Theses and Dissertations

Permanent URI for this collectionhttps://hdl.handle.net/10217/100433

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Open Access
Predictive models of individual tree health: the utility of uncrewed aerial system data to inform forest management
(Colorado State University. Libraries, 2025) Lad, Lauren E., author; Tinkham, Wade T., advisor; Stevens-Rumann, Camille S., advisor; Smith, Alistair M. S., committee member; Vanderhoof, Melanie K., committee member; Vogeler, Jody C., committee member
Informed forest management is an essential tool for increasing forest resilience as global climate change increases the frequency and severity of disturbances. Drought and fire are inherent components of natural forest ecosystems, yet the increase in their occurrence combined with increasing severity threatens forest recovery pathways and their ability to sequester carbon. Fire is an essential disturbance that regulates both local and global ecosystem processes and functions. In forests of the United States, fire exclusion during the 20th century drove increases in vegetation density and connectivity, while altering ecosystem composition and structure. As a result of this increase in forest density and fuels, the U.S. has experienced increases in the severity, size, and frequency of wildfires, and drought. Fuels treatments in the form of mechanical thinning and prescribed fire provide opportunities to reduce forest density and fuels, research treatment effectiveness, and reduce the risk of catastrophic fires. Remote sensing allows researchers to collect spatially continuous data on forest conditions both before and after treatments, to study treatment-based impacts. Uncrewed aerial systems (UAS), specifically, provide a tool with user-controlled temporal and spatial resolutions. These systems enable the collection of multispectral and three-dimensional data, via structure from motion (SfM) or LiDAR, allowing researchers to examine changes to structure, composition, and health at ultra-high-resolution. The research within this dissertation focuses on combining pre- and post-treatment multispectral and structural data to assess individual tree health and changes to that health induced by disturbances. Chapter 2 investigates the utility of band-equivalent reflectance (BER) data from a consumer-grade multispectral UAS camera to predict sapling drought stress in western white pine (Pinus monticola) and Douglas-fir (Pseudotsuga menziesii var. glauca) through a controlled laboratory experiment. The results demonstrate that BER data can reliably detect physiological stress under controlled conditions, providing a strong foundation for using low-cost remote sensing to monitor tree health. Chapter 3 evaluates the transferability of the lab-developed BER models to mature ponderosa pine (Pinus ponderosa) and Douglas-fir forests in northern Colorado. This chapter evaluates the models' ability to predict relative drought stress in natural forests and explores the development of site-specific models to improve accuracy. Results reveal that while lab-based models provide valuable insights, field-developed models significantly enhance predictive performance, emphasizing the importance of adapting methodologies to specific field conditions and species. Chapter 4 quantifies the impact of compounding drought stress and fire, of varied intensities, on sapling physiology and mortality for western white pine and Douglas-fir. This chapter modeled the interaction of sapling drought stress and fire intensity on mortality using a dose-response strategy and pre-fire physiological and morphological characteristics. Results demonstrate that increasing drought stress results in higher post-fire mortality compared to less-stressed saplings subjected to the same fire intensity, regardless of species. Chapter 5 examines our ability to predict individual tree crown volume scorch in longleaf pine (Pinus palustris) forests treated with prescribed fire. This chapter assesses the impacts of data collection timing, inclusion of pre-fire data, and spectral range on model accuracy. The results of this chapter demonstrate that crown volume scorch can be successfully modeled using post-fire imagery as soon as one-day post-fire, with any sensor that includes red-green-blue data. This collection of research advances our understanding on the use of UAS data for modeling forest health. The models of relative drought stress could be integrated with forest structure and composition metrics to inform site-based thinning to optimize post-treatment stand resilience. Further, scorch classification models could be used to examine patterns of fire effects, providing critical feedback about prescribed fire ignition patterns. These models have the potential to be integrated into operational forestry practices and can provide actionable insights to guide management that promotes forest resilience and disturbance recovery.
Embargo
Evaluating the impacts of fuel treatments on burn severity across the Front Range
(Colorado State University. Libraries, 2025) Hettema, Sarah L., author; Stevens-Rumann, Camille, advisor; Battaglia, Mike, committee member; Vogeler, Jody, committee member; Vorster, Tony, committee member
Understanding how wildland fuel treatments interact with more frequent extreme wildfire events is an increasingly pressing issue. Quantifying the effectiveness of fuel treatments is difficult for many reasons including dynamics between treatment type, time since treatment, weather, climate, the fuels present, and topography. This study investigated wildfires along the Front Range from southern Wyoming to northern New Mexico to evaluate under what conditions treatments reduce the ecological impacts of fire, as measured by remotely sensed burn severity. We first evaluated methods and metrics to measure burn severity on the Front Range landscape. We found the Parks et al. (2018) Google Earth Engine (GEE) method and the relativized burn ratio (RBR) to have the highest correlation with field data. Additionally, the GEE method provided the advantage of allowing us to include small wildfires, which have historically been underrepresented in the data. We then determined (1) factors influencing the relationship between treatments and burn severity, (2) how burn severity differed across forest and treatment types, and (3) how extreme fire weather conditions influenced burn severity across treatment types. Across the Front Range, lower elevation forest types burned at lower severities compared to higher elevation forest types. Treatment effects varied across forest types but treatments generally had lower burn severity in lower elevation forest types compared to spruce ‒ fir and lodgepole pine forests. Areas that previously experienced low to moderate severity wildfire had the lowest burn severity outcomes across forest types and in extreme conditions. Intentional surface fuels reduction treatments (i.e. prescribed fire, removal plus surface fuel reduction, and removal plus fire) had a relatively minor impact across our study area. That said during non-extreme conditions, treatments that included previous fire (prescribed burning or low to moderate severity wildfire) had lower subsequent burn severities. Higher elevation forests (spruce – fir and lodgepole pine) burned at high severity regardless of intentional treatment effect. This better understanding of the outcomes of treatment efforts will help land managers strategically utilize resources and employ adaptive management strategies that account for changing wildfires.
