54 BULLETIN 544, U. S. DEPARTMENT OF AGRICULTURE. 
would be prohibitive. The remaining trees would be particularly 
liable to windthrow, and tbe thinning would produce doubtful results 
in securing an accelerated growth. With the attainment of their 
principal height growth, the trees composing a crowded stand have 
adjusted themselves through the abnormal reduction of their crown 
surface to the restricted growing space, and the possibilities of stimu- 
lating the growth in such a stand are not promising, unless the stand 
is to be left intact for upwards of 30 years afterward. 
The principle to be followed in making thinnings depends upon the 
object of management and the age when thinnings can be begun. If 
it be desired to secure the maximum volume production, which cul- 
minates, according to Table 14, between the thirty-fifth and seventieth 
year, depending on the unit of volume and the site quality, thinnings 
should be undertaken by the twenty-fifth or thirtieth year on the 
best sites and be confined to the dominant and intermediate trees. 
If. however, quality production is the object desired, the first thin- 
nings may be delayed until the thirty-fifth or fortieth year, being 
confined to the lower and intermediate crown classes until the 
sixtieth or seventieth year. This would especially encourage the 
development of form and quality. Thereafter the stand would be 
thinned more heavily. Tne last third of the rotation, or approxi- 
mately after the eightieth or the one hundredth year, the cuttings 
would be in the form of accretion cuttings which would isolate a 
certain number of the best trees for the encouragement of a more 
rapid growth in volume. 
The object of thinnings for volume production should be to free 
the tallest trees and gradually reduce their numbers without removing 
the weakest, except where they have a dry top, since they assist 
natural pruning, cover and protect the soil, and add to the strength 
of a close canopy. In the early period, when the trees are only to a 
limited extent merchantable, the fewest number of trees possible 
should be removed. The greatest advantage, accordingly, can be 
derived by cutting only those trees which occupy a position in the 
upper crown level, but which are interfering with the development of 
the stronger growing individuals. This will relieve the intense strug- 
gle taking place among those trees which are finally to form the 
mature stand and will allow them to develop with a minimum of 
hindrance from their neighbors. To be most effective, thinnings 
should be frequent and fight in early life and heavier and less fre- 
quent in later years. Such early thinnings, however, involve a con- 
siderable expense, while the later ones may render the stand liable 
to windthrow, so that it will often be necessary to compromise. 
In judging of the need for thinning, the relation of the crown length 
to the total height of those trees which are to form the final cut should 
