Browsing by Author "Paschke, Mark, advisor"
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Item 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 memberTo view the abstract, please see the full text of the document.Item Open Access Assessing vegetation reestablishment on disturbed high mountain lakeshores following historic dam removal in Rocky Mountain National Park, Colorado, USA(Colorado State University. Libraries, 2016) Goodrich, Amy C., author; Paschke, Mark, advisor; Meiman, Paul, advisor; Steingraeber, David A., committee member; Jonas-Bratten, Jayne, committee memberDam removal has entered the public spotlight in recent years, due to growing safety, economic, and environmental concerns related to dams. Removal is increasingly seen as a way to address not only the risks associated with aging and/or obsolete dams, but also as a tool for ecological restoration. In 1982, then-79-year-old Lawn Lake Dam in Rocky Mountain National Park failed, resulting in three deaths, and extensive monetary damages and destruction of natural resources within the Park. This was followed by a policy decision to remove three dams in the Park between 1988 and 1990, returning the former reservoirs to their previous natural lake water levels, and re-exposing nearly 13 hectares of scoured shoreline, completely denuded of vegetation by approximately 80 years of inundation. The disturbed lakeshore areas were left to undergo passive restoration. In the years immediately following dam removal, one short-term (3 year) revegetation study was conducted at Lawn Lake, and informal observational data were gathered by NPS personnel at a handful of plots established at the disturbed lakeshores of Bluebird, Sandbeach, and Pear Lakes. However, no further published analyses of data were made available, and until 2014 the vegetation at these lakeshores had not been surveyed to determine longer-term effects of damming and dam removal to reestablished vegetation. The goal of this study was to identify any persisting effects of historic damming and subsequent dam removal on vegetation characteristics such as species richness and diversity and community composition in the previously submerged lake margin areas surrounding the formerly dammed lakes, as well as the more elevated surrounding areas that had not been inundated. To do this, in July to September of 2014 I conducted surveys of vascular plant cover by species in 150 plots at nine high mountain lakes, including the four formerly dammed lakes and five undammed reference lakes. Site-specific environmental variables slope, aspect, elevation, elevation above current waterline, and soil texture were recorded at each plot. Plots were categorized as “elevated” or “lake margin” based on an elevation cutoff from the current waterline, to separate plots that had been previously submerged at dammed lake sites from more elevated sites that had not. I analyzed data from plots in each category for the effect of lake type (formerly dammed or reference) by fitting linear mixed models to species richness and diversity response. I performed a hierarchical cluster analysis that identified eight distinct vegetation communities, and performed non-metric multi-dimensional scaling (NMS) to explore relationships between vegetation community composition and site-specific measured environmental variables. No significant differences in vegetation characteristics of the elevated areas were found between formerly dammed and reference lakes. In previously submerged areas of formerly dammed lakes, however, species richness was significantly higher, compared to the similarly-located lake margin areas surrounding reference lakes (+3.361, χ2=8.919, p-val=0.003). All eight identified vegetation communities occurred at both formerly dammed and reference lakes. Slope and elevation were the measured environmental variables most strongly correlated with NMS axes (cumulative r2 values of 0.18 and 0.086), indicating that they are the most influential measured environmental variables in structuring plant communities at these study sites.Item Open Access Cheatgrass (Bromus tectorum L.) interactions with arbuscular mycorrhizal fungi in the North American steppe: prevalence and diversity of associations, and divergence from native vegetation(Colorado State University. Libraries, 2011) Busby, Ryan Ray, author; Paschke, Mark, advisor; Beck, George, committee member; Gebhart, Dick, committee member; Meiman, Paul, committee member; Stromberger, Mary, committee memberTo view the abstract, please see the full text of the document.Item 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 memberThe 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.Item Open Access Experimental restoration treatments for burn pile fire scars in conifer forests of the Front Range, Colorado(Colorado State University. Libraries, 2014) Shanklin, Amber, author; Paschke, Mark, advisor; Rhoades, Charles, advisor; Stromberger, Mary, committee memberDrastic changes in soil physical, chemical, and biotic properties following slash pile burning and their lasting effects on vegetation cover have been well documented in ecosystems worldwide. However, processes that inhibit burn scar recovery are poorly understood as are the means for their rehabilitation. This study compared plant and soil responses to a number of surface treatments designed to alter microclimate, moisture