25 



3. Sninmary of the chief points to be remembered with regard to 

 ithe constitution of the growing stoclc. — If we suppose that the 

 darkened rectangles in figs. Nos. 1 and 2, page 19, represent 

 the volume of material produced in each coupe in any given 

 year, the chief facts to be remembered with regard to the 

 -constitution of the growing stock may be readily understood. 



{a) In order that a forest may furnish uninterruptedly 

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

 {i.e., groicing stock) on the ground must contain a complete 

 series of trees or crops of all ages from the seedling to the 

 mature trees. 



This, it may be seen, is certainly 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 

 distributed. 



{b) 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 me^n 

 average production 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 tig. 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- 

 ■duclion. 



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

 Kjonstitoted, the trees that become exploitable during any period of years are equiil to 

 the average production on the whole area for that period. For instance, in a period 

 of 10 years, it wonld be within the production to fell all the trees that uttain exploit- 

 able size during the 10 yenrs. 



(c) The quantity of exploitable material felled»inany 

 period bears e fixed proportion to the growing stock, but the 

 amount of this forest 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. 3. We may suppose that 

 this figure represents the growing stock on the ground. The 

 amount of this stock remains constant and, as will be seen, 

 may be practically represented by one-half the rectangle 

 taving for its base the line representing the area of the 



