1. S. A. Zimov is at the North-East Scientific Station, Pacific Institute for Geography, Russian Academy of Sciences, Cherskii, Republic of Sakha 678830, Russia.
2. E. A. G. Schuur is in the Department of Botany, University of Florida, Gainesville, FL 32611, USA.
3. F. S. Chapin III is at the Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775-7000, USA.