3O Forest Mensuration 



c. Proceed as indicated in the last three paragraphs, keeping in mind, 

 however, that only the cubic volume of the boles is thus obtainable. The 

 branch-wood-percentage or the timber-percentage of the bole must be 

 estimated. 



The Hartig method (Paragraph XLVI.) might be combined with the 

 use of Pressler's telescope, and the bole volume of a wood above breast 

 height. might be ascertained as 2/3 of the total sectional area of the 

 forest, multiplied by the arithmetical mean of the rectified heights of 

 the sample trees representing the various diameter classes. 



r 2 + r a + r, f r s ) 



The bole volume below breast height in cubic feet is equal to the 

 sectional area of the wood times 4^/2. 



PARAGRAPH XLIX. 



COMBINED MEASURING AND ESTIMATING. 



If measuring and estimating are combined, the following typical meth- 

 ods may be used to ascertain the volume of woods : 



1. The form factor method (Paragraph L.). 



2. The form height method (Paragraph LI.). 



3. The volume table method (Paragraph LI I.). 



4. The yield table method (Paragraph LIII.). 



These methods might be used in connection with the so-called "dis- 

 tance figure" of Paragraph LIV. 



In applying these methods, one or the other of the three factors of 

 volume (sectional area, height and form factor) are obtained by estima- 

 tion. 



The paragraphs following Paragraph LVIII. give a number of methods 

 practically used and also based on combined measuring and estimating. 



PARAGRAPH L. 



FORM FACTOR METHOD. 



The form factor method ascertains the sectional area by calipering, 

 according to species, and, if necessary, according to height classes. The 

 average height of the wood (by species, classes) is obtained by actual 

 hypsometric measurement. The form factor is read from local form 

 factor tables. 



The average height is obtained not as the arithmetic mean of a num- 

 ber of heights measured, but much more correctly from the ratio exist- 

 ing between the sum total of the ideal cylinders and the sum total of 

 the sectional areas of the trees hypsometrically measured. The form 

 factors appearing in form factor tables must be averages obtained by 

 many hundreds of local measurements. 



