147 



Service 1984). The effects of forest fire, air pollution, logging, farming, grazing, and 

 homesteading arc discussed, yet devastation from major pest infestations is virtually 

 ignored. Pests have altered entire forest ecosystems in eastern North America and 

 have had a major impact on western forests in certain localities. Exotic pests from 

 other continents have proven to be more destructive than endemic insects and dis- 

 eases. Native insects, other arthropods, and fungi are part of the natural forest ecosys- 

 tem. Native forest trees have evolved with native pests, and have developed defense 

 mechanisms. Over the long term, these mechanisms keep the essential balance of the 

 natural ecosystem inuct. However, when alien or exotic insects, arachnids, saprophyt- 

 ic plants, fungi, and diseases are introduced into the forest, extensive damage or mor- 

 tality can occur. Natural controls for introduced pests are usually abscnL Native trees, 

 without a history of natural interaction with exotic pests, often have litde or no resis- 

 tance mechanisms. As a result, native species can be seriously damaged or eventually 

 eliminated. 



Tht TUUurui mnge of whiubark ptru 



