1. M. L. Goulden, S. C. Wofsy, B. C. Daube, S.-M. Fan, D. J. Sutton, A. Bazzaz, J. W. Munger, Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.
2. J. W. Harden and T. Fries, U.S. Geological Survey, Menlo Park, CA 94025, USA.
3. S. E. Trumbore, Department of Earth System Science, University of California, Irvine, CA 92697, USA.
4. P. M. Crill, Complex Systems Research Center, University of New Hampshire, Durham, NH 03824, USA.
5. S. T. Gower, Department of Forest Ecology and Management, University of Wisconsin, Madison, WI 53706, USA.