21 8 ECONOMICS OF FORESTRY. 



determined, and upon this basis a yield table is 

 constructed which shows the amount of material 

 obtainable from decade to decade according to the 

 difference of felling size. That diameter limit 

 then is chosen which in the long run appears most 

 profitable. 



If, for instance, the actual survey showed of the 

 exploitable species an average per acre of — 



28 trees above 10 inches diameter, 

 23 trees above 12 inches diameter, 

 18 trees above 14 inches diameter, 



and it is ascertained that it requires 12 years for 

 an 8-inch tree to grow into the lo-inch diameter class, 

 16 years for a lO-inch tree to grow to 12-inch, and 

 14 years for a 12-inch tree to grow to 14-inch di- 

 ameter, then if a lo-inch standard were adopted 

 the present cut would remove the 28 trees above 

 lo-inch diameter, and no exploitable size will again 

 be found before 12 years; while if the 12-inch 

 standard were adopted, the return for another har- 

 vest based on the same standard could not be 

 made before 16 years, and the 14-inch standard 

 would permit a return in 14 years. These data 

 would then permit a tolerably accurate finance 

 calculation, to determine which the profitable size 

 in the long run would be. This calculation the 

 Bureau of Forestry does not make, but instead 

 ascertains and compares merely volume produc- 

 tion by constructing a yield table. 



In a given case the yield table approximately 



