Browsing by Subject "Grassland"

Now showing 1 - 5 of 5
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    Consequences of elevated temperature on prairie plants: legumes, nitrogen, and phenology.
    (2012-05) Whittington, Heather Renee
    Because prairies are often nitrogen (N) limited, prairie legumes can have significant impacts on the nitrogen (N) dynamics of these communities because of their ability to add fixed N to their surroundings through symbiotic biological N2-fixation and their N-rich tissues that can stimulate net nitrogen mineralization. Predicted increases in temperature have the potential to alter legume traits and functioning, which can feedback to affect ecosystem dynamics. The goal of this dissertation was to examine the effect of elevated temperature on the growth, phenology, and N nutrition of four prairie legumes: Amorpha canescens, Dalea purpurea, Lespedeza capitata, and Lupinus perennis, using both a growth chamber experiment and a manipulative field warming experiment. In the growth chamber experiment, seedlings of Lespedeza exhibited higher biomass and shoot N content at 28°C than 25°C, while Lupinus seedlings displayed decreased nodulation and lower shoot N concentration at the higher temperature. In the field warming study, Dalea and Lupinus displayed higher biomass under warming and all species exhibited lower shoot N concentrations under warming. Neither N2-fixation nor net N mineralization were affected by warming. Warming accelerated flowering for several species, including Amorpha and Dalea, and accelerated spring green-up, as evidenced by higher normalized difference vegetation index (NDVI) values in warmed communities in May. These results indicate that prairie legumes are responsive to increases in temperature in a species-specific manner and that warming may alter N-cycling by changing legume abundance and tissue N chemistry. Additionally, significant interannual variation in many variables and in their responses to warming emphasizes the need for long term studies to better understand and predict potential consequences of elevated temperature on plants and their ecosystems.
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    Data for divergent responses of butterflies and bees to burning and grazing management in tallgrass prairies, 2016-2017
    (2022-12-12) Leone, Julia B; Pennarola, Nora P; Larson, Jennifer L; Oberhauser, Karen; Larson, Diane L; leone050@umn.edu; Leone, Julia B
    We studied the impacts of fire and grazing management on butterfly and bee abundance and species richness in tallgrass prairies. This dataset consists of data collected at 10 burned and 10 grazed Minnesota remnant prairies during the summers of 2016 and 2017. We measured insect data (butterfly and bee species richness and abundance), vegetation data (plant species richness, forb frequency, native and invasive graminoid frequency), site characteristics (proportion of sand in the soils, percent of prairie within 1.5 km of each site, site area), and management characteristics (management type (burned or grazed), cattle stocking rate, time since last fire, number of years each site was managed) at sites owned and managed by the Minnesota DNR, U.S. Fish and Wildlife Service, The Nature Conservancy, and private landowners. These data are associated with Leone et al. (2022). Divergent responses of butterflies and bees to burning and grazing management in tallgrass prairies. Ecology and Evolution. 12(12) e9532. http://dx.doi.org/10.1002/ece3.9532. In association with this paper, we hope these data will assist land managers and conservationists in protecting and managing native grasslands and contribute to our understanding of bee and butterfly responses to fire and grazing management practices.
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    Extractability of carbon, nitrogen, and phosphorus in United States grasslands
    (2015-02) Thompson, Seth K.
    Tracking how energy flows within and across ecosystems is imperative for understanding interactions among biogeochemical cycles. Aquatic ecosystem metabolism is inextricably linked to the terrestrial landscape, with many lakes getting over 50% of their carbon from terrestrial sources. Nonetheless, there are few large scale measurements of actual carbon export from terrestrial ecosystems. Instead, scientists have relied on a mass balance approach to estimate the quantity of carbon coming into aquatic ecosystems based on estimates of riverine carbon delivery to the ocean. This approach has left many unanswered questions related to the controls on terrestrial organic matter export, both in terms of quantity and quality. Here I used Water Extractable Organic Carbon (WEOC) to estimate potential terrestrial carbon export and to understand the mechanisms controlling these exports. Results from extractions performed at 19 grassland sites across the United States suggested that 1-5% of their total soil carbon was in the water extractable organic carbon pool. In addition, this work suggested that soils selectively retained nitrogen and phosphorus, with less organic nutrient export relative to organic carbon to aquatic ecosystems. These data demonstrated the usefulness of measuring water extractable organic matter (WEOM) on broad spatial scales to gain a better understanding of both the amounts and types of organic matter that are available for export from terrestrial ecosystems.
