Current Literature. 401 



As the location of the point of attack of the bending force is 

 determinative of form, this point is called the "form point," and 

 its height is expressed in percentage of the total height of the 

 tree. 



When decided on form class the form point, where the wind is 

 considered to exercise its concentrated pressure, is estimated, af- 

 ter which its height in per cent, of the total height of the tree 

 is read off with a special instrument. At the foot of each page in 

 the table is given the form point height corresponding to each 

 form class (see also sketch on p- 4). These figures are intended 

 for volume measurements inside bark or for trees with bark of 

 practically uniform thickness, such as the Swedish spruce (Picea 

 excelsa.) Some species, however, have a bark the relative thick- 

 ness of which increases towards 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 measure- 

 ments outside bark of thick-barked species, such as the Swedish 

 pine (Pinus silvestris.) 



When estimating the volume of trees with root swelling reach- 

 ing above breast height, it is necessary to raise the calipers above 

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

 When a whole stand or type is estimated and an average form 

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

 form class, founded on density is recommended by Jonson : 

 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, since the codominant and intermediate 

 trees have relatively less crown space and therefore better bole 

 form 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 (see p. 

 62,) corresponding to the average form class of the stand with 



