1. Pacific Northwest Research Station, USDA Forest Service, Corvallis, Oregon 97331 USA
2. Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331 USA
3. Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah 84602 USA
4. Department of Biology, Linfield College, McMinneville, Oregon 97128 USA