FOREST MENSURATION. 169 



the volume. For example: A White Pine has a diameter 

 at breast-height of 18.7 inches, and the height of the 

 tree is eighty-four feet; what is the volume? By refer- 

 ence to the table of areas of circles the area correspond- 

 ing to a diameter of 18.7 inches is found to be 1.9072 square 

 feet. Multiplying this by one-half the height, the ap- 

 proximate volume of the tree is found — 1.9072X42 = 

 80.1024 cubic feet. 



The Volume of a Standing Tree may be Obtained by 

 Employing a Form Factor which has been previously 

 determined for that particular species by the felling and 

 accurate measurement of a great many sample trees 

 of approximately the same dimensions and grown under 

 the same conditions. The form factor is expressed as 

 a decimal, and is the ratio of the mean volume of the 



Fig. 61. — Diagram illustrating method of determining the 

 volume of a felled tree. 



sample trees to the volume of a cylinder with the same 

 diameter as the diameter of the mean sample tree at breast- 

 height, and whose length is equal to the height of the tree. 

 For example: A Tamarack measures 6.9 inches in diam- 

 eter, breast-high, and the height of the tree is fifty-one 

 feet. Its volume by accurate measurement of the felled 

 tree is 7.21 cubic feet, and the volume of a cylinder with 

 a diameter of 6.9 inches and a length of fifty-one feet 

 is 13.24 cubic feet. The form factor or factor of shape is 

 therefore 7.21 -^ 13.24 = .54, and if this Tamarack represents 

 the mean of a large number of trees of ajJproximately the 

 same dimensions, the factor may be applied to all of them, 

 or to all trees of the same size and grown under the same 



