1. Division of Biological Sciences University of Montana Missoula Montana 59812 USA
2. Department of Plant Pathology, Physiology and Weed Science Virginia Polytechnic Institute and State University Blacksburg Virginia 24061 USA
3. Rocky Mountain Research Station U.S.D.A. Forest Service Missoula Montana 59801 USA
4. Division of Biological Sciences and the Institute on Ecosystems University of Montana Missoula Montana 59812 USA