456 Forestry Quarterly 



From the set of curves (Fig. 1) the diameter 5 and 10 years ago 

 is computed and a curve made for each diameter, showing the 

 direction of the growth for the last 10 years (Fig. 2). This oirve 

 is produced to show what the diameter of each diameter class will 

 be in 10 years if the growth continues as indicated by the growth 

 curves for the past 10 years. In order to predict the volimie 

 growth it is necessary to determine the height growth. Since no 

 special study of height growth is made, it is assumed that the pres- 

 ent height curve will apply to the stand and form class 10 years 

 from now. That is, a 10-inch tree will have the same height as 

 an 11 -inch tree now has when it has grown to be 11 inches in 

 diameter. With both height and diameter growth measured, it 

 is possible to compute a percent growth figure for each diameter 

 class by means of a volimie table. Any method of interpolation 

 in the volume table will accomplish this. The writer's method is as 

 follows : 



The first two columns in the tabulation (Table I) are the same 

 as used in computing a volume estimate by means of a volimie 

 table. The volimies given in column 2 are for the height taken 

 from the height curve for this particiilar stand. Since this height 

 curve is assumed to apply to this stand 10 years from date, the 

 difference in volume between any inch class and the one next 

 higher is the measure of the increase in voltmie for a tree in that 

 stand and form class while growing from one diameter to the next 

 higher. This increase for each diameter is given in column 3. 

 The expected increase in diameter during the next 10 years, as 

 shown by the second set of curves (Fig. 2), is tabulated for each 

 diameter class in colimm 4. This column shows the growth in 

 diameter in inches which may be expected during the next 10 

 years. For example, a 9" tree is expected to grow 2.7 inches and 

 to be 11.7 inches in diameter 10 years from now.^ Therefore, in 

 order to get the growth in volume which may be expected in the 

 next 10 years from a 9" tree, we must add the growth of the 9-inch 

 diameter class, the 10-inch class, and .7 of the 11-inch class, 

 making a total of 13.8 board feet, which the 9" tree may be ex- 

 pected to produce in volume during the next 10-year period. 

 The increase in volume computed in this way for each diameter 

 class is tabulated in colvunn 5. This increase in volume for each 

 diameter class during a 10-year period divided first by 10, to 

 reduce it to a one-year basis, then, by the volume of a single tree 



