LOCAL VOLUME TABLES 



175 



and diameters, a local table based on diameter alone may be made 

 directly, from whatever number of measurements can be secured. The 

 volumes of all trees of the same diameter are averaged regardless of 

 height. These averages must then be plotted, and a single curve drawn 

 similar to that shown in Fig. 27 but containing trees of all heights. 

 From this curve average volumes for each diameter class are read. 



When diameter is shown in the table, such tables are useful only 

 within the same stand, age class or site class in which they are con- 

 structed. Timber whose average height is greater or smaller, for any 

 cause, for trees of the same diameter classes, cannot be measured by 

 this local table but require a new basis of volumes. If it is found that 

 the heights do average the same for each diameter the local table can 

 be used unless it is known that other factors influence form sufficiently 

 to require its correction. But where no record is made of heights of 

 the trees used in constructing the table, as frequently happens, the 

 cruiser has no way of knowing whether the table applies to any stand 

 but that in which it was made. Where it is expected that such local 

 tables may be used again, heights should be measured as well as diam- 

 eter, and a curve of height on diameter drawn. The full data for such 

 a local table, which is to be saved for possible future use, are: 



TABLE XXXI 

 Local Volume Table, Form 



143. The Derivation of Local Volume Tables from Standard Tables. 



Where a reliable standard volume table is available, it is not necessary 

 to construct a local volume table based solely on diameter. If the 

 estimator does not need or desire to distinguish different heights in 

 tallying trees, he may select the volumes from the standard table which 

 represent trees of the average heights of the given stand, and tally 

 diameter only. 



The first step is to determine the average height of trees of each 

 diameter class, by means of a few measurements, and the plotting of 



