FOREST, FISH AND GAME COMMISSION. 85 



The sum of the ci-oss areas of the stand 



The sum of the cross areas of the sample trees 



is substituted, and by multiplying this quotient by the volume of the sample wood, 

 the volume of the stand is found. 



If the sample trees are worked up, keeping the sorts of wood separate, each sort 

 will present the chosen per cent of that sort in the whole stand, and the volume can 

 be determined as explained above. 



The disadvantages of the method are that in rounding off the fractions of sample 

 trees in each class inaccuracies occur, and that frequently no sample tree at all is. 

 taken from classes which contain only a small number of trees. The larger the 

 stand the larger will be the number of trees in each class and hence the more accurate 

 will be this method when applied to the stand. 



The Urich Method. 



This is the same in principle as the Draudt Method, but takes a sample tree for 

 the same number of trees and thus endeavors to avoid the small errors occasioned 

 by rounding off the fractions resulting from multiplying by the rate per cent. 



By this method the trees of the stand are arranged in groups so that each group 

 contains the same number of trees. For each group a mean sample tree is then 

 reckoned. 



As in the Draudt Method the sample wood is all worked up together, and the 

 volume of the stand, as well as the division of the same into sorts, is reckoned by 

 multiplying the volume of the total sample wood, or, for the latter requirement, that 

 of the particular sort by the quotient: 



Sum of the cross areas of the stanch 

 Sum of the cross areas of t lie sample trees 



The method does not insist upon any fixed number of groups, still they should 

 not be too few, at least not fewer than three, lest the trees with mean cross areas 

 may not possess the mean contents of the group. Too large a number of groups 

 is inconvenient as it involves repeated separation of the diameter classes, and since 

 for each group a sample tree must be reckoned. 



The Association of German Forestry Experiment Stations, which in 1889 adopted 

 the method, prescribes the number of five groups. This number meets the demands 

 in both directions, and need be increased only in stands with great diiTerences 

 between the diameter classes. 



Here, as in the method of the mean sample tree, several sample trees should be 



