1. Earth Systems Research Center, 8 College Road, Morse Hall, University of New Hampshire, Durham, New Hampshire 03824, U.S.A.
2. Department of Ecosystem Science and Management, 405 Forest Resources Building, Pennsylvania State University, University Park, Pennsylvania 16802, U.S.A.
3. College of Forestry, 140 Peavy Hall, 3100 SW Jefferson Way, Oregon State University, Corvallis, Oregon 97331, U.S.A.
4. Center for Ecosystem Sciences and Society, Department of Biological Sciences, Box 5640, Northern Arizona University, Flagstaff, Arizona 86011, U.S.A.
5. Ecosystems Center, Marine Biological Laboratory, 7 MBL Street, Woods Hole, Massachusetts 02543, U.S.A.
6. Department of Biological Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario, M1C 1A4, Canada
7. Institute of Arctic Biology, 311 Irving 1 Building, University of Alaska Fairbanks, Fairbanks, Alaska 99775, U.S.A.