16 



BULLETIN 153, U. S. DEPARTMENT OF AGRICULTURE. 



stands of slower growing species, such as ash, oak, or walnut. Intol- 

 erant trees, such- as cottonwood, European larch, black locust, or 

 black walnut, require large openings in the crown cover. Cottonwood 

 and European larch in particular die for no apparent cause except 

 insufficient light, even when apparently receiving an abundance. 

 For white pine and Norway spruce the openings need not be large. 



There are no instances in this country where thinnings have been 

 systematically carried on, and for this reason it is not possible to 

 cite examples of their effect. The comparative size of trees grown 

 in open-spaced and close-spaced stands, however, is something of an 

 indication of the results to be expected from thinning, and a few exam- 

 ples of this sort are given in Table 2. Comparisons should be made, 

 of course, only between stands or rows of nearly the same age. 



TABLE 2. Size of trees in open and close spaced stands. 



i 5 feet apart in row. 



2 Trees 6 ieet apart. 



PRUNING. 



3 2 to 4 feet apart in row. 



Pruning is the removal of living or dead branches from a tree. 

 The purpose is to improve the tree's form; to increase growth in its 

 leading shoot by eliminating some of the lateral shoots and to improve 

 the quality of the lumber by getting rid of the source of knots. 



Most trees in forest plantations, especially those closely spaced at 

 the start, will prune themselves; the additional value gained by 

 pruning them by hand is usually not sufficient to pay for the opera- 

 tion. The cost, therefore, would have to be reckoned as a fixed 

 charge, to run at interest, against the final cost of the plantation. 

 In small plantations, however, it may be possible for the owner him- 

 self to do the pruning at odd times, and thus avoid an additional 

 charge. Side branches can not well be pruned to a greater height 

 than a man can reach from the ground with an axe, and this amount 

 of pruning will scarcely have much effect in increasing the stumpage 

 value of the timber. 



