142 UNITS OF MEASUREMENT FOR STANDING TIMBER 



for the first log, and then subtract the estimated thickness of bark at 

 this point, or at the top of the first log instead of at the butt. 



A third plan is to estimate directly the diameter, minus bark, at 

 the top of the first log, without measuring the butt. Or, a table may 

 be prepared showing diameter, inside bark, at the top of the first log, 

 for trees of different diameters at 4^ feet. 



Each of these plans aims to secure the diameter, inside bark, at 

 the top of the butt log as the basis from which to figure the top diam- 

 eters of the remaining logs. 



The eye may be trained to estimate log lengths and taper by the use of a pole 

 with a cross-piece at the top, marked off in inches. The length of pole (about 

 12 feet) permits holding the cross-piece at the height of the top of the first log 

 plus an allowance for height of stump. By comparison with this measured length, 

 the number of logs in the upper bole may be estimated by eye. By measuring 

 the tree at 4^ feet, and reading the cross-arm, the taper, in inches, for the butt 

 log is shown. Bark thickness is then subtracted as determined for the species 

 by observation on felled trees or logs. This varies for the top of the butt log, 

 from 2 inches to 1 inch for most species. The total number of logs, to the limit 

 of merchantable diameter, gives the total taper to that point. If 6 inches is the 

 merchantable limit, this diameter, subtracted from that of the top of the butt 

 log inside bark, indicates the taper to be distributed between the upper logs. 

 Bearing in mind the tendency to more rapid taper in the crown, the actual taper 

 of each log can be approximated with reasonable accuracy and its diameter inside 

 bark recorded. Two men usually work together in this practice, or in training. 

 One man may use the method if the pole is made long enough to be leaned against 

 the tree (17 to 18 feet), while he gets far enough off to judge its height. 



This method assumes that the eye can be trained to judge diameters 

 to an inch, at varying distances and heights above ground. But in 

 timber estimating only the general character of the tree is noted, and 

 its total height, or the number of standard-length logs. The taper 

 of the successive logs is obtained from measuring the diameters of 

 felled or wind-thrown trees of the same character as the standing timber. 

 The taper for a 16-foot log may vary from 1 to 10 inches or even more, 

 depending on site, density of stand, butt diameter, and position of the 

 log in the tree. 



Many cruisers assume that once the difference in diameter between 

 the top of the second and the first log is ascertained or assumed, each 

 successive upper log will have an equal taper, giving to the tree a uniform 

 taper per log of 2, 3 or more inches. They know that the butt log 

 will taper more rapidly than the second log, but the above practice 

 ignores the taper of the butt log. 



They also know that as soon as the green crown is encountered, 

 the taper per log again increases. But in regions where rough logs 

 in the crown are seldom utilized, this assumption of a uniform taper 

 for the second and higher logs in the bole is approximately correct. 



