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  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen 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.
  • ItemOpen Access
    Characterizing 30-years of conifer regeneration patterns in high-severity wildfires: a snow-cover remote sensing approach
    (Colorado State University. Libraries, 2023) Menick, Casey, author; Hoffman, Chad M., advisor; Tinkham, Wade T., advisor; Vanderhoof, Melanie K., committee member; Vogeler, Jody C., committee member
    The number of large, high-severity wildfires has been increasing across the Western United States. It is not fully understood how wildfire intensification may impact conifer forests of the West, whose resilience is dependent on successful seedling regeneration. It is important to understand how conifer-dominated forests are able to recolonize high-severity burn patches and subsequently respond to shifting disturbance regimes. The goal of our research is to characterize patterns of conifer recolonization within high-severity burn patches over a 30-year study period. We investigate 34 high-severity wildfire complexes that occurred between 1988 and 1991 in conifer-dominated ecosystems of the northern Rocky Mountains. Composite snow-cover Landsat imagery was utilized to isolate conifer-specific vegetation by diminishing spectral contributions from soil and deciduous vegetation. Conifer regeneration was determined to be detectable by Landsat 11-19 years post-fire across forest types and at >10% canopy cover using snow-cover imagery. The trajectory of snow-cover Landsat NDVI was utilized to project future recovery time to pre-fire conifer vegetation levels for lodgepole pine (29.5 years), Douglas-fir (36.9 years), and fir-spruce forests (48.7 years). The presence of conifer regeneration was then modeled at 3-year intervals post-fire to characterize the progression of recolonization. Conifer recolonization analysis showed that 65% of the total high-severity burn area was reforested after 30 years. Across all high-severity patches, median patch recolonization was 100% within lodgepole pine, 91.1% within Douglas-fir, and 41.3% within fir-spruce. Patch fragmentation occurred across all size classes and forest types, with the majority of the remaining unforested area in Douglas fir (76%), lodgepole pine (61%), and fir-spruce (50%) transitioning to smaller unforested patch size classes. While we identified overall patterns of conifer resilience, high-severity burn patches with lower likelihoods of 30-year conifer recovery had lower edge-densities, drier climates, steeper slopes, higher elevations, and fir-spruce forests. These findings have implications for climate change resilience and may be applied to support forest restoration decision-making following high-severity wildfire. Future analyses should be conducted using snow-cover remote sensing imagery to identify patterns of post-disturbance conifer recovery over a wider spatial and temporal extent.
  • ItemOpen Access
    Fire, fungi, flora, and flow: post-fire fungal community assemblages, vegetation establishment, and soil hydrophobicity in forests of the southern Rocky Mountains
    (Colorado State University. Libraries, 2023) McNorvell, Michael A., author; Stevens-Rumann, Camille, advisor; Rhoades, Charles, committee member; Remke, Michael, committee member; Wilkins, Michael, committee member
    Wildfire is an important ecological driver of ecosystem dynamics in the southern Rocky Mountains at multiple landscape scales, guiding establishment of forest biota both aboveground and below. Size, frequency, and severity of wildfires in coniferous forests across the western United States is increasing at an unprecedented rate. Despite wildfire's significant but disparate influences on forest soils, post-fire research has often focused on aboveground vegetation in isolation from study of belowground soil characteristics and the fire ecology of soil biota. Fungi are vital to forest ecosystems for their functional roles, however, the effects of wildfire on forest-specific fungal communities and how those communities subsequently influence post-fire vegetation communities and soil environments has not been extensively researched in the region over the past several decades. This is a prominent knowledge gap, especially as fungi are highly variable across functional groups, space, and time even in unburned systems. Thus, to build on our understanding of contemporary fire ecology in forested ecosystems of the Southern Rockies, we investigate three wildfires that burned in the state of Colorado during the 2020 fire season and address three research objectives: 1) Examine the influence of forest type and fire severity on post-fire fungal community composition across soil depth and temporal gradients; 2) Determine the effects of post-fire fungal community diversity on forest understory plant diversity and abundance; and 3) Explore relationships between fungal assemblages and observed soil hydrophobicity in burned forested environments. We found that though fire severity and soil depth were the primary influences on quantified fungal diversity, the composition of fungal community assemblages was most heavily influenced by forest type: forests developed fungal communities compositionally unique to one another just two years after fire. Diversity of fungi showed significant influence on aboveground plant diversity and abundance, especially mutualistic fungi (ecto- and arbuscular mycorrhizae) and their respective plant hosts. Finally, significant relationships between fungal diversity and soil hydrophobicity were observed mediated by forest type, fire severity, soil depth, and year post-fire, though these patterns were difficult to surmise and the influence of other important variables may be at play. By more fully understanding how soil fungi interact with aboveground vegetation establishment and belowground soil conditions after wildfire, this research may help inform managers of pathways to better achieve desired post-fire outcomes by leveraging fungal relationships in soil remediation, site preparation, and conservation of post-fire forest ecosystems.
