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Item Soil health response to cropping systems in semi-arid Montana(Montana State University - Bozeman, College of Agriculture, 2024) Ashford, Zane Ann; Chairperson, Graduate Committee: Catherine A. ZabinskiTraditional cropping systems in the northern Great Plains (NGP) were dominated by cereal-fallow rotations until the 1970s, resulting in increased soil erosion, decreased soil organic matter (SOM) accumulation, and declines in soil biological activity. Recent shifts toward continuous and more diverse no-till crop production attempt to increase sustainability, diversify economic opportunities, and keep up with the growing food demand without converting more land into agriculture. With a two-year study, I explored the effects of crop types in diverse, no-till, crop sequences on soil health in dryland and irrigated systems on one farm in semi-arid Montana, using biological indicators of potentially mineralizable nitrogen (PMN), soil enzyme activity (beta- glucosaminidase, beta-glucosidase, arylsulfatase, and acid and alkaline phosphatases), and permanganate oxidizable carbon (POxC), a measure of labile carbon. Crop sequences included four crop types -- cereals, oilseeds, legumes, and root crops. Root crops, namely sugar beet, drove soil responses in PMN, evident by increased plant-available N in soils following sugar beet. Soil enzyme activity, an indicator of nutrient cycling capacity, was strongly correlated with SOM, but did not follow a pattern based on crop type. Labile carbon changed in soils between years but did not respond consistently to crops. This research also explored the soil health gap by comparing soil health in cultivated systems to nearby grasslands. In a paired-site comparison on two farms in Montana, biological health indicators were 45% lower, on average, in cultivated soils compared to adjacent uncultivated soils. This difference was consistent with lower SOM averages, offering a simple assessment to quantify the maximum attainable soil health capacity within a specific agroecosystem. Soil acidification, a growing concern for producers across the NGP, contributed to 42% lower soil enzyme activity, based on four enzymes, compared to adjacent neutral pH cultivated soils. Enzyme activity was the only soil health parameter that was lower in acid soils compared to neutral pH soils, demonstrating the sensitivity of soil enzymes. Overall, these results indicate that biological soil health indicators are sensitive to changes in crop production, changing yearly, and provide farmers with the opportunity to fine- tune their management practices to meet their soil health goals.Item Woody plant expansion in the northern Great Plains: a multi-scale assessment of the drivers and ecological implications of increasing woody abundance in a temperate open ecosystem(Montana State University - Bozeman, College of Agriculture, 2022) Currey, Bryce Alan; Chairperson, Graduate Committee: Jack Brookshire; This is a manuscript style paper that includes co-authored chapters.Open ecosystems (i.e., non-forested ecosystems) are inherently dynamic ecosystems that are essential to the persistence of humankind; yet many are being altered, degraded, or lost. One of the largest changes to open ecosystems globally is an increase in greenness, driven by increasing plant photosynthetic capacity or altered species composition. Often this transition in species composition occurs when woody species (i.e., trees and shrubs) increase in dominance or replace contemporary herbaceous species, a phenomenon referred to here as woody plant expansion (WPE). WPE has been proposed as a possible solution to climate change, yet ultimately has the potential to alter grasslands into a novel state. This dissertation improves the understanding of how open ecosystems have been altered by WPE. The chapters within this document offer a multi-scalar examination of the drivers and ecological implications of WPE in the Northern Great Plains (NGP) of North America, one of the largest grasslands remaining globally. Specifically, I answer three main questions: (1) What is the extent and magnitude of WPE across the NGP? (2) What are the drivers, ecosystem implications, and biogeochemical impacts of WPE? and (3) Moving forward, how should research be prioritized in ecosystems like the NGP, particularly concerning climate mitigation and management? I begin with an introduction to the NGP, the implications of WPE, and an overview of this dissertation. I then examine the drivers and interactions of WPE and the recent increase in vegetative productivity. Next, I couple high-resolution