142 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



Clear definition of the term " form-factor " is not a simple 

 matter, but the following is submitted as covering all types: — 



A form-factor is a figure expressing the relationship between 

 the specified type of volume of a tree and the volume of a 

 regular geometrical solid, which has for its base a measurement 

 readily obtainable on the tree as it stands, and a height equal 

 to the height of the tree. Geometrical solids which have been 

 employed in this capacity are the cone and the cylinder, and, in 

 quarter-girth measurement, the rectangular prism. The cone is 

 not now used in general practice, but from America comes the 

 suggestion to utilise the frustum of a cone. 



Neglecting quarter-girth measurement for the purposes of this 

 article, we may modify the definition as follows : — A form-factor 

 of a tree is the figure, expressed in decimals, by which the 

 volume of a cylinder of the same base and height as the tree 

 must be multiplied to give the volume of that tree. 



Different bases and different types of volume, however, give 

 different types of form-factor. We have three main types, 

 dependent upon the position of the base. 



Type i. — Artificial or Breast-height Form-factor, where a 

 fixed height of 4 ft. 3 ins. (sometimes 4^ feet) 

 above ground, is chosen as the base. 

 Type 2. — Absolute Form-factor, where the base is measured 



level with the ground. 

 Type 3. — True or Normal Form-factor, where the base is 

 measured at a constant proportion of the height 

 of the tree, e.g. at one-tenth or one-twentieth of the 

 height. 

 There are several subdivisions of the types, depending upon 

 what is understood to be the volume of the tree. 



(a) Stem Form-factor (sometimes Timber or Merchantable 

 Form-factor), where the volume understood is the 

 volume of timber in the stem up to a certain fixed 

 diameter or girth. In the preparation of the British 

 Yield-Tables this girth was 9^^ inches. 

 This Form-factor may be for volume (i) with bark, or 

 (2) without bark. 

 {/f) Tree Form-factor, where the volume is the total volume 

 of the tree up to the tip. 

 Similarly this may be (i) with bark, or (2) without 

 bark. 



