414 



JOURNAL OF FORESTRY 



Table i. — Merchantable Form Factors Arranged According to Diameter and 



5-foot Lengths 



The small figure in the squares denotes the number of trees of the respective 

 diameter and length upon which the form factor was computed. 



table and the correct one applied to a tree or group of trees falling 

 within certain size limits. If very accurate results are sought, a table 

 should be used in the first place. 



It was with the above-mentioned requirements in r^iind that I tried 

 to evolve an empirical formula which would be sufficiently accurate 

 to be of use in many cases of estimating. Part of the tree measure- 

 ments upon which it is based were made by myself and students in 

 the Manitou Forest — adjoining the Pike National Forest — and part by 

 Forest Service officers on the Montezuma Forest for volume-table 

 purposes, the data being lent to me by the district forester. The trees 

 may be considered representative of the mature western yellow pine in 

 the Central Rockies. The make-up of the formula and the principle 

 upon which it is based are expressed by the following equation, which 

 is nothing more than the formula itself before reduction to its simplest 

 form: 



Bf= i_l- 



144 



XLXFXR 



Bf = volume in board feet. 

 D = breast-height diameter in inches. 

 L = merchantable length in feet. 

 F = the merchantable form factor. 

 R ^ ratio of board feet to cubic feet. 



The expression must be divided by 144. because D is expressed in 

 inches and L in feet. It will be seen at once that all the terms except 



