246 



THE MEASUREMENT OF STANDING TREES 



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ment of heights largely avoids this specific error since the eye 

 allows for the leaning position of the tree while the instrument 

 does not. 



Where total heights are measured to the tip of the crown, the 

 greatest accuracy is obtained in the measurement of conical-crowned 

 conifers. Broad- or deliquescent-crowned trees are difficult to measure 

 accurately. The source of error is the same as that which applies to 

 leaning trees. A line of sight AB, in order to be directed at the tip 

 B, must penetrate the foliage of the crown while if directed tangential- 



ly to the edge 

 of this crown, 

 it will take 

 the position of 

 AB\. The error 

 from the meas- 

 urement of broad- 

 crowned trees, 

 unless this pre- 

 caution is ob- 

 served, is cumu- 

 lative and tends 

 to over-estimate 

 their heights. 



Merchantable 

 heights are meas- 

 ured by exactly 

 the same princi- 

 ples as are ap- 

 plied to total 

 upon broad-crowned trees may be obtained more 

 element of uncertainty in the measurement of mer- 

 is not height, but the determination of the point 

 which the used length will terminate, that is, the 



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y 



.#' 



./- 



Ci 



Co 



Fig. 53. — Errors which may be incurred in measuring the 

 height of a leaning tree. To avoid error the measurement 

 should be taken at right angles to the plane in which the 

 tree falls. 



heights, and 

 exactly. The 

 chantable bole 

 on the bole at 



merchantable top diameter of the bole. Merchantable heights may be 

 measured in 16-foot log lengths by the use of the principle in Fig. 43. 

 (Merritt hypsometer, § 195.) This same principle may be more accu- 

 rately applied by leaning a pole of known length against the tree and 

 then noting the length of a pencil required to take up this given length at 

 the distance of the observer. This pencil length may then be measured 

 off by eye on the remainder of the tree to divide it up into logs. 



It is common practice amongst timber cruisers to measure the 

 total or merchantable height of windfalls as a check on ocular timber 

 estimating. 



