FORM QUOTIENT AS THE BASIS OF FORM CLASSES 



207 



different trees, could be indicated by the relation between diameter at 

 one-half height and D.B.H. (not diameter at stump). 

 In its standard form of expression: 



Form quotient: 



D' 



In 1908 Tor Jonson corrected a slight inconsistency in Schiffel's 

 method by insisting that the middle diameter be taken not at the middle 

 point of the stem but at the middle point measuring from B.H. This he 

 termed the absolute form quotient. This improvement finally secured a 

 consistent basis for expressing tree forms, eliminated height as a varia- 

 ble, and got rid of the great drawback of butt swelling. The absolute 

 form quotients of trees were now found to vary between .575 and 

 .825, i.e., the diameter at the middle point above B.H. bore this 

 relation to the D.B.H. , whether both measurements were taken out- 

 side or inside the bark. 



It was also discovered that in most cases the form quotient if reduced by a 

 constant would give the form factor for cubic contents of the tree. For instance, 

 J. F. Clark found that the reduction factor for the form quotients for balsam in the 

 Adirondacks was 0.21. This fact is of minor importance since it aids only in 

 obtaining the cubic contents of trees. 



This standard of measuring form permitted the classification or 

 differentiation of the third variable of volume, namely, form independ- 

 ent of diameter or of height. Trees could be grouped into form classes 

 expressed by form quotients. Seven main form classes were formed, 

 namely, .50, .55, .60, .65, .70, .75, .80. Five sub-classes were also inter- 

 polated as .575, 625, .675, .725, .775. The extreme lower and upper 

 classes shown will be found only in individual trees. The average 

 form class for a given stand will fall usually between .575 and .75 and 

 may be correlated with the density of the stand as shown below. 



But most important of all, the question as to whether the form of 

 trees was independent of species, site and region and dependent on gen- 

 eral laws, could now be determined. 



