26 Forest Mensuration 



The volume of a wood is ascertained by cruisers' estimates in the fol- 

 lowing ways : 



a. By estimating the number of trees and the volume of the average 



tree with due allowance for defects. 



b. By counting the trees and estimating the volume of average trees 



with allowance for defects. 



c. By estimating the volume of each tree separately, sounding it with 



an axe, when necessary, and judging its soundness from all 

 sides. 



The above methods (a, b, c) are applied either to sample plots or to 

 sample strips or to the entire area. 



A blazing hammer is often used to prevent duplication ; the revolving 

 numbering hammer might be used in case of scattering trees, so as to 

 allow of control of the estimates by the owner, his forester or the pros- 

 pective purchaser of stumpage. 



In irregular forests hardwood forests of the United States the only 

 safe way is separate estimating of each individual tree after careful in- 

 specting. Incredible errors result from wholesale and rapid estimates. 



In the case of even aged woods, a look at the height growth and a 

 knowledge of the age gives a good idea of the forest's volume. Under 

 very poor conditions of growth, the annual timber production per acre 

 and year is as little as 15 cubic feet; under the best conditions it is as 

 much as 250 cubic feet per acre and year. On an average (on absolute 

 forest soil), 50 cubic feet per acre and year may be considered as the 

 production of healthy and densely stocked forests. 



PARAGRAPH XLI. 



PRINCIPLES UNDERLYING THE EXACT MENSURATION OF FOREST VOLUME. 



The basis of any exact measurement of volume is formed by a survey 

 of the sectional area, combined with an account of the number of stems ; 

 sectional area and number are found by calipering (valuation survey). 

 Whatever rule of log measurement may be at stake, the total sectional 

 area of the forest is always of first importance for a survey of forest 

 volume. Next in importance is the calipering of sample trees, followed 

 by an exact survey of their volume. The ratio r existing between the 

 volume of the sample trees (expressed in any unit or mixture of units) 

 and the sectional area of the sample trees is identical with the form 

 height (compare Par. XXXII. , towards end) of the sample trees. The 

 form height of sample trees properly selected is the form height of the 

 forest. The sample trees are usually cut and worked up into logs, cord- 

 wood, tannin wood, etc., for the purpose of volume survey. 



__I_!l!L and V-S.f.h 



