TOP DIAMETERS, FIXED OR VARIABLE LIMITS 183 



logs of a standard length, since this basis coincides with the application 

 of the table by timber cruisers (§ 119). Sixteen feet is the standard 

 most commonly adopted, to which is added a trimming allowance of 

 .3 foot. Volume tables for hardwoods may, if advisable, be based on 

 logs 12 feet long but this is the exception. The objections to the alter- 

 native method of scaling the contents of the logs as sawed are summed 

 up in § 135, but this latter method has been extensively used in the past 

 in volume-table construction. The base from which log lengths are 

 measured is usually the actual height of the stump, as sawed. This 

 introduces a variable factor dependent upon the standard of heights 

 secured in felling. 



155. Top Diameters, Fixed or Variable Limits. The field measure- 

 ments of tree volumes are the same as for cubic contents of logs (§ 135). 

 If 16 feet is the standard log length, the taper measurements are com- 

 monly recorded for each 8-foot point as well. The purpose of the work 

 is to determine the merchantable contents. This evidently calls for 

 the omission of the volume of the top portion of the bole, which is not 

 merchantable. But shall the length of the rejected top be based upon 

 the actual utilization of the specific tree? If so, the last saw cut will 

 indicate the limit of merchantability, beyond which the contents of 

 the top is classed as waste. By the method of measuring the volume 

 of the logs as sawed, this top is rejected as it lies, regardless of whether 

 the utilization of the tree has been close or wasteful. If on the other 

 hand diameters are taken at fixed intervals, the point of measurement 

 will seldom coincide with that of the last cut, but will fall above or 

 below it. 



If actual utilization practice is to be adopted as the basis of the 

 table, while at the same time the fixed length of section is to be retained, 

 the top diameter of the last " merchantable " log for the volume table 

 should be taken at the point which falls the nearest to the' last saw cut, 

 whether this point is above or below the cut. When the saw cut is 

 midway between two points, the lower measurement may be taken, 

 or else the character of the bole may be made the basis of choice (p. 184, 

 Fig. 30). 



When, by method B, only the merchantable volume is desired, if last cut is 

 at (1), the volume will be taken to the nearest 8-foot point B6. If cut at (2), Be 

 is still the nearest point. But if cut at (3) equidistant from B6 and B7, either the 

 upper point B7 would be chosen on alternate trees or the point best representing 

 merchantable volume, in this case B6. 



Utilization, especially where sawlogs are cut from trees with limby 

 tops, is seldom to a uniform diameter. The actual top diameter varies 

 widely but the average increases with the D.B.H. of the tree. By the 

 method outlined above, the contents of the volume table are made to 