estimates of WPE from the heart of the NGP with data from sampling plots to examine the impact that WPE has on ecosystem biogeochemistry. Next, WPE is examined against agricultural expansion and I propose that future work examining large-scale changes and the subsequent management of open ecosystems be reframed towards weighing the impacts on biodiversity, carbon storage, and ecosystem resilience. Finally, I summarize all findings with implications for future research. The NGP has the potential to represent the future of North American grasslands and, while this dissertation answers many questions, the future remains highly uncertain.Item Evaluating grazing and defoliation effects on ponderosa pine grassland following the lodgepole complex wildfire(Montana State University - Bozeman, College of Agriculture, 2020) Williams, Amanda Rae; Chairperson, Graduate Committee: Clayton B. Marlow; Lance T. Vermeire, Richard C. Waterman and Clayton B. Marlow were co-authors of the article, 'Evaluating grazing effects on ponderosa pine grassland following the lodgepole complex wildfire' submitted to the journal 'Rangeland ecology and management' which is contained within this thesis.; Lance T. Vermeire, Richard C. Waterman, Clayton B. Marlow were co-authors of the article, 'Season of defoliation effects on ponderosa pine grassland following the lodgepole complex wildfire' submitted to the journal 'Rangeland ecology and management' which is contained within this thesis.Previous research indicated rangelands need rest from grazing after fire, while others show grazing the first year following fire has no negative effects on the plant community. This caused uncertainty around post-fire grazing management. In July 2017, the Lodgepole Complex fire burned ponderosa pine grasslands of the northern Great Plains, including areas burned in 2003 for fuels mitigation. We examined effects of post-fire grazing and season of defoliation. For the grazing study we wanted to determine 1) plant community response to grazing or rest the first growing season after fire in ponderosa pine grassland communities, and 2) whether prescribed fire alters plant community response to subsequent wildfire. For the season of defoliation study we wanted to determine 1) timing of defoliation effects on the plant community one growing season after fire and 2) whether defoliation effects are altered by prescribed fire preceding the fire. Eight exclosures (25 x 15 m) were built, 4 reburned sites and 4 wildfire sites. A non-grazed (15 x 10 m) section inside each exclosure was paired with a grazed section outside the exclosure. Plots (5 x 10 m) were mowed in the exclosure to 10 cm in June, July, or August, or not mowed during 2018. In 2019, biomass samples were clipped at peak production, with species composition and diversity measured by point-intercept transects. We observed a trend for reduced cool-season grasses (P =0.0675) and annual grasses (P =0.0071) if defoliated earlier; a trend for reduced forbs (P =0.0699) if defoliated later; and reduced total current-year biomass (P =0.0362) if defoliated. Functional group composition was not changed, but some individual species were shifted due to fire history. The grazing study only showed a trend for greater old dead biomass on non-grazed sites (P = 0.0600), higher composition of forbs on reburn sites (P = 0.0324), and a trend for a higher composition of Psoralidium tenuiflorum (Pursh) Rydb. on reburn sites (P = 0.0559). Results indicate mowing the first year following fire shifts the plant community, but the community is resistant to post-fire grazing. Prescribed fire 14 years before wildfire had small impacts on community composition.Item Associations of broad scale vegetation characteristics and abundances, nest densities, and nest survival of mixed-grass prairie songbirds in northern Montana(Montana State University - Bozeman, College of Agriculture, 2019) Pulliam, John Patrick; Chairperson, Graduate Committee: Lance McNewGrassland bird populations are declining faster than any other avian guild. In northern Montana, four species are experiencing severe population declines: Baird's sparrow (Centronyx bairdii), chestnut-collared longspur (Calcarius ornatus), McCown's longspur (Rynchophanes mccownii), and Sprague's pipit (Anthus spragueii). In 2017 and 2018, I evaluated abundance, nest density and nest survival of these species in relation to local vegetative conditions with the goal of identifying important breeding season vegetation conditions to inform management. I conducted fixed-radius point-counts at 100 sites to estimate local abundance, rope drag surveys to estimate nest density, nest