14 YELLOW POPLAR IN TENNESSEE. 



wood has retarded their use for lumber to a considerable extent. Young, 

 thrifty sap trees are called "hickory poplar," on account of the toughness 

 of their wood. 



Soil and moisture conditions cause a considerable variation in the 

 amount and color of heartwood and the percentage of moisture in the 

 wood. Trees growing on uniformly moist but well-drained soils (well 

 aerated), such as fertile coves and best limestone soils have a thin sap- 

 wood, heartwood, dark brownish-yellow or canary yellow in color, con- 

 taining a low percentage of moisture ancf the lumber from such trees 

 consequently is not so subject to shrinking, checking, or warping. Large 

 old trees on such sites, as a rule, have less than one inch of radial sap- 

 wood. Second growth trees on similar sites, 12 inches in diameter and 

 sixty years old, often have less than 1.5 inches of sapwoocl on the radius. 

 On the other hand, on dry soils, the trees have a small, pale yellow or 

 nearly white heartwood ("white" or blue poplar") and a very thick sap- 

 wood. Such dry soils may be either physically dry as in the case of coarse 

 sands, fissured slates or very fine grained clay, when the water table is 

 low or fluctuates, or physiologically dry, as in the case of such sour soils 

 as are poorly drained, because of deficient aeration. On "dry" sites the 

 sapwood which acts as a water reservoir is sometimes so thick as to in- 

 clude one-half the radius of a tree two feet in diameter. The wood of 

 "white poplar" and "blue poplar" has a high percentage of moisture and 

 is subject to shrinking, checking, and warping, but is tougher than that 

 which is deep yellow. Trees with pale-colored heartwood are most sub- 

 ject to windshake and discolored (calico) wood. The canary yellow wood 

 is most prized for general uses. 



The lumber can be easily and quickly kiln-dried. The best results in 

 commercial kiln drying are obtained by first subjecting the wood to live 

 steam or to hot moist air which is subsequently replaced by a free circula- 

 tion of warm dryer air ; but the wood is not refractory when a dry chamber 

 system is employed, and is not prone to case harden and check. Sapwood 

 blues if piled closely. This can be prevented by immersing the timber in 

 a 10 per cent, solution of bicarbonate of soda. Air drying, though slow, 

 is effective. The wood is easily impregnated with preservatives, either 

 with copper sulphate by the gravity process or with creosote or zinc 

 chloride.* 



The wood has other qualities which give it a very wide range of use- 

 fulness. It works easily and smoothly when dried, that from any one tree 

 being comparatively uniform in quality and as a rule that from trees in 

 one locality is very uniform in character. It absorbs stain easily, but on 



*Branch of Products, U. S. Forest Service. 



