The increased concern for forest health and the role of anthropogenic deposition, including acidic/wet deposition and gaseous air pollutants, has led to the need to understand which forest species face the highest risk from atmospheric deposition. In order to address this issue for the Western U.S., a number of important western conifer species have been assessed with regard to seedling growth response to each of three different deposition scenarios likely to occur in the Western U.S. The exposure scenarios include acid fog (fall-winter)/ozone (summer) in a seasonal interaction of each pollutant over the year, acid fog only in fall-winter exposure, or SO2 gaseous pollutant over the fall and winter months. Seasonal occurrence of the pollutants, rather than concurrent pollutant combinations, represent a realistic exposure scenario for much of the climatic conditions of the coastal Western U.S. and the Cascade and Sierra foothills. Five species were selected for study based on economic and ecological importance in the West. These included Douglas-fir, ponderosa pine, lodgepole pine, western hemlock, and western red cedar. Douglas-fir and ponderosa pine seedling sensitivity was assessed as a growth response over two growing seasons, including the spring following the previous year's pollutant exposure. The various responses to the exposure scenarios for the first year's study are reported here. The study was repeated a second year, and these results are briefly discussed.

"Paper presented at the "TRANSACTIONS' Symposium on the Effects of Air Pollutants on Western Conifers. Annual Meeting AWMA, Anaheim, CA, June 28-30, 1989." Includes bibliographical references. "EPA/600/D-89/111"--Cover. Microfiche.