1. P. A. Matson, Ecosystem Sciences Division, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720–3110, USA.
2. W. J. Parton, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, USA.
3. A. G. Power, Section of Ecology and Systematics, Cornell University, Ithaca, NY 14853, USA.
4. M. J. Swift, Tropical Soil Biology and Fertility Programme, c/o UNESCO/ROSTA, Post Office Box 30592, Nairobi, Kenya.