Abstracts
The Second Perennial Cool-Season Invasive Grasses of the Northern Great Plains: Ecology and Management Workshop
March 15-17, 2023,
Fargo, ND
Oral Presentation Abstracts
Wednesday, March 15
Keynote: Roots matter: How smooth brome alters the structure of soil microbial communities and soil ecosystem services
Dr. Eric Lamb – Department of Plant Sciences - University of Saskatchewan – Saskatoon, SK
Abstract: Invasions by smooth brome (Bromus inermis) displace native species and strongly alter plant community structure. These plant community changes cascade into the soil ecosystem, alter the nitrogen cycle, and cause profound changes in soil microbial community structure. Extensive research over the last decade in western Canada has explored both how smooth brome alters soil ecosystems and the long-term consequences of those soil ecosystem changes. Post-invasion changes include the selective suppression of dominant bacterial species that, in turn, allows the competitive release of a large number of rare bacterial species, with a small number of “keystone” microbial species driving plant root-bacterial-archaeal-fungal relationships. These patterns suggest that the dominant mechanism structuring post-invasion microbial communities in this ecosystem is a causal cascade initiated by the loss of the roots of native plant species following brome invasion, followed by an indirect plant-fungal pathway mediated by bacteria. Our understanding of smooth brome-soil relationships has lessons for how we should investigate the soil ecosystem consequences of other cool-season grass invasions, invasions by more than one species, and how those invasions, in turn, drive soil ecosystem services in grasslands.
Speaker’s Bio: Dr. Eric Lamb (BSc. University of British Columbia; MSc. Lakehead University; PhD. University of Alberta) is a plant ecologist with broad research interests including fire ecology, grazing ecology, plant-soil interactions, plant competition, statistical ecology, and natural history. His current research is multifaceted, with a primary focus on the role disturbance by fire and grazing plays in structuring grassland plant community composition and diversity. He is also involved in projects ranging from the ecology of species at risk to the application of ecological theory to solve practical problems of rangeland management.
Ecological drivers of perennial grass invasion
John Hendrickson and Jeff Printz
Abstract: Cool-season invasive perennial grasses have expanded rapidly in the Northern Great Plains, especially in the last quarter of the 20th century. While the exact cause of this rapid increase is not known, a greater understanding of ecological processes and their drivers can provide insight into why the rapid increase occurred and enhance the effectiveness of potential control mechanisms. We discuss the water cycle or the capture, storage and safe release of precipitation, the nutrient cycle, or the way nutrients cycle through the physical and biotic components of the environment and the energy cycle, or how sunlight is converted to plant and then animal matter. We then discuss the interrelatedness of these cycles and give examples of their linkages. We will define positive and negative feedbacks and show how they impact ecological processes. We will then link feedbacks and processes by using an example with nitrogen and provide a conceptual model on how nitrogen feedback can move plant communities to an invaded state. Humans interact with ecological processes and we will give examples of human impact on ecological processes. When managers implement strategies targeting cool-season invasive grasses, they need to 1) consider which ecological process and driver they are targeting and 2) develop a monitoring program focusing on that process or driver. Finally, because changes in ecological drivers cause plant communities to change, land managers need to adapt and realize strategies that worked in previous vegetative states may not work, or may even be counterproductive, in new ecological communities.
Climate and land use driven ecosystem homogenization in the Prairie Pothole Region
Kyle McLean*, David Mushet, and Jon Sweetman
Abstract: The homogenization of freshwater ecosystems and their biological communities has emerged as a prevalent and concerning phenomenon because of the loss of ecosystem multifunctionality. The millions of prairie-pothole wetlands scattered across the Prairie Pothole Region (hereafter PPR) provide critical ecosystem functions at local, regional, and continental scales. However, an estimated loss of 50% of historical wetlands and the widespread conversion of grasslands to cropland make the PPR a heavily modified landscape. Therefore, it is essential to understand the current and potential future stressors affecting prairie-pothole wetland ecosystems in order to conserve and restore their functions. We developed a conceptual model that illustrates how (a) historical wetland losses, (b) anthropogenic landscape modifications, and (c) climate change interact and have altered the variability among remaining depressional wetland ecosystems (i.e., ecosystem homogenization) in the PPR. We reviewed the existing literature to provide examples of wetland ecosystem homogenization, provide implications for wetland management, and identify informational gaps that require further study. We found evidence for spatial, hydrological, chemical, and biological homogenization of prairie-pothole wetlands. Biological homogenization was primarily driven by the increased prevalence of invasive perennial grasses and cattails in many wetlands and the uplands they are embedded in. The dominance of invasive plant species has resulted in a reduction of native plant communities and their ecological functions. Our findings indicate that the maintenance of wetland ecosystem multifunctionality is dependent on the preservation and restoration of heterogenous wetland complexes, especially the restoration of small wetland basins and their plant communities.
Smooth brome and Kentucky bluegrass – Does increased invasion decrease management effectiveness in mixed-grass prairies?
