42 MEASUREMENT OF STANDING TREES. 



If he estimates the decrease of the girth at 15 per cent., the 

 girth at 25 feet from the ground would l)e 32 inelies, and 



T — \ , , — = 22*2 cubic feet. 

 144 



If he estimates the decrease at 25 per cent., the girth at 

 25 feet comes to about 28 inches, and 



r='^' J ]</'» = 17-0. 



In fact, the vohime thus estimated would range from 17 to 

 22*2 cubic feet, and the only chance of obtaining the exact 

 amount depends on the skill of the estimator, thus intro- 

 ducing a factor of considerable uncertainty. Hence, the most 

 urgent need for the estimation of trees grown in fairly well- 

 stocked woods is the collection of data, from which form 

 factors can be calculated, whether for determining the volume 

 in the round, or according to quarter girth measurement. 

 Tbe method is, however, not applicable in the case of hedge- 

 row trees, or others grown under similar conditions. In the 

 latter case, each tree must be measured, or estimated, 

 separately. 



