432 MEASUREMENTS FOR FOREST MANAGEMENT 



Now, by Weise's method, the average sample stem is 

 21-1008 cubic feet, and the contents per acre = 21- 1008 x 

 3000 = 63,302-400 cubic feet, a difference of less than J per 

 cent. 



Various other methods have been evolved for determin- 

 ing the contents of an area by the estimation of sample 

 trees. 



These, for the most part, divide the total number of trees 

 into classes of equal numbers, and take one or more sample 

 trees for each class, and thus arrive at the total contents. 



By Draudt's method, a constant proportion (usually I per 

 cent.) of the number of trees in each class is taken for 

 samples ; the I per cent, being reckoned roughly on every 

 hundred, or fraction of a hundred over fifty; and two or 

 more diameter classes, if containing under 50 trees, are 

 grouped together. 



By Urich's method, one sample tree is taken for every 

 100 trees, and is considered to have the diameter of that 

 class from which most of the trees making up that 100 are 

 drawn. 



But Weise's method, and that of finding the contents of 

 each diameter class, are far preferable for ordinary use. 



2. Measurement of Sample Plots. 



By this method, several plots of about one-half or one 

 acre each are selected and measured at various spots over 

 the whole area ; their contents computed ; and then the con- 

 tents of the whole area found according to the proportion the 

 total area bears to the plots. 



This method has to some extent already been indicated 

 when describing the method of selecting sample stems on a 

 single given measured area if the total area be very large. 



But the method now under consideration presupposes the 

 taking of several small plots ; and it will often be expedient 

 to measure every tree on each of the plots, or the contents 

 may be found by the taking of sample trees as previously 

 described. 



In selecting the plots, care should be taken that they are 



