i 3 2 FORESTRY 



size of the forest, depends upon the species, the quality of 

 the locality, the sylvicultural system, treatment, and length 

 of rotation. With I representing the normal increment, 

 and r the number of years in the rotation, the normal stock 

 S is found from the equation 



The quantity of timber that may be taken each year under 

 normal conditions is called the normal annual yield.. Corre- 

 sponding to this in practice is the actual produce available 

 for use without interference with the permanent revenue of 

 the forest. 



If the increase of the growing stock exceed the amount 

 calculated as being the normal yield, the surplus may be 

 allowed to accumulate to form a reserve. Reserve stock may 

 consist of specified woods which, as a provision against acci- 

 dent, are not included in the estimate for the income, or the 

 returns may be calculated at a figure below that which the 

 forest is known to be capable of yielding. 



Factors determining the Course of Future 

 Management 



The survey of the forest, the estimate of the volume and 

 increment, and the detailed description of the woods, furnish 

 the information on which the course of future management is 

 based; It is necessary first to consider the object the owner 

 has in view in maintaining the woodlands. In strictly economic 

 forestry, some financial calculation is necessary to decide 

 when it will be most profitable to harvest the crop. This 

 may be reckoned by either the highest forest rent or the 

 highest soil rent theory. The former represents the difference 

 between the average annual income and expenditure ; but it 

 does not take into account the time occupied in the realisa- 

 tion of this. In the second case, the effort is to earn the 

 highest rate of interest on the capital invested represented 