  • ItemOpen Access
    A comparative analysis of wetland and riparian vegetation on Bureau of Land Management land in the western US
    (Colorado State University. Libraries, 2023) Binck, Elin, author; Sueltenfuss, Jeremy, advisor; Reynolds, Lindsay, committee member; Smith, Melinda, committee member; Havrilla, Caroline, committee member
    In 2011, the BLM deployed its first of three Assessment, Inventory, and Monitoring (AIM) programs as a large-scale, standardized ecological monitoring effort across the agency's land. The first two programs, known as Terrestrial AIM and Lotic AIM, were designed to sample all terrestrial and river ecosystems throughout the landscape. In 2019, the agency piloted its third AIM program, specifically targeting riparian areas and wetlands. This study addressed two main questions: 1) How do wetland and riparian areas sampled with the Terrestrial AIM program compare to those sampled with the Riparian and Wetland (R&W) AIM program, and 2) What are the drivers of plant community composition of the wetlands and riparian areas sampled on BLM land? I developed a set of criteria to identify sites sampled with Terrestrial AIM that had characteristics of wetlands or riparian areas. I then compared vegetation cover, floristic quality metrics, and species composition using nonmetric multidimensional scaling (NMDS) to those sites sampled with R&W AIM. R&W AIM sites had much greater foliar cover, hydrophytic species cover, and perennial cover, but Terrestrial sites had slightly higher floristic metric values. I similarly analyzed the R&W sites on their own, incorporating wetland-specific data that is collected with the new program. I found that sites that met the criteria to be classified as wetlands in the Terrestrial data were a distinct population from the sites sampled with R&W AIM. The main drivers of plant community composition among sites sampled with R&W AIM were elevation and the distribution of surface water, but impacts of grazing were also apparent. All sites assessed by both AIM programs had floristic quality metrics characteristic of highly impacted wetland systems. This study indicates the value of the new R&W AIM program for its ability to perform wetland-specific ecological monitoring, provide valuable data on the health of wetlands, and provide baseline condition that can help guide land management practices into the future.
  • ItemOpen Access
    Assessing post-fire tree regeneration and forest conversion across an elevational gradient in southern Colorado
    (Colorado State University. Libraries, 2023) Hastings, Amanda K., author; Stevens-Rumann, Camille, advisor; Fornwalt, Paula, committee member; Rocca, Monique, committee member
    Increased wildfire activity, with anticipated novel climate scenarios, raises concerns about forest resilience—particularly in semi-arid regions of the western US. Specifically in southwestern US and Southern Rocky Mountain forests, lack of conifer seed sources and shifts in temperature or precipitation post-wildfire may limit the recruitment of dominant conifer species. Meanwhile, hotter and drier conditions may promote the proliferation of resprouting angiosperm species, resulting in vegetative type conversions. To better understand forest susceptibility to type conversion following wildfire, I assessed early vegetation assembly 3 years post-fire, in sites that burned at low and high severity and spanned a climatic gradient in the Sangre de Cristo range of southern Colorado. Research sites were located in lower montane, upper montane, and subalpine forests, with relative dominances of Pinus ponderosa- Pseudotsuga menziesii; Abies concolor- Pinus contorta- Populus tremuloides; and Abies lasiocarpa- Picea engelmannii- Pinus flexilis- Pinus aristata; respectively. I quantified post-fire tree seedling densities and other site-specific attributes to evaluate a) how do burn severity and forest type influence early post-fire tree regeneration, b) are these forest types undergoing conversions? and c) if so, what factors are driving type-conversion?In this early assessment, I found concerns of forest conversion may be warranted for lower montane forests, with greater abundances of deciduous tree-shrub species, Quercus gambelii and Robinia neomexicana, and high shrub cover. Meanwhile, upper montane forests are likely regenerating to a similar forest composition, with early Populus tremuloides dominance and Pinus contorta regeneration. For both lower and upper montane forest types, conifer regeneration was positively correlated with legacies of low-moderate severity fire, such as overstory cover and litter/woody debris. Meanwhile, subalpine tree regeneration was driven by site-climate and topographic position, regardless of fire severity. In subalpine forests, this study suggests early post-fire conifer regeneration may be dominated by xeric and drought-tolerant species, Pinus flexilis, Pinus aristata, and Pinus contorta, where decades may pass before the establishment of shade-tolerant species characteristic of this forest type. Across all forest types, greater time is required in the post-fire period to predict ultimate recovery trajectories. However, this study serves as one of the first within southern Colorado to evaluate post-fire regeneration across a full elevational gradient and multiple forest types within a single fire footprint.
