STANDARD BREAST-HIGH FORM FACTORS 



213 



176. The Derivation of Standard Breast-high Form Factors. The 



two possible uses for form factors are seen to be, first, an expression of 

 relative forms of trees, second, a means of computing their total vol- 

 umes from that of cylinders. 



It is not possible to combine these two functions in the same table 

 of form factors. The absolute form factors for total tree volume can- 

 not be correlated with D.B.H. nor with any other point on the bole, 

 while the form factors which are based upon D.B.H. and total volume 

 are not absolute but vary with height. But these Riniker's absolute 

 form factors can be used to obtain a set of breast-high form factors 

 which represent the relative volumes of normally formed trees of all 

 diameters and heights when compared with the corresponding cylinders. 



The steps in this calculation are: 



1. Compute the Riniker form factor for trees of each form class. 



2. Obtain the normal stump diameter from Hoejer's formula. Stumps were 

 taken as 1 per cent of the height of the tree. The actual stump diameter is always 

 too large, due to butt swelling. The conception of a normal stump diameter is 

 the diameter which the stump would have if the normal curve of the stem from 

 top to D.B.H. were prolonged downward to stump height. 



3. Find the diameter at one-half the distance from stump to top, by Hoejer's 

 formula. 



4. Express both the stump diameter and the diameter at one-half height in 

 per cent of D.B.H. and compute the new form quotient, this time based on height 

 above stump. 



If diameter at |A = 67.7 per cent of D.B.H. 



Stump diameter =103.0 per cent of D.B.H. 



67.7 

 Form quotient = =0.657. 



