FOREST MANAGEMENT 



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breast height, thereby finding the diameter. From special tables 

 giving the areas of circular surfaces of known diameter ready 

 calculated, the contents of all transverse sections of the several 

 trees are found. By the addition of these sums the sectional 

 area S of the wood is obtained. The average height H is 

 found by measuring a considerable number of trees. From 

 tables prepared from averages, the form-factor F is obtained. 

 The contents of the wood are then as V = SxHxF. 



When volume tables are used, the trees are callipered and 

 the number of stems in each diameter class is found. The 

 diameter classes are generally made to differ from each other 

 by gradations of 2 inches ; thus all stems of I o inches are 

 arranged together, then 12, 14, 16 inches. The mean 

 height of trees of the several diameters is then taken. On 

 finely squared paper the heights are shown graphically as 

 ordinates, and with the respective diameters as abscissas a 

 "height-curve" is drawn. Fig. 29 gives one of these 



W 



30 



& 40 4J 



FIG. 29 



curves. In the figure the heights are shown in metres 

 ( = 39 inches), and the diameters in centimetres (=-39 of 

 an inch), but it is similar when expressed in feet and inches. 

 Such a curve being constructed, one may read from it the 

 average height of trees of every diameter. The age does 

 not require to be more than approximately estimated. The 

 volume of each diameter class is found by the multiplication 



