1. Department of Plant Biology, University of Vermont, Burlington, VT 05405, USA
2. Appalachian Laboratory, University of Maryland Center for Environmental Science, Frostburg, MD 21532, USA
3. Bent Creek Experimental Forest, USDA Forest Service, Asheville, NC 28806, USA
4. USDA Forest Service, Southern Research Station, University of Vermont, Burlington, VT 05405, USA