infiltration, and nutrient status of recently burned slash piles along the Front Range of Colorado. Hand-applied surface manipulation treatments including: scarification, woodchip mulch, and tree branch mulch were compared with untreated burn scars, both with and without addition of a native species seed mix at 19 sites. Pile burning effects were observed by comparing fire scar centers with unburned reference areas while restoration treatment effectiveness was observed by comparing treated scar centers with untreated scar centers. I found surface manipulations had little effect on vegetation recovery while seeding scars increased total plant biomass significantly. Woodchip mulch consistently increased soil moisture, decreased inorganic nitrogen availability, and inhibited plant regrowth in scars. Branch mulch and soil scarification showed no effect on plant regrowth and little effect on soil physical and chemical properties. Non-native species did not have a significant presence within slash scars and were no more prevalent in fire scar centers than reference conditions (unburned areas). Recommendations based upon results of this study include seeding native species in fire scars to promote native species reestablishment.Item Open Access Implications of facilitation and heterogeneity for plant community restoration in the Rocky Mountain region(Colorado State University. Libraries, 2023) Harris, Rebecca F., author; Paschke, Mark, advisor; Havrilla, Caroline, committee member; Rhoades, Chuck, committee member; Smith, Melinda, committee memberSeeding is the most widespread and viable method to revegetate degraded dryland ecosystems. Despite its prevalence, efforts to establish plants through seeding frequently fail. Variable weather conditions, competition with dominant and invasive species and herbivory pose barriers to the establishment of seeded plants. As a result, there is a great need and demand for innovative restoration practices that can aid revegetation efforts. Pit, mound and slash pile treatments create spatial and resource heterogeneity and thus can provide niches for different plants to find suitable habitat. I completed a four-year study that tested the impacts of seeding in conjunction with heterogeneity treatments on measures of plant community structure and cover compared to untreated but seeded plots and unseeded controls. Research sites were located in California Park, Colorado USA, a 11,000-ha Artemisia cana (silver sagebrush) meadow in the Medicine Bow Routt National Forest. In 2018, replicated test plots containing four treatments (unseeded control, seeded only, seeded plus soil pits and mounds, and seeded plus slash) were established at degraded sites in California Park. Seeded plots received a high diversity native seed mix (39 species) at a high rate (1496 Pure Live Seed [PLS] / m2). I monitored seeded species density and total plant species cover in the summers of 2019 through 2022. I analyzed treatment effects on plant Shannon Wiener diversity (H), richness, seeded abundance (plants / m2), Pielou's evenness (J) and percent cover with linear mixed-effects models. Plots that received the seeded only and seeded plus soil pits and mounds treatments contained higher seeded species diversity than control plots in 2019 and 2022. While seeded plus slash pile treatment plots increased seeded species diversity in the first year of monitoring, this effect diminished after 2019. It is important to note, no seeded diversity differences emerged between heterogeneity treatment plots and untreated but seeded plots in any year. Findings suggest that seed application can increase the diversity of desirable seeded species and may be a useful tool to shift plant community composition. Shrub subcanopies accumulate moisture and nutrients in a manner that can facilitate understory plants. Consequently, seeding beneath shrubs may improve seedling establishment and survival in dryland ecosystems where harsh environmental conditions are present. I set up a study to evaluate whether seeded shrub islands had higher seeded species abundance and richness compared to seeded interspaces and unseeded controls. Study sites were located outside of Grand Junction, Colorado in Dominguez Escalante and McInnis Canyons National Conservation Areas (NCA) (Figure 2.1). Six sites were established in fall of 2020, three within sagebrush and three within salt desert shrublands. Five seeded shrub islands, five seeded interspaces, five unseeded shrub island controls and five unseeded interspace controls were established at each site. In addition, I evaluated if the impacts of these treatments were different between sagebrush and salt desert shrublands. Furthermore, I assessed whether plant functional groups and soil chemical properties were impacted by treatment type. I analyzed treatment effects on seeded species richness, seeded species abundance, cover by plant functional group, surface soil moisture, temperature and chemical properties with separate linear mixed-effects models. While sub canopy microsites were on average nutrient enriched and cooler than interspace plots, they did not facilitate seeded species establishment. In contrast to expectations, seeded interspaces contained higher seeded species richness than all other plot types. Lower richness in seeded shrub islands may be due to sodic, saline and or saline-sodic soil