THE TREE RECORD 155 



of securing as wide a range of diameter and height classes as possible, 

 by distributing the selection of the trees, applies within the limits of 

 the predetermined region, type or age class. 



The number of trees necessary to secure a good basis for a volume 

 table increases with the range of diameter and height. Ten trees in 

 each separate diameter and height class will suffice, and only in a few 

 standard tables has this number been secured. This would call for a 

 total of 500 to 2500 trees. Ordinarily, a sufficient number of trees 

 is easily obtained for the smaller and more common diameter and height 

 groups, but the material becomes scarce as the larger sizes are reached. 

 The graphic methods of averaging are chiefly useful in overcoming this 

 deficiency (§ 138). The use of form factors also facilitates the con- 

 struction of tables from fewer trees (§ 175). Standard tables, com- 

 puted by averaging the volumes of trees by the method given in this 

 chapter should be based on at least 300 trees, and if used as a general 

 reference table should never have less than 500 and preferably over 

 1000 trees. Local tables based on diameter alone can be made from 

 10 to 50 trees. It is desirable to tabulate the number of trees measured 

 in each diameter and height class in the field as the work progresses, 

 and to make a special effort to find trees of the less numerous sizes to 

 fill out the table. On the other hand, the more common sizes should 

 be represented by somewhat greater numbers of trees in the table 

 than odd sizes, as errors in the table affect the results of estimating 

 in proportion to the per cent of volume of the stand which falls in 

 the specified classes. 



To secure trees of sjnaller sizes than are considered merchantable 

 by loggers, in order to show total cubic contents for these classes, or 

 contents in terms of smaller products not being utilized in that locality, 

 the trees may be felled by the mensuration crew. This must be done 

 for all sizes in absence of logging, but it adds greatly to the time and 

 cost of the work. 



133. The Tree Record. The data for each tree must be entered 

 on a separate blank, or printed form, and headed by the items, 



Species, 



Locality, 



Date, 



Name of investigator, 



Number of analysis. 



Records should be carefully filled in with legible figures, using a 



4H or 6H pencil. They constitute permanent records of tree form 



and may be available for use in compiling data many years afterward. 



Description of site factors are useful in determining their influence, 



if any, on the form and volume of trees of the same diameter and height. 



