Theses and Dissertations

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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
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.
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
Study on the growth of white bamboo (Dendrocalamus membranaceus Munro) under different ecological factors
(Colorado State University. Libraries, 2009) Le, Truong Xuan, author; Binkley, Dan, advisor
White bamboo is one of the most popular and valuable forest products in mountainous areas of Northern Vietnam. Long-term, sustainable management of white bamboo plantations will require improved knowledge about the ecological features of white bamboo in relation to growth. I examined patterns of bamboo growth and light interception in relation to topographic position and management intensity. I also determined how ecological factors relate to white bamboo growth, identifying possible nutrient limitation, and the efficiency of light use as a factor explaining growth patterns. Topographic position had strong effects on white bamboo growth. The differences between white bamboo growth on footslopes and hilltops were in total culm volume, DBH and height, and number of economically valuable culms. Management intensity had significant effects on DBH and height, total culm volume and culm wall volume as well as on dry culm mass. Pure intensive management had greatest white bamboo growth among the three management intensities. Topographic position significantly affected culm DBH, culm height, culm volume, and number of economically valuable culm light use efficiency. Management intensity affected culm DBH, culm height, culm volume, culm wall volume; and on dry culm mass light use efficiencies. Total culm volume correlated well with soil moisture. Culm wall volume had strong correlation with soil pH, and a moderate correlation with pH was also demonstrated by dry culm mass. The number of economically valuable culms correlated moderately with soil pH and cation exchange capacity. A fertilization experiment of 4 fertilizers (nitrogen, potassium, phosphate, and N+P+K) in 12 plots in Cau Hai showed a growth increase in response to N. In general, this study supported the hypothesis that topographic position and management intensity strongly influence white bamboo growth. There was a difference in white bamboo growth across four fertilizer experiments but the difference was only significant for nitrogen.
Open Access
Canada thistle (Cirsium arvense [L.] Scop.) response to mowing, herbicide, competitive grasses, and soil amendments on wetland, upland, and mesic sites
(Colorado State University. Libraries, 2009) Knudson, Julie A., author; Redente, Edward F., advisor; Meiman, Paul J., advisor
Canada thistle (Cirsium arvense [L.] Scop.) is one of the most problematic weeds of temperate regions and is found throughout North America, Europe, Africa, and across central Asia. Canada thistle's ability to spread quickly and recover from many control methods makes managing Canada thistle a significant challenge for land managers. Herbicide application can be effective, but mixed results, toxicity concerns, and the need for re-application demand new, more efficient strategies that reduce herbicide use. A greenhouse study tested effectiveness of clipping and grass seeding for Canada thistle control. Grasses used included two natives (western wheatgrass [Pascopyrum smithii {Rydb.} A. Löve], streambank wheatgrass [Elymus lanceolatus {Scribn. & J.G. Sm.} Gould ssp. lanceolatus]) and one sterile hybrid (common wheat [Triticum aestivum L.] x tall wheatgrass [Thinopyrum ponticum {Podp.} Z.W. Liu & R.C. Wang]) called Regreen™. Grasses were seeded alone or in combination (Regreen+western wheatgrass) in pots with Canada thistle. Field Study I tested combinations of mowing, herbicide, and grass seeding across two habitats (wetland, upland) and three different local climatic regimes for control of Canada thistle. Grass treatments involved seeding western wheatgrass (upland sites) or prairie cordgrass (Spartina pectinata Bosc ex Link) (wetland sites) alone or in combination with Regreen (upland and wetland sites). Six sites (three wetland, three upland) were paired geographically across Colorado with each wetland site in close proximity to an upland site. Field Study II tested combinations of mowing, herbicide, soil amendment addition (organic matter, manganese), and grass seeding (western wheatgrass, intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey] on a Colorado mesic site. In greenhouse trials, clipping inhibited Canada thistle growth, while grass seeding did not. In Field Study I, herbicide application produced effective control. In Field Study II, tilling enhanced herbicide effectiveness. Organic matter or manganese alone did not reduce Canada thistle growth. Manganese addition reduced herbicide effectiveness. In both field studies, neither mowing nor grass seeding enhanced herbicide effectiveness, and tilling did not increase Canada thistle biomass. Future research should address restoration of infested wetland sites, the importance of irrigation during drought for restoration, and the mechanism through which manganese sulfate inhibits herbicide effectiveness.
