Ling KA, Ashmore MR.
Acid Rain and Trees. Focus on Nature Conservation No. 19. . 1987 .
Organization WH.
Air quality guidelines for Europe. Copenhagen: World Health Organization; 1987.
Bilderback DE, Carlson CE.
Effects of Persistent Volcanic Ash on Douglas-fir in Northern Idaho . Ogden, Utah: U.S. Dept. of Agriculture, Forest Service, Intermountain Research Station; 1987.