FOREST ECONOMY. 



219 



corresponding to the above enumeration shows as 

 follows (rounded off) : — 



This table shows that, while the cut to lo-inch 



yields of course a larger harvest, the same harvest 



in amount can theii only be again had in about 50 



years; while the harvest is replaced in less than 



30 years if the cut is made to 14-inch, and the 



average annual production is then largest, namely, 



3.32 



— — = 1 10 feet B.M. per year. 



The report of the bureau nevertheless chooses 

 the 12-inch limit because "the present yield to a 

 14-inch limit is not large enough to justify the 

 construction of logging roads, the building of camps, 

 and other expenses necessary for lumbering." 



In other words, these calculations serve only as 

 a general guide to direct the judgment. And es- 

 pecially with this method caution is necessary, as 

 it is based upon the assumption, probably not often 

 correct, that reproduction will take place, and that 

 younger age classes in sufficient number and amount 

 are in existence to take the place of the older ; 