Open Access
A triadic relationship on the northern Great Plains: bison (Bison bison), native plants, and native people
(Colorado State University. Libraries, 2007) Garrett, James J., author; Woodmansee, Robert G., advisor
The dissertation investigates and documents the historic relationship that exists among Bison bison, native plants, and Native People. An exhaustive in-depth review of each ecological component is given. Lakota Indian participants were interviewed for their qualitative knowledge of the three ecological components being studied. Interviewees were selected for their individual expertise in ethnobotany. Lokota culture, and/or indigenous ecological knowledge. Participant contributions are synthesized into a running narrative that describes the relationship in intimate detail. Detailed analysis shows that there are many facets to the relationship that exists among the three major ecological components. Recommendations are made for further research and the appendices include Lokota terminology, interview protocol and questions, data codes, and maps of Lakota territory before and after colonization.
Open Access
Mapping Tamarix: new techniques for field measurements, spatial modeling and remote sensing
(Colorado State University. Libraries, 2009) Evangelista, Paul H., author; Romme, William, advisor; Stohlgren, Thomas, advisor
Native riparian ecosystems throughout the southwestern United States are being altered by the rapid invasion of Tamarix species, commonly known as tamarisk. The effects that tamarisk has on ecosystem processes have been poorly quantified largely due to inadequate survey methods. I tested new approaches for field measurements, spatial models and remote sensing to improve our ability measure and to map tamarisk occurrence, and provide new methods that will assist in management and control efforts. Examining allometric relationships between basal cover and height measurements collected in the field, I was able to produce several models to accurately estimate aboveground biomass. The best two models were explained 97% of the variance (R 2 = 0.97). Next, I tested five commonly used predictive spatial models to identify which methods performed best for tamarisk using different types of data collected in the field. Most spatial models performed well for tamarisk, with logistic regression performing best with an Area Under the receiver-operating characteristic Curve (AUC) of 0.89 and overall accuracy of 85%. The results of this study also suggested that models may not perform equally with different invasive species, and that results may be influenced by species traits and their interaction with environmental factors. Lastly, I tested several approaches to improve the ability to remotely sense tamarisk occurrence. Using Landsat7 ETM+ satellite scenes and derived vegetation indices for six different months of the growing season, I examined their ability to detect tamarisk individually (single-scene analyses) and collectively (time-series). My results showed that time-series analyses were best suited to distinguish tamarisk from other vegetation and landscape features (AUC = 0.96, overall accuracy = 90%). June, August and September were the best months to detect unique phenological attributes that are likely related to the species' extended growing season and green-up during peak growing months. These studies demonstrate that new techniques can further our understanding of tamarisk's impacts on ecosystem processes, predict potential distribution and new invasions, and improve our ability to detect occurrence using remote sensing techniques. Collectively, the results of my studies may increase our ability to map tamarisk distributions and better quantify its impacts over multiple spatial and temporal scales.
Open Access
Maintaining fuel treatments with prescribed fire in ponderosa pine forests of the Black Hills, South Dakota
(Colorado State University. Libraries, 2007) Battaglia, Michael A., author; Smith, Frederick W., advisor; Shepperd, Wayne D., advisor
Recent wildfires in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests have increased efforts to create forest structures that reduce the risk of crown fire. In the Black Hills, these fuel-reduction treatments often result in a new cohort of ponderosa pine regeneration. If no action is taken, the efficacy of these fuel treatments eventually diminishes as the regeneration grows and creates a ladder fuel complex. In this dissertation, I examine the utility of using prescribed fire to control this regeneration. I also explore if restoration of historical forest structure would result in reduced crown fire risk.
