Graduate Thesis Or Dissertation
 

Identifying site characteristics that explain variation in Douglas-fir site productivity and stem form

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3n2042894

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  • Foresters care about site productivity and stem quality in Douglas-fir plantations for many reasons. The profitability of forest land and the economic returns on silvicultural investments are directly related to site productivity. Thus, understanding the relationships among Douglas-fir productivity, stem form and site characteristics is important economically. My objective was to identify the specific site characteristics that explained variation in Douglas-fir productivity and stem form throughout western Oregon and Washington by using progeny tests that substantially reduced the confounding effects of genotype by environment interaction. These assessments were undertaken to advance our understanding of near-term climate change effects on Douglas-fir productivity and stem form. The site characteristics I focused on include climate, soils and topography. Measures of site productivity and stem form were explained using correlation, random forest, and linear regression analyses. The results of these analytical methods were summarized as total importance scores. The consistency of important site characteristics identified by the analytical methods and the consistency of important site characteristics for explaining variability in different productivity measures were assessed using Spearman rank correlations. The results of this study provide new direction and insight for future research on understanding and modeling the effects of site characteristics on tree growth and form. It may be reasonable to focus future research on summer drought, cold season temperatures and precipitation interactions with soil properties, particularly available water capacity when examining site productivity. Additionally, examining genotype by environment interactions at the family level may provide insight to the driving site characteristics for stem forking, ramicorn branching and sinuosity.
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