(a) In order that a forest may furnish uninterruptedly 

 a regular supply of material of a definite kind, the capital 

 on the ground must contain a complete series of trees or 

 crops of all ages from the seedling to the mature tree. 



This, it may he seen, is certaioly true with regard to 

 crops which are regularly constituted by area. By analogy, 

 as has been explained, we may also assume it to be true as 

 regards crops in which the age-classes are irregularly distri. 

 buted. 



(6) Where the part of the capital, as represented by the 

 growing stock, is normally constituted, the material becoming 

 exploitable in a given year is equal to the mean average pro- 

 duction during that year over the whole area. 



This is very important as showing how, by felling over 

 yearly coupes, the annual production is obtained. It would 

 be impossible to collect annually this production over the 

 whole area of the forest. It will be observed from fig. 1 

 that the exploitable material for the year concerned (the 

 shaded rectangle) is equal to the production during that year 

 over all the coupes, and that this is the average annual pro- 

 duction. 



It follows that, in a selection-worked forest of whict the capital is normally 

 constituted, the trees that beonme exploitable during any period of years are equal to the 

 avci'age production on the whole area for that period. For instance, in a period of 

 10 yeais, it would he within the production to fell all the trees that attain exploitable 

 size during the 10 years. The danger of applying this rule is that we cannot ascer- 

 tain with accuracy whether the capital in a selection -worked forest is normal or not, 

 and consequently are unable to say whether such a felling is or is not in excess of tlie 

 production. If, for instance, all the trees were nearljj mature, almost the whole of the 

 Ciipital might, under such a rule, be removed in one year. 



(c) The quantity of exploitable material felled in any 

 period bears a fixed proportion to the forest capital, but the 

 amount of this capital varies with the age at which the 

 forest is exploited and increases as that age is prolonged. 



The truth of this most important principle will be evi- 

 dent from an inspection of fig. 1, We may suppose that 

 this figure represents the wood capital on the ground. The 

 amount of this capital remains constant, and, as will be 

 seen, may be practically represented by one-half the rect- 

 angle having for its base the line representing the area of 

 the forest and for its height the growth during the exploit- 

 able age. If the exploitable age were doubled, the capital 



