22 MENSURATION AND INCREMENT [ch. hi 



20. Yield-tables. 



Lastly, for fuUy-stocked crops that may be considered as 

 fairly normal, the increment past, present and future, raay be 

 obtained from average yield-tables, in countries where such 

 yield-tables exist. 



Yield-tables are constructed by measuring a very large number 

 of woods of all different ages, normal sample plots fully stocked, 

 of aU species and qualities, and then plotting the volumes thus 

 obtained by means of co-ordinates indicating cubic feet verti- 

 cally and age horizontally. The outside points, that is, the 

 highest and lowest volumes recorded, are connected severally by 

 two curves, and the intermediate space is divided into three or 

 four equal strips through the middle of which a hne is drawn 

 to represent the mean volume curve for each of the three or four 

 quality classes. 



A tabular statement of this kind for each species shows the 

 course of development of a wood throughout its life-time, under 

 each quality of soil and cUmate, and vmder each method of 

 treatment, and affords average statistics for each unit of area, 

 at every age, as to the number of trees, their mean height, 

 diameter, volume, increment and form-factor. Such yield-tables 

 which afford information which is indispensable for a full and 

 proper knowledge of all the economic and financial questions 

 which have to be dealt with in forest management, may be 

 either general or local. 



