Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. v —_ alle Lap wel - = Ait Y Ode A99.9 F764Un Gre uN ‘ if Southwest cro } Research Note RM-492 September 1989 USDA Forest Service Rocky Mountain Forest and Range Experiment Station Fibril Angle in Young-Growth Ponderosa Pine as Related to Site Index, D.B.H., and Location in Tree Craig E. Shuler, Donald D. Markstrom, and Michael G. Ryan‘ Young-growth ponderosa pine on two different sites in northern New Mexico were evaluated for differences in fibril angle. Measurements were made radially at the butt end, mid-length, and top end of the merchant- able stem divided into multiple 8-foot log lengths. Results indicated that the butt ends have larger fibril angles than the other two locations. Fibril angle did not vary significantly with either site index from 55 to 100 or d.b.h. from 9 to 14 inches. Keywords: Ponderosa pine, fibril angle, young growth, site index Management Implications Loss of lumber grade from excessive warp usually results from abnormal and/or asymmetrical shrinkage when lumber dries. In conifers, fibril angle, juvenile wood, compression wood, grain orientation, and knots have been associated with excessive lumber warpage. Longitudinal shrinkage typically ranges from 0.1% to 0.3% when wood is dried from green to ovendry condi- tions. Longitudinal shrinkage greater than 0.3% from green to overdry conditions for straight grain material is considered abnormal and is related to deviation of the microfibrils (fibril angle) from the longitudinal axis of the tracheid. Study results indicated that the fibril angle of young-growth ponderosa pine did not significantly vary with site index from 55 to 100 or d.b.h. from 9 to 14 inches. Introduction Fibril angle of the S, layer of woody cells has been shown to affect some properties of wood material (McMil- lin 1973, Meylan 1972, Panshin and de Zeeuw 1980, Piirto ‘Authors are, respectively, Associate Professor, Colorado State Univer- sity, Fort Collins; Research Wood Technologist and Biometrician, Rocky Mountain, Forest and Range Experiment Station. Headquarters is in Fort Collins, in cooperation with Colorado State University. et al. 1974, Voorhies and Blake 1981, Voorhies and Groman 1982). Variations in shrinkage and mechanical behavior have been the properties of primary interest. The researchers cited generally agreed on two aspects of fibril angle: (1) large fibril angles (as measured from the longitudinal axis) in softwood tracheids and hard- wood fibers result in reduced mechanical properties parallel to the grain and in increased longitudinal shrinkage; (2) fibril angle is inversely related both to distance from the pith and to cell length, with regions of a tree undergoing rapid growth (i.e., earlywood, juvenile wood, reaction wood) generally having larger fibril angles than regions growing more slowly. The increased longitudinal shrinkage associated with larger fibril angles often results in warp, specifically crook and bow, when there is a marked asymmetric distribution of fibril angles throughout a piece of lumber. This fibril angle study was part of a larger project in- vestigating the development of warp during drying in young-growth ponderosa pine from the southwestern United States (Markstrom et al. 1984). Significant results of that study were that lumber grade recovery and warp were related primarily to tree and log diameters, and the factor of height location in the tree had no effect on the amount of warp that developed. The objective of this research was to develop an equation that would predict fibril angle in young-growth ponderosa pine (Pinus ponderosa Dougl. ex Laws) using the variables of site index, diameter at breast height (d.b.h.), relative height location in the tree, and distance from the pith. Methods Forty-one trees ranging from 9 to 14 inches d.b.h. were cut from an area with a site index of 55. Another 41 trees with the same diameter range were cut from an area with a site index of 100. Both sites were located in the Santa Fe National Forest in northern New Mexico. Studs cut from these trees were used for the earlier drying study (Markstrom et al. 1984). Sixty of the trees (5 for each of the 6 d.b.h. classes on each site) were sampled for fibril angle. When the trees were felled, a 1/2-inch-diameter increment core was taken at the merchantable stem mid-length; and approximately 2-inch-thick disks were cut from the butt of the lower log and from the top of the upper log. Sections were cut from these disks and cores for determining the fibril angles. Fibril angle was measured as follows: 1. From each disk or core, a true radial surface was exposed from the pith to the cambial zone. 2. Sections were marked on this radial surface at 5- year intervals from the pith to the cambial zone. For the larger butt sections, the intervals were marked every 10 years from the thirtieth ring to the cambial zone. 3. At each marked ring, thin sections were cut by hand using a razor blade. These sections were placed in water on a microscope slide, covered, and observed on the screen of a Reichert Veripan? microscope at a magnifi- cation of 130. 