Open Access
Assessing wildfire risk reduction through fuel treatments and educational activities
(Colorado State University. Libraries, 2025) Gyawali, Kritagya, author; Baral, Srijana, advisor; Wei, Yu, committee member; Bayham, Jude, committee member
Hazardous forest fuel reduction and prevention education are key strategies for reducing wildfire risk. While fuel reduction efforts have become a shared goal of many agencies, the cost of implementing them remains a significant challenge. Increasing biomass utilization can be a strategy for reducing these costs. Yet little is known about the impact of wood manufacturing facilities on fuel treatment activities. Additionally, human activities cause nearly 84% of wildfires, often leading to rapid spread and severe impacts, including health issues, environmental damage, suppression expenditures, degraded air and water quality. As such, evaluating the effectiveness of educational prevention activities is crucial at reducing undesirable human-caused ignitions and enhancing cost-effectiveness of wildfire management. This study examines two interrelated research objectives related to wildfire risk reduction: (1) the impacts of forest market proximity on fuel treatment activities in National Forests (USFS) and Bureau of Land Management (BLM) lands in Colorado, and (2) the effectiveness of wildfire prevention education (WPE) in reducing undesirable human-caused ignitions on tribal lands in the U.S. To address objective 1, we developed a mixed linear model using fuel treatment data (n = 779 BLM sites and n = 9,709 USFS sites), the location of active wood manufacturing facilities, and climatic variables from 2012 to 2020. We found that proximity to facilities significantly impacts treatment activities, with sites relatively closer in proximity treating more acres and utilizing more biomass than those further away, in both BLM and USFS lands. Additionally, we identified a threshold of 70 minutes beyond which proximity had no significant effect on fuel treatment on both lands. To address objective 2, we employed Poisson regression by using seven categories of monthly WPE activities (mass media coverage, signage placements, programs/events, individual/key-personnel contacts, community contacts, brochures, hazard assessments), wildfire ignitions, acres burned, and climatic factors across 35 U.S. tribal units from 2012 to 2020. After controlling for potential endogeneity biases, the Poisson model revealed that certain WPE activities, such as community contacts, significantly reduced ignitions caused by debris and open burning, fireworks, fire misuse by minors, power generation, recreation/ceremony, firearms/explosives and smoking. Hazard assessments were marginally significant, whereas individual/key-personnel contacts, informational brochures, and programs/events were negatively related to fire ignitions. In contrast, media coverage and signage had no significant effect, although the lagged six-month aggregates showed a significant and negative effect on the number of ignitions. Our findings underscore the role of strategic planning of well-distributed wood-processing facilities for optimizing fuel treatment costs and the importance of continued WPE efforts to reduce human-caused ignitions.
Open Access
Cross-scale evaluation of fuel maps in Colorado ponderosa pine-dominated forests
(Colorado State University. Libraries, 2025) Johnston, Katelyn J., author; Hoffman, Chad, advisor; Tinkham, Wade, advisor; Hawbaker, Todd, committee member; Vogeler, Jody, committee member
Fuel maps are used in every aspect of wildfire management, allowing managers to assess fire risk, predict fire behavior and effects, and guide fuel hazard treatment planning. Despite widespread use of national fuel maps like LANDFIRE, FCCS, and FastFuels, quantitative data on their accuracy and biases across ecosystems and scales remain limited. The few studies evaluating LANDFIRE's canopy fuel maps and FCCS have identified a wide range of errors and conflicting bias trends. Additionally, LANDFIRE's 40 standard fire behavior fuel models have yet to be assessed for their ability to represent fuel component loadings, despite growing use in fuel maps like FastFuels for physics-based fire behavior modeling. The accuracy of FastFuels has not been evaluated due to its recent development. The overall objective of this study was to assess the accuracy and bias of three national fuel mapping products – LANDFIRE, FCCS, and FastFuels – at five different scales. To meet this objective, I sampled surface and canopy fuels from seven sites representing the range of ponderosa pine (Pinus ponderosa Dougl. Ex Laws.) fuel complexes across the Colorado Front Range. Plots at each site were arranged in a 5x5 grid of 0.09 ha pixels to allow for accuracy assessment at 0.09, 0.12, 0.81, 1.44, and 2.25 ha scales. My results indicate that all three national fuel mapping products performed poorly across fuel attributes, with systematic biases and mean absolute errors ranging from 36% to 2590%. Errors and biases associated with LANDFIRE canopy metrics suggest that LANDFIRE is likely to overestimate fuel hazards associated with crown fire initiation, but underestimate crown fire spread hazard, while FastFuels underestimates the hazards associated with both crown fire initiation and spread. Similarly, FBFM40 overestimates key surface fuel components, such as fine fuel loading, which would likely lead to overpredicted surface fire behavior. FCCS metrics crucial for smoke and emissions forecasting, particularly 1000-hour fuels, are also overestimated, potentially inflating emissions projections. I found no significant relationship between mean error and map scale from 0.09 ha to 2.25 ha. The variation observed within and between fuel components and layers of LANDFIRE, FCCS, and FastFuels highlights inherent challenges associated with mapping wildland fuels. The high errors and biases observed in my assessment may have broader implications for fire management and planning, warranting further investigation, as these fuels play an important role in dictating fire behavior and effects. Although advancements in remote sensing and modeling offer opportunities to improve these national fuel mapping products, uncertainties in current products should continue to be quantified and considered when implemented in management activities until these improvements are successfully integrated.
Open Access
A damming history: an analysis on the legacy effects of beaver dams on the composition and structure of a montane riparian ecosystem
(Colorado State University. Libraries, 2025) Brunngraber, Kara, author; Sueltenfuss, Jeremy, advisor; Paschke, Mark, committee member; Wohl, Ellen, committee member
Landscape heterogeneity is widely recognized for its positive influence on ecosystem diversity and stability. As an "ecosystem engineer," the American beaver (Castor canadensis) increases heterogeneity in riparian systems through dam-building activities, resulting in diverse wetland complexes. This study explored the impact that historic, off-channel beaver dams have on the structure and composition of the surrounding vegetative communities. Specifically, I explored how vegetative communities differed in areas of beaver occupancy history, land management impacts, and distance from the river. This study was conducted in the Kawuneeche Valley of Rocky Mountain National Park, Colorado. Field methods focused on vegetative surveys around historic, off-channel beaver dams, the Colorado River, and its major tributaries. Observed beaver sign was classified by age (historic, recent/current, absent), and statistical analysis assessed compositional differences among variables of interest. I found that historic beaver dams supported more wetland-adapted and less disturbance-tolerant plant communities. Notably, shrub cover at historic dams was similar to that of exclosed sites. In contrast, upland, disturbance-adapted species dominated areas of historic beaver activity where dams were not present. Impacts of historic agriculture are still present on the landscape, with higher intensity farming areas dominated by herbaceous species. Finally, the effects of river incision reduced shrub cover within the valley, restricting communities to the river corridor. This study demonstrated that off-channel, historic beaver ponds function as a refuge for wetland plant species in disturbed riparian systems. Incorporating these underutilized structures already present on the landscape could enhance restoration success by increasing heterogeneity and wetland health.
