Preliminary analysis of data from this study in the mountains southwest of the Anaconda Copper Smelter, an industrial source of SO2 and heavy metal particulate, reflects a complex pattern of pollutant impact. The differential effect of smelter emissions on plant life in the study area is best explained by the interrelationship of several factors including distance from the smelter, elevation, topography, and the position of the plant community on the landform. The data indicates that the ecological consequences of air quality degradation can be severe. Dramatic changes in plant community composition and serious reductions in vegetative cover were observed in the two forested ecosystems sampled. Tree coverage up to 66 percent was measured on control sites but dropped to less than 20 percent within 8 miles of the smelter. Shrub cover also varied directly with exposure to SO2 concentration; near the smelter coverage was only 3 to 6 percent but was 50 to 66 percent at the remote sites. Living trees near the smelter had only one half the needle retention of those on the distant sites. Up to 30 cm. of soil has eroded from the severely affected sites and normal microbial decomposition and nutrient cycling may be severely impaired. The results of this study provide the land manager with information regarding the ecological consequences of air quality degradation in forested mountainous areas.