1. School of Forest Resources, University of Maine, Orono, ME 04469, USA.
2. Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN 47907, USA.
3. College of Life Science and Agriculture, University of New Hampshire, Durham, NH 03824, USA.
4. Northern Hardwood Research Institute, Edmundston, NB E3V 2S8, Canada.