Martyn M. Caldwell1, Todd E. Dawson2, James H. Richards3
1Department of Rangeland Resources and the Ecology Center, Utah State University, Logan, UT 84322, USA Fax: 435 797 3796; e-mail: [email protected], US
2Section of Ecology and Systematics and the Laboratory for Isotope Research and Analysis at Cornell University, Ithaca, NY 14853, USA, US
3Department of Land, Air and Water Resources, University of California, Davis, CA 95616, USA, , US