168 A MANUAL FOR NORTHERN WOODSMEN 



was known that single trees depart widely from the 

 type, it was assumed that for trees having the same di- 

 ameter and height an average volume could be ascer- 

 tained which would hold approximately throughout the 

 distribution of the species. Proceeding on this assump- 

 tion, tables were worked out for the different tree species 

 and these when applied in actual business proved close to 

 the fact and vastly improved the work of timber valuation 

 in Germany a hundred years ago. 



European measurements of logs and standing timber do 

 not recognize anything corresponding to the board foot, 

 but everything is reckoned in solid contents. The same 

 rule holds in the scientific study of tree form in all coun- 

 tries where it has been pursued, the unit in the United 

 States being the cubic foot. For all such studies, too, the 

 total height of the tree as a well-defined factor capable 

 of ready measurement has usually been employed rather 

 than any size limit set part way up, and a diameter breast 

 high, or 4j feet above the ground, has been settled upon 

 as the basis of all diameter comparisons. The area of a 

 cross-section of a tree at this point is called the basal area, 

 and the same term is applied to a number of trees or to a 

 stand of timber. In the study of tree form, the term form 

 factor has proved to be a useful one. The form factor of a 

 tree is the percentage which the volume of any tree (usu- 

 ally reckoned in cubic feet, outside the bark) makes of 

 the volume of a cylinder having the same height and the 

 tree's breast diameter. Illustration: A tree 15 inches in 

 breast diameter and 75 feet high may, after caliper meas- 

 urement every 4 feet along it, prove to have 38.6 cubic feet 

 in it. A cylinder of these dimensions contains 92 cubic 

 feet. The form factor, therefore, is .42. 



For many years past the study of tree form has been 

 ardently pursued, and many interesting facts and laws 

 have been ascertained. In large measure these results 

 have been brought to bear on the actual business of Euro- 

 pean countries where timber is grown as a crop under 

 uniform conditions. In this country, where the forests 

 are natural and as a rule irregular, it will be many years 

 before the same can be true. The following, however, 