Open Access
Habitat variation effects on cavity-nesting bee fitness, community assemblages, and parasite interactions in the Colorado Front Range
(Colorado State University. Libraries, 2024) Dodge, Jessie M., author; Davis, Thomas S., advisor; Galbraith, Sara M., committee member; Paschke, Mark, committee member; Stewart, Jane E., committee member
Although many dry forested ecosystems in the western US are shaped by disturbances like wildfire and forest management treatments, little is known about their effects on native solitary bee fitness. This is an important knowledge gap, as most bees in the western US are solitary and are crucial for pollination in forested ecosystems. Therefore, I test how wildfire and forest management treatments affect cavity-nesting solitary bee fitness traits including diet breadth and quality, provisioning ability, reproduction and brood development, parasite abundance, and community network metrics. This was done by deploying artificial nesting boxes in the ponderosa pine forest of Boulder County, CO that either burned at higher severity, thinned by hand, or were unburned and untreated control. For my first two chapters, I used the solitary bee, Osmia lignaria as a model species to evaluate bee fitness responses to variations in forest structure, floral density, and climatic conditions. I found that O. lignaria foraged for pollen from specific flora, regardless of on-site presence, which was affected by climate and forest structure, but effects varied from year to year. Otherwise, habitat variation did not affect O. lignaria nest provisioning, reproduction, or development. However, the abundance of their kleptoparasite, Tricrania stansburyi, decreased with increased wildland urban development. Finally, in my last chapter, I utilized artificial nest boxes to collect local cavity-nesting bees and wasps to compare differences in community composition, host-parasite interactions, and emergence rates among Burned, Control, or Treated sites. The solitary bee, Osmia calla was found to be the most abundant species, indicative of burned sites whereas the kleptoparasite, Nemognatha sparsa, and parasitoid, Monodontomerus spp., were the most abundant parasites found within all habitat types. Control sites were found to have the most host-parasite interactions, with parasites exhibiting more generalist relationships with hosts, followed by treated sites, with burned sites having the most specialized host-parasite interactions. Collectively, my results demonstrate that disturbance-caused habitat variations had little effect on the fitness of the solitary bee, O. lignaria, despite affecting their access to nutritional opportunities, suggesting they can reproduce within various dry, mixed conifer forested habitats. However, urbanization in forested ecosystems likely decreases exposure to nest parasites. Alternatively, local, cavity-nesting bee-parasite interactions differed among habitat types, with hosts inhabiting control sites portraying more parasitic pressure. Thus, some cavity-nesting bee species may be more influenced by habitat variations than O. lignaria, and this is likely mediated by interactions with parasitic species. The interacting effects of disturbances and parasite pressure on bee fitness found here can be used to inform native bee conservation strategies. For one, floral surveys may not reflect floral species bees are using for foraging so alternative methods investigating pollen sources bees are using for forage are suggested. Secondly, the loss of natural habitat with increasing urbanization within forested habitats can decrease kleptoparasite abundance but provide early season solitary bees with additional foraging sources. Finally, cavity-nesting bees and wasps in unburned and untreated habitats demonstrate higher parasitic pressure than burned and treated habitats, suggesting habitat variations caused by these disturbances may relieve parasitic pressure. Overall, monitoring bee parasite abundance may indicate healthy pollinator habitats within the forests of the Colorado Front Range.
Open Access
Long term in vivo observation of maize leaf xylem embolism, transpiration, and photosynthesis during drought and recovery
(Colorado State University. Libraries, 2024) Allen, Brendan S., author; Ocheltree, Troy W., advisor; Gleason, Sean M., advisor; Knapp, Alan K., committee member
Plant water transport is essential to maintain turgor, photosynthesis, and growth. Water is transported in a metastable state under large negative pressures, which can result in embolism, i.e., the loss of function by the replacement of liquid xylem sap with gas, as a consequence of water stress. Unfortunately, the detection of embolism is difficult because any manipulation of the xylem to facilitate measurement (e.g., cutting) can unintentionally introduce embolism. Therefore, our understanding of the timing of embolism, relative to other physiological responses, is incomplete. To avoid experimental artifacts, we used non-invasive methods to quantify embolism occurrence in maize leaves to characterize the sequence of physiological responses (leaf shrinkage, photosynthesis, chlorophyll fluorescence, and transpiration) during severe water stress. Embolism formation occurred after other physiological processes decreased and was irreversible upon rewatering. Recovery of transpiration, net CO2 assimilation, and photosystem II efficiency were aligned with the severity of embolism, whereas these traits returned to near pre-stress levels in the absence of embolism. A better understanding of the relationships between embolism occurrence and downstream physiological processes during stress and recovery is critical for the improvement of crop productivity and resilience.
