Graduate Thesis Or Dissertation
 

The effects of thinning on stand and tree growth in a young, high site Douglas-fir stand in western Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gq67jt20q

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  • The Levels-of-Growing-Stock Studies in Douglas-fir is a regional cooperative to investigate the effects of levels of growing stock on young stand growth. The Hoskins installation, in western Oregon, was established in a dense, high site natural stand at total age 20 years. The initial thinning resulted in an immediate 131 percent increase in diameter growth. Subsequent crown type thinning treatments retained eight different, predetermined percentages of the gross basal area growth on the control plots. At age 45, diameter growth remains strong on the heavily thinned treatments, but decreases with increased growing stock. Gross volume growth increased with growing stock, while gross basal area growth was much less influenced by growing stock. Volume growth was strongly related to density because of the rapid height growth of this young stand. Heavy thinnings reduced volume production because of the depletion of growing stock. Total volume production was only slightly reduced on the light thinnings, whereas merchantable volume was greater than the unthinned control. Mortality was heavy on the control, but negligible on the treated plots. Heavy mortality in the last period, reduced net volume growth on the control to less than the treatments. Periodic annual increment (PAI) for cubic foot volume appear to have culminated for the treatments, although they are nearly twice the mean annual increments on the thinned plots. Board foot volume PAI does not appear to have culminated for any of the treatments. The diameter growth of individual trees was particularly influenced by the amount of density in trees larger than any given tree. Density had only a minor effect on height growth. Trees in lower densities had longer crowns and greater taper. Results from simulations of alternative thinning regimes show the desirability of early thinnings. Compared to thinning from below, crown thinning appeared to give the greatest release to the residual stand and produce high volume growth. Management must consider the trade-off s between greater diameter growth at low densities and greater volume growth at high densities.
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