Browsing by Author "Brown, Cynthia, committee member"

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Open Access
Addressing constraints to restoration of highly disturbed ecosystems affected by cheatgrass invasion and slash pile burning
(Colorado State University. Libraries, 2021) Lawrence, Ryan L., author; Paschke, Mark, advisor; Brown, Cynthia, committee member; Meiman, Paul, committee member
To view the abstract, please see the full text of the document.
Open Access
Approaches for creating sustainable biomass production in a reclaimed fen in the Alberta Oil Sands Region, Canada
(Colorado State University. Libraries, 2019) Messner, Lewis Erwin, author; Cooper, David J., advisor; Paschke, Mark, committee member; Brown, Cynthia, committee member
Oil sands surface mining in the boreal region of Alberta, Canada alters the natural hydrologic processes, vegetation, and geochemistry of affected ecosystems. Peat accumulating bogs and fens cover approximately 30% of the oil sands region and function as long-term carbon sinks. The government of Alberta has legislated that disturbed areas be reclaimed to "equivalent land capacity." However, no guidelines exist for reclaiming peatlands in post-mined landscapes. A pilot fen was constructed on Suncor's Millennium oil sands mine in 2013 and I analyzed the effects on annual biomass growth by introducing plants as seeds, seedlings, and rhizome fragments from locally harvested material. Total above-ground biomass (AGB) in year five was 460 ± 30.7 g m-2 (n 56) and was comparable to natural fens in the region. Total living below-ground biomass (BGB) averaged 1640 ± 99.9 g m-2 (n 56) by year five, falling slightly below ranges for regional fens. When averaged across all treatments, C. aquatilis produced the greatest AGB (404 ± 32.8 g m-2, n 56) in year five and represented over 70% (se 1.520) of the site total biomass. AGB of C. aquatilis and J. balticus and total AGB and BGB were positively correlated with water table depth. Total BGB was positively correlated with electrical conductivity. Typha latifolia AGB was significantly affected by removal treatments when averaged across sampling years. Plant derived carbon inputs to reclaimed peatlands and long-term storage are characterized in part by the effects of abiotic variables on vascular plant biomass. Results from this study provide guidance for evaluating reclaimed post-mined fens in Alberta, Canada.
Embargo
Buffering the effects of a changing climate: Salsola tragus as a potential source of stress tolerance genes
(Colorado State University. Libraries, 2024) Lemas, John M., author; Gaines, Todd, advisor; Brown, Cynthia, committee member; Henriksen, James, committee member
The tumbleweed Salsola tragus is an allotetraploid C4 weedy member of the Salsola polyploid complex. Commonly referred to as Russian thistle, it develops a thorny habit during inflorescence, and commonly separates at an abscission layer near the soil to form a tumbleweed. This species is economically important to all land use types and is especially impactful in the Northwestern United States where it affects spring cereal production. The International Weeds Genomics Consortium recently completed a fully annotated reference genome assembly for each of the sub genomes in the somatic cells of this allotetraploid. Polyploids, in general, are overrepresented in the most troublesome weeds globally, and Salsola tragus is no exception. Recurrent formation of polyploids, increased activity of transposable elements, and increased mutation rates that follow genome duplication may lead to the de novo formation and selection of novel highly adapted alleles over time. We utilized the reference genome assembly for this species to align a stress-response transcriptome to investigate how this species responded to two selected abiotic stressors. Many expected response pathways are represented, including response to stress phytohormones, sodium-proton antiporters, calcium exchangers, and cold-responsive binding factors. In addition, several uncharacterized proteins were differentially overexpressed in the shoot and root tissues of this species. Identified genes from this species may present novel alleles for osmotic and temperature stress tolerance. Uncharacterized genes may represent novel stress response genes and can be used to improve the provided reference annotation for this species. These genes of interest may provide the scientific community with additional genomic resources to bolster crop production in this era of climate change.
