- £N Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA MECHANICAL PROPERTIES OF CENTRAL SIERRA OLD-GROWTH AND SECOND-GROWTH INCENSE CEDAR R. A. Cockrell A. G. Stangenberger CALIFORNIA AGRICULTURAL EXPERIMENT STATI O N BULLETIN 852 This bulletin reports the results of strength tests and density, shrinkage and fiber measurements on wood of some old-growth and second-growth incense cedar trees from the central Sierra. It compares these values with those of other softwoods and concludes that incense cedar wood is satisfactory for use as construction material and for pulpwood. JUNE, 1971 THE AUTHORS: Robert A. Cockrell is Professor of Forestry at the School of Forestry and Conservation and Wood Technologist at the Forest Products Laboratory, Richmond Field Station. Alan G. Stangenberger is Research Assistant in the School of Forestry and Conservation. Table 1 AGE AND SIZE OF TREES, AND LOCATION AND SIZE OF TEST BOLTS Approxi- mate age D. B. H. * Total height Log location and size Tree number Large end Small end Height D. I. B.| Height D. I. B. years inches feet feet inches feet inches j 160 139 31 5 19.5 120 76 11 5 7 5 23.8 15.7 20.5 21.3 21.7 2 13.3 6 220 278 26.0 29.0 97 92 7.5 8.0 21.4 22.0 20.5 17.0 18.9 10 20.4 11 53 17.0 70 10 11 5 23.5 9.0 12 53 13.0 50 4 5 11.0 18.0 8.5 13 42 12.8 46 4.5 11.5 18.0 8.0 14 51 18.0 60 9.0 12.3 18.0 10.2 15 49 17.0 60 8.5 12.3 17 5 11.0 16 51 17.5 68 8.9 12.9 17.9 11.7 * Diameter outside bark 4.5 feet above ground. t Diameter inside bark. [2] MECHANICAL PROPERTIES OF CENTRAL SIERRA OLD-GROWTH AND SECOND-GROWTH INCENSE CEDAR 1 INTRODUCTION Incense cedar (Libocedrus decurrens Torr.), which in recent years has been the principal source of wood for pencil slats, originally was one of the least important commercial species found in the mixed conifer forests of the Sierra Nevada, the Coast Ranges, and the southern Cascades. Much of the incense cedar in these forests was infected by brown pocket-rot fungus (Polyporns amarus Hedg.) which caused the trees to be rated as the most defective of all the associated Sierra conifers; the average cull was reported to be 21 per cent for mature dominants and 68 to 77 per cent for overmature dominants (Fowells, 1965). As a result, incense cedar — along with white fir [Abies concolor (Gord. & Glend.) Lindl.] — was long regarded as in- ferior, and with the advent of selective logging with tractors most cedars were left uncut. Having long had only local value (for uses such as posts and mudsills because of its durable heartwood) and little impor- tance for lumber and related uses, scant attention was given to assessing incense cedar's physical and mechanical properties. In recent years, however, old-growth in- cense cedar has increased in value because new uses (such as for pencil slats and rustic siding) have reduced the volume of stand- ing timber. Fortunately, the supply of young-growth incense cedar will probably also increase because the species appears likely to be relatively more aboundant as a component of second-growth Sierra forests. OBJECTIVES The data on the mechanical properties of incense cedar (available in USDA Techni- cal Bulletin No. 479) were obtained from four trees from Lane County, Oregon, near the northern limit of the tree's range, and from additional material, tree sources un- known, from Weed, California; both these areas are in the southern Cascades (Mark- 1 Submitted for publication January 28, 1971. wardt and Wilson, 1935). The green values given in Bulletin 479 are essentially iden- tical to those first reported by the Forest Service in 1917 (Newlin and Wilson, 1917). Because of limited published data avail- able on old-growth, and none at all on young-growth, it seemed worthwhile to gather additional data on the wood prop- erties of this increasingly important spe- cies. In 1965, a study was made on varia- tion in wood quality of 12 incense cedar trees from the University of California's Blodgett Forest — this is a 3,000-acre Uni- versity of California research forest east of Auburn, California, at approximately 4,300 feet elevation. The study described variations and interrelationships of specific gravity, radial and tangential shrinkage, percentage of heartwood, growth-ring width, and