. Site index and height growth curves for unmanaged even-aged stands of western hemlock and sitka spruce in southeast Alaska. Western hemlock Alaska; Sitka spruce Alaska; Forest management Alaska; Site index (Forestry) Alaska. Figure 13.—Mean height of sectioned Sitka spruce as a function of age at breast height for each 10-year age class. Plotted points are actual mean heights minus feet. Solid line is expressed by the equation (HT - feet) = e*5, where x5 is defined in the text Standard error is and r2 is 180 r 160 140 120 100 80 60 40 20. 20 40 60 80 100 Age at breast
. Site index and height growth curves for unmanaged even-aged stands of western hemlock and sitka spruce in southeast Alaska. Western hemlock Alaska; Sitka spruce Alaska; Forest management Alaska; Site index (Forestry) Alaska. Figure 13.—Mean height of sectioned Sitka spruce as a function of age at breast height for each 10-year age class. Plotted points are actual mean heights minus feet. Solid line is expressed by the equation (HT - feet) = e*5, where x5 is defined in the text Standard error is and r2 is 180 r 160 140 120 100 80 60 40 20. 20 40 60 80 100 Age at breast height (years) 120 140 160 Even then there were problems at upper ages because of scarcity of observa- tions. This caused a biased fit of the combined equation at 120 to 150 years. The problem was later corrected by fitting the basic data to a combined nonlinear equation for HT = f(S, A), then solving for mean site index to estimate smoothed mean heights for ages 120 to 150. This avoided any correlation between the residuals and site and age. The derived equation was: x5 = loge(HT - feet =- + (logeage) - (logeage)3 + X 10~5 (logeage)5 - X 10"23 (logeage)30 Now that estimating equations are available for b2 and HT and mean S = is known, the equation is, S - = a2 + b2 (HT - ). Rearranged, a2 = (). The resulting a2 values are those shown in table 3. The a2 and b2 values in table 3 can be used to estimate site index for combinations of height and age. 23. 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 Farr, Wilbur A. cn; Pacific Northwest Forest and Range Experiment Station (Portland, Or. ) cn. [Portland, Or. ] : U. S. Dept. of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station
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