[55] STEM FORM INVESTIGATIONS 219 



class for every tree gave a result 20 % too low since the form class in just 

 that stånd was appreciately higher than what the form point gave, that is to 

 say the form point method's negative error was, in that stånd, greater than 

 what it is on the average. Vahiation gives the best results if no reduction 

 is made for the root swelling's disturbing influence. It may possibly be that 

 the thickness of the bark was measured to high, for which additional reduc- 

 tions merely make the result worse. 



With estimating of timber yield according to the form class method, the 

 following points must be observed: 



1:0. One must procure a statement of the total number of trees distri- 

 buted by species in diameter breast height classes measured outside the bark, 

 with for instance 1" intervals. 



2:0. If distribution in these classes is to be made after falling measure- 

 ments, so that for example the 7" class comprises all trees between 7" and 

 8", then Ihe middle point of the class lies at 7 ^/,,". 



3:0. In the higher diameter classes the average tree of the class lies 

 somewhat displaced again st the lower boundary for which the measurements 

 here considered are somewhat scarser than in the lower diameter classes. 



4:0. Dry trees and the like where the timber yield on account of sickness, 

 technical or other injury or damage is remarkably less than with a normal 

 tree, notations should be made in different classes according to the amount 

 of damage or reduction of yield. 



5:0. Sample trees ought to be investigated in order to give data concer- 

 ning bark thickness at breast height, formclass, and height in the different 

 diameter classes. Bark thickness can be measured suitably with an instrument 

 such as is set forth in fig. 3. Height can be measured with some such 

 instrument as the Christen hypsometer. Form class is reckoned inside bark 

 and measured on felled stems either by careful calipering of the determina- 

 tive diameters- (breast height and middle diameter above breast height) or better 

 through the sectioning and graphical compensation of the stem curve. The 

 form class can also be estimated with the help of the form point method 

 but it should be noted that experience has proven this method to give re- 

 sults which are to low. The felled and sectioned sample stems have the 

 advantage of giving the exact value. It is possible in this case to even study 

 the influence of root swelling. 



6:0. If the forest contains different bark, height and form class types, they 

 should be divided up and sample stems for each type handled by them- 

 selves. In smaller stånds one needs a larger relative number of sample trees 

 in order to obtain accurate results. Sample tree measurements should be made 

 use of through the bringing together of local empirical figures for reference 

 in future estimates. 



7:0. Log division is made, in a given type, for the average tree in every 

 diameter class by the use of the rounded out value of the bark thickness, 

 (eventually also root swelling) height and form class, with a table of yields 

 of trees with known factors, for example Löfgrens graphic tables, This log 

 division is to be accurately made with special attention to which diameters 

 are most valuable and consequently are to be taken out of the tree, so that the 

 value one gets out of a given average tree is the best possible. In this 

 case the demands the buyer places on excess measure and average length 