  • ItemOpen Access
    Forest type and burn severity affect understory response to historic wildfires
    (Colorado State University. Libraries, 2023) Weimer, Kate, author; Stevens-Rumann, Camille, advisor; Rocca, Monique, committee member; Ocheltree, Troy, committee member
    The fire season of 2020 was unprecedented in the Western US. In one summer, three different fires individually broke the record of Colorado's largest wildfire. Understanding the recovery following these unprecedented events can lend insight into the compounding effects of wildfire and climate change. Reorganization of the understory community after disturbance can indicate changes in conditions not yet reflected in tree communities. Understory dynamics also affect watershed characteristics and wildlife, so knowledge about the influence of wildfire on understory plants is crucial. The purpose of this study is to determine if a trend toward thermophilization is being shown in understory vegetation following 4 different wildfires in 2020 and to compare the relative importance of burn severity, forest type, and other environmental factors on understory community composition. We found a trajectory toward thermophilization in high elevation forests that burned with high severity. We also that drivers of community composition varied by forest type. These findings help assess how wildfire is affecting plant communities in the 21st Century and highlight where future management concerns may be.
  • ItemOpen Access
    Understanding soil treatment effectiveness in dryland restoration: ecological barriers, contexts, and baseline conditions
    (Colorado State University. Libraries, 2023) Kimmell, Louisa, author; Havrilla, Caroline, advisor; Cotrufo, M. Francesca, committee member; Sueltenfuss, Jeremy, committee member
    Land degradation is one of the greatest environmental issues our planet faces today, with over 33% of Earth's soils currently degraded. Drylands are especially vulnerable to soil degradation given their history of intensive land use and desertification. However, dryland restoration can be very difficult, and often fails when seeding is used as a sole treatment. Soil-based restoration, which includes abiotic treatments like organic amendments and water collection pits, and biotic treatments like microbial inoculation, may be needed for ecosystem recovery in drylands. Compared to plant-based restoration, however, less is known about how and when to use active soil restoration for optimal results. To improve our understanding of how to best use active soil restoration to restore degraded drylands, we conducted two research studies: (1) a global meta-analysis of dryland soil restoration treatment effectiveness across environmental gradients (Chapter 1), and (2) a regional field study comparing microbial communities across degraded, intact, and revegetated dryland sites to understand baseline conditions and when active soil restoration (e.g., inoculation) may be needed to improve soil conditions (Chapter 2). For project 1, we generated a global database from 155 publications and 1,403 unique studies of responses of soil health variables [i.e., aggregate stability, bulk density, soil moisture, soil organic carbon, soil nitrogen, mycorrhizal colonization, and basal respiration] to soil restoration relative to untreated controls. We then used quantitative meta-analysis techniques to analyze soil restoration effect sizes. In Chapter 2, we collected soil samples from paired reference, degraded, and revegetated plots across seven different dryland sites across the southwestern United States, sequenced the 16S and ITS rRNA gene regions from extracted DNA for bacteria/archaeal and fungal communities (respectively), and analyzed differences in microbial community composition among samples. Results from the meta-analysis suggested that active soil restoration generally improves soil health and is most effective in arid, fine-textured soils. Organic amendments were most effective at increasing soil organic carbon, while fungi inoculation treatments were most effective at increasing mycorrhizal colonization. From the regional microbiome study, we found that soil microbial communities differ between paired degraded and intact sites, and that degraded sites have lower abundances of biocrust-forming bacteria and dark septate endophytic fungi, which are both indicative of reference/intact conditions, making these taxa potential targets for inoculation treatments. However, we found that microbial communities do not differ between degraded and revegetated sites, suggesting that degraded sites may require active interventions beyond revegetation, such as direct microbial inoculation, to replenish microbial communities. These findings advance understanding of the effects of dryland degradation and restoration on soil health and have actionable implications for improving restoration decision-making, and thus improve outcomes in dryland restoration.