Open Access
Development of a sagebrush steppe plant community 33 years after surface disturbance
(Colorado State University. Libraries, 2011) Bowles, Brock, author; Paschke, Mark, advisor; Brown, Cynthia, committee member; Meiman, Paul J., committee member
The sagebrush steppe ecosystem is the most endangered ecosystem in North America due to sagebrush eradication, weed invasions and energy development. Restoration of sagebrush steppe plant communities damaged by these disturbances is extremely important to the survival of endangered or threatened sagebrush dependant species such as the sage-grouse and Columbia Basin pygmy rabbit. In the fall of 1976 a field experiment was initiated in the Piceance Basin of northwestern Colorado to study the effects of six seed mixes and three fertilizer treatments on the restoration of a sagebrush steppe plant community after surface disturbances associated with oil shale development. We revisited these study plots during 2008 and 2009 to determine the long-term effects of these treatments on plant community development. Results from this 33-year study indicate that seed mix has long-term effects on the plant community production and composition. The composition of the plant community in all seeded plots was very similar to that of the seed mix used in 1976. The late-seral dominant shrub species in this system, sagebrush (Artemisia tridentata), which was not seeded in any of the treatments, did not recover as the dominant shrub species. An initial fertilizer treatment had short-term effects on the plant community but its effects have become insignificant over time. A seed mix containing native species with no fertilizer addition appears to be the best long-term treatment for restoring a native sagebrush steppe plant community in this study.
Open Access
Disentangling drivers of colonization success in laboratory and natural systems
(Colorado State University. Libraries, 2017) Vahsen, Megan, author; Hufbauer, Ruth, advisor; Brown, Cynthia, committee member; Hobbs, N. Thompson, committee member
Understanding why colonizing populations successfully establish is important for predicting dynamics of invasive species. Propagule pressure, or the number of individuals in a founding group, is considered the most consistent predictor of establishment success, however, there remains considerable variance around predictions that demography alone cannot explain. The identity of individuals within a founding group (e.g. level of pre-adaptation to the recipient environment, diversity) as well as how individuals are introduced (e.g. frequency and timing of discrete introduction events) can influence establishment. The relative importance of these factors is unclear, and could vary across species and environmental contexts. To address these inconsistencies, we conducted two experiments: one with Tribolium castaneum (red flour beetle) populations maintained in controlled laboratory conditions, and one with Bromus tectorum (cheatgrass) founding populations introduced to a natural environment. For the Tribolium experiment, we varied the level of prior adaptation, diversity, and introduction frequency and timing for groups of eggs colonizing in a novel environment across three levels of propagule pressure (n = 15, 30, 60). Founding groups that were larger and more adapted to the novel environment survived the founding event better than smaller and less adapted groups. Further, we found that a high frequency of smaller introductions reduced initial survival. After a generation of mating, establishment success was driven predominantly by adaptation to the novel environment and diversity of founders. In the second experiment, we introduced groups of B. tectorum seeds at a constant propagule pressure (n = 32) to a common garden in Colorado, varying in source diversity (1, 2, 4, 8, or 16 source populations) and source region (Colorado = pre-adapted or Nevada = unadapted). We evaluated establishment success by deriving the number of seeds produced by each founding group after one generation of growth and reproduction using a hierarchical Bayesian model. We found that increasing source diversity increased the number of seeds produced per founding group, but source region did not influence establishment success. Results from these experiments particularly speak to the context-dependency of the importance of pre-adaptation and diversity in predicting establishment success. This suggests that propagule pressure alone is not enough to explain why founding populations establish.
