,/-^22> JAMES C. SPACE 



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UNITED STATES DEPARTMENT OF AGRICULTURE 

 FOREST SERVICE 



MmMOWTAW FOREST k RAHE EXPERIMENT STATION 



OCDEN UTAH 



No. 100 (Revised) October 1962 



SPECIFIC GRAVITY OF LODGEPOLE PINE IN THE INTERMOUNTAIN REGION 



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David Tack YeM r3 

 Division of Forest Management Research — 



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ABSTRACT _J EJ 



Specific gravity at breast height, calculated by the incrffic — ' 

 ment core method, gives a satisfactory estimate of average ^ 

 tree specific gravity. The relation of tree specific grav- 

 ity to core specific gravity at breast height is expressed 



by: Y = 0.661X + 0.143 



where Y = tree specific gravity 



X = specific gravity at breast height 

 Also, r = 0.754, and SE = 0.021 



Specific gravity decreases noticeably from stump height up 

 to 20 feet, but changes little above that. 



Specific gravity or density is a basic property used in general estimates of wood 

 quality and in converting timber volume estimates to a weight basis. The increment core 

 technique described by Mitchel and by Wahlgren and Fassnacht— ' can be used to estimate 

 the specific gravity of standing trees. This paper presents results of a study of use 

 of this increment core technique in estimating specific gravity for lodgepole pine. 



This study, started in July 1960, used 44 dominant trees from five locations on 

 four National Forests in Idaho, Utah, and Wyoming (table 1). After they were felled, 

 cross sections were cut at stump height, breast height, and at 8-foot intervals. In- 

 crement cores to the pith of each tree were extracted at breast height. Specific grav- 

 ity for both cores and cross sections was determined on the bases of green volume and 

 ovendry weight. Wood density in pounds per cubic foot was computed for each tree. Re- 

 sults are shown in tables 2 and 3. 



Differences in average specific gravity at breast height calculated by two methods 

 (increment core and stem section) and average tree specific gravity estimated by the 

 stem section method are nonsignificant. Therefore, specific gravity at breast height 

 calculated by the core method gave a satisfactory estimate of average tree specific 

 gravity. 



1/ Research Forester, Int ermountain Forest and Range Experiment Station, Forest 

 Service, U.S. Department of Agriculture, Bozeman, Montana. 



2/ Mitchell, H. L. Wood quality evaluation from increment cores. Jour. Tech. 

 Assoc. Pulp and Paper Indus. 41: 150-156. 1958. 



3/ Wahlgren, Harold E. , and Donald L. Fassnacht. Estimating tree specific gravity 

 from a single increment core. U.S. Forest Serv. Forest Prod. Lab. Rpt. 2146, 9 pp., 

 illus. 1959. 



