Pests are almost always present and remain at endemic levels 

 until forest, weather or other factors are right for development 

 of epidemics. When epidemics do occur, management objectives 

 can be threatened. Some of the most important forest pests 

 native to North America include bark beetles (for example, 

 mountain pine beetle, western pine beetle, and southern pine 

 beetle), defoliators (for example, Douglas-fir tussock moth and 

 western spruce budworm), the dwarf mistletoes (for example, 

 lodgepole pine dwarf mistletoe and Douglas-fir dwarf mistletoe), 

 rust pathogens (for example, the fungi that cause fusiform rust 

 and western gall rust), and root pathogens (for example, the 

 fungi that cause armillaria root disease, laminated root rot, and 

 annosus root disease). Important introduced pests include 

 the European gypsy moth and balsam woolly adelgid, and the 

 fungi that cause chestnut blight, white pine blister rust, Dutch 

 elm disease, and dogwood anthracnose. Abiotic factors such as 

 poor soil conditions, flooding, and air pollution also cause tree 

 diseases. In one of the most notable examples, Jeffrey and 

 ponderosa pines in the San Bernardino and San Gabriel moun- 

 tains near Los Angeles have shown ozone injury since the 1960's 

 (Miller 1973), and many of these ozone-injured trees have died 

 due to drought or bark beetle attack (Cobb and Stark 1970). 



Ecosystem management on the national forests in part involves 

 applying our understanding of the historical roles of wildfire and 

 native pests in ecosystems. Wildfire and native pests have been 

 significant factors in ecosystems. For example, Heinselman 

 (1978) states that the presettlement forests of northern North 



Forests in the Bear Mountain Basin (South Dakota) are 

 infested with mountain pine beetle. 



Introduction 



