Browsing by Subject "Grasslands"

Now showing 1 - 5 of 5
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    Climate Change and Tallgrass Prairies: Exploring the Interaction of Extreme Weather and Invasion in Managed Prairie Systems
    (2020-12) Ratcliffe, Hugh
    Climate change will increasingly shift seasonal timing and increase the frequency and intensity of extreme events like drought and severe wet conditions, all of which threaten to amplify other global change drivers like invasion. Consequently, understanding how conservation management actions like prescribed burning interact with climate is increasingly pressing for invasive management. Although prescribed burning has been widely demonstrated to increase native plant diversity and suppress a number of invasive species, understanding under what current and future conditions burning will be most effective remains an ongoing focus of applied prairie ecology research. Earlier springs and extended growing seasons will shift the timing and availability of resources and niche space, which may disproportionately advantage invasive species and also influence the outcome of burning. Furthermore, northern tallgrass prairies will experience intensified extreme precipitation patterns characterized by more precipitation falling in fewer events interspersed with longer dry periods and amplified evapotranspiration. Because moisture availability functions as a key determinant of prairie composition, theory and evidence suggest drought conditions will hinder invasion, whereas wetter conditions will enhance invasion. Here, I conducted two analyses exploring the effect of weather on prairie invasion dynamics from 2010-2019 in 25 observed prairie sites and 267 transects spread throughout Minnesota, USA. First, I estimated the effects of burning, start time of the growing season, and their interaction. Second, I estimated how an increase in extremely wet or dry months altered invasive abundance and influenced the effectiveness of burning. For the first analysis, I determined that burning reduced both total invasive and invasive cool season grass abundance, and that this reduction persisted over time for invasive cover but quickly waned for frequency. Additionally, I found that growing season start does indeed influence community composition but that later starts rather than earlier increased invasive abundance. For the second analysis, I found that a greater occurrence of abnormally wet months increased invasive abundance and minimal evidence that abnormally dry conditions hinder invasion. Furthermore, I did not observe additive interaction effects of drought and prescribed burning but did find that an increase in the number of wet months reduced the effectiveness of burning. Together, these results suggest that, although earlier spring timing is unlikely to be a primary mechanism driving increased invasion, more frequent extremely wet and dry months may intensify invasive dominance and hinder our ability to suppress invasion species via prescribed burning. Ultimately, I propose that future research should seek to better understand abiotic controls on invasive species’ phenologies, how precipitation seasonality influences invasive performance, and also identify potential thresholds in ecological processes to understand whether responses in community invasion dynamics are abrupt or gradual.
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    Climate Change and Tallgrass Prairies: Exploring the Interaction of Extreme Weather and Invasion in Managed Prairie Systems
    (2020-12) Ratcliffe, Hugh
    Climate change will increasingly shift seasonal timing and increase the frequency and intensity of extreme events like drought and severe wet conditions, all of which threaten to amplify other global change drivers like invasion. Consequently, understanding how conservation management actions like prescribed burning interact with climate is increasingly pressing for invasive management. Although prescribed burning has been widely demonstrated to increase native plant diversity and suppress a number of invasive species, understanding under what current and future conditions burning will be most effective remains an ongoing focus of applied prairie ecology research. Earlier springs and extended growing seasons will shift the timing and availability of resources and niche space, which may disproportionately advantage invasive species and also influence the outcome of burning. Furthermore, northern tallgrass prairies will experience intensified extreme precipitation patterns characterized by more precipitation falling in fewer events interspersed with longer dry periods and amplified evapotranspiration. Because moisture availability functions as a key determinant of prairie composition, theory and evidence suggest drought conditions will hinder invasion, whereas wetter conditions will enhance invasion. Here, I conducted two analyses exploring the effect of weather on prairie invasion dynamics from 2010-2019 in 25 observed prairie sites and 267 transects spread throughout Minnesota, USA. First, I estimated the effects of burning, start time of the growing season, and their interaction. Second, I estimated how an increase in extremely wet or dry months altered invasive abundance and influenced the effectiveness of burning. For the first analysis, I determined that burning reduced both total invasive and invasive cool season grass abundance, and that this reduction persisted over time for invasive cover but quickly waned for frequency. Additionally, I found that growing season start does indeed influence community composition but that later starts rather than earlier increased invasive abundance. For the second analysis, I found that a greater occurrence of abnormally wet months increased invasive abundance and minimal evidence that abnormally dry conditions hinder invasion. Furthermore, I did not observe additive interaction effects of drought and prescribed burning but did find that an increase in the number of wet months reduced the effectiveness of burning. Together, these results suggest that, although earlier spring timing is unlikely to be a primary mechanism driving increased invasion, more frequent extremely wet and dry months may intensify invasive dominance and hinder our ability to suppress invasion species via prescribed burning. Ultimately, I propose that future research should seek to better understand abiotic controls on invasive species’ phenologies, how precipitation seasonality influences invasive performance, and also identify potential thresholds in ecological processes to understand whether responses in community invasion dynamics are abrupt or gradual.
