CHAPTER 1. 



A SUSTAINED YIELD. 



In higli forests, tlie yield of which is based on volume, it would 

 s6em possible to realise the condition of a sustained yield by 

 dividing the total quantity of the timber to be felled during the course 

 of an entire rotation by the number of years in the rotation. But 

 this quantity would include not only the actual contents of the 

 standing timber, but also the total annual increment of each crop 

 up to the time of its exploitation. Now it is impossible to estimate 

 •with any degree of exactness the future increment of crops, that are 

 still to grow on for a long series of years, up to the time they reach 

 their turn for exploitation. It is for this reason that it is a point 

 of doctrine in forest organisation to divide the rotation for high 

 forests into a certain number of periods, and to estimate successively 

 beforehand the yield of the given forest during the currency of 

 each of them. To this end, the exploitations to be made during 

 the course of the rotation are arranged in their order of succession 

 and grouped together according to the periods into which they fall, 

 in such a manner as to obtain as nearly as possible equal quantities 

 of produce in equal periods of time. This distribution of the 

 annual exploitations may be effected either accordrng to volume or 

 to area, and it is in this that lies the distinctive character of the 

 two methods of forest organisation. The next .step is to determine 

 the annual quota of the produce to be exploited during the first 

 period. The same process is repeated at the commencement of 

 each of the following periods of the current rotation, and, if on 

 passing from one period to the next, the calculated yield of the 

 forest is found to be appreciably the same as it was for the First 

 Period, it is clear that the yield is a sustained one; conversely, if the 

 conditions necessary for assuring a sustained yield have been 

 correctly determined and established, the annual yield of the forest 

 cannot vary, or, at the worst, it will differ but little from period 

 to period. 



