Browsing by Author "Brown, Cynthia S., advisor"
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Item Open Access Altering water and nitrogen availability after roadside disturbance to favor native plant species(Colorado State University. Libraries, 2016) Ringer, Lindsay, author; Brown, Cynthia S., advisor; Claassen, Victor P., committee member; Schipanski, Meagan E., committee memberThis study evaluates the use of soil amendments in roadside restoration to promote native species and discourage invasive species establishment through manipulation of water and nitrogen (N) availability. Our goal was to decrease soil N availability and increase soil water content to foster growth of perennial native species on roadsides in Rocky Mountain National Park, Colorado. Roadside construction can increase soil bulk density, reduce aggregation, and cause an initial increase in resource availability, which encourages growth of early successional species. In addition, N deposition from the Front Range of Colorado is increasing nitrate and ammonium availability in this National Park. The study objective was to increase or decrease water and/or N availability with soil amendments to reduce weedy annual species establishment on roadsides. Treatments were hypothesized to 1) increase soil moisture and reduce plant-available N (synthetic polymer incorporation), 2) reduce soil surface temperatures, increase moisture and indirectly decrease N (wood mulch blanket), 3) decrease bulk density by changing soil structure and slowly increase N (yard-waste compost incorporation). These amendments were applied alone and in pairwise combinations to six southeast facing roadsides slopes concurrent with seeding in fall of 2013. Ten perennial grass and forb species were hydro-seeded with tackifier to all roadsides. Plant density, cover, mineral nutrients, soil moisture, total C:N, soil temperature, and rainfall were measured during the growing season in 2014 and 2015. A paired greenhouse study was conducted in spring 2014 with analogue native and non-native grasses. Grass root and shoot biomass, plant height, seedling density, and soil moisture were measured after 9 weeks of growth. On these roadsides, soil moisture, and density of native seeded species was significantly changed by soil treatments through time (p=0.039, p=0.040). Wood mulch alone and combined with compost or polymer increased soil moisture after rainfall in the field (p=0.0007) and after irrigation in the greenhouse (p=0.0001). In the field, seeded species density was highest in mulch/compost treatments in 2014 (p=0.029) and mulch/polymer treatments in 2015 (p=0.003). After one year of decomposition, none of the treatments significantly changed carbon to nitrogen ratios (p=0.27) which averaged 18.7:1, although mulch/compost treatment had the lowest C:N ratio of 13.5:1. Mulch or mulch/polymer treatments combined had much less nitrate than yard-waste compost incorporation (p=0.0002). Mulch blanket immobilized N and decreased non-native density in summer 2015 to 2 plants/m2. In contrast, compost/polymer treatments had 12 non-native plants/m2 (p=0.02). In the greenhouse, nitrate was more limiting than water, and mulch blanket increased native grass growth relative to non-native grasses (p=0.002). Because of the immobilization of N, mulch also decreased germination rates (p=0.001) and biomass (p=0.001) across all species. With higher soil moisture availability in the greenhouse, non-native growth was lower than natives in control (p=0.001), polymer and mulch soil treatments. In contrast, compost incorporation, which increased N availability in the field, drastically increased growth of all species (p<0.0001) in the greenhouse. These results begin to demonstrate how increased soil moisture and decreased soil N favors germination and seedling survival of desirable native perennial species, while simultaneously reducing non-native species establishment. By managing soil resource availability after disturbance, we can achieve resilient plant communities dominated by perennial native species.Item Open Access Cheatgrass (Bromus tectorum L.) management and native plant community recovery on sites selectively treated with Imazapic in Rocky Mountain National Park(Colorado State University. Libraries, 2017) Davis, Christopher, author; Brown, Cynthia S., advisor; Paschke, Mark W., committee member; Fernandez-Gimenez, Maria, committee memberCheatgrass, a winter annual grass introduced to North America from Eurasia, has invaded much of the Western United States over the last century. Recently, cheatgrass has become a threat to the montane and subalpine plant communities and ecosystems of Rocky Mountain National Park (RMNP). Cheatgrass aggressively invades disturbed sites and competes with native plant species by rapidly establishing a root system capable of depleting soil moisture and available nitrogen, making