HEIGHT AND DIAMETER BASIS 555 



fusion sometimes results. It was this fact which was found to be the 

 cause of an apparently absurd contradiction in two Montana volume 

 tables for western yellow pine. It appeared, for example, that in one 

 locality a 30-inch, 8-log- tree with an 8-inch top scaled 2,090 feet board 

 measure, while only a few miles away a 30-inch, 8-log tree with an 

 ii-inch top scaled but 1,740! As a matter of fact the 8 and 11 inch 

 top limits noted in the tables were merely diameter class averages and 

 were meaningless when applied to 8-log trees. The former was actually 

 based on trees of a larger top than the latter for the size in question. 

 It was finally found necessary to discard both tables and to prepare a 

 new one based on a fixed top cutting limit, as the only alternative was 

 to append to each a second table showing the average top d.i.b. for 

 each height and diameter class, a result obviously impracticable for 

 field work. 



The foregoing instances indicate that 



(1) While there is a tendency to deviate from a fixed top cutting 

 limit in logging operations, yet there may be no definite standard of 

 top utilization even for the same species in the same region. 



(2) An attempt to adopt some one such standard for a volume table 

 involves great difficulties in insuring that the cruiser estimates heights 

 according to that standard ; if he does not, his errors through such in- 

 consistency will be far more serious than would at first appear. The 

 point of height measurement is of more importance as a volume index 

 than as a standard of utilization, and it follows, therefore, that a 

 measurement that can be definitely and consistently made is of prime 

 importance. The fixed top cutting limit is therefore prefereable by far, 

 even for such species as western yellow pine.* while for others, such as 

 western white pine or western larch, it already expresses existing 

 practice as well. 



It may be objected that when heights are measured to a fixed top 

 cutting limit of, say, 8 inches, in a species which, in its larger diameters, 

 is rarely used beyond the 12-inch point, a fictitious volume (and num- 

 ber of logs) is thereby tallied. This is doubtless true, but it is the 



* Chandler's work on certain eastern hardwoods would seem to indicate that 

 in some species that have no well-defined axis to the top an additional factor or 

 factors must be added to the tables, and that height to neither fixed nor vari- 

 able top with diameter will solve the problem unless taper and form are also 

 recopnized. (B. A. Chandler: "Study of Frustum Form Factors of Hard 

 Maple and Yellow Birch." Bui. 210, Vt. Agr. Exp. Stat., Mar., 1918.) 



