976 JOURNAL Olf FORESTRY 



that initiated by the Federal Plant Quarantine Act (August 20, 1912). 

 Meanwhile, until safe quarantine provisions are completed and strictly 

 enforced, some newly introduced epiphytotic disease or some new out- 

 break of one already occurring in the country is liable to happen at 

 any time. 



The effect of an epiphytotic in the forest is frequently that of the 

 speedy death of a large number of trees over a considerable area. It 

 is in this way that growing stock and distribution of age classes are 

 most directly affected. Suppose, for example, that a certain pathogene 

 shows a decided preference for young growth of a certain species, 

 either on young trees or on branches of older ones, for its activities. 

 It is evident that the younger the tree, the more susceptible it is and the 

 more liable to complete destruction, and the older the tree, the more 

 likely it is to recover from the attack. It is easily conceivable, there- 

 fore, that the entire growing stock of the first age class (i to 20 years) 

 of the species may be practically destroyed, and serious inroads might 

 also be made into the second and even the third age classes. If the 

 particular species is the only one for which the forest is being managed, 

 the supposed epiphytotic will remove from the stand the entire cut of 

 one twenty-year period in the future, and may necessitate planting to 

 offset this loss in future yield. 



The results of such a catastrophe call for a radical readjustment not 

 only in the length of the rotation and cutting cycle, but in the calcula- 

 tion of the allowed annual or periodic cut. It would probably be ad- 

 visable in the suggested example to retain the same rotation, but to 

 increase slightly the length of the cutting cycle so as to reduce the 

 number of the periods of return by one. For the first rotation follow- 

 ing the occurrence of the epiphytotic the allowed periodic cut would be 

 reduced. The volume of the lost age class when it should have reached 

 maturity, divided by the number of cutting cycles retained, would be 

 the reduction factor for each cutting cycle. The remaining volume 

 which is to be cut is also distributed over a longer term of years — the 

 extended cutting cycle — and the allowed annual cut is reduced by that 

 much more than the previously allowed periodic cut. Thus the loss of 

 the volume of one age class is distributed over the rotation, and the 

 felling age increased by a little each period, being at the end twenty 

 years greater than the length of the rotation. 



The marking for any cutting during the time of readjustment must 

 be subservient, of course, to the calculated allowed annual cut to a cer- 

 tain degree, but should primarily concern itself with sanitation, even 

 at a considerable sacrifice of the sustained annual yield sought. In 

 many cases it might be imperative to substitute a new species not sus - 



