38 BULLETIN 544, U. S. DEPARTMENT OF AGRICULTURE. 
VOLUME GROWTH. 
The increase in volume of trees growing in the virgin, or selection, 
forest is seldom considered on the basis of age for reasons already- 
discussed under height and diameter growth. We are not much 
interested, for the present at least, in knowing how long it took, or 
would take again, to produce a spruce of a certain size under similar 
virgin forest conditions. Most lumbermen are desirous of knowing 
what can be expected of trees of given sizes for the immediate future. 
The conditions under which such growth is likely to take place will 
vary widely, so widely in fact that general tables of growth would 
be of little value. A local table made up to fit the special conditions 
of each case is much preferable. Such a table is readily prepared 
from volume or taper tables and the general data already presented. 
In preparing a table of this kind it is usually assumed that a tree 
now 10 inches in diameter at breastheight will, when it has grown 
to a diameter of 11 inches, have the volume of the 11-inch trees with 
which it is at present associated. Diameter growth figures thus form 
the basis of the calculations. If the future growth of a virgin stand 
is to be forecasted, the diameter growth figures employed must be 
those derived from trees growing under these average conditions. 
Usually, however, an immediate partial cutting is contemplated. 
Whether the growth figures for the " average maximum " or " absolute 
maximum" should be used will depend upon the extent to which the 
cutting opens up the stand. Conditions would need to be exceedingly 
favorable to warrant using the " absolute maximum" figures of 
diameter growth. It might even happen that the " average max- 
imum" would show too high results, particularly for forecasting 
results within the succeeding decade. Spruce does not respond 
immediately to an opening up of the crown cover. Intermediate 
trees of from 6 to 10 inches in diameter may not respond at all inside 
of 12 or 15 years. 
The following example will suffice to show how these data are 
combined : 
Suppose one desires to ascertain the probable volume of the 14-inch 
trees in an average stand of spruce in New York 15 years after a 
cutting to a 16-inch diameter limit. Assuming such a sized tree 
to be able to take full advantage of growth conditions and develop 
at the full " average maximum" rate, the annual increment in 
diameter would be, according to Table 10, 0.150 inch. In 15 y T ears, 
consequently, it would have added 2.25 inches to its diameter and 
become a 16.25-inch tree. The average 14-inch tree, according to 
Table 4, is 62 feet tall and has a volume according to Table 9 of 