4. The fibril angle was considered to be defined by the angle formed between the longitudinal axis of the tra- cheids and the aperature of the half-bordered pit pair in the crossfields of the ray parenchyma and the longitudi- nal tracheids (Shottafer et al. 1972). Angles were meas- ured to the nearest degree using a protractor directly on the microscope screen. Measurements were made on earlywood tracheid crossfields. For each thin section examined, three fibril angles were measured. These three measurements were then averaged to obtain the fibril angle for that location in the sample. Results and Discussion The relationship between the fibril angle and rings from the pith is generally accepted to be exponential. The data in this study, however, showed a high degree of varia- bility (fig.1) which, from a purely statistical point of view, indicated a linear relationship. This variability may have The use of trade and company names is for the benefit of the readers; such use does not constitute an official endorsement or approval of any service or product by the U.S. Department of Agriculture to the exclusion of others that may be suitable. 80 = 72 2 1 1 8 iss uf 2 le 2h 64-3 5 fanes 8 B24 54 i 4 7 28 6 3 1 oo 3 5 Ss 35h 7 1 56 ant 2 1 = 2) 3) 16) 56 6 1 1 & A FA) 72 2 $ th Ko is 3 yo a z ® 16 2 7 3 2 1 2 1 2 48 Ait 2 3 1 1 2 fishy 5) 8 1 1 2 21 2 6 17 4 2 2 1 5 <= 40 do ou 1 HN N/WRWOS 32 24 475 14.25 23.75 3325 4275 5225 6175 71.25 8075 9025 99.75 109.25 ie) 95 19 28.5 38 475 57 66.5 76 85.5 95 1045 Number of rings from pith n N@ON@DN-ON =~ 44 64NNNON 20 1 ue 5 1 2 2 5. ae 1 a US| A 1 > Sz 2 SigeS es) Vt 1 £ By, 5 2 3 Siw S50 Siuniy, c-Si = Sy BNz yer 2 es eae S 37446). A 952 1 2 2 = ry ts G) (25 5itat tS. ot 5S aera 2 3 ye Pr i" ew En c liyee eee ieee eB 1 Tee eea| 1 30 Sa Sy? 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The 90 80 70 = 60 50 OUNND MWoerow--- - = 40 Fibril angle (degrees) ~~ ~+-+ON OD, ennan n Nn -_ =N BONO YH NNON 30 N= W8B8WO0FOHAHNSWW == = 20 - +=]+= +=8BnBeunnVwoereanan-= NN=NO BNSF R NNN +--+ NON =“HWNA ON = = nywsan = Number of rings from pith Figure 1.—Data plots of fibril angle versus rings from pith for the three heights; (a, butt; b, mid-stem; c, top) with linear regres- sion curves. contribution of interaction (3) to the correlation (R2) value, however, was not considered sufficient to war- rant its inclusion in the final models shown below. FA 51.6 - 0.462G + 15.3X -1.19Y [1] FA = e (XPH) (3.978 - 0.0114G + 0.281X — 0.0358Y) where FA = fibril angle (degrees); G =rings from pith; and X and Y =dummy variables representing loca- tion in tree coded as: [2] XxX Y Butt 1 0 Mid-stem 0 1 Top 0 0 Because the heights of the mid-stem and top varied with the heights of the trees sampled, the data were evalu- ated also according to actual height in the tree. Plots of the linear curves obtained showed a distinct separation of the butt data and two other groupings, one consist- ing of the 17-, 33-, and 49-foot heights and the other, the 9-, 13-, 21-, 25-, 41-, and 57-foot heights. Although not totally consistent, these latter two groupings tended to follow the mid-stem and top categories, respectively. Thus, we retained the original categories. For equation [2] the data were fit to the model using Marquardt’s nonlinear least squares algorithm (Mar- quardt 1963). R? for both models was 0.590, with a stand- ard error of estimate of 9.4 degrees. While the exponential model did not improve the fit of the data, it still has features indicating it is more suita- ble for describing the relationship. Figure 2 shows the regression curves obtained from equation [2]. Two fea- tures should be noted. First, the slopes of the curves are more shallow through the juvenile zone than past studies would lead us to expect. Second, the slopes of the curves in the mature region (e.g., greater than 50 years of age) are not as flat as might be expected. Whether these con- ditions are the result of the regression