36 CIRCULAR 3 3 3, U.S. DEPARTMENT OF AGRICULTURE 



In measuring the diameters of trees with scaly bark, such as 

 short-leaf pine, great care should be taken to avoid undue removal 

 of bark. Removal of very loose bark is permissible at the time of 

 the first measurement, but not at times of remeasurement, as 

 this would affect the records of diameter growth. An esti- 

 mate as to quantity of bark removed at the time of plot establish- 

 ment should be recorded for each tree so treated. In the case of 

 species having bark plates that curl out and away from the tree, 

 such as shagbark hickory, the portion of each plate that interferes 

 with the breast-height diameter measurement may be cut or broken 

 away at the time of first measurement ; at subsequent measurements 

 no bark should be removed, but the tape should pass under and not 

 over any such protruding bark scales. 



Measurements of bark thickness near the breast-height point are 

 desirable in some investigations as a means of checking up on diam- 

 eter growth — especially in fire studies, in the course of which part 

 of the bark may be burned away. These may be made without 

 injury to the tree by the use of the Swedish bark punch, shown 

 in plate 3, B. How many bark measurements should be made on 

 each tree depends largely upon the purpose of the study. Enough 

 should be made to obtain a reliable sample. 



Unless it is necessary to maintain ecological conditions with the 

 least possible disturbance, dead branches near the breast-height point 

 should be removed in order to permit easier and more accurate 

 diameter measurement. These branches should be cut clean, close 

 to the trunk. 



If a tree forks below breast height, the diameter at breast height 

 on each fork should be measured and recorded as that of an 

 individual tree. 



The diameter tape 19 is standard for the measurement of diameters 

 of standing trees on permanent sample plots. The tape gives con- 

 sistent results, and is easy to carry. It should be used in all cases 

 except in remeasuring plots on which calipers were used in earlier 

 measurements. If calipers are used two diameter measurements 

 should be taken, at right angles to each other. Calipers have fallen 

 into disfavor in American silvicultural research because they are 

 hard to keep in adjustment and because they fail to give consistent 

 results when used on tree boles of irregular shape. They are bulky, 

 and their use, since it involves two measurements and the recording 

 of two figures for each tree, consumes an undue length of time. 

 The use of calipers is sometimes justified where the luxuriance of 

 vines, or the presence of highly toxic vines, makes it difficult to 

 obtain diameters with a tape. It is sometimes justified also on 

 trees that are heavily buttressed, such as southern cypress or western 

 red cedar. 



Diameter tapes and calipers are shown in plate 3, B. 



Under no circumstances should diameters on permanent sample 

 plots be taken with a Biltmore stick or with any other device the 

 standard error of which cannot be accurately determined. 



Diameter at breast height should ordinarily be recorded to the 

 nearest one-tenth inch. 



19 For discussions of tape versus calipers in taking diameter measurements, see the 

 following references in Literature Cited, p. 62 : 9, 42, -ft, ->fi> 63, 67. 