Jill Gannon, Cami Dixon*, and Jennifer Zorn
Abstract: The U.S. Fish and Wildlife Service is working to improve the integrity of native prairies in the Prairie Pothole Region by increasing the native plant cover and decreasing smooth brome (Bromus inermis) and Kentucky bluegrass (Poa pratensis) cover. The Native Prairie Adaptive Management program (NPAM) is a decision framework that aids in meeting this goal and has been operational for more than 10 years. NPAM explicitly incorporates biological uncertainty while providing annual management recommendations for nearly 80 mixed-grass prairie units. In addition to the decision support that NPAM provides, the data collected make it possible to look retrospectively at variables that may affect management outcomes. We completed an analysis comparing the relative importance of seven biotic and abiotic variables and their interactions in terms of how much they explain the change in plant cover. We found that while multiple variables influence the plant cover outcome, management treatment is an important variable that affects the change in the cover of smooth brome and Kentucky bluegrass. One of the variables included in this analysis was invasion level, where we hypothesized that as invasion of smooth brome and Kentucky bluegrass increases, management treatments would become less effective. Our data do not support this hypothesized relationship. For smooth brome, treatment effectiveness of rest, burn, and burn/graze did not vary with invasion level, while grazes were more effective under medium and high invasion than low invasion. For Kentucky bluegrass, rest, graze, and burn treatments become more effective as invasion level increases. Burn/Graze is the only treatment that shows the hypothesized relationship of decreased effectiveness with increased invasion level when combatting Kentucky bluegrass.
Landowner perceptions of an invasive grass in the Northern Plains of the United States of America
David Toledo*, Kiandra Rajala, and Michael Sorice
Abstract: Plant invasions have serious consequences on native plant species diversity and ecosystem services. We explored private landowner perceptions about invasive grasses and their management intention to reduce/control them in the US Northern Great Plains. We used a factorial survey experiment with multiple vignettes that randomly varied based on how a novel grass species expanding in rangelands would affect provisioning services (season of forage availability, forage quality, forage quantity), regulating services (floral resources for pollinators, water infiltration, and availability), and supporting services (grassland bird diversity, grass diversity). Our results show that the acceptability of invasive plants was strongly associated with landowners’ management intentions, and the status of all seven ecosystem services was related to acceptability. Scenario modeling shows that landowners displayed greater sensitivity to losses in a suite of ecosystem services than to equivalent gains. Scenario results indicated that invasive grasses may be considered slightly acceptable during the early stages of invasion. At later stages, when negative impacts are most severe for landowner livelihoods, invasives are rated as slightly unacceptable. Results suggest that ecological losses may need to be severe before individual landowners in the US Northern Great Plains change their management practices to reduce/control the species. Our research suggests landowners may be managing more reactively than proactively. Further landowner awareness, engagement, and extension efforts are needed to prevent and reduce invasives from Northern Great Plains grasslands.
Trends in Prairie Pothole Region plant community composition after a decade of enrollment in the Native Prairie Adaptive Management program
Carlee Coleman, Shawn DeKeyser*, Breanna Kobiela, and Cami Dixon
Abstract: Native prairie currently managed by the US Fish and Wildlife Service in the Prairie Pothole Region is a valuable source of native plant biodiversity of the region. However, this dwindling resource is threatened by cool-season invasive species. The Native Prairie Adaptive Management (NPAM) program is currently being utilized to increase native species diversity by utilizing natural disturbance regimes (i.e., fire, grazing, rest). We explored how native species composition has changed between 2012 and 2020, focused on prescribed fire. Permanent modified-Whittaker plots were established in 2012 to assess plant community composition on 30 sites enrolled in the NPAM program in North Dakota and South Dakota. We revisited the sites in 2020 to assess any changes in plant community composition. Permutational analysis of variance indicated compositional differences (p < 0.025, F = 1.874) between sites burned 0, 1 or 2 times and sites burned 3, 4 or 5 times. T-tests reveal that frequent burning increased the abundance of certain species and decreased others, and floristic quality was higher in 2020 than 2012. There were no significant changes in Kentucky bluegrass (Poa pratensis) or smooth brome (Bromus inermis) relative cover, and an unanticipated finding was an increase (p = 0.036) in sweet clover (Melilotus officinalis) on sites burned at higher frequencies. Native plant community management in the region will be a difficult task in a landscape highly invaded by a number of introduced species.
Oral Presentation Abstracts
Thursday, March 16
Temporal assembly and recruitment of bacterial and fungal communities in invasive Kentucky bluegrass and native switchgrass
Lennel A. Camuy-Vélez
Abstract: Invasive plants are a major problem worldwide causing both impact on the economy and on the diversity and integrity of ecosystems. While previous studies have investigated the importance of plant physiological traits, our understanding of the microbial contribution to plant invasion is limited in the field. In a longitudinal greenhouse study of invasive Kentucky bluegrass and native switchgrass utilizing amplicon-sequencing and metabolomics, we elucidated how the fungal and bacterial communities’ dynamics in the rhizosphere and root varied between these two hosts. We found Kentucky bluegrass roots to have higher Shannon Diversity in both bacterial and fungal communities. Bacterial and fungal communities were structured by hosts and plant compartments with communities differentiating over time. In addition, we found Kentucky bluegrass to have a higher number of unique microbial members (781 bacteria and 134 fungi) than switchgrass (582 bacteria and 105 fungi). While both rhizosphere and root microbiota were dominated by Proteobacteria, Kentucky bluegrass rhizosphere had greater abundance of Xanthomonadales members, while switchgrass rhizosphere had more Burkholderiales. Invasive Kentucky bluegrass showed greater abundance of Rhizophlyctidales in the roots while native switchgrass had Hypocreales. We also identified specific root exudates that are secreted by the invasive plant to recruit members of the microbiota. Overall, our results can offer insights into the dynamics of microbial recruitment by invasive plants and mechanisms that lead to invasive species to outperform native plants. The microbial differences observed here could further reveal why Kentucky bluegrass is a strong invader of new environments.
