WHITE PINE UNDER FOREST MANAGEMENT. 37 
which will occupy the area. If these are pruned of branches to a 
height of 16 or 17 feet, the value of the future increment will be 
materially increased. At the same time the trees removed, which 
would otherwise be wasted, may yield a moderate return. As a 
result of successive thinnings at intervals of from 5 to 10 years, 
the aggregate yield, including the material saved in the thinnings, 
will be increased, while the trees finally harvested will be larger, 
sounder, and better formed than in unmanaged stands. 
The best time to thin a stand is during the period of its most rapid 
height growth, though this occurs so early in its life that enough 
merchantable material to pay for the thinning can rarely be obtained. 
An early unremunerative thinning may, however, more than pay for 
itself by increasing the value both of the final stand and of the mate- 
rial removed in later thinnings (see PL VI). 
In all thinnings any undesirable hardwoods which may be present 
should be removed. Thinnings should leave the stand uniformly 
opened up t© an extent which insures that crowns of the trees left 
will not come together again for four or five years. More space 
should be left between the crowns when the trees are young and 
growth rapid than later. An average distance between the crowns 
of from 3 to 5 feet is probably sufficient in most cases, though the 
removal of undesirable hardwoods or of unsound or poorly formed 
pines may make somewhat larger openings unavoidable. Large 
openings in the crown cover, however, will result in poorly formed 
limby trees and should be avoided. 
In quality I stands which have always been dense, a thinning may 
often be made with advantage as early as the fifteenth year. In 
stands which have been understocked in youth thinnings are, of 
course, unnecessary until considerably later, if warranted at all. 
Early thinnings, of course, represent a direct outlay, since little of 
the material removed will be fit even for cordwood. In farm wood- 
lots such thinnings can often be made during leisure time without 
a real loss. The trees removed will be mainly codominant and 
intermediate. Dead and badly suppressed trees need not be cut, 
since they no longer interfere with the growth of the stand. Subse- 
quent thinnings may be made at about the twentieth, twenty-fifth, 
and thirty-fifth year. Except that the last should be slightly 
heavier to allow the trees full space for volume growth up to the 
time of final cutting, the subsequent thinnings may be made in the 
same manner as the first. When the stand is 20 years old the 
material removed in thinning may be large enough for cordwood, 
and the operation pay for itself. Later thinnings should yield a 
profit. When necessary, the intervals between thinnings may be 
lengthened and the thinnings themselves made more severe. It is 
better, however, to thin lightly and often than heavily and at longer 
intervals. 
