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 years, 

 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 