Open Access
Ecological consequences of increased nitrogen deposition in three northern Great Plains grasslands
(Colorado State University. Libraries, 2012) Smith, Anine, author; Knapp, Alan, advisor; Symstad, Amy, advisor; Brown, Cynthia, committee member; Kelly, Eugene, committee member
Increased nitrogen deposition is an important driver of plant species composition change in terrestrial ecosystems globally. Plant composition change from increased nitrogen inputs can result in substantial species richness declines especially where atmospheric inputs already exceed critical loads. Shifts in community structure can occur through changes in basic ecosystem conditions (such as soil properties) or through alterations in competitive interactions potentially disrupting feedbacks that maintain an ecosystem at a given fertility level. Although there has been a substantial amount of research on the effects of increased N on communities and ecosystems, most studies add large and, relative to natural inputs, unrealistic amounts of N. Thus, responses are often immediate and drastic. This "two-point" approach, comparing control to high-N plots, provides little information about the levels of N inputs at which responses first occur, which is more important for managing and mitigating the effects of increased N deposition in a proactive rather than reactive manner. The overarching goal of this study was to identify response thresholds to N addition in Northern Great Plains grasslands that differed markedly in productivity and soil fertility. Over two years we assessed responses to increased N inputs (from 2.5 to 100 kg N/ha) in soils, leaf tissue, plant community composition, and aboveground net primary production (ANPP) in three northern mixed prairie grasslands that varied 3-fold in ANPP. The results of the study will enable us to better forecast both ecosystem and community responses to increased fertilization in this understudied region. After two years of fertilization (with and without water addition) at levels ranging from 0 to 100 kg N/ha, we found significant effects from increased N inputs on ANPP when nitrogen levels exceeded 68 kg N/ha/year and effects on leaf tissue nitrogen, soil nitrogen content and N mineralization rates, particularly when levels exceeded 45 kg/ha/year. Alterations in soil and leaf nitrogen content and ANPP tended to have linear responses and remained consistent across sites. Significant responses occurred even in low ANPP sites (Badlands NP) which experienced a higher relative response. No significant and consistent effects were found on total species richness, and community metrics such as evenness and diversity indices, plant cover by functional group or canopy cover. Our results suggest that though high fertility and production sites may have a greater absolute biomass response, low fertility and production environments can be quite responsive to nitrogen addition as well. Community change may occur more slowly with these northern grasslands which show little response to two years of increased N inputs.
Open Access
Interactions between Bromus tectorum L. (cheatgrass) and native ruderal species in ecological restoration
(Colorado State University. Libraries, 2012) Stube, Cassandra J. Kieffer, author; Paschke, Mark, advisor; Brown, Cynthia, committee member; Meiman, Paul, committee member
Bromus tectorum L. is an invasive annual grass that dominates much of the rangeland in western North America. It has shown an impressive ability to invade ecosystems, causing substantial changes in the composition and function of native plant and soil communities in ways that promote further exotic invasion through displacement of native plant species and slowing or halting of succession. B. tectorum has several characteristics, including high reproductive rates, affinity for disturbed sites, and the ability to create positive feedback conditions in invaded sites, which make it highly successful at invading new sites, and extremely challenging to remove during revegetation efforts. Traditional control methods including herbicide application, grazing, and burning have largely proven unsuccessful at preventing establishment and spread of B. tectorum. Similarly, restoration seed mixes often consist of native perennial grass species, which tend to be slower growing and less robust in disturbed sites, and therefore provide little competition against B. tectorum and do not promote the reestablishment of native plant communities. In addition, seed mixes are often planted at a fraction of the rate of annual B. tectorum seed production, giving them a distinct disadvantage. Native ruderal species share many traits with B. tectorum and could potentially compete with this invader if used at high, competitive seeding rates in restoration efforts, and may alter site characteristics in ways that promote succession of the native plant community. One key characteristic that may be closely associated with community development is the development and composition of the arbuscular mycorrhizal fungi (AMF) community. AMF are important for resource acquisition by a majority of plant species. They are particularly important for late-seral plant species, which typically exist in low available nutrient conditions. Bromus tectorum causes shifts in the mycorrhizal community that could lead to a loss of AMF species richness and abundance in a very short time period, resulting in conditions that are difficult for late-seral species to colonize, due to a lack of access to resources through host-specific plant-AMF relationships. Utilizing native seed mixes composed of species selected for specific functional and competitive traits, and mycorrhizal status, and creating seeding rates designed to increase interspecific competition with B. tectorum may provide the missing link for successful restoration of B. tectorum-invaded sites. A study was conducted in northern Colorado to determine whether native ruderal species could suppress