conditions found beneath shrubs within the salt desert. In addition, high cover of introduced perennial grasses beneath shrub islands may prevent seedling establishment at sagebrush sites. Results suggest that interspaces provide more favorable conditions for seeded plant establishment than shrub islands in both systems. Land managers are interested in levering positive plant-plant interactions (i.e., facilitation) and heterogeneity to improve seeded plant establishment and plant community restoration outcomes. I investigated whether applying a native seed mix either beneath shrub islands, or in tandem with heterogeneity treatments, increased seeded plant establishment and diversity respectively. I hope this research can contribute to improving plant community restoration outcomes in degraded dryland ecosystems.Item 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 memberBromus 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.Item Open Access Interactions between Bromus tectorum, grasshoppers, and native plants in sagebrush steppe communities(Colorado State University. Libraries, 2014) Cumberland, Catherine, author; Paschke, Mark, advisor; Cooper, David, committee member; Jonas, Jayne, committee member; Pejchar, Liba, committee memberInvasion by the exotic grass Bromus tectorum L. (cheatgrass) has produced widespread, persistent changes in the Intermountain West. As a result of this and other disturbances, sagebrush shrubland is among North America's most imperiled ecosystems. Restoration of B. tectorum-infested areas has often been unsuccessful, and there is a need to understand the factors limiting revegetation success. There is evidence that B. tectorum is a superior competitor for space and resources. But it's also possible that B. tectorum dominance is enhanced by native herbivores through the mechanism of apparent competition: species competing indirectly through shared natural enemies. If an invasive exotic is a less preferred food source for herbivores than native plants, per capita feeding impacts may increase on natives, thus facilitating exotic proliferation. In sagebrush shrubland, grasshoppers are often the dominant herbivores. Their feeding patterns have been shown to limit and structure plant distributions. The objective of this study was to elucidate whether grasshoppers may be promoting B. tectorum spread through herbivore-mediated apparent competition. Using native plants commonly seeded in sagebrush restoration projects and the native generalist grasshopper Melanoplus bivittatus in laboratory trials and greenhouse experiments, I tested how grasshopper herbivory affects native plants in comparison to B. tectorum. Grasshoppers significantly increased mortality rates for most native plants but had minimal impact on B. tectorum mortality. Certain native species were much more highly preferred and / or impacted by herbivory, including the keystone shrub Artemisia tridentata (big sagebrush). However, several native species were either less preferred or more tolerant of herbivory than B. tectorum, and could therefore be good restoration candidates where grasshoppers are common. In addition, my results suggest B. tectorum could promote population increase in certain grasshopper species, particularly agricultural and rangeland pests. Study results could provide guidance regarding seed mixes and possible control of insect herbivores to improve restoration success in B. tectorum-invaded areas.Item 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, advisorSwainsonine 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.Item Open Access Optimal seed mixtures and seeding rates for restoration of surface disturbances on Colorado shortgrass steppe(Colorado State University. Libraries, 2013) Barr, Stephanie, author; Paschke, Mark, advisor; Meiman, Paul, committee member; Brummer, Joe, committee member; Jonas, Jayne, committee memberThe discovery of oil and gas resources over the last decade has led to unprecedented localized and dispersed surface disturbances on shortgrass steppe ecosystems in the western US. Reclaiming and restoring these surface disturbances to native ecosystems through revegetation seeding has proven challenging. Seed mixes and rates currently used are generally similar across private and public sectors (3-10 species at rates ranging from 400-600 pure live seeds (PLS) m-2 broadcast seeded). The objective of this study was to determine an optimal seed mix diversity level and corresponding seeding rate for restoration of surface disturbances in shortgrass steppe. I examined five seed mix diversity levels, 5-50 species, and five seeding rates, 400-1600 PLS m-2 using a response surface regression experimental design at twelve sites. Treatments and overall restoration success were evaluated based on resulting biomass and diversity of seeded, volunteer native, noxious, and non-native species, and the density of seeded species. Results show greatest restoration success occurring during year one at a seed mix diversity level of 43 species and a seeding rate of 1229 PLS m-2, and during year two at a diversity level of 42 species and a rate of 932 PLS m-2. These results suggest that higher seed mix diversity levels and higher seeding rates could lead to greater restoration success for surface disturbances in shortgrass steppe.Item Open Access Soil seed bank composition and implications for