Using axillary buds to assess the impact of management strategies on the abundance of invasive cool-season grasses
John Hendrickson
Abstract: Reducing the proportion of smooth bromegrass (Bromus inermis) and Kentucky bluegrass (Poa pratensis) in the species composition requires understanding how management strategies can influence tiller populations. Examining axillary bud numbers can help to identify management’s influence on future populations. The impact of management strategies on axillary buds of Kentucky bluegrass and smooth bromegrass was examined at the Northern Great Plains Research Laboratory in Mandan, North Dakota. In Experiment 1, rainout shelters were used to simulate drought on 2m x 2 m plots that had ½ of the area (1m x 2m) burned in fall of 2017, 2019 and 2020. The experiment was replicated three times in three different blocks. Five cm in diameter plugs, 2.5 cm deep were taken from each plot in spring and fall of 2020 and 2021. Axillary bud number and viability were assessed after immersion in 0.1% (w/v) solution of 2,3,5- triphenyl tetrazolium. In Experiment 2, 50 ungrazed smooth bromegrass tillers in three different exclosures were marked with a colored wire and randomly assigned to be defoliated in the vegetative, elongation or reproductive stages in 2018, 2019 and 2020. Marked tillers were excavated and the number of axillary buds recorded and viability assessed. Burning under moderate drought reduced the number of Kentucky bluegrass axillary buds; however, smooth bromegrass tillers defoliated in the reproductive stage produced more tillers than the undefoliated controls. Both experiments indicate that management strategies can affect the abundance of invasive cool-season grasses and that axillary buds provide an early indication of that impact.
Invasive grass and litter accumulation constrain bee and plant diversity in altered grasslands
C.K. Pei, Torre Hovick, Ryan Limb, Jason Harmon, and Benjamin Geaumont
Abstract: Exotic cool-season grasses, Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis), have caused functional and structural transformations to Northern Great Plains (NGP) grasslands. These changes accompany other human alterations to grassland landscapes and influence plant communities, as well as, the organisms that rely on plant structure and composition, such as pollinators. We sought to determine if these two invasive grass species and their associated characters such as litter accumulation, grass cover, and bare ground alter bee and forb diversity in NGP grasslands and determined their relationships with bees in various functional groups based on their diet, sociality, nesting habit, and body-size. We surveyed bee and plant communities at 67 sites across North Dakota from 2017-2020 and collected 20,111 bees from 182 species, while observing 249 forb and shrub species. Bee richness was positively associated with forb richness, but forb richness was significantly lower with greater litter accumulation and increased with greater coverage of non-invasive grasses. Bee trait analyses revealed various associations between bees of different life history requirements and invaded plant community characters. For example, ground-nesting bees had negative associations with greater litter depths and Kentucky bluegrass cover while small-bodied bees were increased with bare ground availability. Idle management of invaded grasslands can result in homogenized grassland structure, with greater litter accumulation that affects plant diversity and certain bees. Our results show the importance of promoting diverse grassland structure in the presence of exotic grass invasions to support bee diversity and the pollination services they provide to grassland communities.
The predicted nutrient supply of Kentucky bluegrass does not always meet nutritional recommendations for cow-calf pairs
David Toledo* and Rachael Christensen
Abstract: Grasslands in the Northern Great Plains have been invaded by Kentucky bluegrass (Poa pratensis), which is a cool-season grass. The extent of invasion varies from non-invasion to areas completely invaded. Future weather predictions estimate that growing season precipitation will decrease while the temperature will increase. These weather patterns will affect grass growth and forage quality, especially in areas that are fully invaded. We compared the nutritional requirements of cow-calf pairs to the productivity and nutritional quality of Kentucky bluegrass in drought and non-drought years. Kentucky bluegrass samples were clipped every two to three weeks in mowed and unmowed plots during the growing seasons of 2017, a drought year, and of 2018. Samples were used to determine annual production and were analyzed for minerals and for crude protein using wet chemistry methods and in vitro true dry matter digestibility. We found productivity and nutritional deficiencies throughout the growing season, especially during a drought year. Increasing forage plant diversity and adjusting management to allow adequate growth and plant cover throughout the year can ensure a more consistent supply of forage.
Thinning out smooth bromegrass invasion
Lealand Schoon
Abstract: Smooth bromegrass is increasing and invading undisturbed native rangeland in south central South Dakota. We are investigating a grazing strategy that focuses attention on plants native to the site and ignoring the invasive smooth bromegrass. The objective is to increase the native plant community and decrease the vigor and production of smooth bromegrass. The grazing management strategy used focuses on key vegetative growth regulators of native grasses. Matching the proper timing of defoliation with the growth stage of the native grass is important to maintain vegetative growth of the desired native plant community. The results, after four years, are demonstrating that smooth bromegrass has decreased in plant vigor. Native plant functional/structural groups increased in diversity across the landscape. Monitoring documents nearly 40 percent of the plant community being native grasses and forbs in another example from 2021. With this diversity of active native plant roots, the soil organisms native to the soil are repopulating. Grazing to restore the native soil organism habitat will increase the native plant population. Finally, non-native grass species will be less competitive. In these examples, soil function is being restored to promote a deeper-denser native plant environment.
