300 IMPROVING THE ACCURACY OF TIMBER ESTIMATES 



to the standing timber. The graded log table (§ 74) appears to 

 satisfy the requirements of the problem. Log grades are such as can 

 be recognized in standing trees, on the basis of diameter, surface appear- 

 ance, presence of knots or limbs, and character of the tree and the stand 

 in which it is growing. In turn, these log grades can be analyzed by 

 mill-scale studies, so that the average per cent of grades of timber in 

 each log grade is known. Since three grades are usually made in valu- 

 able species, and at least two for the less valuable, trees of the same 

 D.B.H. can easily be thrown into the lumber grades corresponding 

 with differences in their character, by recording the logs which they 

 contain as grades No. 1, 2 or 3. By contrast, if graded volume tables 

 are used, ordinarily only one classification is available for the tree — 

 that corresponding with the table. 



The final problem is the application of these graded log tables to 

 the standing timber, in a manner to conform to the methods used in 

 timber estimating. Cruisers who use the method of selecting an aver- 

 age tree (§ 209) usually analyze this tree by the use of the log grades, 

 or directly by per cents, into the grades of lumber which they believe 

 it will cut, and apply these per cents to the remainder of the stand. 

 This is a crude method. 



Where the method of tallying the diameter of every log (§ 119) is 

 used, each log can be tallied under its proper log grade. The total 

 volume in each log grade is thus obtained directly. Where timber 

 is sold as logs, it is unnecessary to go beyond this point. 



But where the sawed product determines stumpage value, these 

 log grades are merely the basis of application to the standing trees of 

 the grades of lumber which they probably contain, and the contents 

 of the log grades, in lumber of each grade, w ill be computed for the 

 estimate. 



235. Combination Method Based on Sample Plots and Log Tally. 

 Where the tree tally and volume tables are used in estimating (§ 121), 

 the application of the log-grade unit to each tree is not possible, since 

 it would mean a shift to the tally of logs and not trees. Here a com- 

 bination method is necessitated, based on the principle that grades 

 or quality of timber can be determined by the measurement of a much 

 smaller per cent of the total volume than is required for volume estimate. 



The method is to lay out sample or representative areas in the form 

 of strips crossing the types as for timber estimating (§ 209) and com- 

 prising a per cent of the area estimated, sufficient in the judgment of 

 the cruiser to obtain the average quality sought. On these areas, 

 every log in each tree is totaled by upper diameter, in the log grade 

 in which it belongs. Instead of guessing at these upper diameters, 

 taper tables based on D.B.H. (§ 167) and total, or merchantable, heights, 



