1. Department of Botany, University of Wyoming, Laramie, WY 82071, USA;
2. Center for Ecology and Evolutionary Biology, University of Oregon, Eugene, OR 97403, USA;
3. Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA;
4. Department of Biological Sciences, Box 5640, Northern Arizona University, Flagstaff, AZ 86011, USA;
5. The Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA 02543, USA;
6. Department of Natural Resources and Environmental Science, University of Nevada, Reno, Reno, NV 89557, USA;
7. Department of Forest Science, Oregon State University, Corvallis, OR 97331, USA;
8. Department of Botany and Microbiology, University of Oklahoma, 770 Van Vleet Oval, Norman, OK 73019, USA;
9. Smithsonian Environmental Research Center, PO Box 28, 640 Contees Wharf Road, Edgewater, MD 21037, USA;
10. Geobiosphere Science Centre, Lund University, 223 62 Lund, Sweden;
11. USDA Forest Service Rocky Mountain Research Station 240 West Prospect Rd., Fort Collins, CO 80526, USA and Department of Forest Rangeland and Watershed Stewardship and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA;
12. Institute of Botany, the Chinese Academy of Sciences, Xiangshan, Beijing 100093, China, and Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA