Bell, John F.

Berg, Alan B.

Faqir Mohammad Khan

Oregon State University. Forest Research Laboratory

Undetermined

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67i7ESE _ . H Nc.hooi of ForestryOregon State UniversityL No. 59°:. r st Research i.;s a; Lf ,.)1 t i l i7ESTIMATING DIAMETER INSIDE BARK AT VARIOUS HEIGHTSIN YOUNG DOUGLAS-FIR TREES'Faqir Mohammad KhanGraduate StudentJohn F. BellProfessor of Forest ManagementAlan B. BergProfessor of Forest ScienceINTRODUCTIONIntensive management of young-growth Douglas-fir forests requires accurateestimates of tree volume. Diameters at upper stem points that are necessary todetermine tree volume directly in standing trees have been difficult to measure untilrecently. With the development of high-performance optical dendrometers, height upthe stem and diameter outside bark (dob) in the upper stem can be measured withconsiderable accuracy (1). Diameter inside bark (dib) in the upper stem, however, isstill difficult to measure directly.Johnson (2) has presented regression equations for computing bark factors forconverting dob to dib in upper stems (16 feet and higher) of Douglas-fir. The purposeof this paper is to present regression equations for estimating dib at upper stem pointsin Douglas-fir from measurements of dob. The equations cannot be used to estimatedib at breast height or stump height.PROCEDURESData came from two areas: 237 trees from 4.1 to 20.7 inches in diameter atbreast height in a 40-year-old stand of Douglas-fir on the Black Rock ForestManagement Research Area2 in Polk County, Oregon, and 302 trees from 2.6 to 30.0inches in diameter at breast height from 23 plots representing a wide variety of standsfrom 13 to 99 years old scattered throughout western Washington (3). The trees ofboth sources had been felled and measured at 16-foot intervals up the tree.Five basic independent variables were examined in a stepwise regression procedurefor their effect on dib (dependent variable) at the point of interest on the stem. Thebasic independent variables were dob at breast height, bark ratio at breast height (dibdivided by dob), total tree height, length up the stem to the point of interest, anddob at the point of interest on the stem.Based on "Developing an Equation for Making Estimates of Diameter Inside Bark at Various Heightsup the Stem in Douglas-fir." 1966. M.S. thesis, Oregon State University, Corvallis, by FaqirMohammad Khan.2 Part of the George T. Gerlinger Experimental Forest administered by the Oregon State ForestryDepartment.n;,'3.'"f<.rAs information on tree age was available from data of the State of Washington,tree age was added in the analyses of these data. All squares and cross products ofthe basic independent variables were also included.RESULTSTwo equations resulted from separate regression analyses of the data. Theequations3, which can be solved easily with a desk calculator, are:dib = 0.928712 (dob) + 0.0416447 Equation 1, Black Rockanddib = 0.934242 (dob) - 0.01916 Equation 2, Washington,where dib and dob are at the point of interest for upper stems. Either equation canbe used for predicting dib of upper stems of Douglas-fir in Oregon and Washington.The additional variables contributed little in predicting upper-stem dib.A high correlation between dob and dib also was evident from a plot of the datafrom the ' State of Washington. (Figure 1).Until additional studies can be made, these equations are recommended forpractical use in young Douglas-fir forests throughout Oregon and Washington.282624`-1 I2wwa04 6 8 10 12 14 16 18 20 22 24 26DIAMETER OUTSIDE BARK, INCHESFigure 1. Relation of dib to dob of various upper stem points in Douglas-fir.LITERATURE CITED1. GROSENBAUGH, L. R. Some Suggestions for Better Sample-Tree-Measurements. IN:Proceedings, Society of American Foresters, Washington, D.C. P. 36-42. 1963.2. JOHNSON, Floyd A. Bark Factors for Douglas-fir. U.S. Dept. of Agric., ForestService, Pacific N.W. For. and Range Expt. Station. Portland. Res. Note PNW-34. 3 p.1966.3. TURNBULL, K. J., G. R. LITTLE, and G. E. HOYER. Comprehensive Tree-VolumeTarif Tables. Department of Natural Resources, Olympia, Washington. 23 p. 1963.3quuation 1 has a standard deviation about the regression line of ± 0.14 inch or ± 2.36 percent,and Equation 2 has a standard deviation about the regression line of ± 0.22 inch or ± 2.36 percent.The r2 was equal to 0.988 for both equations.20F162

Estimating diameter inside bark at various heights in young Douglas fir trees

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Estimating diameter inside bark at various heights in young Douglas fir trees

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