Graduate Thesis Or Dissertation
 

Effects of stand density on site index in thinned stands of Douglas-fir in the Pacific Northwest

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8336h4931

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  • In site index studies, the hypothesis that height growth of most conifers is independent of stand density is commonly accepted. However, some studies have shown height growth to be influenced by density particularly on medium to poor sites. In this study two locations representing a high quality site (Hoskins area, Oregon) and a relatively lower site (Rocky Brook area, Washington) were selected to examine the effect of stand density on site index in natural stands of Douglas-fir which has been repeatedly thinned at different intensities. The data for the study were obtained from the periodic measurements of the stand characteristics at the end of each thinning treatment period. The average height of the largest 40 trees per acre was used as basis for the comparison of height growth patterns among the different thinning regimes. Simple linear regression was found adequate to describe height growth of the individual plots over the age range studied (20 to 36 years at the Hoskins and 27 to 44 years at the Rocky Brook). Covariance analysis using multiple regression was used to test differences in height growth within plots under similar thinning treatments. The coefficients of the height growth equations from individual plots were used in the analysis to test for differences in height growth among the different thinning regimes. The results of the study indicated that on both sites, site index was not influenced by density over a wide range of stocking and within the age range studied.
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