QUNTITY INCREMENT PER CENT. 185 



This gives : 



as before. 



The increment per cent, p is naturally very large during the 

 early youth of a tree or wood ; but as the volume increases 

 year by year, that is to s&y the denominator in the above 

 equation, while the annual increment does not increase in any- 

 thing like the same proportion, and in fact begins to decrease 

 comparatively early, it follows that the increment per cent. 

 becomes smaller year by year. Heavy thinnings can tempo- 

 rarily produce an exception to the above rule, as they may 

 retard the sinking of the increment per cent. 



Instead of comparing i with v, it can be brought into re- 

 lation with F; in that case the increment per cent, becomes : 



=x 100=x100. 



As the determination of the increment of a single year is a 

 difficult and inaccurate operation, it is usual to determine it 

 for a number of years, 5, 10, or, generally, n years, and to 

 consider V as the value produced by placing v for n years at 

 compound interest, working with p v per cent., as : 



From this 



and 



or- 



