Graduate Thesis Or Dissertation
 

Changes in plant communities following rangeland brush control

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/7h149t32q

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  • Recently, the big sagebrush taxa has been split into subspecies and forms. Four habitat types related to subspecies of big sagebrush were studied in Eastern Oregon. Response of understory vegetation was measured following three range improvement techniques implemented on the four habitat types for several ages of treatment. Crown cover, density, and frequency of three subspecies of big sagebrush were measured, the relationship of sagebrush to improvement treatment and composition of understory vegetation was evaluated. In general, the same plant species responded differently on four habitat types manipulated by spray-release treatment. Approximately one-third of the perennial grass species increased, one-third decreased, and one-third showed no change in frequency, density, and cover between treated and untreated areas four years after treatment on the basin big sagebrush-bluebunch wheatgrass-bottlebrush squirreltail habitat type. However, total grass representation increased after treatment. Perennial forb and shrub species generally showed no change in frequency, density, and cover in the fourth year following spray-release treatment on the same habitat type. Perennial grass and shrub species generally showed no change while perennial forb species generally decreased in frequency, density, and cover between treated and untreated areas in the fourth year following spray-release treatment on the Wyoming big sagebrush-Thurber needlegrass habitat type. Perennial vegetation generally showed no difference in frequency, density, and cover between treated and untreated areas in the sixth year following spray-release treatment on mountain big sagebrush-Idaho fescue habitat type. Perennial grass species generally increased, perennial forb species generally showed no change, and shrubs species generally decreased in frequency, density, and cover between treated and untreated areas in the sixth year after spray-release treatment on the Wyoming big sagebrush-bluebunch wheatgrass habitat type. The same plant species responded differently to three improvement treatments implemented on the Wyoming big sagebrush-Thurber needlegrass habitat type. Annual vegetation generally increased in frequency on treated areas compared to untreated areas in six years following spray-seed treatment on this habitat type. Approximately half of the native perennial grass species decreased and half showed no change in frequency, density, and cover after six years following spray-seed treatment on this habitat type. Total grass representation increased after treatment. Perennial forb and shrub species generally showed no change in frequency, density, and cover after six years following spray-seed treatment on this habitat type. Approximately half of the annual forb and grass species increased in frequency and the rest either decreased or showed no change in frequency on treated and untreated areas in ten years following plow-seed treatment on this habitat type. Total representation of annual vegetation increased after treatment. Perennial grass species generally decreased in density, frequency, and cover in ten years following plow-seed treatment on this habitat type. Total grass representation, however, increased after treatment on this habitat type as a result of seeding crested wheatgrass. Perennial forb and shrub species generally showed no change in frequency, density, and cover ten years after plow-seed treatment on this habitat type. Sagebrush did decrease in representation while green rabbitbrush increased after treatment. Annual vegetation generally showed no change in frequency in the fourth year after spray-release treatment on the Wyoming big sagebrush-Thurber needlegrass habitat type. Perennial grass species generally showed no change, perennial forb species generally decreased, and shrub species generally showed no change in frequency, density, and cover between treated and untreated areas in the fourth year after spray-release treatment on this habitat type. Sagebrush was found to reinvade at a constant rate in the Wyoming big sagebrush-Thurber needlegrass habitat type in the sixth year following spray-seed treatment. Extrapolation of data showed in approximately 7.4 years the density of sagebrush on the treated area would be the same as on untreated areas. The reinvasion of sagebrush was found to be highly variable on Wyoming big sagebrush-Thurber needlegrass habitat type following plow-seed treatment. Sizes of improved areas on the study were calculated from high flight photography. Results obtained from the photos differed from known acreage by 8%.
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