B. tectorum establishment and persistence in a disturbed site, and how these effects compared to similar effects by sterile wheat. In this study, B. tectorum was seeded with and without a high rate native ruderal seed mix and a sterile wheat species (QuickGuardTM) used in revegetation efforts for erosion control. Bromus tectorum biomass and density data were collected, as well as biomass and density for all seeded native species and sterile wheat. All treatments were seeded in the fall of 2010, and vegetative data collection occurred during the summers of 2011 and 2012. To assess the immediate effects of the establishing plant community on the AMF community, soils were collected from three of the field study treatments after one year of growth: 1) B. tectorum, 2) a mixture of native early-seral species, or 3) B. tectorum plus native early-seral species. Three mycorrhizal host plant species (Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths, Ratibida columnifera (Nutt.) Woot. & Standl., Sorghum bicolor (L.) Moench ssp. drummondii (Nees ex Steud.) de Wet & Harlan) were grown in these soils under greenhouse conditions. Roots were harvested after 30 days and analyzed for AMF colonization. After one growing season, the native ruderal mix significantly reduced B. tectorum biomass in the field. After the second growing season, the effect was no longer detectable in biomass measurements, but was still observed as a reduction in density of B. tectorum in the native ruderal plots. The sterile wheat reduced B. tectorum biomass after one growing season, but to a lesser extent than the native mix, and had a positive effect on density. In 2012, effects on both biomass and density disappeared. Results from the AMF colonization analysis indicated that the presence of the native species had an impact on AMF richness or abundance within the soils and that B. tectorum alters the AMF community in a way that is unique in comparison to weedy native vegetation. Soils from beneath native early-seral plant species had much higher colonization of the host plant species relative to soils from beneath B. tectorum. In addition, the native host R. columnifera had much higher rates of colonization than the non-native host, S. bicolor, indicating that there may be some host-dependent plant-AMF relationships that are more beneficial to the native plant than the non-native plant. The results of these studies could have important practical field applications for restoring invaded sites, particularly when the goal is to create conditions that promote development of late-seral native plant communities. Utilization of native ruderal species in revegetation mixes could provide a critical missing link for facilitation of late-seral, native plant communities through suppression of B. tectorum, as well as rapid facilitation of AMF communities that successfully colonize native late-seral host species. Continued monitoring and assessment of this study site could lend further insight to the long-term dynamics of the native ruderal plant community with B. tectorum and development of a late-seral plant community.
Open Access
Is thin and chip an ecologically viable fuels reduction option? Initial results in Black Hills ponderosa pine forests
(Colorado State University. Libraries, 2011) Cueno, Katherine L., author; Rocca, Monique E., advisor; Rhoades, Chuck, Affiliate, committee member; Brown, Cynthia, committee member
Across the dry western forests of the United States, accumulated hazard fuels increase the risk of catastrophic wildfires. Chipping or mastication of mechanically thinned fuels is becoming a common fuels reduction technique that aims to both reduce the risk of catastrophic fire and dispose of non-merchantable thinned material. We conducted an experiment to examine the ecological effects of thinning and chipping in ponderosa pine forests at two National Park Service locations in the Black Hills, South Dakota. By using an unthinned control and a thin-only treatment to compare to thin-chip treatment we were able to separate the effects of thinning from the effects of wood chip application. A greenhouse experiment was used to assess the effects of wood chip depth on seedling emergence and growth of several grass and forb species common to the study sites. Thin-only and thin-chip treatments greatly reduced hazard fuels by lowering pole tree density by 96%. Thinning did not elicit much of an understory response in the first year following treatment, while wood chip application caused slight decreases in understory plant richness and cover. Thin-chip plots had one-third lower graminoid cover than unthinned plots and half the number of annual species richness than thin-only plots. There was no difference in non-native species cover or richness, or in overall plant community composition as a result of treatments. Ponderosa pine germinated equally well in wood chips as in other areas. We observed a small decrease in NO3--N in thin-chip plots at one study site, but no effect at the other site. In the greenhouse, increasing wood chip depth created an increasing barrier to seedling emergence and growth in both grass and forbs. Complete suppression of plant emergence in the greenhouse occurred at wood chip depths ≥ 6 cm and plant biomass was undetectable at wood chip depths ≥ 3 cm. Our initial results suggest that thin-chip is a viable fuels treatment option. Although wood chip application slightly reduced some measures of understory cover and richness, the results we detected were subtle. Future examination will determine if delayed thinning effects reverse the slightly suppressive effects of wood chip application on understory vegetation.
Open Access
Spatial dynamics of weeds in irrigated corn
(Colorado State University. Libraries, 2011) O'Meara, Scott, author; Westra, Phil, advisor; Khosla, Rajiv, advisor; Brown, Cynthia, committee member; Reich, Robin, committee member
To view the abstract, please see the full text of the document.
