Sect. I. Background. 1. Physiography and Forest Types / R.K. Olson. 2. Climate / M.R. Rose, M. Bohm and R.K. Olson. 3. Air Quality and Deposition / M. Bohm. 4. Sensitivity of Forest Soils in the Western U.S. to Acidic Deposition / D. Binkley. 5. Physiological Effects of Air Pollutants on Western Trees / A. Bytnerowicz and N.E. Grulke. 6. Pollution Impacts at the Stand and Ecosystem Levels / D. Binkley, T.D. Droessler and J. Miller. 7. Methods of Assessing Responses of Trees, Stands and Ecosystems to Air Pollution / K.W. Stolte, D.M. Duriscoe, E.R. Cook and S.P. Cline -- Sect. II. Regional Studies of Forest Growth and Condition. 8. Old-Growth Douglas-Fir in Western Washington / L.B. Brubaker, S. Vega-Gonzalez, E.D. Ford, C.A. Ribic, C.J. Earle and G. Segura. 9. Coniferous Forests of the Colorado Front Range. pt. A. Mixed Species In Unmanaged Old-Growth Stands / D.A. Graybill. pt. B. Ponderosa Pine Second-Growth Stands / D.L. Peterson and M.J. Arbaugh. 10. Coniferous Forests of Arizona and New Mexico / D.A. Graybill and M.R. Rose. 11. Mixed Conifer Forests of the Sierra Nevada / D.L. Peterson and M.J. Arbaugh. 12. Mixed Conifer Forests of the San Bernardino Mountains, California / P.R. Miller -- Sect. III. Summary and Projections. 13. Summary, Projections, and Recommendations / R.K. Olson, D.L. Peterson and M. Bohm -- Appendix I: Map of Western Forest Types.