Open Access
Juvenile tree dynamics in changing landscapes: effects of overstory-mediated microclimates on dryland tree recruitment vary across climatic gradients
(Colorado State University. Libraries, 2024) Hill, Edward M., author; Redmond, Miranda D., advisor; Ocheltree, Troy W., advisor; Bradford, John B., committee member; Smith, Melinda D., committee member
Climate change impacts the future viability of plant species and communities directly through effects on demographic processes and indirectly through structural dynamics. Regeneration, establishment, growth, and survival of juvenile trees can be especially vulnerable processes in forest and woodland community development because juvenile trees are typically not able to tolerate abiotic stress as effectively as more mature trees. Because of this elevated sensitivity to climate-related stressors, juvenile establishment patterns are fundamental to understanding long-term species persistence. Overstory tree structure is an important mediating influence of the impacts of climate change in forest and woodland communities, particularly through influences on resource availability. Fine-scale variation in overstory tree size, density, and species influence primary plant resource requirements, including light availability, atmospheric heat and moisture, precipitation throughfall and soil water availability, and soil nutrient availability. Juvenile trees of different species can benefit from buffering of microclimate conditions by overstory trees, like direct radiation and extreme temperature variation, and experience competitive interactions for light and soil resources, especially in resource-limited communities. Yet, juvenile trees can span a range of sizes and physical maturity and vary in their capacity to acquire resources or tolerate resource limitations, and therefore can differ in facilitative versus competitive relationships with overstory conditions. Amplifying the complexity of these relationships, interannual variation in weather conditions, such as drier or wetter years than normal, influences the degree to which juvenile trees experience facilitative or competitive relationships with overstory trees. Indeed, the extent of microclimate effects on regeneration processes depend in part on the complex covariance of air temperature and humidity (thus, vapor pressure deficit), moisture availability (precipitation and soil moisture), and photosynthetically active radiation (i.e., light). In the absence of temperature and moisture limitations, trees may benefit from additional light availability for photosynthesis; alternatively, if temperature or moisture conditions are limiting, juveniles may benefit more from buffering influences of overstory, at the expense of decreased light availability. For dry forests and woodlands of the western U.S. which are at the forefront of climate change-driven tree recruitment vulnerabilities, greater resolution into juvenile relationships with overstory structure, and microclimate buffering, will substantially enhance the ability to evaluate and predict the effects of increasingly marginal climate space on their persistence. In this dissertation, I evaluated juvenile tree regeneration, growth, and survival in dryland forest and woodland systems relative to the mediating influences of overstory trees, across ranges of juvenile sizes, interannual weather variation, and broad climatic and elevational environmental gradients. In Chapter 1, I investigated survival and growth of ponderosa pine and Douglas-fir newly germinated seedlings, and older, larger seedlings to variation in overstory structure and associated microclimate conditions at fine-spatial scales. This study showed that while newly germinated seedlings were more sensitive to interannual variation in microclimates, overall survival and growth of younger and older seedlings were highest in microclimates with above-average warm and dry air during early-growing season months, and above-average light conditions. Importantly, the structural and microclimate influences on survival and growth over three years of study were primarily associated with the first year of study during which spring weather was abnormally cool and more humid. These results illustrated the environmental context for the initiation of survival and growth trajectories observed in this study, and demonstrate both spatially and temporally narrow conditions in which survival and growth was collectively greatest for both species. In Chapters 2 and 3, I investigated physiological and growth differences of juvenile piñon pine in dead and live overstory microenvironments over two years following experimentally-induced mortality of overstory trees. In Chapter 2, I measured photosynthetic and stomatal conductance rates of juveniles from among the smallest to largest individuals present in a middle-elevation piñon-juniper site in the core of the geographic distribution of two-needle piñon pine. Larger juveniles in dead overstory environments showed the highest photosynthetic and stomatal conductance rates. However, juveniles of all sizes were overall similarly limited by lower soil moisture and hot and dry microclimate conditions in both live and dead overstory environments. Given these limitations, the results of this study demonstrate the susceptibility of all juvenile piñon trees to hot and dry microclimates, which can be exacerbated both by mortality of overstory trees and by projections of future hotter and drier climate in these woodlands. In Chapter 3, I measured branch growth of juvenile piñon trees at six different sites spanning a gradient of latitudinal climate differences from hotter and drier southern locations to cooler and dry northern locations, and local elevation gradients from low to mid to high elevation piñon-juniper woodlands. Growth in post-overstory mortality years relative to mean growth prior to overstory mortality ("growth ratios") of juveniles across sizes was consistently higher in dead compared to live overstory environments only for middle- and high-elevation sites in our mid-latitude study region of southwestern Colorado, which had cooler and wetter post-overstory mortality weather conditions compared to other regions. Moreover, differences among sites were likely also related to typical climate differences associated both with latitude, where drier sites at southern and northern latitudes showed little growth responses to overstory mortality, and associated with elevation, where growth ratios were highest at the highest elevation site which has more moderate temperature and precipitation conditions on average. The results of this dissertation provide evidence for microclimate and juvenile tree survival outcomes in a dry forest restoration treatment and show the impact of acute structural change following overstory tree die-off on physiological and growth activity of juvenile piñon pine. The findings presented here provide ecologists and land managers with new information on the nuances of spatially and temporally narrow regeneration niches of species in dry mixed-conifer forests, and potential patterns and mechanisms of juvenile piñon pine resilience – but also potential future sensitivity – following overstory mortality. Importantly, results of these studies emphasize the role of interannual variation in weather conditions in driving specific forest and woodland development trajectories.
Open Access
The influence of provenance on radial growth and drought resilience of lodgepole pine in Fraser Experimental Forest, Colorado, U.S.A.
(Colorado State University. Libraries, 2024) Warnick, Katarina J., author; Hart, Sarah, advisor; Tinkham, Wade, advisor; Battaglia, Mike, committee member; Dahl, Jamie, committee member
Climate change poses unprecedented challenges to forested ecosystems, particularly in drought-affected areas in the western United States, where increased temperatures and shifting precipitation regimes are negatively impacting locally adapted tree species. In response, researchers and land managers are exploring innovative forest adaptation strategies to maintain forest resilience, such as assisted migration. This study examines the potential of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) to be utilized in forest assisted migration efforts in western North America, drawing from the understanding that this widespread species displays intraspecies variation in growth-climate associations due to local adaptations across its extensive geographic range. We make use of a provenance study established in the early 1980s in Fraser Experimental Forest, Colorado, U.S.A. to examine the effect of seed source, or provenance, on growth-climate responses and drought resilience of lodgepole pine in its southernmost range. We investigate two primary research questions. First, does provenance climate influence the radial growth response of lodgepole pine trees? Second, do lodgepole pine trees from climatically drier provenances exhibit greater resilience to drought, as measured by annual radial growth before and after drought events? To address our first question, we employed dendrochronological methods and a generalized linear mixed-effects modeling approach utilizing climate data to analyze the variation in overall radial growth of trees explained by the difference in provenance and study site climates during our study period, 1992-2021. In addressing our second question, we utilized the Standardized Precipitation Evapotranspiration Index (SPEI) and metrics of quantifying drought resilience to determine the impact of provenance site aridity on tolerance to drought during our selected drought period, 2001-2002. Our analyses revealed significant differences in radial growth between trees from different provenances. Specifically, we found that trees originating from provenance sites with greater growing season average vapor pressure deficit, yet higher precipitation, exhibited increased radial growth. In analyzing drought resilience, we found that trees from provenances with higher average temperatures and greater evapotranspiration showed greater resilience to drought, aligning with previous research linking seed source climate aridity to drought tolerance. Interestingly, we also found that trees from sites with greater climate moisture index compared to their growing site exhibited greater radial growth resilience to drought, suggesting that certain populations may be less sensitive to moisture deficits. Our research sheds light on the relationship between provenance climate with radial growth response and drought resilience in an assisted migration context. Our findings suggest that provenance climate aridity may confer resilience to trees during resource-limited events. More broadly, our study underscores the potential of utilizing local adaptations and intraspecies variability of tree species in climate adaptation efforts aimed at mitigating the impact of climate change in forested ecosystems.
