Range Science Doctoral Work
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Item Restoring Heterogeneity-Based Management to Rangelands for the Benefit of Grassland Birds and Floral Resources(North Dakota State University, 2021) Duquette, Cameron AlbertWorldwide grassland loss necessitates careful consideration of management practices occurring on those grasslands that remain. Concerns with overgrazing in the early twentieth century led to overcorrection via uniform, moderate stocking. While these practices reversed some forms of rangeland degradation, they also suppressed variability in vegetation structure that is characteristic of native systems. Reduced heterogeneity resulted in biodiversity declines across many trophic levels. In an effort to restore heterogeneity, we reinstated the historic processes of fire and ungulate grazing. We studied the impacts to grassland birds and floral resources, as the Northern Plains are valuable landscapes for breeding grassland birds and both native and managed pollinators. We conducted our research at the Central Grasslands Research Extension Center in Streeter, North Dakota, USA. From 2017-2020, we evaluated grassland bird community composition, nest survival, and floral resource availability. We found that patch-burn and season-long grazing pastures had higher avian diversity than modified twice-over rotational grazing. Avian community composition was also sensitive to ecological site, topographic variability, and wetland area, suggesting that both the fire-grazing interaction and underlying inherent topoedaphic variability maintain biodiversity. Species densities were sensitive to different sources of heterogeneity, with some responding to inherent landscape conditions and some responding to imposed grazing management. We found no differences in nest survival between grazing treatments for any of our 12 focal species despite treatment differences in vegetation and structural components associated with survival. Survival of five species was associated with vegetation structure, and one was associated with litter depth, smooth brome, and forb cover, respectively. We found higher nesting densities of three species (Chestnut-collared longspur, Northern pintail, Brewer’s blackbird) in patch-burn pastures compared to season-long pastures. All are associated with shorter, sparse vegetation. At a treatment scale, we found that patch-burn grazed pastures had shallower litter, less smooth brome, more forbs, and shorter vegetation structure than season-long pastures. Patch-burn grazing pastures increased floral resources across the majority of species. Patch-burn pastures had higher species richness, seasonal availability, and maximum abundance compared to season-long grazing. Our results broadly show the benefits of heterogeneity-based management on two important grassland guilds, birds and flowering plants.Item An Exploration of the Effects of Cattle Grazing, Prairie Dog Activity, and Ecological Site on Plant Community Composition and Western Wheatgrass Vegetative Reproduction in Northern Mixed Grass Prairie(North Dakota State University, 2017) Field, Aaron LeeModern range scientists and managers are tasked with feeding more people than ever before while maintaining or improving the ecological function of over half of the world’s land surface. Often, these tasks are in conflict. This disparity is evident in the relationship between rangeland livestock producers and black-tailed prairie dogs (Cynomys ludoviciana). Prairie dogs are considered a keystone species and an ecosystem engineer, but they also reduce available forage for livestock. In this disquisition we investigated the dynamic relationship between prairie dog activities and cattle grazing in respect to their combined and separate influences on plant community composition and western wheatgrass (Pascopyrum smithii) reproduction in northern mixed grass prairie. Our study took place on a private ranch in north-central South Dakota on the Standing Rock Indian Reservation, near McLaughlin. Using paired plots that either allowed or excluded cattle grazing, we were able to quantify the effects of different grazing intensities and grazing removal. While plant community composition and bare ground percentage were different among grazing regimes and ecological sites, removal of cattle grazing pressure did not change plant community composition over the three-year study in comparison to full use grazing (40 – 60% degree of disappearance). These findings show that short term (3 year) changes in grazing intensity did not lead to plant community change in northern mixed grass prairie. This was true regardless of ecological site and prairie dog occurrence. Western wheatgrass bud banks were also not influenced by herbivory type or intensity. This finding underscores the importance of aboveground tiller numbers as an indicator of reproductive capability rather than bud bank in western wheatgrass. Taken together, our results suggest that full use cattle grazing is a sustainable practice in northern mixed grass prairie. Our results also indicate that western wheatgrass vegetative reproduction is not likely to be inhibited or promoted by grazing.Item Method Selection and Estimating Densities for Grassland Butterflies