Timing prescribed fire in tallgrass prairies based on plant phenology
Sara Vacek*, Cami Dixon, Jill Gannon, and Jennifer Zorn
Abstract: The U.S. Fish and Wildlife Service (USFWS) uses prescribed fire to manage native prairies in the Prairie Pothole Region. Management goals include increasing native plants and decreasing smooth brome (Bromus inermis) and Kentucky bluegrass (Poa pratensis). The Native Prairie Adaptive Management program (NPAM) provides a decision framework to aid in meeting this goal. Tallgrass prairie management units enrolled in NPAM receive annual recommendations that provide specificity for timing burns based on smooth brome phenology. Literature and expert opinion at the onset of NPAM suggested that burning smooth brome at the elongation stage provided the best opportunity to decrease smooth brome and increase warm-season native plants. USFWS staff worked with partners over the past decade to identify smooth brome growth stages consistently and accurately. Recent retrospective analysis of NPAM tallgrass data indicate that this targeted burn time is not producing the expected results; burning at the elongation stage of smooth brome is not decreasing the smooth brome cover nor increasing the native plant cover. Conversely, the data indicate that burning outside of the elongation stage decreases the smooth brome cover and increases the native plant cover. The results of this analysis reinforce the need to continually challenge our assumptions about managing prairies.
Effectiveness of glyphosate herbicide at controlling non-native cool season grasses in a degraded prairie remnant
Tyler Janke
Abstract: Non-native invasive grasses present significant threats to grassland biodiversity. Despite efforts, much uncertainty surrounds the effectiveness of various control methods and their impacts to non-target vegetation in remnant prairie settings. The objectives of this study were to evaluate the effectiveness of dormant season glyphosate application at controlling smooth brome (Bromus inermis) and Kentucky bluegrass (Poa pratensis) in a degraded prairie remnant and identify any negative impacts to non-target vegetation resulting from herbicide application. Plant species and cover data were collected along two 50 meter transects in a cool season infested prairie in Northwest Minnesota between 2020 and 2022. Following pre-treatment data collection, the study area was mowed and transects were designated treatment and control. In October 2020, the treatment transect was sprayed with a 3% glyphosate solution following two hard frosts. Post-treatment plant species and cover data were collected from both treatment and control transects in 2021 and 2022. Dormant season glyphosate application significantly reduced smooth brome and Kentucky bluegrass cover in the treatment transect, and that control has remained significant for two years post treatment. Additionally, evaluations of native species functional group cover, individual species cover, individual species frequency of occurrence, and plot-wise floristic quality index values have shown negligible impacts to non-target species attributable to herbicide application. These results suggest that dormant season glyphosate application can provide selective control of non-native cool season grasses in degraded native prairies by altering the season of application and implementing a few site preparation measures.
An evaluation of prairie reconstruction results with emphasis on native plant species performance and invasive grass recolonization using multiple prescribed management techniques on U.S. Fish and Wildlife Service lands, North Dakota
Mark Fisher
Abstract: Prairie reconstruction is an upland habitat restoration technique where habitats are restored using 14-25 species of native grasses and forbs. Reconstructed sites have been annually monitored within the ENDWMD since 2017 with the primary goals of understanding planted and invasive species performance with various habitat management techniques. Management techniques evaluated included burning, haying, mowing, grazing and idleness. Test plots equaling 10m x 10m were non-randomly established at WPAs at a rate of 13.8 acres per site. The average size of restored habitat per WPA equaled 119 acres. Plant species were monitored for mean percent cover and frequency of distribution per plot. Management techniques were evaluated by measuring mean plant cover both pre- and post- management, management prescriptions varied by site. In addition, Redundancy analysis was used to model environmental variables coupled with species performance. By fall of 2022, 210 releves covering all management techniques were evaluated. Big bluestem provided the highest mean cover at 27.9% per site. Wild bergamot provided the highest mean forb cover across all sites at 7.43%. Noxious weed densities were below 5% mean cover. Kentucky bluegrass mean cover averaged 15.3% and was present at all sites regardless of management. Smooth bromegrass plant cover averaged 2.93%. Redundancy analysis and ANOVA results indicated that management was a significant variable (p < 0.005) determining plant species mean cover values. Fall burning provided the highest percent cover values on at least 16 native plant species while idling habitat was positive for 14 native plant species.
