DISEASE CONTROL AND FOREST MANAGEMENT 975 



creditable success. Insects, like disease-producing pathogenes, require 

 special extensive and intensive study to determine their influence on 

 rotation and cutting cycle and the various available means of control. 

 In the consideration of diseases it is advantageous to treat separately 

 with enphytotics and epiphytotics. 



Enphytotic Diseases 



The effect of enphytotic diseases upon the forest is a more or less 

 constant factor, as far as forest management is concerned ; for the for- 

 ester works over long periods, dealing with cutting cycles and rotations, 

 and variations in the factors influencing decay and other enphytotic 

 diseases are compensating. It is with an enphytotic disease that Mei- 

 necke (1915) deals, and his study shows that, given a knowledge of the 

 liability to attack and decay with reference to age and condition, the 

 rotation, and therefore the regulation and distribution of the cut, can 

 be altered to fit the conditions found. In treating with white fir {Abies 

 concolor), Meinecke (191 5; 59) concludes that thrifty, unwounded 

 trees might be allowed to exceed 150 years of age ; wounded but thrifty 

 trees should not be allowed to exceed 150 years, and wounded, sup- 

 pressed trees should not pass the 130-year mark, because on the average 

 after these respective ages the increment in the several classes of trees 

 is so far offset by decay as to render it unprofitable to keep them longer. 

 A study of decay in other species would undoubtedly result in the estab- 

 lishment of similar rotational limitations. 



With regard to the cutting cycle, it is evident that the period must be 

 of sufflcient length to produce enough volume above the diameter limit 

 to make a return profitable. On the other hand, it must be as short as 

 such a requirement will permit, in order to reduce the chances for such 

 catastrophes as windfall, fire, frost injury, and lightning injury, which 

 directly reduce the volume of merchantable material and create dan- 

 gerous infection centers. 



In the marking rules, such requirements should be made as would 

 not only comply with the above conditions of the rotation age and the 

 volume produced during the cutting cycle, but would also eliminate as 

 far as possible all diseased trees or trees liable to be infected because 

 already injured in some way. This would reduce the centers from 

 which other trees may become diseased and would gradually accomplish 

 sanitation in the forest. 



Epiphytotic Diseases 



The problem of dealing with epiphytotic diseases is an exceedingly 

 difificult one, and apparently the only safe method of handling them is 



