[53] STEM FORM INVESTIGÄTIONS 217 



difFerent conditions namely, the branching of the root system, character of 

 the soil etc. Under the same conditions the root swelling becomes greater 

 in larger trees and less in smaller trees. 



I have investigated stem curve material and have found in this respect 

 that with Lappland pine the root swelling may be as large as lo X of the 

 stem's length measured from the ground. The maximum amount that root 

 swellings enlarge the diameter breast height in a stånd, I have found to be 

 about 3 % . For certain trees however the variation is very important. In 

 general the enlargement is not to be considered in the reckoning of the 

 yield. Three percent of the diameter inside bark constitutes, in a tree of 

 14" outside bark, less than i cm. By taking the maximum values from that 

 stånd v.'hich showed the greatest root swelling I have deduced empirical 

 numbers for the maximum reduction in diameter for Lappland pine which 

 one may safely maintain and which under no conditions should be över 

 stepped. The figures are given in fig. 6 and table II and should constitute 

 the uppermost boundary for variations in that respect. 



Form class distribution within the stånd. 



For estimating the yield it is of significance to know whether the stand's 

 form class can be used for all dimensions or if a lower form class value helps for 

 the larger trees. Therefore investigative work was carried on with the question 

 as to how the form class value normally varies within the stand's different 

 size classes and in this connection classification of the trees was made on 

 the basis of height. To begin with, the crown height of trees of different 

 lengths in the same stånd was investigated. It shows that in general the 

 highest form class diameter is found below the crown. The longer the trees 

 the higher the crown. (See fig. 7.) So the question arises as to crown's 

 relative length with respect to the stem. This factor expressed in percentage 

 of the tree's height is called the crown ratio. The greater the crown ratio 

 the greater length the crown has. The conclusions of table III shöw that we 

 get a minimum crown ratio for trees which are somewhat under the average 

 size. The investigations show that one can consider the crown form to be 

 constant within a given stånd; consequently the form point's distribution 

 ought to be such that we get a maximum in the neighbourhood of the average 

 stem and in turn it follows iha.t/orm class values also have the same maximum. 

 (See fig. 9 and table V.) The form class for the smallest trees in the stånd 

 increases with increasing heights, after with they reach a maximum and then 

 fall off for the largest trees. With yield estimating the small trees do not play 

 such a large part. In such a case the economical value lies in the larger 

 dimensions. If correction is to be taken into consideration it should therefore 

 first apply to the larger dimension classes. Investigation shows that the largest 

 depression of form class values which occurs in the material reaches 3,4 %, 

 corresponding to a reduction in the average formclass from 0,725 to 0,70 

 for the largest trees. 



Form point and form class. 



Now we come to the question of the manner in which form class shall be 

 determined, We must think whether to use the form point method or each 



