METHOD OF YIELD TABLES. 7 J 



If tables are available, which are suited to a particular part 

 of a country, it is necessary to ascertain in the wood to be 

 estimated — 



(1.) The quality class of the locality. 

 (2.) The density of the crop. 

 (3.) The age of the crop. 



The first is judged by the height of the trees; the second 

 by ascertaining the basal area of the trees on a sample plot ; 

 the third by counting the concentric rings on stumps or on 

 a few trees cut close to the ground, unless the age is known 

 from records. Based upon these data, the volume can be taken 

 from the yield table. If, for a certain age, the basal area given 

 in the table differs from that of the wood, the volume of the 

 table must be modified accordingly ; a second correction may 

 be necessary owing to a difference in the height. 



The method just indicated is, however, not much used, 

 because, if basal area and mean height of the wood have 

 been ascertained, it is much shorter to calculate the volume 

 by means of form factors or volume tables. Yield tables are 

 better adapted for ascertaining the increment of woods ; 

 hence, the method of preparing them will be described in 

 Chapter VI. 



