Graduate Thesis Or Dissertation
 

Seedling response to vegetation management in northeastern Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/st74ct954

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  • Northeastern Oregon geology and climate provides moderately productive conditions for forest management and timber production. Although site preparation and planting are commonly used silvicultural practices, little research exists on the efficacy of specific forest herbicides and responses of seedling survival and growth in this region. This research seeks to improve the knowledge and understanding of these practices by examining the short and long-term effects of controlling competing vegetation on early plantation establishment and growth. The first study re-evaluates ponderosa pine (Pinus ponderosa) growth and survival twenty years after hexazinone was applied in broadcast and spot treatments for control of competing vegetation. Early treatment differences in survival and growth were detected (Oester et al. 1995), and tree size has continued to diverge among treatments twenty years after planting. The second study evaluated a suite of chemical site preparation treatments and several responses: western larch (Larix occidentalis) and Douglas-fir (Pseudotsuga meziesii) seedling survival and growth, vegetation cover development, and change in growing season volumetric soil moisture. Seedling survival, seedling volume growth, and volumetric soil moisture at the end of the first and second growing seasons did not always differ among treatments, but consistently decreased where competing vegetation cover was greater. These studies provide evidence that controlling competing vegetation on these sites increases survival and growth of western larch and Douglas-fir seedlings in the first few years after planting. Although direct effects of treatment do not persist, differences in tree size among treatments are still evident after two years for Douglas-fir and western larch, and after 20 years for ponderosa pine. Results pertain directly to ponderosa pine, western larch, and Douglas-fir planted in Douglas-fir/spiraea (Pseudotsuga menziesii/Spiraea betulifolia) and Douglas-fir/common snowberry (Pseudotsuga menziesii/Symphoricarpos albus) plant associations in northeastern Oregon, but may reasonably be applied to similar sites with the same species composition throughout much of the Intermountain West.
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