HEIGHT AND DIAMETER BASIS 



551 



It will be seen that as was to be expected, d.i.b. 16 feet is decidedly 

 superior. Between d.b.h. and d.i.b. stump there is little choice. It is 

 evident that in some species the root swelling distorts the stump meas- 

 urement more than the bark thickness distorts the d.b.h. measurements, 

 and vice versa. For the four species examined the advantage is slightly 

 in favor of the d.b.h. standard and, since that point is also more con- 

 venient, the belief of foresters in the d.b.h. seems justified. 



THE HEIGHT MEASUREMENT 



There is considerably more room for argument on the question of 

 the point of height measurement. Three systems have ardent ad- 

 herents among foresters, namely, total height, merchantable height to 

 a fixed top cutting limit, and height as actually used by loggers. Ne- 

 glecting, for the moment, purely practical considerations, let us examine 

 the merits of the three from the standpoint of their relative accuracy 

 as volume indices. Thirty trees of each species were chosen at ran- 

 dom from a single 1-inch diameter class. Three volume-height curves 

 based on total, merchantable, and used heights, respectively, were then 

 drawn for the group. The actual volume of each tree was then divided 

 by the corresponding volume given by each curve for an average tree 

 of the same height and diameter. By this means the probable deviation 

 of individual trees from each curve was computed. 



Table 2. 



■ Values not included. 



