430 MEASUREMENTS FOR FOREST MANAGEMENT 



of that stem by the number of trees on the area. If the area 

 be very large, the average tree and the number of trees, on a 

 comparatively small measured area, are first ascertained, and 

 the contents completed ; and from this the contents of the 

 large area are calculated. 



The initial difficulty is to find the average stem. 



An excellent method is that adopted by Weise, in which 

 every stem is counted and assigned to a diameter class (each 

 class usually varying I inch in diameter). When all the 

 stems are thus counted and classified, a count back up to 40 

 per cent, of the total number of stems is made, beginning 

 with the stems in the biggest diameter class. The diameter 

 class into which this count back leads, will contain the true 

 average stem which is required. 



Thus if an area contained 3000 trees classified thus : 



Then a count back of 40 per cent. 



40 x 3000 



IOO 

 = 1200 



equals 1200 trees from the 1 6-inch diameter class; this 

 would lead into the 1 2-inch diameter class. 