Open Access
Scaling up collaborative governance for better fit and flexibility: a case study of the Two-Rivers Three-Watersheds Two-States (2-3-2) partnership
(Colorado State University. Libraries, 2024) Bruce, Lily Appleby Calfee, author; Schultz, Courtney, advisor; Cheng, Tony, committee member; Scott, Ryan, committee member
Over the past ten years, multiple place-based collaborative groups have partnered across jurisdictional divides to form a unique structure of nested collaborative groups, but little is known about what drives the formation of these umbrella collaborative groups or how they function. Due to the changing climate and a legacy of fire suppression, the United States Forest Services (USFS) and academic scholars have promoted the planning and implementation of forest restoration activities at larger geographic scales than has been typical in forest management. To achieve landscape-level restoration, efforts must be coordinated across jurisdictional boundaries. Collaborative governance arose as an alternative to the centralized and adversarial approaches that had dominated environmental policy since the passage of core environmental statutes in the 1970s. Collaborative groups seek to overcome conflict by facilitating cooperative decision-making between government and non-government actors to achieve ecological and community benefits, reducing the risk of uncharacteristic wildfires, and addressing watershed function. Collaborative groups that are focused on forest restoration operate at larger scales than ever before, filling gaps resulting from limited government capacity and addressing complex and multi-jurisdictional environmental challenges. In the last fifteen years, federal and state policies emerged to support landscape-level collaboration, including the 2009 Collaborative Forest Landscape Restoration Program (CFLRP). An important question is how collaborative groups operate in response to such drivers that require scaling up when they typically have existed at smaller spatial extents of individual national forests or communities. In this thesis, I explore the formation of an umbrella collaborative group and the opportunities and challenges associated with collaborating at the multiple-watershed level. I use qualitative analysis of a series of interviews with partners of the Two Watershed-Three Rivers-Two States Cohesive Strategy Partnership (2-3-2), an umbrella collaborative, to understand opportunities for adaptation and adapting to a variety of scale-fit needs that arise for collaborative governance regimes. In forest policy, scale mismatch is the lack of fit between the temporal or spatial scales of policy mechanisms, collective action, and ecosystem processes. Scale mismatch is prevalent in natural resource management; perhaps a better way to conceive of this issue is the need to have flexibility to adapt to drivers or concerns that operate and vary across scales. Collaborative governance may improve scale fit, especially for ecological processes and federal-level policies that require restoration work across huge acreages, but we also know from research that the trust- and relationship-building required by collaborative processes work best at smaller scales. This thesis consists of four interrelated but independent chapters. Chapter 1 introduces my research and provides foundational concepts to understand collaborative and adaptive governance. Chapter 2 summarizes interview results and is intended as a practitioner paper for partners and leaders of the 2-3-2. I describe interviewee perspectives on the current priorities of the 2-3-2, the advantages and challenges of collaboration at the multi-watershed scale, and recommendations for further strengthening the efficacy of the 2-3-2. Chapter 3, intended for a peer-reviewed journal, discusses these results in the context of collaborative and adaptive governance theory to understand factors that drive the formation of umbrella collaborative groups, as well as how umbrella collaboratives allow for greater adaptiveness to different scale dynamics. Finally, in Chapter 4, I summarize and draw overarching conclusions from my separate analyses of the interview data and address the limitations of this research with a view to future research.
Open Access
State climate adaptation policy and forest management case studies in the American West: Colorado and Washington State
(Colorado State University. Libraries, 2024) Breidenbach, Tamera Elizabeth, author; Schultz, Courtney, advisor; Cheng, Antony, committee member; Scott, Ryan, committee member
Climate change and past management practices are impacting and creating hazards for forests and forest-adjacent landscapes and communities. State governments are considered leaders in climate policy and increasingly are facilitating a state-led response to observed and predicted future impacts from climate-related hazards. Hazards and risks to forests and forest-adjacent communities include wildfire, insects and disease, drought, and a loss of economic and social goods and amenities. Adaptation facilitates a response to risks and provides opportunities to adjust to and become resilient to current and future hazards. Utilizing a qualitative approach and a policy design framework, my research had two primary objectives: characterize state-level natural resource adaptation goals and objectives for forests and how these efforts are implemented by state agencies and with other actors (e.g., collaborative groups and non-governmental organizations (NGO's), other government entities, industrial and private forestry, etc.); and analyze the policy design utilized to address climate hazards through climate adaptation for forested landscapes. I interviewed 43 individuals, including state-level policy decisionmakers, federal and state land managers, local governments and utilities, industrial and private forestry entities, collaborative groups and NGO's, academics and practitioners from universities, other forestry-related professionals, and key partners. This thesis explores state climate adaptation policies for forested landscapes in Colorado and Washington State through four chapters. Chapter 1 consists of a brief introduction to this study, including a literature review on relevant climate-induced impacts to forests and forest-adjacent lands, state-level climate adaptation planning, and policy design theory, along with other intersecting and sensitizing concepts important to facilitating a thorough and holistic approach towards climate adaptation. Chapter 2 is a practitioner report intended for federal and state policy decisionmakers, land managers and practitioners, and land management partners. In this chapter, I discuss key research findings and offer recommendations based on research outcomes. Chapter 3 highlights research findings in a product intended for a peer-reviewed journal utilizing the policy design framework. This chapter focuses only on findings from Washington State. Chapter 4 highlights the overall findings from this study, discusses study limitations, and offers recommendations for future research exploration. My thesis contributes to the novel and growing area of literature working to understand climate adaptation and the role that state governments have in facilitating a future's thinking approach and response to climate hazards, particularly for forested and forest-adjacent landscapes and communities. The insights from my work help to inform policy decision-makers and land management practitioners on how states are facilitating climate adaptation through state policy, how states are working to implement climate adaptation actions, the perceptions of state climate adaptation policy, and the potential areas of growth and opportunity for climate adaptation efforts on forested lands. There are still gaps in knowledge that exist for state-related climate and adaptation policies, including how states are incorporating pillars such as equity and environmental justice, how recent federal law, legislation, and funding have increased or facilitated climate adaptation implementation through state partnerships, and future research can further explore how states are working across boundaries to address climate hazards through adaptation.