ecological restoration in degraded Colorado shrublands(Colorado State University. Libraries, 2020) Schroeder, Ryan W. R., author; Paschke, Mark, advisor; Rhoades, Chuck, advisor; Meiman, Paul, committee member; Grant-Hoffman, M. Nikki, committee member; Melzer, Suellen, committee memberSoil seed banks of shrub-dominated ecosystems in western North America are poorly understood. The potential of the soil seed bank – the species composition and abundance of seeds – to impact ecological restoration has rarely been considered in ecological restoration of shrublands and could influence management decisions. I analyzed the germinable soil seed bank composition and distribution in two high-conservation priority ecosystems in Colorado. Studies were carried out to characterize seed bank composition and relationship to aboveground vegetation in "undesirable" and "desirable" plant communities; determine if "shrub islands" influence seed bank distribution; and assess the landscape and vertical distribution of the seed bank in a Bromus tectorum L. (cheatgrass) invaded rangeland. For all seed bank studies, soil seed bank samples were collected to a depth of 5 cm and grown in greenhouse conditions to determine the species composition and abundance of germinable seeds. I found that seed bank species richness and Shannon-Wiener diversity (H) did not differ in either shrubland between undesirable sites dominated by non-native vegetation and desirable sites dominated by native vegetation. Total seed abundance in a montane sagebrush shrubland was significantly greater in desirable sites (1401 ± 165 seeds m-2) compared to undesirable sites (588 ± 190 seed m-2). In a salt desert shrubland of the Colorado Plateau, total seed abundance did not differ, but on average non-native species seeds made up more than 60% of the total seed bank in undesirable sites, compared to 40% in desirable sites. In a separate study, shrub islands across Colorado were not associated with increased seed bank species richness or seed abundance compared to adjacent shrub-less interspaces. Differences in seed bank Shannon Wiener diversity (H) varied between shrublands, with salt desert shrublands having significantly greater (p-value < 0.05) seed bank diversity inside of shrub islands compared to shrub-less interspaces. Another study was conducted in a Bromus tectorum L. (cheatgrass) invaded rangeland of the Colorado Plateau to determine the seed bank horizontal and vertical distribution. The germinable soil seed bank had a greater abundance and lower spatial variability of native species seeds (3390 seeds m-2, CV = 75%) than non-native species seeds (1880 seeds m-2, CV: 124%) across the sampled landscape. Non-native species (primarily Bromus tectorum L.) seed were concentrated in the upper 2 cm soil (1294 ± 155, p-value <0.0001), but were found in substantive abundance in the 2 – 5 cm seed bank layer (585 ± 91). In addition to seed bank studies, in the fall of 2018, I established a study in a montane shrubland to test the effectiveness of seeding a high diversity native seed mix (39 species, 1496 PLS m-2) and treatments to increase site heterogeneity to increase native plant species diversity. One growing season following plot establishment, I found that plots that received a high diversity seed mix and those that received heterogeneity treatments had greater seeded species diversity (H) and richness than control plots.Item Open Access Turning the tide on the sagebrush sea: long-term invasive annual grass control and rangeland restoration with indaziflam(Colorado State University. Libraries, 2022) Courkamp, Jacob S., author; Meiman, Paul, advisor; Paschke, Mark, advisor; Dayan, Franck, committee member; Ocheltree, Troy, committee memberThe invasive winter annual grass downy brome (Bromus tectorum L.) has invaded vast expanses of sagebrush-grassland in western North America, and the fine fuel associated with invasion increases the frequency of burning such that native plants struggle to persist. Recent research suggests that B. tectorum invasion may expand across an even larger portion of the US Intermountain West in the absence of effective and proactive management. The herbicide imazapic is widely used to manage B. tectorum, but control often declines after one year and reinvasion is typical. Several trials have demonstrated that the newer herbicide, indaziflam, can selectively control annual grasses for three or more years, and past studies indicate that B. tectorum seed banks are relatively short-lived in the field (<5 years). This suggests that consecutive years of control with indaziflam may eliminate B. tectorum seed banks and increase the duration of control, but it is unclear if this will require multiple applications. In addition, existing studies evaluating the effects of treatment on native rangeland plant communities are limited by small plot sizes, and the potential for impacts to native species seed banks is unclear. The studies detailed in Chapter 1 evaluated the effectiveness of imazapic and indaziflam for reducing B. tectorum density and cover over a period of approximately 5 years (57 months after treatment; MAT) at two invaded sagebrush-grassland sites near Pinedale, Wyoming. Treatments included three different indaziflam rates (51, 73, and 102 g ai ha-1) and imazapic (123 g ai ha-1) and were reapplied to half of each plot 45 MAT to evaluate the effects