7 



4 



Volume, all trees 



Volume In trees 8 inches d.b.h. and larger, 

 wild stand 



Volume in trees 8 inches d.b.h. and larger, 

 regulated stand 



1 3 



10 



20 30 40 



Stand age (years) 



50 



60 



70 



Figure 3. — Expected development of fully stocked western larch stand 

 with and without stocking control, as represented by 

 volume in different tree size classes. 



In both situations, however, the aim is to 

 compare the estimated cost of the manage- 

 ment treatment being considered with the 

 expected effect on yield, considering the time 

 that will elapse between the point when the 

 cost is incurred and the point when benefit 

 is realized. 



The time period or rotation used is an im- 

 portant element in financial calculations. How- 

 ever, it must be recognized here that there is 

 a certain element of guesswork in the establish- 



ment of timber rotations. Circumstances are 

 continually changing in a way that may affect 

 the length of the timber growing period. Har- 

 vesting may be required short of the rotations 

 established, to avoid serious loss due to some 

 forest enemy, Siinilarly, technology or wood 

 values may change, making either a shortening 

 or lengthening of rotations desirable. 



The Northern Region has established some 

 tentative rotations and tree-size objectives by 



12 



