The effects of repetitive grazing on Schizachyrium scoparium and the role it plays in woody plant encroachment of Texas grasslands




Baldwin, Andrew Ross

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The composition and structure of the semiarid grasslands of Central Texas have been changing over the past 200 years. Selective grazing of domesticated animals is thought to be one of the main causes of these changes; however there are many factors that contribute to the encroachment of woody plants, such as global warming and underground root herbivory. This Thesis research, which built on a previous experiment, analyzed the direct effect of aboveground grazing on Schizachyrium scoparium (little bluestem) a naturally occurring grass all over Texas, at different rates of grazing for five weeks. The previous experiment tested dry biomass of little bluestem vs. Prosopis glandulosa (honey mesquite) in grazed vs. ungrazed scenarios. In the second experiment, 60 pots (15 cm X 15 cm) were filled with a thin layer of crushed limestone at the bottom with soil collected from the University of Texas at San Antonio 1604 campus. Two hundred seeds were sown into each of the 60 pots and given 3 days to germinate in a greenhouse. After germination each pot was watered as needed for one month while they had time to establish some structure. 60 pots of S. scoparium were trimmed with scissors once a week at various repetitions; simulating high intensity grazing for the next five weeks. It was predicted that the S. scoparium pots with greater intensities of grazing would have a significantly lower total dry biomass. Therefore, with correct land management, grasslands and ranchlands can be preserved and prevent the woody plant encroachment. Results will indicate the most abundant dry biomass, and the intensity of grazing scenario with this biomass. The results can be used to create the most effective way to manage a grassland/ranchland for maximum growth to keep woody plants from encroaching. Thus, controlled herbivory of grasslands and ranchlands by domesticated animals could play a positive role in preventing woody plant encroachment.


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Grazing, Land Management, Little Blue Stem, Schizachyrium, scoparium, Texas



Earth and Environmental Science