Open Access
Comparing crown fire predictions in ponderosa pine stands among four fire behavior models
(Colorado State University. Libraries, 2024) Ney, Jacob, author; Hoffman, Chad, advisor; Linn, Rodman, committee member; Fischer, Emily, committee member
Fire and land managers commonly use fire behavior modeling systems to support their planning and decision-making process. Fire modeling systems have been increasingly used across the western United States to plan fuel treatments that reduce hazard fuels, especially as a drier climate has resulted in more frequent high severity wildfire. Given differences in model types, approaches, assumptions, and sensitivity to various input parameters, modeling systems can produce different predictions and lead to different management decisions. Variability arising from model selection results in increased uncertainty within the decision-making framework. Multi-model comparisons help identify areas of model agreement and disagreement, reduce uncertainty associated with management decisions, and identify directions for future experimentation. Here, I compare predictions of fire type and crown fire rate of spread (ROS) among four modeling systems that represent a range of model types and complexities—Wildland-urban interface Fire Dynamics Simulator (WFDS), QUIC-Fire, a Rothermel-based modeling framework, and Crown Fire Initiation and Spread (CFIS). Comparisons (n = 297) were made based on a range of forest structure and environmental conditions representative of treated and untreated ponderosa pine forest stands in the southern Rocky Mountains. All four models predicted crown fire occurrence for 71% of simulations in total. WFDS, QUIC-Fire, and CFIS agreed on fire type more than 65% of the time. Rothermel predicted crown fire for 41% of simulations with ROS predictions 45% lower than the other models. Models tended to agree on crown fire occurrence in scenarios with a low canopy base height and greater surface and canopy fuel loading, indicating lower uncertainty in predicted fire behavior among models when fuel hazard is greatest. Differences among model predictions were more evident in scenarios with greater canopy base heights, moderate surface and canopy fuel levels, and at lower windspeeds. These results suggest that uncertainty introduced by model selection is likely greatest for designing and evaluation of fuel treatments, and that further research on fire behavior in treated forests stands is needed.
Open Access
Governance approaches for scale mismatches in pre-wildfire planning and post-wildfire response and recovery
(Colorado State University. Libraries, 2024) Buettner, William Cole, author; Schultz, Courtney, advisor; Cheng, Tony, committee member; Scott, Ryan, committee member
Wildfires in the western United States have become an increasingly complex management challenge. Increased fire extent and severity, longer fire seasons, housing development in the wildland-urban interface, jurisdictional complexities, and interactions between fire and other disturbances combine to exacerbate risks to different critical values. Managers have recognized the need for greater pre-wildfire planning by reducing wildfire risk through fuel treatments and contingency planning in anticipation of fire. Less explored, however, are how managers are responding to changing environmental conditions after wildfires and planning for long-term recovery efforts. Challenges in pre-wildfire planning and post-wildfire response and recovery share similar scalar mismatches that frustrate effective governance. Scale is the spatial, temporal, and functional dimensions used to measure and study any phenomenon, and mismatches arise from challenges within relationships between ecological and social systems. In this thesis, I explore different scale mismatches in pre-wildfire and post-wildfire management to derive an understanding of potential adaptation options in complex management systems. This thesis consists of five standalone chapters. The first chapter introduces the two primary studies and reviews relevant literature related to wildfire governance and tools used to facilitate adaptive management approaches. The second chapter is a peer-reviewed manuscript that investigates the use of Potential Wildfire Operational Delineations (PODs) for fire and fuel management. In collaboration with the Colorado Forest Restoration Institute, we filled gaps in PODs research by investigating how PODs are being utilized in non-incident management contexts to align forest and fire planning objectives with incident response tactics. We found that PODs help validate fuel treatment plans and support communication among agency staff, and with private landowners and collaborators. Challenges included lack of technical knowledge and skills, unclear leadership direction, potential misalignment with other forest management goals, and community and agency buy-in to using PODs. Recommendations from interviewees were to address knowledge gaps and capacity challenges. In our paper, we offer insights into how PODs are being utilized within our case studies and align these findings with the diffusion of innovation literature. This second chapter of my thesis has already been published in the International Journal of Wildland Fire as a Research Note. The third chapter, intended for a practitioner audience, explores the governance approaches to post-wildfire policies and programs following the Hermit's Peak-Calf Canyon Fire response and recovery efforts. Interviewees shared program and policy challenges, adding that policies did not incorporate local contexts, had prolonged treatment timelines, and federal staff were uneducated on program nuances. Facilitators of success were the Monsoon Taskforce and Lines of Effort Framework created by New Mexico State Agencies to allow for greater communication, coordination, and collaboration. Interviewees recommended an increase in workforce capacity and education, as well as legislative changes. The fourth chapter, intended for a peer-reviewed journal, aligns adaptive governance theory and literature on boundary organizations with the governance approaches following the Hermits Peak Calf Canyon Wildfire. I found that adaptive governance arrangements are occurring in New Mexico and that boundary organizations are playing a significant role by facilitating information transfer and addressing knowledge gaps. In chapter five, I share concluding thoughts for both studies and suggestions for further inquiry and policy guidance.
Open Access
Occurrence, distribution, and driving environmental factors of quaking aspen regeneration by seed in the Cameron Peak Fire burn scar
(Colorado State University. Libraries, 2024) Carter, Sarah, author; Hart, Sarah, advisor; Rhoades, Charles, committee member; Rocca, Monique, committee member
As a result of the increasing frequency and severity of wildfires in the mountain west region of North America, greater mortality of montane and subalpine forests has led to changes in forest regeneration patterns and species composition. Increased drought conditions pre- and post-fire due to warming climate and destruction of existing seed have led to loss of historically conifer-dominant forests. This has subsequently opened a niche for post-fire aspen establishment, particularly through seed. The understanding of aspen regeneration by seed is understudied in comparison to the more broadly emphasized vegetative reproduction: a process which is limited spatially by the presence of surviving root networks and a lack of adaptive capacity of clone genetics. In this study, we aimed to (1) quantify the presence and density of post-fire aspen seedling establishment and (2) assess the environmental drivers of post-fire seedling establishment in a recent burn scar in northern Colorado. Two growing seasons following the fire, we conducted field surveys at 38 sites within the Cameron Peak Fire burn scar. We aimed to quantify regeneration of all tree species, including aspen as well as the dominant pre-fire conifers ponderosa pine (Pinus ponderosa), lodgepole pine (Pinus contorta), subalpine fir (Abies lasiocarpa), and Engelmann spruce (Picea engelmannii). Across our study area we found widespread establishment of aspen seedlings, particularly at high elevations, where soil moisture is less limiting. Given the occurrence of aspen seedlings within a site, we found seedlings were most likely to occur in moss seedbeds, near large coarse woody debris, and within microsite concavities, where soil moisture availability is likely higher. Collectively, our findings highlight the importance of moisture availability for the germination and initial survival of aspen seedlings. Further we found occurrence of aspen seedlings far outweighed that of any conifer species. These findings support projected changes in forest composition, species dominance, and range shift following stand replacing fire to favor early successional species such as aspen. The successful dispersal and establishment of aspen seeds in large, high severity burned patches have potential to facilitate the range shift of aspen forests towards higher elevations. These implications become more prevalent as changes in climate increase the risk of high severity fires and loss of seed sources, while decreasing suitability for montane and subalpine forest species to persist and regenerate.