cheatgrass control a priority when restoring disturbed areas within RMNP. The purposes of this study were to determine the effectiveness of imazapic for cheatgrass control, its effects on non-target native species, and how the plant community recovers following cheatgrass control. In 2008, 12 permanent monitoring plots were established in six sites in RMNP, each with one reference and one imazapic treatment plot. Reference plots were chosen to represent the desired final condition for each imazapic treatment site. Imazapic (23.6% a.i.) was applied to cheatgrass infestations post-emergence in 2008 (105 g a.i./ha) and pre-emergence in 2009 (105 g a.i./ha) and 2010 (70 g a.i./ha). Imazapic was applied to cheatgrass patches selectively, avoiding application to native species as much as possible. Cheatgrass cover was reduced more than fourfold to approximately 5% in 2013, and there was no decrease in cover of native forbs, grasses, or shrubs. There was no subsequent increase in native species abundance following cheatgrass removal, suggesting further action is needed if the ultimate management goal is to encourage native species recovery in treatment plots after satisfactory cheatgrass control is achieved.Item Open Access Development and use of a database with information about Bromus species for research on invasions(Colorado State University. Libraries, 2013) Atkinson, Sheryl Yvonne, author; Brown, Cynthia S., advisor; Steingraeber, David, committee member; Ward, Sarah, committee memberInvasive plants are a serious problem worldwide. Plant invasions cause damage to agricultural and natural ecosystems, and contribute to loss of biological diversity. They are difficult to predict, prevent, and control. The Poaceae or grass family contains many species that have been introduced into areas outside of their native ranges and have become invasive. Brome grasses are a group of C3 grasses that grow primarily in temperate regions. A number of brome grasses have been introduced into the North America, sometimes accidentally, and sometimes for use as hay and forage, or for other purposes. Introduced brome grasses display varying levels of invasiveness. In conjunction with a research project focusing on invasive brome grasses in the western United States, I developed a database that contains information about traits of brome grasses, and about their interactions with biotic and abiotic features of their native and introduced ranges. The database contains information about over 150 species and is designed both to support research into the causes and effects of plant invasions, and to provide information useful for anyone dealing with the use, management, and control of brome grasses. It is hosted on the Great Basin Research and Management Project website at http://greatbasin.wr.usgs.gov/GBRMP/bromus/bromus.html. I used the data in the database to look for patterns of invasion. Correlations were found between invasiveness (defined as wide distribution outside of the native range combined with weediness), and taxonomic section, seed awn length, polyploidy, human use and availability of cultivars. Annual brome grasses have been widely introduced into new regions around the world and have a high probability of being destructive agricultural, ruderal, and environmental weeds. Long awn length is correlated with invasiveness, especially in annual species. Perennial brome grasses generally remain confined to their native regions unless they are cultivated for hay, forage, or revegetation. Once introduced, perennial bromes can escape cultivation and damage natural communities. The few invasive perennial species are polyploid, while invasive annual species may be diploid or polyploid. Invasiveness in brome species is associated with human activities including habitat disruption, agriculture, grazing, and use for revegetation. Climate change and habitat disruption are likely to change the way brome grasses invade. Most research on brome grasses focuses on highly invasive species, and information about less-invasive and non-invasive species is limited. Collection of information about all brome species in a central location facilitates comparisons among species, and provides data that can be used for modeling, prediction, management and control of brome grass invasions.Item Open Access Evaluating risk for current and future Bromus tectorum invasion and large wildfires at multiple spatial scales in Colorado and Wyoming, USA(Colorado State University. Libraries, 2015) West, Amanda M., author; Brown, Cynthia S., advisor; Kumar, Sunil, advisor; Evangelista, Paul H., committee member; Hufbauer, Ruth A., committee memberThe Western United States is experiencing rapid ecologic change. These changes are driven largely by anthropogenic factors including introduction of alien invasive species, wildfire ignition and suppression, climate change, and feedbacks between