Prescribed fire reduces exotic perennial grasses in invaded northern mixed-grass prairie but creates small invasion risk in uninvaded areas
Amy J. Symstad*, Max Post van der Burg, and Heather Q. Baldwin
Abstract: The Annual Brome Adaptive Management decision support tool (DST) was built from 20 years of monitoring data to support vegetation management decision making of seven National Park Service units in the Northern Great Plains. Although focused on annual bromes, the DST also predicts the behavior of exotic perennial grasses in response to prescribed fire. Specifically, in areas moderately invaded by exotic perennial grasses, fall fire’s reduction of these invasives is immediate and relatively steady over 5 years. In contrast, spring fire’s reduction increases over 5 years to the point of being ~50% more likely to result in low exotic perennial grass cover than fall fire, and three times as likely as no fire. More heavily invaded areas show the strongest reduction in exotic perennial grasses in the first year after a fall fire but 4-5 years after a spring fire. At that longer timeframe, improvement is nearly as likely to occur without fire as with a fall fire. However, burning, especially in spring, puts prairie uninvaded by exotic perennial grasses at a greater risk of moderate invasion in the first growing season following fire, and of high invasion 4-5 years following fire, than not burning. The probability of maintaining low exotic perennial grass cover after 4-5 years is greater in fall-burned areas than unburned areas, and least probable in spring-burned areas. These results show that prescribed fire is a useful tool for reducing exotic perennial grass invasion, but caution is warranted when burning areas not already invaded by these species.
Ecosystem benefits of invasive winter annual grass removal
Shannon Clark
Abstract: Invasive winter annual grasses are altering rangeland ecosystems across millions of hectares in the western United States (US). Two new invaders in the Great Plains ecoregion, Ventenata dubia and Taeniatherum caput-medusae, have been spreading at an alarming rate since their detection in 2016. These winter annuals outcompete native plants for soil moisture and nutrients, leading to devastating impacts on ecosystem functions. Negative effects include decreased native vegetation, reduction in wildlife and pollinator habitat, and increased fire frequency. The winter annual grass seed bank is short-lived and often does not persist beyond 3 years. Indaziflam, a pre-emergence herbicide, provides winter annual grass control for three or more years. Indaziflam’s extended soil residual control and tolerance of perennial species creates the opportunity to deplete the annual grass seed bank, allowing time for remnant plant communities to recover. Research trials have been conducted on sites across the western US where annual grasses were managed using indaziflam. The long-term management of the annual grass seed bank has led to significant increases in native species richness, cover, and biomass within the native plant community. The shift from an annual grass dominated community to a healthy native plant community has resulted in improved pollinator and wildlife habitat in these sites. Removal of these invasive annuals has the potential to reduce the spread and devastation caused by annual grass-fueled wildfires in the western US. By changing the management paradigm to target the annual grass seed bank, land managers can achieve long-term restoration.
Oral Presentation Abstracts
Friday, March 17
Adaptive management on tallgrass prairie for native species composition
Alison Long
Abstract: In a cooperative effort among The Nature Conservancy, Minnesota Department of Natural Resources, the United States Fish and Wildlife Service, and other partners, we are using adaptive management to make recommendations for the management of native tallgrass prairie plant communities in western Minnesota and eastern North Dakota and South Dakota, USA. The purpose of this ongoing work is to evaluate which management actions (i.e., burning, grazing, rest) have the greatest likelihood of improving cover and composition of native plant communities. The cool-season introduced grasses, Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis), are particularly problematic across the region, seriously impacting the quality of ecosystems and therefore influencing land management. Since 2008, we have used a rapid assessment protocol to collect vegetation data related to prairie structure and composition. Plant community composition is assessed through the observation of native and invasive indicator species and through the assignment of plant group codes spanning the native-invasive, herbaceous-low shrub-tall shrub, and graminoid-graminoid/forb-forb axes. These data are used to annually inform a stochastic dynamic programming model to generate management recommendations dependent on the current conditions of the site (i.e., level of invasion and predominance of herbaceous vs. shrub cover). Overall, we found that native plant cover has increased at low-quality sites and burning has enhanced the native plant community. Grazing has negatively affected the native plant community, especially at low-quality sites. In a new analysis, we also explored trends in the prevalence of Kentucky bluegrass and smooth brome across 14 years of data.
Benefits from management are lost after several years in Kentucky bluegrass (Poa pratensis) invaded rangelands
Esben L. Kjaer*, Torre J. Hovick, Ryan F. Limb, Benjamin Geaumont, Jason P. Harmon,
and Kevin K. Sedivec
Abstract: Rangelands in the northern Great Plains are being converted into novel ecosystems by invasive grasses, especially Kentucky bluegrass (Poa pratensis; hereafter ‘bluegrass’). Bluegrass invades rangelands and forms a dense litter layer, which leads to the formation of thatch, a unique pseudo-soil layer. Thatch and litter accumulation alter water and nutrient cycling, suppress native plants, and alter soil microbial communities. These factors transform once native rangelands to novel ecosystems, warranting bluegrass management and mitigation. In south-central North Dakota, we monitored how bluegrass and the surrounding plant communities responded to different management practices. Specifically, we examined previous studies that monitored plant community composition in rangelands managed with patch-burn grazing, heterogeneity-based rotational grazing, continuous grazing, rest, and physical bluegrass removal. We found that disturbances such as grazing, fire, and physical removal can reduce bluegrass for a few years (e.g., bluegrass cover can be up to 12% lower three years post-disturbance). Disturbance also reduced bluegrass litter and thatch depth (thatch depth was 1.79 cm in patch-burn grazing and 3.9 cm in ungrazed areas). Additionally, disturbances promote native plants, with native forb abundance being higher in disturbed areas than undisturbed for at least three years post-disturbance. However, the differences we observed, and those observed in other studies are eventually lost over time as bluegrass re-invades disturbed areas. This loss is likely because the management practices used treat the symptoms of invasion, not the mechanisms underlying bluegrass invasion. To create more effective management strategies, a better understanding of the mechanisms underlying bluegrass invasion is needed.
