Forest Menstiration 



55 



culminates at a very high age only, if ever, owing to the late culmina- 

 tion of the current annual average increment. 



The volume increment percentage forms as in all cases of increment 

 a steadily but irregularly decreasing progression. This percentage is in- 

 variably equal to or higher than the sectional area increment percentage 

 at chest height. 



Roughly speaking, the volume increment percentage amounts to from 

 I to 1.75 times the sectional area (at chest height) increment percentage, 

 or, as Pressler gives it, to from 2 to 3^ times the diameter (at chest 

 height) increment percentage. 



Since the average volume increment of a tree is equal or closely equal 

 to the current annual increment at a high age only, it is usually not 

 permissible to substitute the average increment, which is easily ascer- 

 tained, for the current annual increment 



PARAGRAPH LXXXVIII. 



VOLUME-INCREMENT PERCENTAGE OF STANDING TREES. 



In the case of standing trees the volume increment percentage cannot 

 be measured, owing to the impossibility of ascertaining a change of form 

 height. 



The Pressler data given in the preceding paragraph allow of estimating 

 the volume increment percentage of standing trees on the basis of a 

 diameter-increase, measured at breast height. 



The Pressler "accretion borer" is used for the purpose, or an axe. 



Stoetzer, Director of the Forest Academy at Eisenach, modifies the 

 Schneider formula for sectional area percentage, writing it 



P = 



nd 



wherein n indicates number of years (rings) required to form one inch; 

 d represents the diameter at the beginning of the period of investigation, 

 whilst C (the so-called "constant factor of increment," which is not a 

 constant factor at all) must be ascertained for a given species, soil, diam- 

 eter, age and position by actual tests on felled trees. 



In old dense beech woods C is, e. g., 540. After a seed cutting in the 

 same woods during the final stage of regeneration C is only 450 (observa- 

 tion by Dr. Wimmenauer). 