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    Grasslands and Brushlands of the Oak Savanna Region of Minnesota as Biomass Feedstock Sources
    (2010-01) Gillitzer, Peter Andrew
    Abstract summary not available.
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    The role of photodegradation in plant litter decomposition in grassland ecosystems
    (2009-08) Brandt, Leslie Alyson
    Decomposition of plant litter is the primary process by which carbon and nutrients are returned from plants to the soil and atmosphere. Although plant litter decomposition is primarily driven by plant litter chemistry, temperature, and precipitation these factors have failed to fully explain decomposition patterns in arid and semiarid grassland ecosystems. In my dissertation, I tested the hypothesis that solar radiation, particularly in the UV range (280-400 nm) contributes to the decomposition process in these systems via the process of photodegradation. In a three-year field study in the semiarid shortgrass steppe in Colorado, I examined whether photodegradation by UV radiation played a role in plant litter decomposition and whether the role of photodegradation in the decomposition process was affected by plant litter chemistry and precipitation. In a series of laboratory experiments, I examined the pathways by which mass is lost via photodegradation. In a two-year cross-site field experiment, I examined whether photodegradation may explain the difference in litter decomposition patterns among mesic, semiarid, and arid grassland ecosystems. The combined results of this research show that photodegradation is an important process in plant litter decomposition in mesic grassland ecosystems as well as arid and semiarid grassland ecosystems, accounting for up to 50% of litter mass loss. Results also show that litter mass loss via photodegradation is the result of photochemical production of carbon dioxide, which can be up to 4 g C m-2 y-1 in arid ecosystems. This research has important implications for future basic research in biogeochemical modeling, photochemistry of natural compounds, and plant litter decomposition in arid ecosystems.
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    Validation of Wetland Mitigation in Abandoned Borrow Areas – Phase II
    (Minnesota Department of Transportation, 2016-03) Johnson, Kurt W.
    Road construction in northeast Minnesota often causes wetland impacts that require compensatory mitigation. Borrow areas excavated for road construction material can be developed into wetland mitigation sites if hydric vegetation, hydric soils and adequate hydrology are provided. Fourteen wetland mitigation sites were constructed north of Virginia, Minnesota along the U.S. Trunk Highway 53 reconstruction project corridor. The sites were established with the goal of mitigating for project impacts to seasonally flooded basin, fresh meadow, shallow marsh, shrub swamp, wooded swamp, and bog wetlands. Monitoring results indicate that the 14 mitigation sites range in their potential to receive wetland mitigation credit. All but one of the sites consistently meet wetland hydrology criteria. The sites contain a variety of plant communities dominated by wet meadow, sedge meadow, and shallow marsh. Floristic Quality Assessment (FQA) condition categories for the sites range from "Poor" to "Exceptional." Invasive plant species, particularly reed canary grass and narrow leaf cattail, are present on a number of sites and should be controlled. Tamarack and black spruce plantings have been successful on some of the drier areas and should be expanded to increase the quality and potential mitigation credit for other sites. These sites have shown the potential for creating mitigation wetlands in abandoned borrow pits in conjunction with highway construction. Adaptive management, particularly water level regulation, early invasive species control, tree planting, and continued long-term annual monitoring can make mitigation sites like these successful options for wetland mitigation credit. Continued site monitoring to determine potential for mitigation credit is recommended.