A FORMULA METHOD FOR ESTIMATING TIMBER 421 



of trees each of a few diameter classes be selected, the classes represent- 

 ing, respectively, the smallest, medium, and largest sized trees of the 

 timber in question. The curve for b could then be plotted upon these 

 points and the intermediate values obtained from it. The method would 

 involve a minimum of both field-work and computation. 



Whether this method will give accurate results when applied to the 

 large timber of the Pacific coast may depend chiefly on whether one 

 merchantable form factor will serve for each diameter class, irrespec- 

 tive of length. If the form factor varies considerably with length, then 

 several values of b for each diameter class would have to be com- 

 puted. 



But very little opportunity has as yet been afiforded for testing the ac- 

 curacy of this method, but it is presented as possibly possessing some 

 merit and perhaps susceptible of improvement. I would consider it a 

 favor to receive suggestions, and would be very glad, if any foresters 

 in other regions care to try it, to be informed of the results obtained. 



Comment on Professor Terrv's Article 

 By W. N. Sparliawk 



The purpose of the board-foot form factor proposed by Professor 

 Terry appears to be to simplify the work of computation in working 

 up timber estimates by doing away with the use of volume tables. It 

 is evident that the use of b for all trees of a given diameter, regardless 

 of their heights, by making separate consideration of the different height 

 classes unnecessary, will considerably shorten this work. 



I believe, however, that the method of computing b can be very much 

 simplified without any sacrifice in accuracy. Dividing the values in 

 column 4 (Table 2) by corresponding values in column 3, we get the 

 following values for b: 



D. b. h. D. b. h. 



(inches) b (inches) b 



12 2.7 24 9.2 



13 2.8 25 9.7 



14 3-6 26 12.4 



15 4-1 27 13.2 



16 4.6 28 14.6 



17 5-2 29 15.0 



18 5-5 30 • 16.0 



19 6.1 31 17. 1 



20 6.7 32 18.9 



21 7.1 33 20.6 



22 7.8 34 23.0 



23 8.5 35 21.8 



36 22.1 



