Graduate Thesis Or Dissertation
 

A stand management strategy for young western hemlock-Sitka spruce forests

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rx913s60d

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  • Western hemlock-Sitka spruce forests, where prior precommercial thinning has occurred, constitute one of the most productive young-growth management types along the Pacific Coast from Oregon to southeast Alaska. These stands are ready for a first commercial thinning entry, however, the costs and benefits of such entries and resulting impacts at final harvest are not well documented. The purpose of this study was to provide appropriate harvesting, silviculture and economic data in a comprehensive evaluation of four alternative stand management treatments (three different thinning prescriptions with a basal area per acre removal ranging from 49 percent to 67 percent and a no-thin, control prescription) conducted on a 32 year old managed western hemlock-Sitka spruce plantation. A detailed logging production/cost study of Skyline thinning showed high harvesting cost and resulting negative stumpage values. Thinning treatments influenced harvesting costs; herringbone strip thinning costs 31 percent less than a conventional selective thinning method with the same volume removal. Also, a residual tree damage study, conducted during logging, showed that damage was considerably lower for strip thinning compared with selective thinning. Various logging techniques and crew skill levels influenced stand damage. An assessment of wind damage and tree growth rates was completed two years after skyline thinning. Annual windthrow losses totalled only 0.28 trees per acre for all treatments and was significantly lower in strip thinning than selective thinning. Windthrow also appeared to be related to specific site, tree or stand conditions. Diameter growth increment rates declined in the unthinned units. However, in all thinned units, an immediate diameter growth response occurred. In the herringbone strip thinning method, trees exhibited a growth response regardless of distance from strip edge. A stand table projection model and harvest simulation model were used for determining costs and revenues from clearcutting at rotation age. Final harvest costs and revenues per cunit were similar for all treatments. The unthinned stand had the highest present net worth per acre. A sensitivity analysis of real interest rate changes along with changing harvesting cost and pond values during thinning or final harvest did not alter the outcome. Results of this study suggest that managed plantations of western hemlock-Sitka spruce can receive sufficient density control from precommercial thinning to maintain adequate stand development to a rotation age harvest without commercial thinning entries.
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