EASTERN CASCADES (M242C), 



MODOC PLATEAU (M26IG),AND 



BLUE MOUNTAINS (M332G) 



Ecology 



The Eastern Cascades and Modoc Pla- 

 teau — ^This region comprises the eastern 

 slopes of the Cascade Range and the dry vol- 

 canic area at the southern end of the eastern 

 Cascades. The eastern Cascades include sev- 

 eral high volcanic peaks: Mount Hood, Mount 

 Jefferson, and the Three Sisters, all with 

 elevations over 10,000 feet. 



The mixed conifer forests of this area are 

 very complex and variable in terms of species 

 composition and structure. Typically, mixed 

 conifer stands on moist sites are characterized 

 by a sparse overstory of large ponderosa pines 

 and Douglas-firs, and a dense understory com- 

 posed primarily of true firs with fewer lodge- 

 pole pine, occasional western larch, and west- 

 ern white pine. Historically, these stands were 

 predominantly pine, maintained by frequent, 

 low-intensity ground fires. 



On dry sites, the structure and species com- 

 position are simpler, normally consisting of 

 only two species (white fir and ponderosa pine) 

 in a distinctly two-storied arrangement with 

 large pines in the overstory. The most com- 

 mon pine species in this area are ponderosa 

 and lodgepole. Each species covers a large area 

 where it is the domingmt climax species. Less 

 common are the five-needled pines, including 

 western white and sugar pines. 



The Blue Mountains — Two major moun- 

 tain ranges dominate the Blue Mountains re- 

 gion, the Blue Mountains in the center and 

 southwest and the Wallowa Mountains in the 

 northeast. Wide, low valleys separate the 

 mountain ranges and channel two major riv- 

 ers, the John Day and the Grande Ronde. The 

 eastern boundary of this region follows the 

 Snake River through Hells Canyon, separat- 

 ing Oregon and Idaho. Elevations range from 

 1,000 to 10.000 feet. 



Conifer forests are the dominant vegetation 

 at middle elevations in the Blue Mountains. 

 The forests range from spruce and fir at higher 

 elevations to mixed conifers (grand fir, Douglas- 

 fir, lodgepole pine, western larch, and ponder- 

 osa pine) at mid elevations to ponderosa pine 

 at lower elevations. Important hardwood spe- 

 cies, such as black cottonwood, quaking as- 

 pen, and willow, as well as many rare, endemic 

 plant species, are concentrated in wetlands 

 and riparian areas. Fire frequency once de- 

 termined the composition of low and mid 

 elevation forests in the Blue Mountains. De- 

 cades of fire suppression and selective logging 

 of serai conifers (such as ponderosa pine and 

 larch) have created forests that are more sus- 

 ceptible to disturbances from insects, diseases, 

 and stand-replacing fires. 



All Species 



Drought, wind, and severe winters injure 

 trees — Precipitation patterns are a key driv- 

 ing force for determining the character of the 

 forested vegetation on the east side of the Cas- 

 cade Range and the Blue Mountains. Mois- 

 ture, falling as rain or snow in the spring and 

 fall, is abundant at upper elevations but de- 

 creases rapidly with decreasing elevation. 

 Summers are usually very dry throughout the 

 area, especially at the lower elevations. 



Various weather-related events common to 

 this area are important to forest health. Peri- 

 odic droughts reduce the capacity of trees to 

 protect themselves against insects such as 

 bark beetles and defoliators; large-scale out- 

 breaks often occur during dry periods. Dry 

 years from the mid to late 1980s to the mid 

 1990s contributed to widespread tree mortal- 



Oregon — 33 