these occurrences. Average temperatures in some areas of the Western U.S. increased as much as 1.1 °C between 2000 and 2006. The advancement of spring also provides evidence for climate change in the region; earlier snowmelt and runoff has been documented in recent decades for areas of the Intermountain West. These rapid changes will certainly affect the distribution of the alien invasive B. tectorum and large wildfires in Colorado and Wyoming as well as their associated feedbacks and cascading ecosystem effects. Prompted and inspired by natural resource manager concerns, this research evaluates these ecological phenomena at three spatial scales: Rocky Mountain National Park, Colorado; a wildfire disturbance in Medicine Bow National Forest, Wyoming; and the area encompassed by these two states. The products from this research are maps that can be incorporated into decision support systems for land management and vulnerability assessments for climate change preparedness. An evaluation of the current and future suitable habitat for B. tectorum in Rocky Mountain National Park was conducted at a 90 m² spatial resolution using a MaxEnt model fit with climatic, vegetation cover, and anthropogenic covariates (i.e. distance to roads as a surrogate for propagule pressure). One of the important considerations of this research was spatial scale; 250 m² and 1 km² resolution climate surfaces cannot capture climate refugia in a small area such as Rocky Mountain National Park (1,076 km²) with high topographic heterogeneity (2,300 m to 4,345 m elevation). Based on model results, the suitable habitat for B. tectorum in the Park increases more than 150 km2 through the year 2050. Four multi-temporal and multiscale species distribution models were developed for B. tectorum in the Squirrel Creek Wildfire post-burn area of Medicine Bow National Forest using eight spectral indices derived from five months of 30 m² Landsat 8 imagery corresponding to changes in species phenology and time of field data collection. These models were improved using an iterative approach in which a threshold for abundance (i.e. ≥40% foliar cover) was established from an independent dataset, and produced highly accurate maps of current B. tectorum distribution in Squirrel Creek burn with independent AUC values of 0.95 to 0.97. The most plausible model based on field observations showed the distribution of B. tectorum has increased 30% from pre-disturbance observations in the area. This model was incorporated in a habitat suitability model for B. tectorum in the same area using topographic covariates with inclusion of propagule dispersal limitations to provide an estimate of future potential distribution. Three historic (years 1991 – 2000) environmental suitability models for large wildfires (i.e. > 400 ha) in Colorado and Wyoming were developed at a 1 km² spatial resolution and tested using an independent dataset of large wildfire occurrence in the same area from the subsequent decade (years 2001 – 2010). The historic models classified points of known fire occurrence exceptionally well using decadal climate averages corresponding to the temporal resolution of wildfire occurrence and topographic covariates. When applied to an independent dataset, the test sensitivity was 0.91 for the best model (i.e. MaxEnt). We then applied the model to future climate space for the 2020s (years 2010-2039) and 2050s (years 2040-2069) using two future climate ensembles (i.e. two representative concentration pathways; RCP 4.5 and RCP 8.5 with ensemble average projections from 15 global circulation models) to rank areas for large wildfire risk in the future.Item Open Access Pile burn scar restoration at Lily Lake: tradeoffs between abundance of non-native and native species(Colorado State University. Libraries, 2019) Sexton, Ian C., author; Brown, Cynthia S., advisor; Fornwalt, Paula J., committee member; Paschke, Mark W., committee memberAccumulation of fuels in forests across the western United States is producing larger and more severe wildfires. To decrease wildfire severity and increase forest resilience, foresters regularly remove excess fuel by burning woody material in piles. This common practice can also cause persistent ecosystem changes that include alteration of soil physical and chemical properties due to extreme soil heating, which can favor invasion by non-native plant species. Abundance and species richness of native plant communities may also remain depressed for many years after burning has removed vegetation and diminished propagules in the soil. This adds to the vulnerability of burned areas, which can transition to dominance by invasive species. Research into the use of revegetation techniques following pile burning to suppress invasion is limited. Studies conducted in various woodland types that investigated revegetation of pile burn scars have met with varying success. To assess