Open Access
Constraints on mechanical fuel reduction treatments in USFS Wildfire Crisis Strategy priority landscapes
(Colorado State University. Libraries, 2024) Woolsey, George, author; Hoffman, Chad M., advisor; Tinkham, Wade T., advisor; Battaglia, Mike A., committee member; Ross, Matthew R. V., committee member
The US Forest Service recently launched a Wildfire Crisis Strategy outlining objectives to safeguard communities and other values at risk by substantially increasing the pace and scale of fuel reduction treatment. This analysis quantified layered operational constraints to mechanical fuel reduction treatments including existing vegetation, protected areas, steep slopes, and administrative boundaries in prioritized landscapes. A Google Earth Engine workflow was developed to analyze the area where mechanical treatment is allowed and operationally feasible under three scenarios representing a range of management alternatives under current standards. Results suggest that a business-as-usual approach to mechanical fuel reduction is unlikely in most landscapes to achieve the 20-40% of high-risk area treatment objective using mechanical methods alone. Increased monetary spending to overcome physical constraints to mechanical treatment (e.g., steep slopes and road access) opens sufficient acreage to meet treatment objectives in 18 of 21 priority landscapes. Achieving treatment objectives in the remaining landscapes will require both increased spending and navigating administrative complexities within reserved land allocations to implement fuels treatments at the pace and scale needed to moderate fire risk to communities. Broadening the land base available for treatment allows for flexibility to develop treatment plans that optimize across the multiple-dimensions of effective landscape-scale fuel treatment design. Spatial identification of the constraints to mechanical operability allows managers and policymakers to effectively prioritize mechanical and managed fire treatments.
Open Access
Self-medication in horses
(Colorado State University. Libraries, 2008) Williams, David Earl, author; Rittenhouse, Larry R., advisor; Norris, Brian J., advisor
Horses are known herbivore generalists that must rely upon available plant forage for dietary needs. Diet selection in rangeland herbivores has been shown to be based upon post-ingestive physiological consequences. The basic premise of post-ingestive physiological consequences is the ability of an animal to associate the taste of a particular food with its possible hedonic shift. A negative hedonic shift results in the animal to avoid the taste in future encounters, while a positive hedonic shift results in the animal to seek the taste in future encounters. Thus, taste determines the palatability of plant forages thereby leading to an animal's ability to form a preference for food. Many available plants consumed by horses in natural habitats are known to contain secondary compounds referred to as toxins and all toxins are known to be drugs. Locoweed contains the toxin swainsonine and is known to cause the neurological condition described as locoism in large continuous doses. However, recent studies have shown that swainsonine has medicinal affects in humans and animals. The current study tested four chronically lame horses to examine their ability to form an association of a flavor, either carrots or apples, with a possible post-ingestive physiological consequence induced by a drug. There were two drugs utilized in this study; locoweed that contained swainsonine, and butorphanol tartrate a synthetic opiate analgesic (brand name Torbugesic). The horses were divided into two groups and each group was assigned a respective drug throughout the duration of two separate trials. The first trial associated a flavor with each group's respective drug treatment and the second trial involved the reversal of flavors while holding the drug treatments constant for each group. Each trial involved a conditioning period followed by test days when horses were challenged to make a decision between the treatment associated flavor or the non-treatment associated flavor. The horses were then challenged with the drugs returned to flavored feeds. The results suggest that horses do have the ability to associate a taste with a post-ingestive consequence induced by a drug. This suggestion gives insight into the horse's possible capability of self-medication.
Open Access
Mutualisms relation to swainsonine in Oxytropis from the United States and China
(Colorado State University. Libraries, 2008) Valdez Barillas, José Rodolfo, author; Child, R. Dennis, advisor; Paschke, Mark, advisor
Swainsonine producing Oxytropis can establish mutualisms with dinitrogen fixing bacteria and endophytic fungi. Dinitrogen fixation facilitates the growth of Oxytropis species in low nitrogen soil, while sustaining the fungal-plant symbiosis. Contributions from dinitrogen fixation in Oxytropis sericea development and swainsonine synthesis were studied in a greenhouse experiment. The role of Oxytropis mutualisms in swainsonine production was also tested beyond O. sericea by studying swainsonine producing Oxytropis from China. For the greenhouse study it was hypothesized that fixed dinitrogen is used by the fungal endophyte during the synthesis of swainsonine inside Oxytropis. It was also hypothesized that dinitrogen fixing Oxytropis growing under nitrogen stress conditions can allocate fixed nitrogen toward plant biomass and still sustain swainsonine synthesis by the fungal endophyte. In a second study, it was hypothesized that endophytic fungal and rhizobial mutualisms in Oxytropis from the United States and China are similar. It was also hypothesized that alkaloid similarities in Oxytropis from both continents could be explained by similar fungal endophyte hosted by Oxytropis from the US and Chinese. 15N-enrichment on dinitrogen fixing and non dinitrogen fixing O. sericea was detected in 15N-swainsonine produced by non-dinitrogen fixers. Low 15N-swainsonine was detected in dinitrogen fixers as a result of 14N incorporation. These results suggest the fungal endophyte is a nitrogen sink. Non-dinitrogen fixing O. sericea with no fungal endophyte had greater biomass than non-dinitrogen fixers with fungal endophyte. Non-dinitrogen fixers with fungal endophyte produced similar levels of swainsonine, but no increase in biomass. Dinitrogen fixers with fungal endophyte had greater biomass than non-dinitrogen fixers with fungal endophyte. Older dinitrogen fixers produced more swainsonine than non dinitrogen fixers, increased plant growth and fungal biomass. Results from the second study suggest that dinitrogen fixing Oxytropis from China produced swainsonine in association with a fungal endophyte that is 99% similar to the fungal endophyte in Oxytropis sericea from the United States. These studies suggest that dinitrogen fixation increases the ecological niche of Oxytropis in both continents and sustains the plant-fungal symbiosis, as well as swainsonine production. Fungal symbiosis and dinitrogen fixation are old mutualisms that have been maintained by Oxytropis populations in both continents.