percentage of summerwood (Resch and Huang, 1967). Our study re- ports on the mechanical properties of four older trees used in the 1965 study, and on the same properties of six second-growth trees also obtained from Blodgett Forest. Data on fiber-length were also obtained for two of the old-growth and three of the second-growth trees. MATERIALS AND METHODS Four-foot bolts were cut from the trees in general conformity with the procedure prescribed in American Society for Testing and Materials Designation D 143-52. The location of bolts with respect to height in tree was adjusted when advantageous to obtain a maximum of clear length. Al- though no tree was sampled to test for variation with respect to height, an addi- tional 4-foot bolt was obtained for two of the old-growth and three of the second- growth trees. Table 1 gives general infor- mation on the trees. The 2 1/2 x 2i/9-inch test blanks were pre- [3] pared in accordance with the ASTM desig- nation and assembled at time of prepara- tion into two groups, one to be tested green and the other dry. Because incense cedar is tolerant and retains its branches for many years, the wood was quite knotty; this necessitated departing from the prescribed sampling procedure by utilizing some clear material located in sectors of the log adjacent to cardinal di- rection zones. Even with these additional blanks, however, there was a shortage of specimens for some dry tests of second- growth trees. All the mechanical properties tests and specific gravity and volumetric shrinkage determinations conformed to ASTM D 143-52. Shrinkage measurements were made to the nearest 0.001-inch on 1 x 1 x 4- inch specimens cut with growth rings aligned so as to parallel tangential and radial directions. On these blocks the lon- gitudinal shrinkage was measured over the 4-inch dimension, and tangential and ra- dial shrinkage was determined from mea- surements taken in the middle of the 4-inch surfaces. Data on fiber length were obtained by macerating matchstick-size samples of wood with an aqueous solution of 10 per cent nitric and 10 per cent chromic acids, and then staining with safranin and mounting directly on slides in dilute polyvinyl ace- tate. Averages were based on 40 measure- ments of fibers selected at random from slides prepared for each sample (Echols, 1969). RESULTS AND DISCUSSION Table 2 lists basic data for tests on green specimens of old-growth trees, and table 3 lists data on second-growth. Table 4 gives basic data for dry specimens of old-growth, and table 5 lists them for second-growth. As the number of tests on each property varied for the different trees, mean values in the tables were determined from tree means rather than from individual test values in order to give each tree-test equal weight (Cockrell, 1959). Moisture content. Old-growth green wood moisture content values ranged from 30 to 45 per cent for heartwood to 160 to 225 per cent for sapwood. Second-growth sapwood moisture content values ranged from 200 to 280 per cent, with most speci- mens being higher than the maximum for 4 the old-growth. Second-growth heartwood moisture content was similar to the old- r growth. The moisture content of air-dry test material for the old-growth trees and second-growth trees numbered 14, 15, 16 was approximately 12 per cent. Air-dry * specimens of second-growth trees 11, 12, 13 , had about 15 per cent moisture content and were adjustd to 12 per cent according « to the U. S. Forest Products Laboratory exponential formula using an intersection point (Mp value) of 25 (USDA, 1955). Growth rate. The growth rate of old- growth test material ranged from 8 to 28 rings per inch, with most specimens rang- ing from 15 to 20. Most second-growth fl specimens varied between 4 to 9 rings per inch, and in all cases the specimens far- thest from the pith had the slowest growth rate. Figures 1 and 2 (page 8) illustrate the trend of decreasing ring width from pith to bark in trees 1 and 14. In tree 1, bolt A — which had 149 rings in the cross section — «.. the average radial thickness of the first 50 rings from the pith was 6 inches and, for the last 50 rings, 2.5 inches. For tree 2, bolt A, the corresponding figures are 123 rings total, 4.15 inches first 50 rings, and 