  • ItemOpen Access
    Interaction between light, nitrogen and mycorrhizal fungi on photosynthesis of ectomycorrhizal pine
    (Colorado State University. Libraries, 1983) Ekwebelam, Sebastian A., author; Reid, C. P. P., advisor; Doxtader, Kenneth G., committee member; Wallner, Stephen J., committee member; Hunt, H. William, committee member
    The importance of mycorrhizae to the physiological functions of plants is relatively well documented. Despite the obvious benefits of mycorrhizae for the enhancement of seedling growth, study of the relationship between applied cultural practices, such as shading, fertilization and mycorrhizae formation, and growth and photosynthesis of containerized nursery stock has been limited. The long-term objective of the present study, therefore, was to gain a more complete understanding of how the aggregate factors of light, nitrogen fertilization and mycorrhizae formation influence growth and photosynthesis of containerized seedlings, aimed at optimizing seedling production in a nursery environment. Seedlings of lodgepole pine (Pinus contorta Dougl.) were grown for 16 weeks without ectomycorrhizae in the greenhouse at 3 level s of irradiance (high, medium and low) by use of shadecloth, and ammonium nitrate (3, 62 and 248 ppm N) . Measurements at 5, 10 and 16 weeks of age indicated that biomass increased significantly with increasing levels of irradiance and nitrogen over the ranges studied. Although root/shoot ratios increased from low to high irradiance at each harvest, nitrogen application resulted in increased ratios from 3 to 62 ppm N, but decreased ratios at 248 ppm N. Nitrogen and phosphorus concentration generally decreased with increase in irradiance, but total N content and photosynthesis per unit leaf area generally increased from low to high levels of both irradiance and nitrogen. In a mycorrhizal fungi inoculation study, lodgepole pine seedlings were grown for 10 weeks without ectomycorrhizae at the aforementioned 3 levels of irradiance and nitrogen. At 10 weeks, mycorrhizal treatments, inoculation with either Pisolithus tinctorius or Suillus granulatus, were superimposed on the light and nitrogen treatments, and the seedlings were grown for an additional 6 weeks. Mycorrhizae formation increased with increase in irradiance, while fertilization with 62 ppm N resulted in greater mycorrhizae formation than either 3 or 248 ppm N. Further, inoculated plants had significantly greater biomass and nutrient contents than nonmycorrhizal seedlings. Inoculation with P. tinctorius and granulatus resulted in photosynthetic rates, 1.87 and 1.85 mg CO2dm-2h-1, respectively, significantly greater than nonmycorrhizal plants (1.41 mg CO2dm-2h-1). Although the increase in growth of the mycorrhizal seedlings was associated with increased photosynthesis, the magnitude of this response depended on specific combinations of irradiance and nitrogen fertilization. These results emphasize the importance of the interactions among irradiance, nitro gen fertilization, and mycorrhizae development in the growth of containerized seedlings.
  • ItemOpen Access
    How do ecological restoration treatments affect understory plant communities in dry conifer forests of the Colorado Front Range?
    (Colorado State University. Libraries, 2022) Demarest, Arièl, author; Redmond, Miranda, advisor; Fornwalt, Paula, advisor; Rocca, Monique, committee member
    Ecological restoration efforts are progressing in dry conifer forests across the western United States to increase resilience to fire and other disturbances. While such treatments primarily aim to create overstory change, impacts beyond the canopy should also be considered – such as effects on understory plants. Several studies have investigated outcomes of ecological restoration thinning treatments for understory plants, but few of these have examined effects across a landscape and at a time interval long enough for plants to potentially adjust to the disturbance. Additionally, none have investigated how specific aspects of treatment and local climate might interact to modify understory responses. In this study, we investigated the effects of ecological restoration thinning treatments on understory plant communities in dry conifer forests of the Colorado Front Range using a Before/After/Control/Impact study design. We collected data at 1-2 years pre-treatment, 1-2 years post-treatment, and 4-6 years post-treatment in 156 plots distributed across 8 sites, encompassing 15 treatment units and 15 nearby untreated areas. We found 1.6 times higher native understory plant cover and 1.1 times higher richness in treated compared untreated plots at 4-6 years after treatment. Heightened cover and richness values in treated plots were not driven by a single native plant functional group, but by a large portion of the community. Short- and long-lived, forb and graminoid, and vegetatively spreading and non-vegetatively spreading native plants all grew in cover. Both lifespans, forb, and non-vegetatively spreading native plants had heightened richness. Introduced plants showed 2.3 times higher cover and 3.9 times higher richness in treated plots compared to untreated, but were still present at very low levels. Greater native plant cover and richness were associated with lower basal areas that more closely resemble historical norms for the landscape. Thirty year average climatic water deficit (CWD) was not as strong of a predictor of native cover or richness as was a short-term relative measure, final spring CWD z-score, which describes how different the spring climatic conditions of the sampling year were from average conditions. Overall, the broad longer-term benefits to the native understory plant community that were found for numerous sites across the Colorado Front Range suggest that these results may generalizable to elsewhere on this and similar landscapes.