Forest Mensuration 53 



It is, however, a well known fact that the diameter growth at the 

 stump especially at a low stump is particularly unreliable as an index 

 of volume growth, owing to the exaggerating influence on stump growth 

 exercised by light, by water, by depth of soil and by superficial roots. 



Stump analysis as a means to bring a volume in reference to a sec- 

 tional area at the stump is permissible only as a necessary evil. 



PARAGRAPH LXXXV. 

 PRESSLER'S METHOD. 



Frequently the task before the forester is merely that of ascertaining 

 the increase of bole volume during the last 10 or 20 years. Then after 

 Pressler, one single investigation into the growth of the sectional area is 

 sufficient when made with the help of the accretion borer in the midst of 

 the "decapitated" bole. The volume increment in cubic feet equals the 

 sectional area increment in question multiplied by the height of the 

 tree. 



The bole is decapitated by that number of top shoots which have been 

 formed during the period of observation. This operation corresponds 

 very well with the usual practice of judging the bole increment per- 

 centage from the sectional area increment ascertained at 0.45 of height 

 of tree. 



Pressler measures the sectional area at the end of the period of observa- 

 tion too large, measuring it at too low a point. He multiplies this sec- 

 tional area, however, by too small a height namely, the decapitated 

 height; thus a mistake made in the positive sense is apt to be eliminated 

 by a mistake made in the negative sense. 



The axe can be used to better advantage frequently than the accretion 

 borer. 



PARAGRAPH LXXXVI. 



BREYMANN'S METHOD. 

 Breymann gives the following formula : 

 I. For the current annual volume increment T: 



wherein "S" and "X" denote the annual increase of diameter "d" and 

 length l 'l" respectively. 



2. For the corresponding increment percentage P: 

 , 8 A\ 



It appears that for trees of old age and hence of little height growth 

 the increment percentage is merely dependent on the diameter increase. 



