54 BULLETIN 811, U. S. DEPARTMENT OF AGRICULTURE. 



Since in the intermediate range all but an insignificant percentage 

 of the trees are suppressed in a greater or less degree, it becomes 

 obvious that in this region incense cedar should be cut by the time 

 it reaches 165 years, the critical age. 



In the optimum range, suppressed trees must not be allowed to 

 pass 165 years and dominant individuals 210 years (the age of decline) 

 before felling. 



Even in the distant future, when the risk of wounding in the 

 forests is reduced to a rninhnuni, it is highly problematical whether 

 a new age of decline can be established at a higher age, on account of 

 the entrance of decay through knots. Damaging dry-rot has entered 

 trees through knots beginning at 105 years, and while such cases are 

 rare in the years below the critical age and age of decline, yet they 

 are sufficient to indicate that this condition will always have to be 

 reckoned with. Furthermore, as. time goes on, the increasing value 

 of timber will result in noticeably lowering figures as to what con- 

 stitutes an allowable percentage of cull in any species. 



From a pathological viewpoint the critical age must limit the rota- 

 tion of incense cedar in the intermediate range. It is doubtful 

 whether even in the managed stands of the future the incense cedars 

 in this range will be other than suppressed in most cases, since the 

 present widespread suppression does not seem to be the result of any 

 influence that could be removed by a system of forest management, 

 arising apparently from the fact that the cedar is removed from the 

 region of its optimum development. 



In the optimum range the rotation must be limited by the age of 

 decline. The critical age is not so important except during the period 

 of transition, for suppressed trees, while common enough in the virgin 

 stands of to-day in this range, will have little place in the managed 

 stands of the future. Here, the species being in its optimum, nothing 

 but thrifty, dominant individuals should be produced under a rational 

 system of management. 



The influence of decay on harvesting a timber crop was hinted at 

 years ago by Von Schrenk (27, p. 203) and clearly pointed out by 

 Meinecke (16, p. 61) for white fir. Mitchell (17, p. 32) took this 

 so-called pathological rotation carefully into account, recommending 

 a rotation of 150 years, at which time the species attains a good 

 merchantable size. The rotation recommended by Mitchell is based 

 on Meinecke's preliminary study of dry-rot. 



As a result of the present study, the pathological rotation for 

 incense cedar must be placed at 165 years in the intermediate and 

 210 years in the optimum range. During the transition period, while 

 suppressed trees are still a factor in the optimum range, these should 

 be cut when not older than 165 years. This does not mean that in 

 the two regions under consideration cedar can best be cut at regular 



