METHOD OF YIELD TABLES. 71 



give useful data for estimating the crop of the adjoining 

 woods. In all such cases the estimate is based on the volume 

 per unit of area. 



4. Estimating the Volume by means of Yield Tables. 



In the same way as volume tables of single trees are con- 

 structed, which give the average volume of trees arranged 

 according to diameter, height, form factor and age, so tables 

 can be compiled on the basis of extensive measurements 

 in cut woods, which show the volume of woods according to 

 species, age, quality of locality, etc. 



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 best 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 very 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. 



