Jia Hu (co-chair); Yuriko Yano and Jia Hu were co-authors of the article, 'Linking nitrogen allocation in douglas-fir to soil nitrogen availability in a western montane conifer forest' submitted to the journal 'Oecologia' which is contained within this thesis.; Diego Riveros-Iregui and Jia Hu were co-authors of the article, 'Climate and invasion drive soil nutrient dynamics in tropical montane forests of the Galapagos archipelago' submitted to the journal 'Ecology' which is contained within this thesis.I built on our fundamental understanding of ecosystem function by examining how climate variability influences feedbacks between plant processes and soil nutrient dynamics. At Lubrecht Experimental Forest, I examined how variability in snow depth, precipitation, and soil moisture influenced seasonal nitrogen allocation in Douglas-fir. I then examined if N cycling within Douglas-fir synchronized with patterns of N availability in the soil. In this case, N availability in the soil influenced plant nutrient dynamics. On the other hand, on San Cristobal Island in the Galapagos Archipelago, plants fed back and influenced soil nutrient dynamics. Changes in precipitation, soil moisture, and temperature strongly controlled nutrient concentrations in the soil, and to a lesser degree, plant community type determined nutrient concentrations, especially N concentrations, in the soil.Item Late Holocene vegetation and fire history in subalpine forests of northwestern Montana(Montana State University - Bozeman, College of Letters & Science, 2020) Sly, Shelby Fulton; Chairperson, Graduate Committee: David McWethyMid-to high- elevation forests of the Northern Rocky Mountains are dynamic systems that change in time in response to climate, disturbance and human activities. Climate models suggest these ecosystems will experience warmer temperatures, decreased spring snowpack, drier summers, and longer fire seasons, highlighting a need to better understand how these systems respond to changing climatic conditions. Sediment cores were extracted from two lakes in the Mission and Reservation Divide Mountains of Montana and analyzed for pollen and macroscopic charcoal to reconstruct fire and vegetation histories. The records from Mud Lake and Three Lakes Peak span the last 5400 and 4600 years respectively, and highlight the long-term persistence and relative stability of closed, mixed conifer/subalpine forests. During the mid-Holocene (approx. ca. 5000 yr BP), Pinus pollen percentages increased, suggesting closed forests which then transitioned to mesic forest of Pinus, Abies, and Picea over the last ca. 4000 years. Modern forests established between 3500-3000 cal yr BP at both sites. Both sites experience elevated fire activity during the Medieval Climate Anomaly c. 1000-900 cal yr BP which is consistent with other sites in the region. While relatively infrequent (2-4 fires per millennia), wildfires played a role in maintaining early successional vegetation (Poaeceae, Alnus spp.) and taxa that benefit from post-fire reduction in competition such as five-needle pines. Paleoenvironmental records from these two sites indicate subalpine forests of northwestern Montana persisted with relative stability throughout the mid to late-Holocene. With projections for increased warming, longer fire seasons and the possibility for increased occurance of short-interval fires in higher elevation ecosystems of the Northern Rocky Mountains, subalpine forests may become vulnerable to rapid transitions to different forest types or even non-forest systems.Item Examining the impacts of reforestation and bioremediation projects on high school environmental science students' feelings of biophilia and learning about environmental issues in Hawaii(Montana State University - Bozeman, College of Letters & Science, 2019) Forster, Lorinda; Chairperson, Graduate Committee: Greg FrancisThis action research study focused on the overall problem of how to promote biophilia in students while learning in experential, place-based settings. Surveys, relections, scientific terminology probes, anootated drawings, modeling and pre/post quizzes were used to access the results of the study. Results of the study indicate that some students were inspired to follow career paths in the natural sciences while others were further disconnected from nature. Some progress was made in learning vocabulary and facts about places visited. Further work is needed to promote deeper learning and feelings of biophilia for students prone to disconnecting from nature.Item Snowshoe hare habitat use and silvicultural influences in the Greater Yellowstone Ecosystem(Montana State University - Bozeman, College of Agriculture, 2019) Kurzen, Mark Daniel; Chairperson, Graduate Committee: Bok SowellSnowshoe hares (Lepus americanus) are the main prey base of the Canada lynx (Lynx canadensis) and are an important food source for many forest carnivores. Snowshoe hare research in the Greater Yellowstone Ecosystem is lacking and current research conclusions differ in regards to the types and ages of forests that snowshoe hares prefer. The US Forest Service has implemented limitations and prohibitions on silviculture in this area based on previous snowshoe hare studies. However, some research in the Greater Yellowstone Ecosystem suggests that regenerating lodgepole pine (Pinus contorta) stands that are associated with silviculture benefit snowshoe hares. We implemented three snowshoe hare use indices in southwest Montana within a portion of the Custer-Gallatin National Forest during 1999-2012 to assess snowshoe hare use of forest cover types in Greater