the effectiveness of restoring pile burn scars in Rocky Mountain National Park, Colorado, we monitored vegetation in 26 scars at Lily Lake the growing season after burning. Later that summer we selected 14 scars for restoration that included soil scarification, seed addition, and pine duff mulch cover. We monitored the scars for 3 years following restoration and found that cover of seeded species exceeded surrounding unburned areas. This suppressed cover of non-native species as well as native species that were not seeded during restoration relative to controls. Productivity of a native forb planted as seed in scars 3 years after restoration was depressed relative to unrestored scars. We conclude that restoration of pile burn scars can be a useful management tool that will likely need to be part of an integrated pest management program addressing preexisting infestations near scars. Monitoring for periods longer than 3 years will help us understand how long suppression of native and non-native species by restoration species may persist.Item Open Access Restoring semi-arid lands with superabsorbent polymers under reduced precipitation and threat of Bromus tectorum invasion(Colorado State University. Libraries, 2016) Garbowski, Magda, author; Brown, Cynthia S., advisor; Johnston, Danielle B., advisor; Hardegree, Stuart P., committee member; Schipanski, Meagan E., committee memberRestoration of arid ecosystems in the western United States (US) is often constrained by low and variable moisture and invasion by exotic species. After disturbance, variability in resources as well as inherent soil moisture and temperature regimes may influence the susceptibility of an ecosystem to exotic species invasion. The invasive winter annual grass, Bromus tectorum (B. tectorum), is particularly competitive in disturbed semi-arid areas, has invaded tens of millions of hectares throughout the western US, and its range is projected to expand under predicted climate scenarios. Increasing soil moisture and resources in restoration projects may decrease soil moisture variability and promote establishment of a native plant community that is resilient to disturbance and resistant to invasion of B. tectorum. With their ability to absorb moisture when it is abundant and slowly release it over time, superabsorbent polymers (SAP) may increase overall soil moisture and decrease soil moisture variability during restoration. In this study, we aimed to investigate the interactive effects of precipitation timing, drought, B. tectorum, and SAP on soil resources and developing restoration plant communities. The study was established in 2014 at two climatically distinct sites: one site was located on the Eastern Slope (Larimer County) and one on the Western Slope (San Miguel County) of Colorado. Both sites fall under the mesic soil temperature regime and ustic-aridic soil moisture regime but vary in their susceptibility to invasion largely due to differences in seasonal precipitation patterns. While the Eastern Slope receives most of its growing season moisture in the early spring and summer, the Western Slope site receives most of its growing season moisture in the late summer and early fall. Two levels of three treatments (drought: exclusion of 66% of ambient rainfall or ambient rainfall; B. tectorum presence: 465 seeds m-2 or none; SAP: 26 g m-2 or none) were fully crossed in three blocks at each site resulting in a complete factorial experiment. After one year of monitoring soil moisture, plant available nitrogen (at the Western Slope site), and plant community responses, we observed significant effects of exclusion at both sites on soil resources and the developing plant communities. Independent and interactive effects of drought and SAP at the Eastern Slope site and drought and B. tectorum at the Western Slope site influenced plant communities and soil resources. Overall B. tectorum establishment was low on the Eastern Slope and high on the Western Slope in the first year of the study. At the Eastern Slope site, drought limited seeded species recruitment late in the season and the positive effects of SAP on seeded species were apparent only under ambient precipitation conditions. Total and annual seedling densities were higher under SAP treatments at this site. At the Western Slope site, total seedling densities were lower in drought treatments, and native seedling densities were lower in drought treatments at the end of the growing season. The effects of B. tectorum on seeded annuals at the Western Slope site depended on date and precipitation treatment. Seeded annuals densities were highest in mid-summer in treatments without B. tectorum and ambient precipitation. Interestingly, at the Western Slope site, B. tectorum under ambient precipitation had a stronger negative impact on soil moisture at 30 cm depth than drought treatments regardless of level of