Cool-season invasive grasses are driving composition of Prairie Pothole Region wetlands
Seth Jones*, Shawn DeKeyser, Breanna Kobiela, and Cami Dixon
Abstract: Prairie pothole wetland plant communities are highly variable depending on hydrology, salinity, and anthropogenic disturbances in and adjacent to the wetland. The U.S. Fish and Wildlife Service (USFWS) has managed prairie potholes since the passing of the Duck Stamp Act in 1934, employing various management techniques in the subsequent decades. In 2020 and 2021 we conducted a regionwide assessment of prairie potholes on USFWS fee-title lands in North Dakota, South Dakota, and Montana to inform future prairie pothole management. While several of the included fee-title lands are remnant native prairie, most were cultivated in the past and reseeded into perennial grassland. Our goal was to determine the primary plant species influencing wetland plant community composition of these lands. We collected species-level cover data at 200 randomly selected wetland sites located on fee-title lands. We determined that few sites accounted for most of the diversity in the region while most sites had low diversity and high abundance of invasive species. We employed nonmetric multidimensional scaling and multi-response permutation procedure to explore wetland plant communities. We found that invasive species, especially Bromus inermis, Phalaris arundinacea, and Typha ×glauca, play major roles in the wetlands surveyed. Native and reseeded plant communities possess distinct species compositions, largely due to the abundance of invasive species in reseeded areas. Our research has identified invasive species are driving species composition and pose a major threat to biological diversity. Despite land management efforts to convert past agricultural land into diverse, productive ecosystems, invasive species continue to dominate these landscapes and are encroaching into native areas as well. Our results reveal a need to protect the remaining few “biological hotspots” on these USFWS lands within the region and implement native species restoration efforts on their land that was in agriculture in the past.
Poster Abstracts
Thursday, March 17
Influence of cool-season invasive grasses on the stability of prairie streams
Benjamin Menapace, Miranda Meehan, Peter O’Brien, and Garrett Hecker
Abstract: Sod-forming grasses such as Kentucky bluegrass (Poa pratensis) and smooth bromegrass (Bromus inermis) decrease water infiltration and increase runoff. Presence of these invasive grasses in riparian areas could destabilize stream banks by increasing soil surface erosion and outcompeting deep-rooted native riparian species. Studies have shown the importance of deep-rooted native grasses and sedges in riparian greenline plant communities. Desirable riparian species in the greenline stabilize the bank and reduce erosion by trapping sediment and decrease the impact of high energy floods. Greenline plant community composition was evaluated for 29 stream reaches across five watersheds in southwest Bowman County, North Dakota in 2016 and 2022. Plant canopy, total cover, and relative abundance by species metrics were gathered from greenline plant communities using line point intercept. Data from 2022 will be compared to data from 2016 in order to analyze changes in total cover and relative abundance of smooth brome, Kentucky bluegrass, and other cool-season invasive grasses. The greenline data will also be correlated with stream geomorphic data from the associated stream reach to determine influence on stream stability. This study will help project future risks that cool season invasive grasses pose to prairie streams.
Effects of heavy cattle grazing during the early spring and late fall in a smooth brome dominated rangeland
Zachary Johnson, Shawn DeKeyser, Breanna Kobiela, John Hendrickson, Kevin Sedivec,
and Cami Dixon
Abstract: Smooth brome is a perennial grass that has invaded much of the Northern Great Plains and led to drastic declines of biodiversity within the region. Because increasing evidence suggests that diverse plant communities benefit ecosystems and livestock producers, restoration of diverse plant communities could be a desirable investment. Considering this, we started a grazing study to evaluate the potential of heavy cattle grazing during the early spring, fall, or both toward improving plant diversity in a smooth brome dominated rangeland. To monitor changes in plant community composition, we started measuring the abundance of plant species within areas grazed during the spring, fall, both spring and fall, and non-grazed controls. Additionally, we started studying the effects of grazing on the smooth brome population and the species vegetative reproduction. We have not identified definite effects from grazing but we do not expect to see measurable changes until later in the study. We believe our study could provide insight into the nature of smooth brome dominated ecosystems and we hope to see diversity improve within this rangeland. We expect heavy grazing during both the early spring and fall to be most effective at improving diversity, while we are unsure what effects grazing treatments will have on smooth brome’s reproduction. If our management successfully improves plant diversity, that management strategy might help land managers struggling with smooth brome dominated rangelands. In addition, our study of smooth brome’s reproduction may benefit from further research before including in management decisions.