Yellowstone Ecosystem. Our study area was located in a designated US Forest Service timber management area where a history of silviculture has resulted in a heterogeneous landscape of multiple successional stages intermingled with other old growth stands. We analyzed 11 years of snowshoe hare pellet plot surveys using linear mixed models and AIC c model selection. Our results suggested that the understory conifer species was the best predictor of use and that the youngest two classes of regenerating lodgepole pine stands had the greatest snowshoe hare use. We analyzed 13 years of snowshoe hare track counts on roads within our study area using Chi-squared goodness-of-fit tests based on proportional road segment lengths and the associated cover types. We observed the greatest snowshoe hare habitat use in the youngest two classes of regenerating lodgepole pine stands. We live-trapped snowshoe hares for one winter in our study area and observed the greatest number of hares captured per night in the youngest lodgepole pine stands. The findings from our 13 year study suggest that snowshoe hare use was greatest in early successional lodgepole pine forests that were approximately 30-60 years old and associated with clear cutting and pre-commercial thinning.Item Scaling nitrogen retention from trees to forests through succession(Montana State University - Bozeman, College of Agriculture, 2016) Scott-Klingborg, Aaron James; Chairperson, Graduate Committee: Jack Brookshire; Jack Brookshire was an author of the article, 'Large trees dominate nitrogen retention across forest succession' submitted to the journal 'Ecology letters' which is contained within this thesis.; Jack Brookshire was an author of the article, 'Expression of sink-driven and transactional nitrogen limitation following stand-replacing disturbance in an inland pacific northwest coniferous forest' submitted to the journal 'Ecosystems' which is contained within this thesis.We seek to understand how the ability of trees to acquire and retain nitrogen (N) changes throughout their lifetimes. This capacity enables trees to act as carbon (C) sinks individually and collectively in forest ecosystems over successional time scales. We evaluate how properties that govern nutrient retention change with tree size and forest age, and how allometric relationships scale up to influence ecosystem-level patterns of N cycling and retention. Most generally, we hypothesized that changes in N uptake and recycling efficiency with increasing tree size would vary with forest age and N availability. Additionally, we evaluated changes in ecosystem-level C and N accumulation throughout secondary forest succession following clear-cut logging disturbances in an effort to understand how N limitation may become expressed over time and interact with forest successional dynamics. Our findings highlight the importance of large trees in ecosystem N cycling and growth. We find that increasing mass growth rates are matched by an increasing capacity to acquire and retain N without necessitating increases in growth efficiency. Research findings indicate that mortality of single trees may hold profound consequences for stand-level N retention in addition to C storage. At the ecosystem scale, we find N accumulation and limitation are dynamic processes that fluctuate in strength and source over forest succession, and that ecosystem accumulation of N was driven predominately by increasing N in plant biomass rather than in soil pools.Item The influence of forest on the distribution and size of surface hoar in small meadows(Montana State University - Bozeman, College of Letters & Science, 2015) Wieland, Matthew Allen; Chairperson, Graduate Committee: Jordy HendrikxSnow avalanches pose a significant hazard to winter recreationalists travelling in the backcountry and are difficult to predict on individual slopes. Weak layers responsible for these avalanches may form at the surface multiple times during the winter season and are buried by subsequent snowfall. Understanding causes of slope-scale weak layer variations during formation and destruction periods is crucial for gaining an understanding of their distribution after burial. Persistent weak snow layers, such as surface hoar, can pose hazards for months after burial. This study examines surface hoar crystals on the surface, directly after formation, in two small meadow openings in southwest Montana. Data collection occurred during two winter seasons for three surface hoar formation events. Three environmental metrics associated with surface hoar growth processes in meadow openings are explored and their relationships with crystal size examined using spatial regression and regression tree analysis. The spatial structure for each event is described using multiple crystal sizing measures through semi-variograms. Surface hoar crystals tended to grow largest in areas that were both shaded and possessed large unobstructed views of the sky on north and south aspects. The range of spatial autocorrelation for surface hoar crystal sizes varied from 7 m to beyond 25 m and differed depending on event or crystal sizing measure. Results vary between events and suggest the drivers controlling surface hoar growth are unique to each area and not consistent between events. This research highlights the need for multiple slope-scale snow stability assessments for understanding the distribution of a buried weak layer of surface hoar in a meadow opening. Targeted areas for assessment should incorporate a basic understanding of a meadow's shading and canopy openness and how this varies over a winter season.