2.15 inches last 50 rings. Structural qualities. Comparison of * table 2 with table 3, and of table 4 with table 5, shows that wood from second- growth incense cedar 50 years old or less is appreciably weaker than old-growth. Particular note should be taken of the . lower bending and compression parallel values of tree 13 (tables 3 and 5). This tree was younger (37 rings at 4.5 feet height) than the other five, and its test specimens " included a higher percentage of juvenile wood (wood closer to the pith). Inspection of bending-strength data for individual old-growth specimens close to the pith re- vealed that these all had lower values than those farther from the pith and, as previ- ously reported for Monterey pine (Cock- - rell, 1959), the central core wood was less dense and weaker than material farther out in the cross-section. Table 6 compares data on old-growth and second-growth material used in this study with pre- viously reported U. S. 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'3 O "C &> > "5 C 2 C % o O «- 03 rT 3d a § X 3*.S o w -3 T oi a 3 03 — H .3 TO .3 TO gaga m O o H ffi S o S s Table 4 MECHANICAL PROPERTIES OF DRY OLD-GROWTH INCENSE CEDAR Tree number, number of specimens tested, and magnitude of property Stan- Mini- Maxi- Species mean dard devia- tion of tree means mum indivi- dual test value mum Property Tree number indivi- dual test 1 2 6 10 value Specific gravity: Volume green, weight oven-dry 0.34 0.38 0.33 0.37 0.36 0.02 0.31 0.42 Volume oven-dry, weight oven-dry 0.37 0.42 0.36 0.40 0.39 0.03 0.34 0.46 Static bending: (13)t (7) (9) (10) Fiber stress at pro- portional limit (psi)* 5,530.0 6,050.0 5,670.0 5,430.0 5,670.0 272.0 4,200.0 7,090.0 Modulus of rupture (psi) 8,440.0 10,480.0 8,640.0 9,620.0 9,300.0 943.0 6,090.0 12,180.0 Modulus of elasticity (1,000 psi) 1,070.0 1,350.0 951.0 1,210.0 1,150.0 173.0 780 00 1 , 630 Work to proportional limit (in.-lb. per cu. in.) 1.63 1.58 1.89 1.39 1.62 0.21 1.0 2.35 Work to maximum load (in.-lb. per cu. in.) 6.2 9.1 8.1 9.1 8.1 1.4 2.7 16.8 Total work (in.-lb. per cu. in.) 7.2 13.0 8.1 10.4 9.7 2.6 2.7 20.6 Compression parallel to grain: (27) (9) (18) (16) Stress at proportional limit (psi) 4,170.0 5,040.0 3,680.0 4,390.0 4,320.0 564.0 2,620.0 5,750.0 Maximum crushing strength (psi) 5,120.0 6,570.0 4,890.0 5,700.0 5,570.0 749.0 3,790.0 6,880.0 Compression perpendi- cular to grain: (19) (7) (12) (12) Stress at proportional limit (psi) 540.0 700.0 580.0 630.0 610.0 69.0 280.0 950.0 Toughness: (14) (5) (13) (12) (in. lb.) 92.0 142.0 118.0 122.0 118.0 21.0 48.0 243.0 Hardness: (64) (24) (44) (52) Side (lb.) 410.0 500.0 400.0 470.0 440.0 48.0 330.0 590.0 En (36) (12) (22) (26) End (lb.) 700.0 830.0 760.0 860.0 790.0 72.0 620.0 1,000.0 Maximum shearing strength parallel to grain (22) (9) (16) (9) (psi) 910.0 1,040.0 970.0 1,110.0 1,010.0 87.0 750.0 1,540.0 Cleavage (25) (11) (19) (ID (lb. per in. of width) . . 140.0 160.0 150.0 160.0 150.0 10.0 100.0 220.0 Maximum tensile strength perpendicu- lar to grain (28) (11) (18) (18) (psi) 260.0 250.0 270.0 280.0 260.0 13.0 180.0 400 Maximum tensile strength parallel to grain (6) (3) (5) (7) (psi) 12,380 13,400 10,160 11,960 11,960 1,350.0 8,190.0 15,260.0 * Pounds per square inch. t Numbers in parentheses refer to number of specimens tested for each property. [7] v Fig. 1. Cross section of old-growth tree 1 at large end of log. for incense cedar, Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], and white fir (comparison was on the basis of certain mechanical properties). Douglas fir is in- cluded because its working stresses for construction uses such as joists, planks, studs and framing are the highest of west- ern softwoods (Western Wood Products Assoc, 1968). White fir is included among the true firs which (with hemlock) are in the next highest working stress (design value) species category. The values for old- growth material tested in our study are consistently higher than those reported by the Forest Service in 1917 and 1935 and, except for stiffness (modulus of elasticity) of the dry wood, they compare favorably with white fir — which is generally accepted Fig. 2. Cross sections of young-growth tree 14 at large and small end of first 4-foot bolt. +. 