4 6 



METHODS OF TREATMENT 



[CH. 



all over the forest, and take countings over 5 or 10 per cent, of 

 the whole area. These figures multiplied up will give us an 

 estimate of the stock, and the proportion of the different groups 

 of size-classes throughout the whole forest. An inspection of 

 these gradated totals will at once tell us (more or less) if the suc- 

 cession of age-classes be anything like complete and regular, and 

 we may have similar figures for other forests of the same kind, 

 growing under similar conditions, with which to compare them. 



It is possible, however, to gauge the corrections of the pro- 

 portions in another way. 

 If we represent graphically 

 five groups of age-classes 

 of equal area, as in the 

 figure, the volumes of these 

 five size-groups will be 

 proportional to the five 

 vertical columns A, B, C, 

 D, and E, into which the 

 triangle representing our 

 whole growing stock, is divided; and these five areas evidently 

 bear the proportion of 9 : 7 : 5 : 3 : i. The volume of A then 

 is -fg of the whole; of B, ^ ; and so on. 



Now suppose that in the beech-woods of the Chiltern hills, 

 it is known from a large number of past measurements, that the 

 average stem of each of the following five size-groups contains 

 the number of cubic feet given in the second column of the 

 table here shown, and that the total volume per acre of a fully 

 stocked crop is say 3000 cubic feet. 



Per Acre. 



Area. 



