1. Direction de la recherche forestière, ministère des Forêts, de la Faune et des Parcs, 2700 rue Einstein, Québec, QC G1P 3W8, Canada.
2. USDA Forest Service, Northern Research Station, P.O. Box 267, 335 National Forge Road, Irvine, PA 16329, USA.
3. Department of Biology, Center for Environmental Studies, Virginia Commonwealth University, 1000 West Cary Street, Richmond, VA 23284, USA.