GROWTH OF TREES AND FORESTS 195 



tree in percentage falls with increasing age, in spite of the fact 

 that it lays on more wood each year even if the width of the 

 rings remains the same. Although the actual amount of wood 

 made may increase, this increase is an ever-decreasing propor- 

 tion of the total volume of the tree. Suppose, for example, that 

 the red oak mentioned above grew 3 cubic feet during the decade 

 between sixty and seventy years, the percentage of growth would 



be ~ or 35 per cent. 

 8.4 



The growth of standing trees can be conveniently studied by 

 the use of a Pressler's increment borer. With this instrument a 

 core of wood may be removed showing the width of the outside 

 rings. By means of Schneider's formula which was devised in 

 1853 the percentage of growth, which the tree has been making, 

 can be determined. This formula is: 



/=* 



nd 



in which 



p = percentage of growth^ 



n = number of rings in the last inch of radius, 



d = diameter at breast height. 



This formula is applicable only to mature or nearly mature trees 

 which have completed their height growth. 



B. GROWTH OF STANDS. 



Thus far the growth of individual trees has been considered; 

 it is important for many purposes to ascertain the growth of 

 stands or whole forests. Forest management depends very 

 largely on this knowledge, especially the more intensive forms 

 of management, such as are in use in Europe. In Austria, for 

 example, the policy is to cut and reproduce a stand as soon as 

 it ceases to yield a satisfactory rate of interest. This is called 

 the financial maturity of the stand. In Baden and other coun- 

 tries the forest working plans prescribe the cutting of an equal 

 amount of wood each year, while in Wiirttemberg, an equal area 