Open Access
The relationships of forest and watershed characteristics to soil water retention, storm runoff, erosion, and wave attenuation in Vietnam
(Colorado State University. Libraries, 2009) Tran, Bao Quang, author; Laituri, Melinda J., advisor
Forests can have a profound impact on the hydrological cycles. Numerous studies in Vietnam, and elsewhere have examined the effects of vegetation cover and geomorphology on hydrological processes at both watershed and regional scales, but the effects of forests in water yield, regulating seasonal water flows, and soil erosion are still in debate. This dissertation focuses on obtaining a deeper understanding about how forests, weather and geomorphology affect hydrological responses and soil erosion in Vietnam. Dissertation is a collection of four independent studies. The first study characterizes soil water retention of four forest types representing different levels of forest degradation. The results suggest that soil water retention, a function of soil moisture, bulk density, and soil depth; varies among forests, and it depends primarily on litter cover, vegetation cover, and porosity. Forest soil moisture can be predicted by a regression model, with the root square mean error of 3%. The second study investigates effects of watershed characteristics on runoff in 15 typical watersheds. The watershed factors, which include watershed size, shape, slope and elevation difference, forest cover and distribution, are analyzed in relation to increasing and decreasing peak flow, and daily streamflow variation, in which forest cover and distribution, shape, and elevation difference are found to be significant impacts on storm runoff. Relationships between peak discharge and initial flow and rainfall are statistically significant in this study. The third study is to define minimum forest areas for protection soils from erosion. A soil loss prediction equation and soil loss tolerance of 10 ton ha-1y-1 are used to generate an erosion risk map and vegetation index for Vietnam. Required forest areas are calculated by comparison erosion risk with vegetation index. Finally, wave attenuation is analyzed in relation to initial wave height, cross-shore distances, and mangrove forest structures. From these relationships, minimum mangrove band width for coastal protection from waves is defined and ranges from 40 m to 240 m depending on mangrove structures.
Open Access
Optimal sampling and modeling strategies for quantifying natural resources over large geographical regions
(Colorado State University. Libraries, 2008) Pongpattananurak, Nantachai, author; Reich, Robin M., advisor
Chapter 1 evaluates a new approach of modeling the spatial distribution of soil attributes over large geographical regions. A combination of three-stage least squares (3SLS) and multivariate regression trees (MRT) was used to model the spatial variability in soil texture. In 2006, 1427 soil samples were collected as part of a state-wide inventory and monitoring program (IMRENAT) implemented in the State of Jalisco, Mexico. A two-way nested stratified design was used to allocate samples throughout the state based on the spectral variability of land cover and climatic conditions. The final set of models described 61% of the observed variability in soil pH, 62% of the variability in sand and 56% for clay. Comparison with other interpolation techniques such as ordinary kriging, suggest that the approach used in this study is far superior in terms of the accuracy and precision. Chapter 2 evaluates three sampling designs (i.e., simple random sampling, systematic sampling and two-way nested stratified design) for modeling the spatial variability in forest tree biomass in the State of Jalisco, Mexico. Monte Carlo simulations were used to implement the three sampling designs using samples of 500 and 1100 30 m x 30 m primary sampling units. Statistically, the two-way-nested stratified design outperformed the simple random and systematic sampling design. There was no significant difference between the simple random and systematic designs. Chapter 3 evaluates the statistical properties of plot size and sample intensities in estimating forest stand characteristics in seasonal dry evergreen forests in Huai Kha Khaeng Wildlife Sanctuary, Thailand. Monte Carlo simulations were used to evaluate plotsizes (5 m x 5 m, 10 m x 10 m, 20 m x 20 m, 25 m x 25 m and 50 m x 50 m) and sample intensities (0.5%, 1%, 2%, 5%, 10%, and 15%) on a 50 ha mapped dataset. All plot sizes and sampling intensities provided unbiased estimates of the population mean and variance for tree basal area and tree density. All plot sizes and sampling intensities were biased with respect to estimating the total number of tree species on the 50 ha plot.
Open Access
Large ungulate effects on nitrogen dynamics in riparian ecosystems of Colorado
(Colorado State University. Libraries, 2008) Przeszlowska, Agnieszka, author; Trlica, M. J., advisor
Large ungulates can affect feedbacks between aboveground and belowground N pools, nutrient mineralization rates, and soil food webs at different temporal and spatial scales. Little is known about the effects of ungulates on nutrient dynamics in riparian zones which are important systems that provide habitat and forage for wildlife and livestock, and act as sediment and nutrient buffers between terrestrial and aquatic ecosystems. Livestock grazing is a predominant land use on public and private lands in the western US while bison are more prevalent in National Parks and Monuments. The main goal of my studies was to investigate if bison and cattle alter N dynamics in riparian ecosystems of the Great Sand Dunes region or Sheep Creek of north-central Colorado. Studies of terrestrial ecosystems have shown accelerating, decelerating, or neutral effects of ungulates on N cycling (N pools or N fluxes). I hypothesized that cattle or bison grazing would accelerate N cycling in riparian zones because they are fertile and productive systems. Bison grazing in Great Sand Dunes riparian corridors and wet meadows did not increase potential net N mineralization while cattle did not affect net N mineralization in wet meadows. Cattle grazing in the Sheep Creek montane riparian zone did not increase aboveground production, aboveground or belowground plant N pools, soil N pools, soil microbial biomass, litter decomposition, net N mineralization or denitrification in the riparian zone as a whole. Cattle also did not affect stream or groundwater NO3- and NH4+ concentrations. Signs of accelerated N cycling were detected only near the stream bank where potential soil net N mineralization was 35% higher in cattle grazed than excluded sites. This could be attributed to more frequent cattle utilization of streambank sites compared with areas further away from the stream. Although there was no strong evidence for accelerated N cycling in riparian zones grazed by bison or cattle, results suggest that increased N cycling is more likely in riparian sites that have a long history of grazing or are grazed frequently at moderate intensity. Season-long, light-to-moderate cattle grazing does not appear detrimental to N cycling and riparian functioning.