Kentucky bluegrass (Poa pratensis) removal promotes native plant biodiversity
Esben L. Kjaer, Torre J. Hovick, Ryan F. Limb, and Kevin K. Sedivec
Abstract: Rangelands were historically heterogeneous with large patches of varying vegetation composition and structure that supported a diverse assemblage of native plants. In recent years, diverse plant communities in the northern Great Plains have been lost due to invasion by Kentucky bluegrass (Poa pratensis; hereafter ‘bluegrass’), suppressing native plant diversity and landscape-level heterogeneity. Reductions in bluegrass abundance may promote native plants, increasing the variety and availability of forage, cover, and food resources for wildlife. To determine how bluegrass reduction may potentially promote native plants, we established 18 plots and manually removed live bluegrass, bluegrass litter, and bluegrass thatch from half of the plots while leaving the other half as controls in a working landscape in south-central North Dakota and then monitored the plant community over three years. Bluegrass abundance was consistently lower in removal plots than control plots (46.4% and 58.2% cover in year three, respectively). Native forb and grass abundance and richness was higher in removal plots than in control plots (15±3.1 and 5.2±0.8 species versus 9.8±1.9 and 3.8±0.5 species per plot, respectively). Additionally, non-native plant abundance was either not different or lower in removal plots than control plots. These results suggest that removal of live bluegrass and bluegrass thatch and litter decreases bluegrass abundance and promotes native plant communities across multiple years, suggesting that a single instance of bluegrass removal will promote native plant communities and benefit wildlife over multiple years. Conservation efforts should favor management practices that initially reduce bluegrass abundance and promote native plant diversity over several years.
Controlling Kentucky bluegrass using prescribed fire and grazing
Eric Lamb
Abstract: This study examines the effectiveness of grazing following a spring prescribed fire for Kentucky bluegrass control on a sandy grassland site in Douglas Provincial Park, Saskatchewan, Canada. Prior to the fire, the site had been ungrazed for several years, and had high shrub (snowberry and wolf willow) and Kentucky Bluegrass cover. Approximately 40 ha were burned in spring 2019 with unburned inclusions left as control plots. Early season grazing began in 2021 with temporary exclosures producing a factorial design. Fire caused a clear initial decline in Poa abundance, suggesting that the initial goal of setting back Poa via fire was achieved. Poa abundance was substantially lower in burned and grazed plots versus the other treatments, suggesting that the interaction of grazing and fire is indeed effective for Poa control.
Smooth brome (Bromus inermis) competition has a stronger negative impact on milkweed (Asclepias spp.) availability for monarchs than cattle grazing
Ellysa R. Johnson, Esben L. Kjaer, Jason P. Harmon, Torre. J. Hovick, and Kevin K.
Sedivec
Abstract: Invasive grasses, such as smooth brome (Bromus inermis; hereafter brome) and Kentucky bluegrass (Poa pratensis; hereafter bluegrass) invade grazed and non-grazed rangelands and suppress native plant biodiversity. A loss in biodiversity can negatively affect wildlife such as the monarch butterfly (Danaus plexippus), a pollinator of high conservation concern. Monarchs use rangelands, particularly the milkweed (Asclepias spp.) host plants within, for forage, cover, and oviposition sites during multiple life stages. It is currently unknown how milkweed is impacted by exotic grass invasion and cattle grazing intensity. Knowing these impacts may help future monarch conservation success of establishing milkweed stems in working rangelands. We measured thatch depth, litter depth, litter abundance, milkweed, brome, and bluegrass abundance in working rangelands managed with varying cattle grazing practices and levels of invasive grass cover. We recorded any flowering or cattle-grazed milkweed stems across 12 different pastures in south-central North Dakota managed with heterogeneity-based rotational grazing, patch-burn grazing, and continuous grazing. We then assessed how cattle grazing, invasive grass abundance, litter, and thatch influenced milkweed availability using Structural Equation Modelling (SEM). We found that cattle grazing and brome, but not bluegrass, negatively impact milkweed availability. Specifically, brome competition has a stronger negative impact on milkweed than direct cattle grazing, suggesting that the benefits of cattle grazing in reducing smooth brome potentially outweigh any direct negative effects of cattle on milkweed availability for monarch use. Therefore, any practice that decreases smooth brome abundance in rangelands may simultaneously aid monarch conservation in rangelands.
Managing crested wheatgrass by restoring soil health
Heather Davis, Caley Gasch, Edward DeKeyser, and Mike Borgreen
Abstract: United States land managers seek to restore diversity of native plant species to crested wheatgrass (Agropyron cristatum) (CWG) dominated areas but have had limited success with aboveground management approaches. This study was performed to analyze impact of various management methods on soil physical, chemical, and biological properties with the aim to reduce CWG and enhance soil for native species establishment. We will address our objectives through a field study and greenhouse study. The field study occurred near Glasgow, MT in the Northern Great Plains region of the United States. The CWG management methods analyzed, both alone and in combination, were: Control (no treatment), Herbicide, Tillage, Cover crops, and a Biological soil amendment. In 2022, data collection included vegetation surveys and analyses of soil properties. The greenhouse project will look at soil properties under the same treatments as the field study followed by a native plant growth phase. This study aims to find the most effective management methods for suppressing CWG growth and improving soil health. We expect that conditioning the soil for future establishment of native perennial plant species will help future grassland restoration efforts.
