THE ABSOLUTE FORM QUOTIENT 533 



wind is considered to exercise its concentrated pressure — is estimated, 

 after which its height in per cent of the total height of the tree is read 

 ofif with a special instrument. At the foot of each page in the table is 

 given the form point height corresponding to each form class. Those 

 figures are intended for volume measurements inside bark or for trees 

 with bark of practically uniform thickness, such as the Norway spruce. 

 Some species, however, have a bark the relative thickness of which 

 increases toward the root by which the outward form of the tree is 

 impaired. 



Below the series of "normal form points" Jonson has given a series 

 of form points which should be used for volume measurements outside 

 bark of thick-barked species, such as the Scotch pine (Pinus silvestris) . 



When estimating the volume of trees with root swelling reaching 

 above breast height, it is necessary to raise the calipers above the swell- 

 ing or the estimated volume of the tree will be too high. 



When a w'hole stand or type is estimated and an average form class 

 applicable to all trees is looked for, the following table form class, 

 founded on density, is recommended : 



Poor density 0.575-0.625 



Fairly good density 0.65 



Good density 0.675-0.70 



Overcrowded density (pine) 0.70 -0.725 



Overcrowded density (spruce) 0.725-0.75 



Best results are obtained if the nearest lower form class is used for 

 the dominant trees, as the codominant and intermediate trees have 

 relatively less crown space and therefore better trunk forms than the 

 dominant trees. 



The highest and lowest form classes are hardly ever used as 

 averages. 



In estimating the content of whole stands one can also reach a fair 

 result by multiplying the breast-height form factor, corresponding to 

 the average form class of the stand, with the estimated average height 

 of the trees and the total sum of the sectional areas at breast height of 

 all trees in the stand. 



An experienced estimator working on felled trees or using the "form 

 point method" will before very long have gained experience enough to 

 judge the form class by eye, but he should not omit to check his figures 

 by taking measurements on windfalls or felled trees when opportunity 

 therefor is given. 



It is ol)viousIy most desirable to investigate the applicability of Jon- 

 son's mcthofl ti) American species. 