process or truly representative of the young-growth ponderosa pine is not clear. The continuing decrease in fibril angle at the greater ages is similar, however, to that shown by Voorhies and Groman (1982). A linear relationship, on the other hand, would imply a continued constant decrease in fibril angle as the tree ages. Although height location in tree was a statistically sig- nificant factor for all three locations evaluated, it appears that much of that significance is the result of the appreciably larger fibril angles in the butt material. The steeper negative slope seen in the curve for the butt material as compared with the other two locations is important. This could have an effect on the amount of warp that develops in lumber. Although our earlier study (Markstrom et at. 1984) indicated it was not possible to correlate the fibril angle with warp development, the possible relationship is of enough importance to merit some discussion. Crook and bow are warp primarily caused by differences in longitu- dinal shrinkage on opposite sides of a piece of lumber. A very steep negative slope in the fibril angle curve indi- cates a relatively large difference in fibril angle would occur on opposite sides of a piece of wood cut from that location. This would likely result in differential longitu- dinal shrinkage. Thus, in the cases where more crook has been reported in lumber cut from butt logs (Blake and Voorhies 1980, Maeglin and Boone 1983), or where the amount of warp is related to smaller log diameters (Mark- strom et al. 1984), a contributing factor may be the fibril 80 60 Fibril angle (degrees) .s ° Butt Top Mid-stem nm oO 0 20 40 60 80 100 Rings from pith Figure 2.—Regression curves for fibril angle versus rings from pith for three X locations in ponderosa pine. angle differential present in the juvenile wood. It must be emphasized, however, that the impact of fibril angle is most likely quite small. Other gross features (i.e., grain orientation, knots, compression wood) are expected to have more influence on the behavior of full-sized wood members. Conclusions 1. The fibril angle in young-growth southwestern pon- derosa pine is related to rings from the pith (i.e., age and diameter) and height location in the tree. 2. Differences in fibril angle related to height location in the tree are heavily influenced by the greater fibril angles in the butt material. 3. Site index and diameter breast height are not sig- nificantly related to fibril angle. Literature Cited Blake, Bradford R.; Voorhies, Glenn. 1980. Kiln drying of young-growth ponderosa pine studs. Ariz. For. Notes No. 13. Flagstaff, AZ: Northern Arizona University, School of Forestry. 14 p. Maeglin, R. R.; Boone, R. S. 1983. An evaluation of saw- dry-rip (SDR) for the manufacture of studs from small ponderosa pine logs. Res. Pap. FPL-435. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 7 p. Markstrom, Donald C.; Shuler, Craig E.; King, Rudy M. 1984. Warpage of studs from young-growth ponderosa pine from New Mexico. Res. Pap. RM-257. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 13 p. Marquardt, A. W. 1963. An algorithm for least squares estimation of non-linear parameters. Society for Indus- trial and Applied Mathematics Journal. 2: 431-441. McMillin, Charles W. 1973. Fibril angle of loblolly pine wood as related to specific gravity, growth rate, and dis- tance from pith. Wood Science and Technology. 7: 251-255. Meylan, B. A. 1972. The influence of a microfibril angle on the longitudinal shrinkage-moisture content rela- tionship. Wood Science and Technology. 6: 293-301. Panshin, Alexis J.; de Zeeuw, Carl. 1980. Textbook of wood technology. 4th ed. New York, NY: McGraw Hill Book Co.: 251-266. Piirto, D. D.; Crews, D. L.; Troxell, H. E. 1974. The effects of dwarf mistletoe on the wood properties of lodgepole pine. Wood and Fiber Science. 6(1): 26-35. Shottafer, J. E.; Kutscha, N. P.; Hale, R. A. 1972. Proper- ties of plantation grown red pine related to its utiliza- tion. Tech. Bull. 61. Orono, ME: University of Maine, Life Science and Agricultural Experiment Station. 72 p. Voorhies, Glenn; Blake, Bradford R. 1981. Properties affecting drying characteristics of young-growth pon- derosa pine. Ariz For. Notes No. 14. Flagstaff, AZ: Northern Arizona University, School of Forestry. 27 p. Voorhies, Glenn; Groman, W. A. 1982. Longitudinal shrinkage and occurrence of various fibril angles in juvenile wood of young-growth ponderosa pine. Ariz. For. Notes No. 16. Flagstaff, AZ: Northern Arizona University, School of Forestry. 18 p.