in the Mixed-Grass Prairie(North Dakota State University, 2018) Kral, Katherine Claire-AnnGrassland butterflies contribute to the larger group of pollinating insects that are vital for continued plant production and food security in agroecosystems. However, grassland butterflies, along with overall biodiversity, are experiencing widespread declines due to global change factors such as landscape fragmentation, climate change, and agricultural intensification. Research and conservation efforts have therefore increased to mitigate dramatic declines of grassland butterflies. Yet, a large amount of baseline information in unknown for butterflies in the mixed-grass prairie region of the Northern Great Plains, especially for obligate species that wholly depend on grasslands to complete their life cycle. We initiated a study to increase the baseline knowledge and availability of rigorous data to inform conservation by investigating 1) butterfly survey methodology, 2) local and landscape influences on butterfly density, 3) invasive plant species impacts on butterfly communities, and 4) butterfly behavior responses to vegetation. We found that visual encounter surveys (VES) and line-transect distance sampling (LTDS) were complementary methods that should be used in butterfly research to improve the availability of quantifiable data. Even though VES were more efficient at detecting individual butterflies, LTDS provided a rapid way to estimate true density estimates for butterflies. Using LTDS density estimates to model species responses to local and landscape variables, we determined that maintaining large grasslands at the landscape level and promoting heterogeneous plant communities and structure at the local level would help conserve obligate grassland butterflies. One way to promote heterogeneous plant communities is to reduce the cover of invasive plant species. Otherwise, flowering forb and plant species richness decline and butterfly communities shift to fewer obligate butterflies. We can better understand butterfly species’ declines by incorporating behavioral surveys at the site level. In doing so, we found that monarch behaviors associated with utilizing a site (e.g., nectaring, ovipositing) did not increase as milkweed (obligate host plant) cover increased because nectar resource availability decline. Overall, maintaining large, heterogeneous grasslands and identifying management strategies like fire and grazing to increase host and nectar resource availability will benefit the largest number of grassland butterflies.Item Belowground Bud Banks of Native, Perennial Grasses and Interactions with Fire in the Northern Great Plains(North Dakota State University, 2013) Russell, Morgan LeeMixed-grass prairies of the northern Great Plains evolved following frequent disturbances such as drought, fire, and extensive grazing by ungulates. As a result of periodic natural disturbances, native grass reproductive mechanisms have adapted to withstand frequent disturbance. Ninety-nine percent of native perennial grasses reproduction occurs through well-protected and densely structured axillary buds. Since vegetative buds are the primary driver of aboveground growth, bud response to differing seasons and fire return intervals may reveal strategies to enhance bud dynamics. The timing of fire may transition dormant buds into active buds elucidating the mechanism responsible for aboveground growth following fire. My objectives were to: 1) reveal belowground bud characteristics of Bouteloua gracilis (Willd ex. Kunth) Lag. ex Griffiths) (C4 species), Pascopyrum smithii (Rydb.) A. Löve) (C3 species), and Hesperostipa comata (Trin. & Rupr.) Barkworth) (C3 species), 2) examine immediate fire effects on belowground bud activity, dormancy, and mortality following seasonal fire and fire return interval treatments, 3) quantify short-term belowground bud dormancy, activity, and mortality trajectories following fire, and 4) determine the effects of soil moisture and soil temperature on bud growth and maintenance. Belowground bud characteristics differed among species, where B. gracilis produced the most buds (6 ± 4 buds tiller-1), P. smithii produced an intermediate amount (4 ± 2 buds tiller-1), and H. comata contained the least amount of buds (3 ± 3 buds tiller-1). Fire treatments did not result in immediate, direct mortality of B. gracilis, P. smithii, or H. comata buds. However, fire treatments enhanced bud activity and reduced dormancy for B. gracilis and P. smithii. Season of fire and fire return interval directly manipulated bud activity, dormancy, and mortality for these species throughout two or more growing and dormant seasons following fire. Soil moisture was found to be a good predictor for bud growth of cool-season species and soil temperature was a reliable predictor for warm-season species bud growth. Prescribed burning can be used to manipulate bud bank dynamics as a management tool and belowground bud dynamics can also be used to improve post-fire management strategies in wildfire situations.Item Influences of Cattle Grazing and Black-Tailed Prairie Dog Activity on Northern Mixed Prairie Plants(North Dakota State University, 2017) Field, AaronVideo summarizing a Ph.D. dissertation for a non-specialist audience.