220 Forestry Quarterly. 



heights which correspond to the D. B. H. and merchantable height 

 classes of the required volume table, using for the upper base the 

 values obtained under a, and assuming the diameter of the lower 

 base equal to the D. B, H. Since this last assumption is also used 

 in calculating the factors for each tree measured, no error is in- 

 troduced in the final results. 



g. The values in this table for each diameter class may then be 

 multiplied by the frustrum form factor obtained under c for that 

 class in order to obtain the final values of the volume table. 



This procedure involves the assumption mentioned above that a 

 table of frustrum form factors can properly be based on diameters 

 alone. This is an assumption which the writer confidently be- 

 lieves can be proved essentially correct by more extensive investi- 

 gation. It is, at any rate, fully justified in a case such as has been 

 discussed above. Until the point has been more thoroughly in- 

 vestigated, however, it may be wiser to abandon the assumption 

 wherever there is sufficient data at hand to render it less essen- 

 tial. In such a case the following modifications of the procedure 

 outlined above are advisable. Instead of calculating the frustrum 

 form factor of each tree measured, considerable time can be saved 

 by averaging together the volumes, upper bases, total merchantable 

 lengths, and D. B. H's of all trees of a given diameter and height 

 rclass, and then calculating the frustrum form factor for the whole 

 -class. Further, instead of finding the average factor for the whole 

 diameter class a complete set of curves should be drawn for the 

 factors just as would be done for the volumes in the usual pro- 

 cedure in constructing volume tables. The transformation of 

 the form factors resulting from the harmonized curves to volume 

 values is then simple. 



Other methods of applying the frustrum form factor will readily 

 suggest themselves. One in particular may be mentioned which 

 should, however, be used in extreme cases. Suppose a situation 

 in which even the first line of attack taken up above is considered 

 too expensive, yet where absolutely no volume tables exist that 

 seem of reasonable accuracy. In this case a very few measure- 

 ments could be taken, the frustrum form factors calculated, and a 

 general average factor for all diameters and heights obtained. 

 This, applied to a table of frustrum volumes such as has been 

 described under the other methods outlined, will give an approxi- 

 mate volume table on a minimum of field measurements. 