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T3 d f « h Q t, J) t- o M M 03 .S -f <° f- 1 o fe M 03 .S £ t- (J B Y 1 > * > M CB •- o bO M 03 .=; 0) -1-2 TJ J; A « c " i3 '» o > -S - -a 2 "° "S c u S "2 T3 << o m CD «3 2 < o CO OQ bB.S as satisfactory for most construction uses (dimension lumber). Shrinkage. Table 7 presents data on longitudinal, tangential, radial, and volu- metric shrinkage. The data show that tan- gential, radial, and volumetric shrinkage of heartwood is conspicuously less than that of sapwood; averages of tangential and radial shrinkage for the oven-dry con- dition of old-growth (heartwood and sap- wood combined) are 5.0 and 3.1 per cent, respectively, and are approximately the same as those reported by Resch and Huang in 1967 for their larger sample of 11 trees. Tangential, radial and volumet- ric shrinkage percentages for second- growth are somewhat lower than those for old-growth, while the T/R ratios (ratio of tangential to radial shrinkage) are some- what higher. Practically all specimens elongated slightly when dried to 12 per cent (air-dry), but showed slight net shrink- age when drying continued to the oven- dry condition. Fiber length. Figure 3 shows the rela- tionship of fiber length to number of rings from pith for two old-growth and three second-growth trees. The basic data sug- gest that at 20 rings from the pith the aver- age length is about 3 millimeters, with minimum and maximum values being ap- proximately 1.5 mm and 4 mm, respec- tively. Beyond 30 rings from the pith, the average length is about 3.5 mm, with min- imum and maximum values being about 1.5 mm and 5.0 mm. ACKNOWLEDGMENTS The authors wish to acknowledge the as- sistance of H. C. Sampert and his staff at Blodgett Forest in obtaining the test ma- terial, and of R. M. Echols of the Pacific Southwest Forest and Range Experiment Station in making available fiber projec- tion and measuring apparatus. 4 5 RINGS FROM PITH ^ V Fig. 3. Relationship of fiber length to rings from pith at large end of logs of two old-growth and three young-growth trees. [12] SUMMARY Strength and some other physical proper- white fir in all strength properties except ties data of wood are reported for a sam- for being distinctly lower in stiffness; in pling of old-growth and second-growth in- the air-dry condition it is also somewhat cense cedar trees from the central Sierra. weaker in bending. Tangential, radial, These data indicate that old-growth in- and volumetric shrinkage of heartwood cense cedar wood compares favorably with was distinctly less than in sapwood, and white fir wood in all mechanical properties this species would be classed with redwood save for being slightly lower in stiffness. as being among those softwoods with the Data for second-growth incense cedar in least shrinkage. Fibers are about same the 50-year-old class indicate that it is length as the average of important pulp- lighter and weaker than old-growth. In the wood species. The wood is suitable for light green condition it is essentially equal to construction and the fibers for wood pulp. LITERATURE CITED ASTM Standards 1952. American Society for Testing and Materials, Philadelphia, Pennsylvania. Cockrell, R. A. 1959. Mechanical properties of California-grown Monterey pine. Hilgardia 28(8): 227- 38. Echols, R. M. 1969. Permanent slides of stained wood fibers without dehydration or cover glasses. Forest Science 15(4) :41 1. Fo wells, H. A. 1965. Silvics of forest trees of the United States. U. S. Dept. of Agr., Agr. Handbook No. 271. Gerhards, C. C. 1964. Strength and related properties of white fir. U. S. Forest Service Research Paper FPL 14, Forest Products Laboratory, Madison, Wise. Markwardt, L. J. and T. R. C. Wilson 1935. Strength and related properties of woods grown in the United States. U. S. Dept. of Agr. Tech. Bui. 479. Newlin, J. A. and T. R. C. Wilson 1917. Mechanical properties of woods grown in the United States. U. S. Dept. of Agr. Bui. 556. Resch, H., and S. Huang 1967. Variation in wood quality of incense cedar trees. Calif. Agr. Exp. Sta. Bui. 833. U. S. Dept. of Agriculture 1955. Wood Handbook. Agriculture Handbook No. 72. Western Wood Products Association 1968. Rules for grading western lumber. Portland, Oregon. 5m-6,'71(P403lL)VL