Open Access
Exploring interactions among biological soil crusts, plant germination, and morphological seed traits: implications for plant community assembly and dryland restoration
(Colorado State University. Libraries, 2023) Bacovcin, John, author; Havrilla, Caroline, advisor; Ocheltree, Troy, committee member; Wrighton, Kelly, committee member; Paschke, Mark, committee member
Arid and semi-arid (dryland) ecosystems make up over 40% of our plant's terrestrial surface and are incredibly vulnerable to land degradation. To combat dryland degradation, active plant and soil restoration is often needed and the role of plant-soil microbe interactions can be key to dryland restoration trajectories. Within drylands, biological soil crusts (biocrusts), collections of cyanobacteria, algae, lichen, and moss are key surface communities that influence soil processes (e.g., stability, nutrient cycling, hydrology) and can thereby strongly influence recruitment of dryland plants. These biocrusts may interact with plant functional traits (i.e., seed morphological traits), and these interactions can influence germination. However, much is still unknown about mechanisms that underlie these interactions and how plant functional traits mediate effects of biocrusts on plant germination. To investigate these knowledge gaps, I conducted two studies: (Chapter 1) a global meta-analysis of the role of morphological seed traits in determining biocrust effects on germination, and (Chapter 2) a full-factorial greenhouse study examining the effects of biocrust inoculum cover treatments and plant functional traits on plant recruitment to investigate questions about how biocrust heterogeneity and biotic components of biocrusts in the context of restoration. To explore effects of morphological seed traits on plant germination responses to biocrusts (Ch. 1), we compiled a global database of 491 studies of biocrust effects on plant germination encompassing 101 unique plant species and their associated morphological seed traits. For the greenhouse study (Ch. 2) we seeded two seed mixes on three different inoculum cover treatments (i.e., 0%, 30%, and 100%) using both biologically active (live) and autoclaved biocrust inoculum, to assess effects of cover heterogeneity, biological biocrust activity, and plant functional traits on percent germination. Results from the meta-analysis showed that morphological seed traits do mediate plant germination responses to biocrusts, and that, in general, germination of smaller seeded species with appendages was increased by biocrusts. Results from the greenhouse study showed that, in a restoration context, increasing cover of biocrust inoculum increases plant germination, and that these effects were explained by physical rather than biotic effects of inoculum on germination. As in Chapter 1, we found that biocrusts effect on germination differed across plant functional groups and that seed traits also influenced germination responses to biocrust inoculum cover treatments. Together, both studies showed that morphological seed traits mediate effects of biocrusts on plant germination. These findings increase understanding of the role of biocrusts in determining dryland plant community assembly and have implications for dryland restoration.
Open Access
The impact of wildfire on avian communities: exploring habitat associations two decades after fire
(Colorado State University. Libraries, 2023) Vicini, Maria, author; Stevens-Rumann, Camille, advisor; Vogeler, Jody, committee member; Fornwalt, Paula, committee member
Large high-severity wildfires have been affecting ponderosa pine dominated systems for decades, yet minimal long-term research has been conducted to address how avian species are responding to vegetation recovery and wildfire-driven conversion multiple decades after wildfire in ponderosa pine ecosystems of the southwestern United States. Understanding how community dynamics differ between low- and high-severity portions of burned footprints, and how vegetation structure relates to species presence is crucial for species conservation efforts, especially as wildfires in the western U.S. continue to have larger proportions of high-severity fire compared to historical fires. To address this in the Southwest, our study sought to quantify vegetation recovery, avian community dynamics across low- and high-severity sites, and quantify species-specific relationships with current vegetation structure in two post-fire footprints two decades after fire. This study focused on the Ponil Complex Fire in northern New Mexico and the Hayman Fire in southern Colorado, both of which burned in 2002. We found continued divergence between vegetation recovery at low- and high-severity sites, though this divergence was more pronounced at the Hayman Fire. We found also significant dissimilarities in avian community composition between low- and high-severity sites, and significantly lower species richness at high-severity sites across both wildfires. Forest-associated bird species presence was associated with more canopy cover and lower severity. Alternatively, lower canopy cover and higher severity were associated with the presence of a variety of grassland-, shrubland-, and desert-associated species. Our findings point to the importance of preserving pyrodiversity on the landscape to maximize suitable habitat for the greatest number of species, especially as it pertains to preserving adequate proportions of low-severity patches for forest-associated species who require intact canopy cover. However, large high-severity patches as the dominant component of the landscape will not support the most diverse array of bird communities 20+ years post fire.