. Twenty-year growth of ponderosa pine saplings thinned to five spacings in central Oregon. Ponderosa pine Oregon; Forest thinning Oregon. Results and Discussion Diameter Growth Table 1—Results of analysis of variance Variable Period Spacing x period Vegetation x period Spacing Vegetation Linear1 Quadratic2 Lack of fit3 interaction interaction Diameter increment Height increment Volume increment Basal area increment Diameter Height Volume Basal area * * * * * * * * * * * * = not significant; * = significant at 5-percent level of probability (significant); ** = signific
. Twenty-year growth of ponderosa pine saplings thinned to five spacings in central Oregon. Ponderosa pine Oregon; Forest thinning Oregon. Results and Discussion Diameter Growth Table 1—Results of analysis of variance Variable Period Spacing x period Vegetation x period Spacing Vegetation Linear1 Quadratic2 Lack of fit3 interaction interaction Diameter increment Height increment Volume increment Basal area increment Diameter Height Volume Basal area * * * * * * * * * * * * = not significant; * = significant at 5-percent level of probability (significant); ** = significant at 1-percent level of probability (highly significant). 1 The linear component of period isolates the variation accounted for if a straight line is fit through the data. 2 The quadratic component of period isolates the variation accounted for if a second degree curve is fit through the data. 3 Lack of fit isolates additional variation not accounted for by the linear and quadratic components. Figure 6.—Periodic annual diameter incre- Period ment during five 4-year measurement periods. Increment is based on the average growth of individual trees living through each Trees per acre Spacing (feet) Spacing and understory vegetation had highly significant effects on diameter growth (table 1). Widely spaced trees grew faster than narrowly spaced trees (fig. 6). During the 20 years of observation periodic annual diameter growth has averaged as follows: Spacing Trees per acre Vegetation left Vegetation controlled Feet Inches 1000 500 18 .21 250 .23 .29 125 .30 .35 62 .35 47 6. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Barrett, James W. (James Willis), 1922- cn; Pacific Northwest Forest and Range Experiment Station (Portland, Or. ) cn. Portl
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