Growing Better Timber 



203 



will have less knot-free lumber than 

 old-growth timber, it is reasonable to 

 expect that clear, second-growth lum- 

 ber will be at a high premium. If 

 forest trees are pruned, the stand can 

 be kept more open without danger of 

 the trees becoming too limby, and 

 hence individual trees will grow faster 

 and produce merchantable timber in a 

 shorter time. 



Less is known about the advisability 

 of pruning hardwood trees. Decay 

 seems to enter the trees through the cut 

 branches more readily, especially in 

 some species, or new sprouts may de- 

 velop along the trunk. More research 

 is needed on this subject, but for both 

 softwoods and hardwoods the trees 

 should be pruned while small because 

 the cost of pruning is less, small branch 

 stubs will heal over more rapidly, small 

 knots do not degrade lumber so much 

 as large knots, and more knot-free lum- 

 ber will be produced. Pruning is of 

 most value for trees that are left to 

 grow to sawlog size. Although pruning 

 of trees grown for poles and pulpwood 

 also would be advantageous from a 

 utility standpoint, its over-all economic 

 benefits are more questionable. 



An interesting result of the study of 

 the knots in Douglas-fir at the Forest 

 Products Laboratory was that the trees 

 growing on one of the poorer sites in 

 Oregon, where growth in height and 

 diameter was at a comparatively slow 

 rate, had smaller, albeit more numer- 

 ous, knots than trees growing on one 

 of the better sites. Because size of knots 

 is a more important factor than num- 

 ber in the commercial grading of com- 

 mon lumber, the poorer site produced 

 a higher grade of lumber on the aver- 

 age than did the better site. On the 

 other hand, in the manufacture of pon- 

 derosa pine box veneer and shocks, 

 some mills make a practice of cutting 

 out clear bolts between knot whorls. 

 In that case, trees from the better sites, 

 which grow faster in height and there- 

 fore have a longer distance between 

 knot whorls, have the advantage over 

 trees from poor sites. 



The apparent inconsistency that bet- 



ter wood sometimes is produced on the 

 poorer sites is explained by the fact 

 that sites are classified on the basis of 

 the volume of wood they can produce 

 per acre per year, regardless of quality. 

 Even in straight, vertical, straight- 

 grained trees, the quality of the clear 

 wood of each species may vary consid- 

 erably, in accordance with the condi- 

 tions under which the trees grew. 



SLOWNESS OR RAPIDITY of growth of 

 a tree influences greatly the properties 

 and usefulness of the wood produced 

 by it. In general, when softwood trees 

 grow rapidly or slowly they produce 

 lighter and weaker wood than when 

 the rate of growth is more moderate. 

 This does not necessarily mean inferior 

 wood, because wood of light weight 

 may have advantages where strength 

 is not essential. Hardwood trees also 

 usually produce light and weak wood 

 when growing slowly, but rapid growth, 

 as a general rule, results in heavier and 

 stronger wood than does a more mod- 

 erate growth. 



In second-growth timber that has 

 come up on cut-over or burned-over 

 lands and in most plantations, the trees 

 grow rapidly while young because they 

 have abundant growing space. Later, 

 as they become larger and crowd each 

 other, they slow down. Consequently, 

 the annual rings of growth are wide at 

 the center and narrow near the bark. 

 Such uneven rate of growth is objec- 

 tionable from several standpoints, 

 especially for lumber from small trees 

 in which the narrow and wide-ringed 

 parts cannot be easily segregated on 

 account of their small size. The inner 

 wide-ringed wood and the outer nar- 

 row-ringed wood may differ in density 

 and strength. When used for flooring, 

 they wear unevenly; they have differ- 

 ent machining and gluing properties; 

 even their pulping characteristics are 

 different. 



Wood of rapid growth in some of 

 the pines shrinks excessively along the 

 grain. The result is crooking of lumber 

 and dimension stock when it is com- 

 bined with wood of slower growth. 



