416 JOURNAL OF FORESTRY 



given in the- western yellow pine volume table for the San Juan and 

 Montezuma Forests, compiled by Hoffman. They vary by about 12 

 per cent for the extreme lowest diameters and by 1 5 to 20 per cent for 

 the extreme highest. For diameters below 24 inches, the formula gives 

 values averaging higher than those given by the table, and above 24 

 inches values averaging lower. It will give results within 6 per cent 

 of the table for nearly all diameters and log lengths if the following 

 denominators be used : 



70 for trees from 12 to 19 inches d. b. h., inclusive. 



60 for trees from 20 to 29 inches d. b. h., inclusive. 



55 for trees from 30 to 35 inches d. b. h., inclusive. 



50 for all trees above 35 inches. 



The San Juan-Montezuma table gives volumes for trees up to 43 

 inches. 



In estimating small to medium-sized timber, such as the yellow pine 

 of the Central Rockies, it is considerably more accurate to use a shorter 

 unit of length than even the half-log (8-foot sections). I have found 

 that estimating to the nearest "quarter-log" and also to the nearest 5 

 feet of merchantable length to give very accurate results. With such 

 a formula as the one here given, the volume for any merchantable 

 length may be computed. Heights can be obtained quickly and with suffi- 

 cient accuracy by using a home-made hypsometer, constructed on the 

 principle of the one on the Biltmore stick or on that of the Christen 

 Height Measure. 



The basic formula 



j,f _ 785 XD^XLXFXR 

 144 



can, of course, be used for other species than yellow pine, but the 

 appropriate data must be collected and worked up for each species, as 

 in making volume tables. In all probability the value (or values) 

 of n will differ for different species. Data have been collected for the 

 other important timber trees of the Central Rocky Mountain region — 

 the lodgepole pine, Engelmann spruce, and Douglas fir — but have not 

 yet been worked up. It may be found that this formula will not give 

 sufficiently accurate results for very large timber, such as that of the 

 Pacific Northwest; or it may do so if several values be used for n, 

 each applied to a certain diameter group. 



II. THE CONSTRUCTION OF VOLUME TABLES BASED ON THE FORMULA 



After deriving the formula it was perceived that a volume table, 

 based on the d. b. h. and any chosen unit of merchantable length, could 