Using adaptive management to reduce smooth brome and Kentucky bluegrass following restoration of a degraded grassland
Monica Polgar, Breanna Kobiela, and Shawn DeKeyser
Abstract: Grasslands throughout the Northern Great Plains face homogenization due to invasion by Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis). Kentucky bluegrass and smooth brome impair grassland plant community structure and function, and both species tend to persist despite management and restoration efforts intended to improve degraded grasslands. In 2010, North Dakota State University personnel initiated a study to evaluate the potential of various restoration and management efforts toward improving plant species composition and forage production on a 30-acre degraded grassland in southeastern North Dakota. Five restoration treatments were installed (interseed (1); interseed and burn (2); interseed, burn, and herbicide (3); interseed and herbicide (4); control/no treatment (5)) and the site has been adaptively managed using grazing and prescribed burning in the years since. Fifteen 40 x 100 m plots were established in 2010 to allow for repeated vegetation sampling to monitor the effectiveness of restoration and management efforts over time. In 2020 and 2021, vegetation sampling indicated that average smooth brome biomass was reduced in each of the restoration treatments from the control, while average Kentucky bluegrass biomass was reduced under three of the restoration treatments (interseed; interseed and burn; interseed, burn, and herbicide). In addition, average native warm-season grass biomass and grass species richness increased under every restoration treatment over the control. While smooth brome and Kentucky bluegrass are still present at this site more than 10 years after the original efforts to improve the site were initiated, it is encouraging to note that the restoration techniques and adaptive management methods employed have helped to meet the goals of improving species composition and forage production on a degraded grassland.
Spring pre-fire grazing trials: Ecology and economics for livestock producers and land managers
Pete Bauman
Abstract: My objective in these trials was to experiment with options that could offset grazing deferment expenses for a livestock producer while ensuring an adequate fuel load to allow for easy, safe, and successful prescribed burns to be conducted during mid-late May for effective exotic cool season grass control. I utilized full season grazing deferment during year 1 for pastures scheduled to be burned in year 2 in order to build an adequate fuel load that would allow a fire to be conducted in the late spring of the second year. During April and early May of year 2, I allowed livestock to ‘pre-graze’ the scheduled burn unit for up to 14 days during peak growth and heading of Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis). Initial results of these trials have been positive. Economic return is positive as there is some grazing opportunity, as well as cost savings related to easy and safe fires requiring reduced labor and resources. In addition, cool season exotic grass control is effective while native plant response (production, diversity, vigor, seed production) are also positive.
Dissecting the role of soil microbiomes in plant invasion using a pairwise competition experiment
Rakhi Palit, Samiran Banerjee, and Shawn DeKeyser
Abstract: Grasslands are one of the most endangered ecosystems in North America. Thus, conservation and restoration of the remnant native prairies in the Northern Great Plains are critical to protecting these ecosystems and preserving biodiversity. The rapid spread of invasive plant species has caused many native grassland ecosystems to be completely outcompeted. There is often a total elimination of native species in the prairies where these species have invaded, resulting in an overall homogenization of ecosystems. Plant-soil feedback has emerged as central to explaining how plant species invade and transform ecosystems. Plant-soil feedbacks arise because plant species differentially alter soil communities by cultivating a microbiota specific to each species. Despite the critical role of plant-soil feedback in invasion dynamics, our understanding remains severely limited due to the difficulty of identifying the soil microorganisms that drive these processes. Furthermore, global estimates suggest that most grasslands will experience increased atmospheric nitrogen deposition by 2030. Native species might lose their natural competitive ability under changing nitrogen levels, with subsequent declines in grassland diversity. Here we conducted a targeted greenhouse experiment to study the pairwise interactions under three different soil nitrogen levels. We selected an invasive cool-season, C3 grass species Kentucky bluegrass, with a functionally similar cool-season, C3 grass species, western wheatgrass, and another functionally dissimilar native warm season, C4 grass, blue grama. Specifically, our goal was to understand whether the invasive and native species influence microbiota differently by examining the structure and composition of rhizosphere microbial communities of invasive species grown with native grasses under different nitrogen regimes. We used quantitative PCR and Illumina MiSeq sequencing of bacterial 16S rRNA and fungal ITS genes to characterize microbial abundance and community structure, respectively. Sequencing analysis is currently underway, and the results will be incorporated in the final presentation.
Can defoliation reduce the abundance of smooth brome? An examination of phenology and defoliation timing
JR Hendrickson, AJ Carrlson, A Field, AK Clemensen, and V Yeomaan-Goodrich
Abstract: Smooth brome (Bromus inermis) is an introduced, cool-season, perennial grass that has invaded grasslands in the Central and Northern Great Plains. Anecdotal evidence suggests grazing may reduce smooth brome abundance. However, little is known about the timing of grazing and how it impacts smooth brome persistence. We compared the crowns of smooth brome tillers that were defoliated either once (V1) or twice (V2) in the vegetative stage, in the elongation stage (E), in the reproductive stage (R), or left undefoliated (C) in three ungrazed exclosures over three years near Mandan, ND. Tillers in each treatment were marked with a different colored wire and excavated in the fall. Tillers were brought back to the laboratory, cleaned and each node position on the crown was categorized as an axillary bud, tiller, rhizome or leaf scar. The tillers were then placed in 0.1% w/v 2,3,5-triphenyl-2H-tetratozolium chloride (TTC) for 24 hours and activity levels on each position recorded. Tillers with inactive node positions were placed in Evan’s blue solution to determine viability. Positions that were not active or dead were considered dormant. Year and defoliation impacted the number of node positions, outgrowth and active meristems tiller-1. The R defoliation treatment had more total positions and active meristems than the controls (C). Outgrowth (tillers plus rhizomes) was less in the V2 treatment than the R (1.18 vs 1.83 outgrowth positions tiller-1 respectively). This data suggests that defoliation timing can impact the abundance of smooth brome. This information will help managers design targeted grazing programs to reduce this invasive grass.