60 FOREST TREE DISEASES. 



mous forests as in the smaller and more valuable Euro- 

 pean forests, or in orchards and parks. Methods must 

 be adapted to existing conditions. 



Very rarely will it be possible to save a tree or a 

 stand which has once been attacked by one of its more 

 dangerous enemies. A tree infected by a heart-rot fun- 

 gus or by a large colony of Dendroctonus beetles is 

 lost. We can not save it. We can not even always save 

 all of its timber; part of it may already be destroyed 

 or at least injured. This leads to our first rule: Save 

 the merchantable timber of a tree as long as the amount 

 to be saved justifies it. This simply means closer 

 utilization of our timber supply. 



The second rule in dealing with disease is to prevent 

 the infection and infestation of sound stuff by getting 

 rid of all diseased and insect-infested living or dying 

 trees. This means sanitation of our forests. Insects, 

 fungi, and mistletoe, however, are so widely and uni- 

 formly scattered throughout our forests, and have such 

 a firm hold, that without improved methods of forest 

 management it will take long and persistent work to 

 control them. 



There is a fundamental difference between attacks by 

 insects and by parasitic plants (fungi and mistletoes). 

 While insects are always present in the forest, it is 

 only at considerable intervals that they do widespread 

 harm in any given locality. A destructive species, 

 however, may multiply enormously and kill a large 

 number of trees in a short time. Under natural condi- 

 tions it may continue to increase in number for years 

 until it is again reduced by some natural agency to a 



