1. Departments of Environmental and Biological Sciences and the Merriam‐Powell Center for Environmental Research, Northern Arizona University, Flagstaff, AZ 86011‐5694, USA;
2. USDA‐ARS, National Peanut Research Laboratory, Dawson, GA 31742‐0509, USA;
3. Department of Forest Resources, University of Minnesota, St Paul, MN 55108, USA