monitoring to estimate nest survival, and vegetation surveys to estimate vegetation structure and composition across grassland habitats in Phillips County, MT. Point-counts and rope drag surveys were carried out with replicated visits to allow estimation of species-specific detection probabilities. Vegetation conditions were measured at the plot level (9-ha) to provide information at scales relevant for land managers. The abundance of Baird's sparrows was positively associated with residual grass cover and litter cover. Chestnut-collared longspur abundance was negatively associated with residual grass, exotic grass, and shrub cover and had a quadratic relationship with biomass. Plot-level abundance of McCown's longspurs was negatively associated with both shrub cover and biomass. Sprague's pipit abundance declined with exotic grass cover and exhibited a quadratic relationship with biomass. Limited sample size only allowed inference of nest density and nest survival for chestnut-collared longspurs. Nest density was negatively associated with plot scale exotic grass cover, biomass, and slope. I did not find support for any vegetation covariates on nest survival for chestnut-collared longspurs. These results provide some guidance for landscape managers interested in improving habitat for these species. The contrasting results among species, however, emphasize the need for heterogeneity in vegetation structure and composition. The disconnect between relevant covariates for nest density and nest survival suggest possible maladaptation for chestnut-collared longspurs. This result suggests that an index of productivity for this species that does not include both nest density and nest survival may produce erroneous results.Item Nonnative plant shifts functional groups of arthropods following drought(2016-05) Mitchell, Adam B.; Litt, Andrea R.Nonnative plants alter the composition of native plant communities, with concomitant effects on arthropods. However, plant invasions may not be the only disturbance affecting native communities, and multiple disturbances can have compounding effects. We assessed the effects of invasion and drought on plant and arthropod communities by comparing grasslands dominated by nonnative Old World bluestem grasses (OWBs, Dichanthium annulatum) to grasslands dominated by native plants during a period of decreasing drought severity (2011–2013). Native plant communities had more species of plants and arthropods (/m2) than areas dominated by OWBs during extreme drought, but richness was comparable as drought severity decreased. Abundance of arthropods was greater in native plant communities than in OWB communities during extreme drought, but OWB communities had more arthropods during moderate and non-drought conditions. We observed a shift in the arthropod community from one dominated by detritivores to one dominated by herbivores following plant invasion; the magnitude of this shift increased as drought severity decreased. Both plant communities were dominated by nonnative arthropods. A nonnative leafhopper (Balclutha rubrostriata) and native mites (Mochlozetidae) dominated OWB communities as drought severity decreased, and OWBs may serve as refugia for both taxa. Nonnative woodlice (Armadillidium vulgare) dominated native plant communities during extreme and non-drought conditions and abundance of this species may be associated with an increase in plant litter and available nutrients. Given the importance of arthropods for ecosystem services, incorporating arthropod data into conservation studies may demonstrate how changes in arthropod diversity alter ecosystem function where nonnative plants are dominant.Item Ammonia volatilization from native grasslands and forests of southwestern Montana(Montana State University - Bozeman, College of Letters & Science, 1984) Aradottir, Asa LovisaItem The leafhopper species assemblages associated with native and replanted grasslands in southwest Montana(Montana State University - Bozeman, College of Agriculture, 1997) Bess, James AlexanderItem Elk effects on sagebrush-grassland after fire on Yellowstone's Northern Range(Montana State University - Bozeman, College of Agriculture, 2001) Rens, Reyer JanItem Simulated effects of supplementary water on two grasslands, Agropyron Smithii and Bouteloua gracilis(Montana State University - Bozeman, College of Letters & Science, 1985) Johnson, Carol AnnItem Comparisons of phenological variability and precipitation of ecoregion and grassland cover types in the northern Great Plains from 1988 to 1993(Montana State University - Bozeman, College of Letters & Science, 1999) Gillett, Linda E.