36 BULLETIN 13, U. S. DEPARTMENT OF AGRICULTURE. 
of lumber which can be marketed. Pine branches are so persistent 
that lumber of higher grades than box boards, match stock, and 
a very little sash and blind stock can hardly be produced in short 
rotations except by means of systematic pruning (see p. 38). 
ROTATION. 
Under " White pine as an investment 77 it was shown that the age 
at which the pine should be cut in order to secure the greatest profit 
varied with the rate of interest used. The lower the interest, the 
greater will be the age, called the age of financial maturity. If, for 
example, the investor demands only 4 per cent, the stand can, under 
most conditions, be profitably left until it is 50 years old. If 6 per 
cent is desired, however, rotation should not be over 40 or 45 years. 
Unfortunately the financial maturity of a stand at the interest rates 
given rarely coincides with its volume maturity in board feet. From 
the standpoint of volume the pine has matured at the age when its 
average annual growth per acre is greatest. The age at which vol- 
ume matures is shown for different qualities in Table 7. In quality I 
situations . the volume maturity in board feet occurs, as a rule, when 
the stand is from 55 to 65 years old; in quality II, between 70 and 80 
years; and in quality III, between 85 and 95 years. In the future, 
when timber is much scarcer than it is now, the volume maturity 
may often coincide with or precede the financial maturity. At the 
present, however, it is the latter which should be the guide in man- 
agement. 
Since the stand should be removed only during heavy seed years, 
which occur at intervals of from 3 to 7 years, it can rarely be cut in 
precisely the year when it is financially mature. A good rule to follow 
if the stand is to be cut clear is to remove it during the seed year next 
following maturity. If two or more cuttings are planned, the first 
may be made during a year of prolific seed production preceding ma- 
turity by from 3 to 7 years, and the later cuttings in subsequent seed 
years. 
THINNINGS. 
In dense stands of pine there is an intense competition between 
individuals for light and growing space. As a dominant tree falls 
behind its more vigorous neighbors it becomes hi turn codominant, 
intermediate, and overtopped, and finally dies for lack of light. The 
struggle is thus most critical in the dominant class. The other classes 
are on the road to elimination, though until finally suppressed they 
continue to crowd the dominant trees and retard their volume growth. 
Thinnings aim to increase the volume growth of dominant trees 
by removing from time to time trees of other classes which are 
unduly crowding them (see PL V). In this way the total growth 
of the stand is concentrated in the smallest number of thrifty trees 
