Growing Better Timber 



tions at the Forest Products Labora- 

 tory, found that both types of abnormal 

 wood shrink excessively and unevenly 

 along the grain in drying, so that large 

 and small pieces alike are crooked, and 

 that they have unreliable strength 

 properties. Compression wood becomes 

 more pronounced the farther the tree 

 trunk leans and the faster it grows. In 

 rapidly growing, second-growth soft- 

 wood stands it is especially important 

 to eliminate trees that lean 5 or more. 

 Less is known about tension wood in 

 hardwoods. 



It is not practical to straighten small 

 trees that are crooked or leaning. De- 

 formed and inclined trees should be re- 

 moved while young; they will not pro- 

 duce high-grade wood. 



Excessive taper also is objectionable, 

 for obvious reasons, in logs for veneer, 

 electric-wire poles, piling, railway ties, 

 and fence posts. 



Taper is governed by the ratio of 

 diameter to height growth. 



ANNUAL GROWTH in height is de- 

 termined principally by the quality of 

 the site, that is, climatic and soil con- 

 ditions. The density of the stand in- 

 fluences the height growth only slightly. 



Growth in diameter is determined by 

 the quality of the site and the density 

 of the stand. On a given site the ratio 

 of diameter to height growth, or the 

 amount of taper, is determined by the 

 growing space of a tree. The faster 

 trees grow in diameter, the more taper 

 they will have. Open-grown trees have 

 too much taper for many uses. As will 

 be seen later, growing space also in- 

 fluences the size and persistence of the 

 lower limbs, hence taper also is an in- 

 dex of the character of the hidden 

 knots in a tree trunk; that is, the 

 greater the taper, the larger the knots. 



Even when trees grow straight and 

 vertical, the grain in them that is, the 

 direction of the fibers often is not 

 parallel with the axis of the stem. 

 Various types of distortions of the 

 fibers, some of them detrimental and 

 some advantageous, may occur. Spiral 

 grain, which is an inclined growth of 



201 



the fibers that gives the trunks a twisted 

 appearance, may occur in individual 

 trees of any species. The twist may be 

 to the right or to the left; usually it is 

 more pronounced in wood the farther 

 it is from the center of the trunk. This 

 is a point in favor of second-growth, 

 because the trees are smaller when 

 harvested than are old-growth trees 

 and consequently the maximum slope 

 of spiral grain should average less in 

 second-growth timber. 



SPIRAL GRAIN is consistently objec- 

 tionable. It causes poles, timbers, ties, 

 and lumber to twist during drying. It 

 has a weakening effect when the slope 

 is greater than 1 in 20. It causes chip- 

 ping and roughness when lumber is 

 planed against the grain. 



We do not know the cause of spiral 

 grain, but we do know that it is not 

 caused by actual twisting of the tree 

 trunk by the wind or otherwise. Opin- 

 ions differ as to whether spiral grain 

 is due to heredity or environment. It 

 seems to be more severe in trees that 

 grow slowly under adverse conditions, 

 as at timber line; it may be that slow 

 growth brings out more strongly any 

 hereditary tendencies toward spiral 

 grain that may be present. 



To BE ON THE SAFE SIDE, Seed for 



forest planting should not be collected 

 from trees that have spiral grain. 

 Young trees with spiral grain should be 

 removed from a forest as soon as con- 

 venient after they are discovered. In 

 trees with stringy outer bark, such as 

 the cedars, cypress, sequoias, and wil- 

 lows, the direction of the grain in the 

 wood can be gaged by the direction of 

 the fibers in the bark or by bark ridges. 

 Even in such trees as pine, Douglas-fir, 

 white oak, elm, ash, and the basswood, 

 which have scaly bark with pro- 

 nounced fissures and ridges after they 

 have passed the young stage, spiral 

 grain can be detected by the direction 

 of the ridges in the bark. In many kinds 

 of young trees with smooth bark, un- 

 fortunately, spiral grain cannot be de- 

 tected by any simple means. 