B. tectorum or SAP. B. tectorum also decreased soil moisture at 5cm depth early in the season at the Western Slope site while exclusion treatments decreased soil moisture later in the growing season at both sites. Our results demonstrate that drought negatively impacts soil resource availability and native plant community development in restoration. Techniques that improved water and nutrient availability especially under drought conditions are needed to promote native species establishment. While SAP did not improve soil moisture, higher seedling densities were found in SAP treatments at one site, especially under ambient conditions. This suggests that incorporating SAP into the soil may improve plant establishment, but effectiveness is likely affected by antecedent soil moisture and precipitation patterns. In our study, B. tectorum negatively impacted soil moisture and native plant establishment at one site demonstrating the need for management of this species in restoration of semi-arid lands.Item Embargo Species distribution models for and policy approaches to invasive plant ecology and management(Colorado State University. Libraries, 2024) Teich, Nathan Benjamin, author; Brown, Cynthia S., advisor; Jarnevich, Catherine, committee member; Pearse, Ian, committee member; Evangelista, Paul, committee memberThe ability of abundance-based Species Distribution Models (SDMs) to predict where invasive plants can be abundant, and to what degree, is a powerful research and management tool. Often, invasive plant abundance-based SDMs are created using similar inputs and approaches as occurrence SDMs. However, invasive plant ecology literature suggests that the factors found to control invasive plant abundance are more diverse and contextual, and therefore not entirely interchangeable with factors that control invasive plant occurrence. To ensure invasive plant abundance-based SDMs are leveraging the robust body of knowledge, this paper aims to highlight and summarize the ecological factors underpinning invasive plant abundance and reviews how those factors can be represented within abundance-based SDMs. I find that while the inclusion of invasive plant abundance governing factors often improves abundance-based SDM performance, certain governing factors are ubiquitously represented while others are less commonly accounted for in model creation despite their ecological importance. Barriers to incorporating invasive plant abundance governing factors into abundance-based SDMs often include data limitations or methodological uncertainty. Finally, we provide future research directions that would help address certain barriers and improve our ability to integrate abundance governing factors into SDMs. Invasive plants, when they become dominant components of a plant community, threaten native species and ecosystem processes. Abundance-based SDMs are gaining traction as a geospatial tool to predict where invasive plants can become abundant and have negative impacts. Biotic interactions influence invasive plant abundance locally but are often not included within the abundance-based SDM creation process. At present, it is unknown to what degree local-scale biotic interactions with other plant species determine locations where invasive plant species can become abundant. Using data from large-scale abundance observations of the invasive plant cheatgrass (Bromus tectorum) paired with data from plant communities in the western United States, we quantified the degree to which biotic interactions explain where cheatgrass is abundant beyond what would be anticipated from an abundance-based SDM created with abiotic and landscape context predictors alone. To this end, we fit Generalized Linear Models (GLMs) for different categories of cheatgrass abundance and used the predicted suitability SDM outputs alongside biotic variables, representing known competitive and facilitative interactions, to determine if including biotic interactions improved a model's explanatory power. The addition of biotic variables marginally improved GLMs for low (5-25%) and medium (25+-50%) cheatgrass abundance but displayed greater improved performance for high (50+%) cheatgrass abundance. Most notable amongst the specific biotic variables was the cover of perennial graminoid cover, representing known competitors of cheatgrass, which interacted with SDM environmental suitability to strongly reduce the probability of high cheatgrass abundance. These findings suggest that considering biotic interactions alongside SDM predicted suitability may indeed improve our ability to predict abundance locations of invasive plant species, but potentially only in specific contexts such as where that species can already achieve high abundance. Invasive plants cost the US billions of dollars each year due to ecological and economic impacts as well as management costs. One of the most common pathways of