Forest Mensuration 19 



PARAGRAPH XXIX. 



FORM FACTOR METHOD. 



The form factor or form figure method relies on the measurement of 

 the sectional area usually the one at breast height, the measurement 

 or the estimation of the total height and the estimation of the form 

 figure. 



The form factor is a fraction expressing the relation between the actual 

 contents of a tree, in any unit, and the ideal contents which a tree would 

 have if it were carrying its girth (like a cylinder) up to the top bud 

 undiminished. 



The form factor may be given in reference to the volume of the entire 

 tree, inclusive of branches in cubic feet; or in reference to the volume 

 of the bole only ; or in reference to the merchantable part of the bole ; 

 in the latter case either in feet board measure or in standards or in cords. 



HISTORIC REMARKS : Some of the older authors on mensuration saw in 

 the cone and not in the cylinder the ideal form of the tree, basing their 



s X^ h 

 form factors on the ideal volume . 



PARAGRAPH XXX. 



KINDS OF FORM FACTORS MATHEMATICALLY. 



Scientifically we distinguish between: 



1. The absolute form factors which have reference only to the volume 

 standing above chest height. They can be readily ascertained with the 



help of Pressler's formula. Generally speaking, V equals Sx H x F. 



a r 

 After Pressler, V equals S x 2/3 x r; thus -* equals F. 



H 



For the cone the absolute form factor is one-third ; for the neilloid 

 one-fourth ; for the paraboloid one-half, whatever the height of the tree 

 may be. Hans Rienicker, the author of these form factors, finds for 

 trees up to 50 years old a form figure of 35% to 43% (in regular, dense 

 German woods); in trees 50 to 100 years old, F increases up to 50%; 

 thereafter occurs a slight decrease below 50%. 



2. The normal form factors which were recommended by Smalian, 

 Pressler and other old-time authors. They have reference to the entire 

 volume and necessitate the measurement of the diameter at a given frac- 

 tion (usually 1/20) of the total height of the tree. Frequently, in case 

 of tall trees, the point of measurement cannot be reached from the ground. 

 The bole form factor for diameters measured at 1/20 of the height is: 

 For a paraboloid, 0.526; for a cone, 0.369; for a neilloid, 0.292. These 

 form factors, like the absolute form factors, are independent of the height. 



3. The so-called "common form factors" which do not express, as a 

 matter of fact, the form of the tree, since they do not bear any direct 

 ratio to the degree of the tree curve. They should be termed, more 



