Forest Mensuration 31 



Mistakes amounting to up to 25% in the sum total of the volume 

 obtained by the form factor method are not impossible, since average 

 form factors appearing from a form factor table are often at variance 

 with the actual form factor. 



Form factor tables for American "second growth" are still lacking. In 

 primeval woods the form factor method seems out of place. 



PARAGRAPH LI. 



FORM HEIGHT METHOD. 



The form heights of merchantable trees are, generally speaking, sub- 

 ject to only small variations. Those, e. g., for Adirondack White Pine 

 scaling from 18" to 36" in diameter breast-high are (for standard rule) 

 close to 1.25. 



Multiplying the sectional area of a White Pine woodlot (say 100 square 

 feet) by the form height previously obtained through official measure- 

 ments (like those by T. H. Sherrard), the volume of the woodlot in 

 the present example about 125 standards is easily obtained. 



Form height tables based on feet b. m., Doyle, are not as simple as 

 those based on the standard rules and cubic foot rules, owing to the 

 mathematical inaccurary of Doyle's rule, which causes the form heights 

 to be pre-eminently dependent on the diameters. 



Form height tables should be constructed for the leading merchantable 

 species in the United States. Of course, such tables are more readily 

 applicable to second growth than to first growth. 



The form height tables should exhibit the number of standards, cords, 

 ties, etc., obtainable per square foot of sectional area in each diameter 

 class. In case of defective trees, proper allowance must be made for 

 defects rather a hazardous risk in primeval hardwoods. 



PARAGRAPH LII. 



VOLUME TABLE METHOD. 



In Paragraph XXXVIII. a number of volume tables have been enum- 

 erated, from which the volume of trees of given species and diameter 

 (and height) can be readily read. 



A valuation survey of the forest (or of a woodlot or of a sample plot) 

 yields the diameters of the trees stocking thereon. The number of 

 trees found for each diameter class is multiplied by the contents of a 

 tree of that diameter appearing from the volume table. The sum total 

 of the multiples is the sum total of the volume of the forest. 



