SAMPLE PLOTS IX SILVICULTURAL RESEARCH 37 



Considerable care is required to get a true measurement by the 

 use of the diameter tape, especially if the diameters exceed 18 inches. 

 In that case the tape should be fastened at the breast-height point 

 and carried around the tree in such fashion that it remains in a 

 true horizontal plane. The practice of throwing the end of the tape 

 about large trees often leads to a considerable plus error because 

 the tape sags or becomes hooked over an obstruction. 



On most sample plots, the man taking the diameter measurements 

 should call the data to the recorder in the following order: Tree 

 number, species, diameter, condition of bole as to injuries, and any 

 other pertinent information that is to be noted. 



After the diameter has been measured the tag should be marked 

 with a piece of crayon, or the bark scratched in a distinctive manner 

 at a point where the scratch will not interfere with any later diameter 

 measurement. This may save much footwork on the part of the 

 man taking the measurements. 



Remeasurements should always be made at the same season of 

 year as the original measurements in order not to complicate 

 growth calculations. This is much more important in regions of 

 rapid growth, particularly in regions where growth is practicalh T 

 continuous during all but a very small part of the year. 



Measurements made in early spring should be timed not in ac- 

 cordance with the calendar but in accordance with actual stages of 

 vegetative development. It is preferable to avoid making any meas- 

 urements during the period of most active growth. 



Both moisture and temperature affect tree diameters; consequently 

 remeasurements should preferably be made under the same general 

 weather conditions as the original measurements. The French 

 forest experiment station recommends (57) that a check measure- 

 ment of all diameters be made a few weeks after the original meas- 

 urement. This would of course serve the purpose of detecting mis- 

 takes in measurements as well as differences due to weather. 



HEIGHT 



The total height of a standing tree is usually defined as the verti- 

 cal distance from a horizontal plane drawn through the average 

 ground level at its base to a horizontal plane drawn through its tip. 



The relative advantages of various hypsometers for measuring 

 tree heights have been studied repeatedly (18, 21, 83, 31, 40, 41, 4.6, 

 SI, 55, 58, 66). The general conclusion has been (5) that the Abney 

 level and the Forest Service hypsometer give more reliable results 

 that any other instruments requiring the minimum of time and care 

 in manipulation. (Hypsometers and the Abney level are shown in 

 plate 3, A.) The type of Abney that is used "on a tripod is more 

 accurate than the hand type. The Klaussner probably exceeds both 

 instruments in accuracy and in freedom from mathematical errors. 

 It is less rugged in construction, however. With this instrument a 

 Jacob's staff should always be used. 



Jacob's staffs can be made on the ground, from almost any suitable 

 material. A Jacob's staff superior to any on the market can be made 

 from a long-handled hoe. The blade of the hoe is removed, and 

 the shank straightened and sharpened. The handle is cut to about 

 5% feet including the spike. The top is fashioned to take the 



