F3/2- U. S. DEPT. OF AGRICULTURE 



UNITED STATES DEPARTMENT OF AGRICULTURE 

 FOREST SERVICE 



mmMommn forest & rahe experiment station 



OCDEN UTAH 



No. 100 September 1962 



SPECIFIC GRAVITY OF LODGEPOLE PINE IN THE INTERMOUNTAIN REGION 



David Tackle!/ 

 Division of Forest Management Research 



ABSTRACT 



Specific gravity at breast height, calculated by the incre- 

 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 = 0.572 X + 0.179 



where Y = tree specific gravity 



X = specific gravity at breast height 

 Also, r = 0.749, and SE = 0.020 



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 l- 2 -/ 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. Incre- 

 ment cores to the pith of each tree were extracted at breast height. Specific gravity 

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

 dry weight. Wood density in pounds per cubic foot was computed for each tree. Results 

 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 calcu- 

 lated by the core method gave a satisfactory estimate of average tree specific gravity. 



1/ Research Forester, Intermountain 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. 



