102 



Dl':TEt;MlXATION OF THE INCREMENT. 



Next two curves are drawn, so that the lower touches the 

 lowest points, and the upper the highest points indicating these 

 volumes. Then the area thus confined is divided into as many 

 equal strips, as there are quality classes to be distinguished. 

 The woods falHng into each strip are considered as belongiii" 



30 40 50 60 70 

 AGE, IN YEARS. 



liU 100 110 



Fig. 30. — Giiiphiu llepreseutatiou of the Kumbcr of 2'rees per Acre. 



to the same quality class. By drawing a mean curve through 

 each strip, the mean volume curve for the quality is obtained, 

 from which the volume table is prepared for successive years. 

 In a similar way, mean curves for the height, basal area and 

 number of trees are constructed for each quality class. The 

 method is of easy ap})lication, and it yields good results. 



