CHAPTER XV 



THE FORM OF TREES AND TAPER TABLES 



166. Form as a Third Factor Affecting Volume. While standard 

 volume tables (Chapter XI) differentiate the volumes of trees of dif- 

 ferent D.B.H. and heights, they make no distinction between trees 

 having paraboloidal forms and those approaching the cone or neiloid 

 (§ 26) in form, but seek to average the differences in volume caused by 

 these variations. Occasionally two separate tables are made for a 

 species, one for old trees, the other for young second-growth, since 

 it has been found that the average volume of trees of these two age 

 classes differed considerably. Any such difference, whatever its cause, 

 is due to difference in form as indicated above, for trees which have the 

 same D.B.H. and height. 



Volume tables have come to stay, since they substitute accurate measurements 

 of D.B.H. and of height, which may be checked by calipers or hypsometers (§ 193), 

 for too exclusive a use of the eye, and for the very uncertain method of guessing 

 at or figuring out the volume of an average tree whose dimensions are in turn 

 arrived at by guess or judgment. 



The difficulty of having to depend solely on volume tables of this character lies 

 not in the tables themselves but, 



(1) in their incorrect application (§ 124); 



(2) in their not being based on the same factors of volume determination as are 

 desired for the estimate; 



(3) in the possibility of not having any tables and being forced to construct them. 

 To summarize here the factors in which the tables must agree with the basis of 

 estimating we find: (a) Choice of unit of measurement as board feet, specific log 

 rules, cross-ties, cords. (6) Closeness of utilization in tops and stump, (c) Point 

 of diameter and height measurement, (d) Thickness of bark. (e) Variations 

 caused by form independent of diameter and height. 



For these reasons the demand for some form of universal volume table in esti- 

 mating is very strong. 



The substitution of a fixed taper per log, and the use of tables showing volumes 

 for trees of the same diameter and height but with different rates of taper (§ 122) 

 is an attempt to differentiate between trees with different form, but, in effect, 

 this plan assumes that all trees have the same form, that of the frustum of a cone 

 and differ only in being tall or short, or tapering slowly or rapidly up to the top 

 diameter. 



The only satisfactory basis of a universal volume table is one in 

 which all three of the variables, namely diameter, height, and form 



196 



