584 



Forestry Quarterly 



growth. Fast-growing Loblolly, in comparison, has relatively 

 much narrower summer wood, grading very gradually into the 

 wider band of spring wood.^^ Table 3 gives the relative physical 

 and mechanical properties of the io\xr important commercial 

 Southern pines, as determined by the Forest Products Laboratory 

 at Madison, Wisconsin. The superiority of Slash over Longleaf 

 in nearly every test will be noted. This gives Slash pine the 

 distinction of producing the heaviest, hardest, and strongest 

 coniferous wood in the United States. ^^ 



Table 3. — Physical and Mechanical Properties of Slash Pine Compared with the 

 Other Important Commercial Southern Pines 



Long- Short- Lob- 

 Quality Slash^* leap^ leaf^^ lolly" 



Specific gravity based on volume when 



oven-dry 68 .64 .58 .59 



Density — weight of wood per cubic foot: 



Kiln dry, pounds 43 40 35 37 



Air dry (12 to 15 per cent moisture), 



pounds 45 42 36 39 



Green, pounds 53 48 45 54 



Shrinkage in volume from green to oven- 

 dry. Per cent of diameter when 

 green 12.7 12.3 12.6 12.6 



Strength in bending. Modulus of rup- 

 ture. Pounds per sq. in 8,800 8,700 8,000 7,500 



Stiffness in bending. Modulus of elas- 

 ticity. 1,000 lbs. per sq. in 1,630 1,630 1,450 1,380 



Toughness. Work to maximum load in 



bending. Inch-pounds per cu. in. . . 7.9 8.0 8.7 8.0 



Crushing strength. Compression paral- 

 lel to grain. Pounds per sq. in 4,470 4,390 3,810 3,580 



Hardness (side) load required to imbed a 

 0.444 inch ball to one half its 

 diameter. Pounds 630 590 560 450 



" Based upon detailed studies of the Forest Service in connection with the 

 grading of Southern pine lumber by density rules. 



" Possibly this may be equally true of all exotic species of conifers. 



" Figtu-es, except for density, from tests of 5 trees from Florida. 



'* Figures, except for density, from tests of 24 trees from Florida, Mississippi, 

 and Ix)uisiana. 



" Figures, except for density, from tests of 6 trees from Arkansas and 

 Louisiana. 



" Figures, except for density, from tests of 10 trees from North and South 

 Carolina and Florida. 



