54 BULLETIN 871, 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 minimum, 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 
