@book {1661, title = {Effects of Persistent Volcanic Ash on Douglas-fir in Northern Idaho }, year = {1987}, publisher = {U.S. Dept. of Agriculture, Forest Service, Intermountain Research Station}, organization = {U.S. Dept. of Agriculture, Forest Service, Intermountain Research Station}, address = {Ogden, Utah}, author = {Bilderback, D.E. and Carlson, C.E.} }