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    Invasive plants, herbivores and the underground: feedbacks with soil biota and their influence on grassland plant communities in the Great Plains
    (2013-04) Haines, Dustin F.
    Exotic plants have the ability to modify soil seed banks and the soil biotic community in habitats they invade, but little is known about the legacy of invasion once an exotic plant has successfully been controlled. Natural areas previously invaded by leafy spurge in the northern Great Plains typically have one of two fates following control of spurge: a return of native plants, or a secondary invasion of other exotic plants. Furthermore, reduced native plant recruitment has been observed in areas where insect biocontrol has been used for leafy spurge control. It is unknown, however, if the reduced recovery of natives is due to a depauperate native plant seed bank, altered soil biotic communities, or interactions of leafy spurge with biocontrol organisms. To address the seed bank question, I monitored soil seed banks and standing vegetation for two years in mixed-grass prairies that were previously invaded by leafy spurge. I found that native plant seed banks were largely intact in areas previously invaded by leafy spurge, regardless of the current living plant community. I conducted a glasshouse experiment to investigate interactive effects of leafy spurge soil conditioning and flea beetle biocontrol insects on native plants. My results indicate that leafy spurge soil conditioning inhibits native plant germination and growth, and that flea beetles have similar inhibitory effects but only on particular native plant species. Lastly, I investigated the interactive effects of leafy spurge root exudates and fungal pathogens on native plant growth in a glasshouse, and the degree to which fungal pathogen growth varies with leafy spurge and native plant root exudates in petri dishes. I found that leafy spurge root exudates and fungal pathogens, when applied together, tended to enhance native plant germination and growth, and that fungal pathogen growth response to root exudates varied between fungal genera, and among native species, but that fungal growth did not respond strongly to leafy spurge exudates. Therefore, regardless of the relatively unaltered native plant seed banks, leafy spurge soil occupancy and fungal pathogens may have significant impacts on native plant recovery.
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    Responses of songbirds and small mammals to harvests of native grasslands for biofuels in Western Minnesota
    (2014-01) Dunlap, Robert Michael
    Some grassland birds and small mammals exhibit changes in abundance following vegetation removal in the previous year, but it is unknown to what extent these organisms respond to harvests of diverse, native grasslands. This thesis examines the effects of harvesting such grasslands on songbirds and small mammals, representing an important step in evaluating the conservation value of grasslands used for biofuel harvest. I analyzed abundance data collected from area-based bird surveys in grassland biofuel plots harvested via different pattern and percentage in western Minnesota, USA, from 2009 to 2013 (Chapter 1). Small mammal trapping was conducted in the same plots from 2009 to 2012, and abundance and occupancy data collected from these surveys was also analyzed (Chapter 2). I estimated relative abundance of 11 species of grassland birds and 7 species/genera of small mammals among the different harvest intensities and years of study. Four bird species and species richness showed declines in abundance following harvests, whereas two species showed increases in abundance. Harvests also resulted in negative impacts on two small mammals. The removal of vegetation in fall results in shorter, less dense vegetation the following spring, which creates largely unsuitable habitat for tall-grass songbirds (e.g., sedge wren) but more optimal habitat for species that prefer shorter vegetation (e.g., grasshopper sparrow). Additionally, the reduction in ground litter is detrimental to small mammals that prefer thicker vegetation (e.g., voles of the genus Microtus). At the community level, harvesting native grasslands appears to have little impact on grassland birds and small mammals, but it is nonetheless important to identify what species are present prior to harvesting so that harvesting activities do not result in detriment to these species.