introduction and spread of invasive plants is through ornamental plant sales. While solutions such as regulations and voluntary self-bans have been implemented in some instances to mitigate this problem, widespread adoption has not occurred. As such, new alternatives should be explored. Opt-in labeling programs are commonly used throughout the agricultural industry to better inform customers about the products they are purchasing. An opt-in labeling program that consists of a partnership between retailers and governments or non-profit organizations could help reduce the spread of invasive plants by influencing customer behavior. This approach would be less costly to retailers than regulations, create new invasive plant prevention opportunities for governments and non-profits, and better inform consumers about specific invasive plant species.Item Open Access The influence of chilling requirement on the southern distribution limit of exotic Russian olive (Elaeagnus angustifolia) in western North America(Colorado State University. Libraries, 2011) Guilbault, Kimberly Rose, author; Brown, Cynthia S., advisor; Friedman, Jonathan, committee member; Shafroth, Patrick B., committee member; Angert, Amy L., committee memberRussian olive (Elaeagnus angustifolia L.), a Eurasian tree, is now a dominant species along rivers in western North America. The southern boundary of Russian olive distribution in western North America runs through southern California, Arizona, New Mexico and Texas. I related the distributional pattern of Russian olive to temperature regime and investigated potential temperature-dependent mechanisms that might explain this distributional limit. Specifically, I investigated whether lack of cold temperatures at the southern limit may prevent the accumulation of sufficient chilling and inhibit dormancy loss of seeds and buds, potentially constraining Russian olive's southern distribution boundary. First, I used field observations to thoroughly define the southern limit of Russian olive across western USA and related this distribution to temperature variables. I found that Russian olive occurrence was more strongly associated with low winter temperatures than with excessive summer heat. I then carried out controlled seed germination and vegetative bud-break experiments and a field survey of fruit production and seed viability. Next, I cold stratified Russian olive seeds in growth chambers with temperature regimes simulating six locations along a latitudinal gradient from Socorro, New Mexico (33.8°N latitude) to Presidio, Texas (29.56°N latitude). Both germination proportion and germination times were highest under temperature regimes simulating locations near the southern range limit and declined for temperature regimes simulating locations north and south of the range limit. This pattern only weakly supports the hypothesis that germination would decrease south of the southern range limit. I then conducted an additional controlled germination experiment containing treatments with varying levels of cold stratification, the results of which suggest that the chilling requirement for germination is partly responsible for the southern range limit. Both seed germination proportion and germination time decreased when the amount of cold stratification dropped below values typical of the southern range limit. I also carried out a preliminary bud-break experiment where Russian olive cuttings that were pre-exposed to natural chilling were subjected to various levels of additional chilling in a refrigerator. The results of this experiment suggest that a high percentage of buds burst with chilling values less than those typical of the southern limit. I then conducted a controlled bud-break experiment with cuttings that accumulated varying levels of chilling naturally. Percent bud break decreased when chilling dropped below values typical of the southern range limit, suggesting that the chilling requirement for bud-break is partly responsible for the southern range limit. In 17-65% of the years from 1980-2000, the chilling accumulated at a site near the southern range limit (El Paso, Texas) would lead to a 10% or more decrease in bud-break. The potential decline in growth could have large fitness consequences for Russian olive trees. Finally, I collected fruit production and seed viability data. While fruit production did not decline towards the southern range limit, seed viability declined with decreasing latitude. If climate change follows a warming trend, it is very likely that the chilling requirement for bud-break of Russian olive trees will not be met in some years and this combined with decreased seed viability at lower latitudes may cause its southern range limit to retreat northward. The retreat of a widespread non-native species, such as Russian olive, may present land managers and ecologists with a unique restoration opportunity.