Open Access
The mathematical modeling and analysis of nonlocal ecological invasions and savanna population dynamics
(Colorado State University. Libraries, 2013) Strickland, William Christopher, author; Dangelmayr, Gerhard, advisor; Shipman, Patrick, advisor; Zhou, Yongcheng, committee member; Brown, Cynthia, committee member
The main focus of this dissertation is the development and analysis of two new mathematical models that individually address major open problems in ecology. The first challenge is to characterize and model the processes that result in a savanna ecosystem as a stable state between grassland and forest, and the second involves modeling the non-local spread of a biological invader over heterogeneous terrain while incorporating the influence of a mass transportation network on the system. Both models utilize and compare work done in other, often more opaque, modeling paradigms to better develop transparent and application-ready solutions which can be easily adapted and inform ecological work done in the field. Savanna is defined by the coexistence of trees and grass in seasonally dry areas of the tropics and sub-tropics, but there is no consensus as to why savanna occurs as a stable state between tropical grassland and forest. To understand the dynamics behind the tree-grass relationship, we begin by reviewing and analyzing approaches in currently available savanna models. Next, we develop a mathematical model for savanna water resource dynamics based on FLAMES, an Australian process-based software model created to capture the effects of seasonal rainfall and fire disturbance on savanna tree stands. As a mathematically explicit dynamical system represented by coupled differential equations, the new model immediately has the advantage of being concise and transparent compared to previous models, yet still robust in its ability to account for different climate and soil characteristics. Through analytical analysis of the model, we show a clear connection between climate and stand structure, with particular emphasis on the length and severity of the dry season. As a result, we can numerically quantify the parameter space of year-by-year stochastic variability in stand structure based on rainfall and fire probabilities. This results in a characterization of savanna existence in the absence of extreme fire suppression based on the availability of water resources in the soil due to climate and ground water retention. One example of the model's success is its ability to predict a savanna environment for Darwin, Australia and a forest environment for Sydney, even though Sydney receives less annual rainfall than Darwin. The majority of this dissertation focuses on modeling the spread of a biological invader in heterogeneous domains, where invasion often takes place non-locally, through nearby human transportation networks. Since early detection and ecological forecasting of invasive species is urgently needed for rapid response, accurately modeling invasions remains a high priority for resource managers. To achieve this goal, we begin by revisiting a particular class of deterministic contact models obtained from a stochastic birth process for invasive organisms. We then derive a deterministic integro-differential equation of a more general contact model and show that the quantity of interest may be interpreted not as population size, but rather as the probability of species occurrence. We then proceed to show how landscape heterogeneity can be included in the model by utilizing the concept of statistical habitat suitability models which condense diverse ecological data into a single statistic. Next, we develop a model for vector-based epidemic transport on a network as represented by a strongly connected, directed graph, and analytically compute the exact optimal control for suppression of the infected graph vectors. Since this model does not require any special assumptions about the underlying spatiotemporal epidemic spread process, it should prove suitable in a variety of application contexts where network based disease vector dynamics need to be understood and properly controlled. We then discuss other methods of control for the special case of the integro-differential model developed previously and explore numerical results of applying this control. Finally, we validate model results for the Bromus tectorum invasion of Rocky Mountain National Park using data collected by ecologists over the past two decades, and illustrate the effect of various controls on this data. A final chapter concerns a problem of cognitive population dynamics, namely vowel pronunciation in natural languages. We begin by developing a structured population approach to modeling changes in vowel systems, taking into account learning patterns and effects such as social trends. Our model treats vowel pronunciation as a continuous variable in vowel space and allows for continuous dependence of vowel pronunciation on time and age of the speaker. The theory of mixtures with continuous diversity provides a framework for the model, which extends the McKendrick-von Foerster equation to populations with age and phonetic structures. Numerical integrations of the model reveal how shifts in vowel pronunciation may occur in jumps or continuously given perturbations such as the influx of an immigrant population.
Open Access
Three essays on the economics of restoring degraded land: from global to local
(Colorado State University. Libraries, 2016) Verdone, Michael, author; Seidl, Andrew, advisor; Frasier, Marshall, advisor; Brown, Thomas, committee member; Brown, Cynthia, committee member
To view the abstract, please see the full text of the document.