Vogler, D. R., and Pronos, J. 1980.
U.S.D.A., Forest Service, Pacific Southwest Region, San Francisco, CA 94111.
Page 253 in Proceedings of the Symposium on Effects of Air Pollutants on Mediterranean and Temperate Forest Ecosystems, Riverside, CA, 22-27 June 1980.
The overall level of forest-wide injury in the southern Sierra Nevada can be termed slight, with some local populations of susceptible pines showing moderate or worse injury. Unexpectedly high amounts of injury detected in certain areas in 1979 placed some plots into the severe category. It is presently unclear whether this is a permanent trend of increasing impact, or just a short-term result of drought stress. With only 3 years of monitoring data, trends in annual ozone dose are difficult to assess. Ozone levels seemed to decrease slightly each year between 1977 and 1979, even though visible injury to pines increased. Measured variations in seasonal ozone dose may be associated more with weather patterns than with decreased pollutants at the source. Maximum daily ozone values in the Sierra still remain about 1/2 or less of those occurring in southern California. As ozone continues to be transported into the western slopes of the Sierra Nevada, sensitive pines will continue to show additional injury and will slowly decline.