Forest Mensuration 49 



Pressler establishes as the "law of bole formation" the following rule : 

 "The absolute increment of the sectional area at any point of a bole is 

 directly proportioned to the leaf surface above that point." 



This rule is, on the whole, correct. An unexpected swelling, however, 

 is often found at 9/16 of the height of the tree. Within the crown of 

 the tree, the decrease of sectional area increment is rapid. 



PARAGRAPH LXXIX. 



RELATIVE INCREMENT OF DIAMETER AND OF SECTIONAL AREA. 



The increment percentage at any point of the bole, like all increment 

 percentages, forms a constantly but irregularly descending progression. 



At any point of the bole the increment percentage of the sectional area 

 is the double of the increment percentage of the diameter. 



Schneider gives a handy formula for the sectional area increment per- 

 centage, viz. : 



400 



P equals - 

 nd 



wherein d represents the diameter at the beginning of the period of ob- 

 servation, and wherein n indicates the number of rings per inch at the 

 time of observation. 



The percentage of the sectional area increment increase along the bole 

 with increasing height of the disk measured, excepting, however, possibly, 

 the case of very isolated trees. 



The average sectional area increment percentage of the bole is found at 

 a point a little below one-half of the total height, namely, at about 0.45 

 of the total height from ground. 



PARAGRAPH LXXX. 



VOLUME INCREMENT. 



The (current and future) volume increment of standing trees is of 

 great interest to forest financiers ; it can be estimated only, and cannot 

 be measured exactly. 



The volume increment of trees cut down may be ascertained as follows : 



1. By the sectional method, or by "section analysis" (Paragraph 

 LXXXL). 



2. From the increment of sectional area chest high, height increment 

 and form figures (Paragraph LXXXIV.). 



3. From the increment of sectional area in the midst of bole (Para- 

 graph LXXXV.). 



4. On the basis of the average annual increment (Paragraph 

 LXXXVIL, last 4 lines). 



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