i6 



Forestry Qtiarterly . 



high diameter of 1.2 inches ; or in other words calHng a tree 37" 

 in diameter when it really was onlj' 35.8. The use of this tree 

 for a volume curve would therefore throw the curve out to the 

 amount that a 36" tree should differ from a 37" tree, less the 

 partial compensation introduced by the extra one half foot in the 

 stump. The following figures will show the amount of error in 

 the case cited : 



Stump ! Stump 

 Height. Diameter 



Difference in 



Volume of 



Stump. 



Difference in 

 Tree Volume. 



Error. 



4.6 cu. feet. 



16.9 cu. ft. that 16.9-4.6 

 I should exist. 12.3CU. ft. 



Or in words a 37" tree is used which contains 12.3 cubic feet 

 less than such a tree should contain. 



"Tapering " a tree offers little other difficulty, and is subject 

 to the same rules regarding regularity of distance as the section- 

 ing of the stem, in fact it would be simpler to take the taper 

 measurements at the .same places as the section cuts, were it not 

 that the length of the log is usually too great to give the true 

 form of the tree if only measured at the log ends. The practice 

 of the Bureau, therefore, is to take taper measurements on large 

 trees at every five feet. 



The simple operation of "tapering" affords little opportunity 

 for error to creep in except by improper use of the calipers or by 

 their inaccurateness. 



Ivrror due to the first cause is exceedingly common in varying 

 degree. It is seldom that two men can taper a tree independently 

 and get the same results. One will neglect to take the two read- 

 ings at each place directly at right angles to one another ; the 

 other n)ay pinch the calipers too hard. With the calipers ordinar- 

 ily in use, if great care is not used a loss of half an inch in diam- 

 eter is easily the result. 



Error resulting from inaccurate calipers is, of course, quite 

 inexcusable, and as it is accumulating, very serious. It is caused 

 by not having the caliper arms parallel. It will be greatest on 

 the large diameters, for they are measured usually nearer the ends 

 of the arms. 



