THE MEASUREMENT OF TREE DIAMETERS 227 



of the tree or stand, but the method is far more uncertain than if depend- 

 ence is placed on the computed volumes of the logs or trees as shown 

 in tables. 



In the use of volume tables, then, the accepted standards of volumes 

 set by these tables are substituted for guessing as to the contents. 

 The measurements required may be : 



1. Diameter at base. 



a. Standardized at D.B.H., outside bark. 

 6. Stump diameter inside bark, still in use by old time 

 cruisers. 



2. Height of tree. 



a. Total height to tip. 

 6. Merchantable height. 



1'. To a fixed top diameter. 



2'. To a variable top diameter. 



3. Actual measurement of an upper diameter to determine 



form (when form classes are distinguished). 



a. At middle of stem above D.B.H. (Jonson). 

 h. At middle of stem above stump (Schiffel). 

 c. At top of last log. 



188. The Measurement of Tree Diameters — Diameter Classes. 

 Stand Tables. Diameters will be averaged in either 1-inch or 2-inch 

 classes. In the East and with species of a small total range of diameters, 

 1-inch classes are preferable. Especially with such species as spruce 

 and white pine, 1-inch diameter classes are necessary to give a proper 

 basis for determination of the rate of growth, and the number of such 

 classes is not great enough to act as a drawback in estimating. 



A stand table is a tabular statement of the number of trees, in 

 each diameter class standing on a given area. By dividing the total 

 stand table by the area in acres, the stand per acre is shown, in which 

 case the trees in each diameter class are usually expressed in decimals 

 to two places, e.g., 12-inch class, 4.63 trees, etc. 



On the Pacific Coast, with a wide range of diameters running up 

 to 60 inches or over, it is unnecessary and inadvisable to make smaller 

 than 2-inch diameter classes.^ 



189. Instruments for Measuring Diameter. Calipers, Description 

 and Method of Use. Calipers have been the standard instrument 



1 In French forest practice, 5 centimeters is the division used. This corresponds 

 to 1.97 inches. 



The centimeter divisions were evidently too small and the next convenient 

 division point was 5 centimeters. This is not an argument against the use of 

 1-inch diameter classes for Eastern species. 