of two sequential applications. Perennial grass cover was also measured because positive perennial grass responses were observed after release from B. tectorum competition in other studies, and perennial grasses may provide resistance to B. tectorum reinvasion. Intermediate and high indaziflam rates (73 and 102 g ai ha-1) resulted in significant reductions in B. tectorum cover and density 45 MAT, and perennial grass cover responded positively to some treatments early in the study. Imazapic reduced B. tectorum initially, but did not have a significant effect on density or cover at either site beyond 21 MAT. Reapplication did not substantially improve B. tectorum control 57 MAT in plots treated with intermediate and high indaziflam rates, suggesting that long-term control with a single indaziflam treatment may be possible in some cases. The studies detailed in Chapter 2 assessed the potential for non-target impacts resulting from indaziflam treatment. Modified-Whittaker multiscale vegetation plots were used to compare diversity (species accumulation) in three treatment (73 g ai ha-1 indaziflam) and three control plots in a sagebrush-grassland plant community near Pinedale, Wyoming that is invaded by B. tectorum. In addition, a seed bank assay assessed the density and richness of shallow (0-1 cm depth) and deep (1-5 cm depth) germinable seed banks in these same treatment and control plots during a 20-week greenhouse study. Vegetation data and seed bank samples were collected during the third growing season after treatment. Species diversity did not differ between treatment and control plots, but this contrasted with the results of the seed bank assay, which showed that the shallow and deep seed banks had significantly fewer germinable seeds and native species richness was significantly lower in the shallow seed bank of treated areas. While significant non-target impacts to native annual seed banks were observed, all impacted species were detected in the aboveground plant community in treatment plots after treatment occurred, suggesting that reduced native annual abundance may be temporary. The results presented herein suggest that long-term B. tectorum control is possible with a single indaziflam application, and that when indaziflam treatment without associated revegetation is a suitable management intervention (i.e., invaded perennial communities), the benefits of protecting and promoting established perennial plants likely far outweigh the potential for non-target impacts to native species and native species seed banks. The ultimate goal of any weed management program is to reduce the impacts of invasive species to the greatest degree possible with the resources available, whether that is through eradication or conciliation and containment. Our results suggest that in the case of B. tectorum invading established sagebrush-grassland plant communities, indaziflam will have a significant role to play in helping managers achieve this objective.Item Open Access Understory responses to mechanical removal of pinyon-juniper overstory(Colorado State University. Libraries, 2014) Stephens, Garrett J., author; Paschke, Mark, advisor; Johnston, Danielle, advisor; Meiman, Paul, committee member; Wilson, Ken, committee memberDeclining Colorado mule deer (Odocoileus hemionus) populations have necessitated improved habitat management techniques. In particular, oil and gas development in the Piceance Basin of western Colorado has impacted critical winter range, creating a need for treatments that will increase forage, and especially palatable shrub species. Pinyon-juniper (Pinus spp - Juniperus spp) tree removal is one technique, however it is unclear which method of tree removal will most effectively promote forage species. This experiment quantified understory responses to pinyon-juniper canopy removal and seed additions using three different methods: anchor chain, rollerchopper, and hydro-ax. Twenty-one 0.8-ha plots were mechanically treated during the fall of 2011 (7 replicates of each treatment). Half of each plot was seeded prior to mechanical treatment with a mix of native grasses, shrubs, and forbs. After two growing seasons, productivity of forbs, grasses, and shrubs combined was roughly three times greater in hydro-ax, rollerchop, and chain plots relative to control plots (where tree removal did not occur). Comparisons of vegetation productivity among treated plots showed that the response of early seral species, some of which were included in the seed mix, was dependent upon the interaction of seeding and mechanical treatments. Specifically, the productivity of annual species was greater in seeded versus unseeded plots for chain and hydro-ax but not for rollerchop. Rollerchop plots, however, had greater productivity of non-native species than chain or hydro-ax (such as Salsola tragus, Descurainia sophia, and Bromus tectorum). Also, the abundance of shrubs, which are an important source of winter forage, was greater in seeded than unseeded subplots. Results after two growing seasons suggest that all three mechanical treatments increase forage productivity and of the three techniques, rollerchop may promote non-native establishment (primarily forbs). At this early stage in plant community development, differences in the effect of mechanical treatments on shrub forage are not yet apparent, but may emerge with future monitoring.