1. Rangeland Resources Research Unit Agricultural Research Service United States Department of Agriculture Fort Collins CO 80526 USA
2. Hawkesbury Institute for the Environment Western Sydney University Penrith NSW 2751 Australia
3. Centre for Carbon, Water and Food Faculty of Agriculture and Environment School of Life and Environmental Sciences The University of Sydney Sydney NSW 2006 Australia
4. Department of Botany University of Wyoming Laramie WY 82071 USA
5. Soil Plant and Nutrient Research Unit Agricultural Research Service United States Department of Agriculture Fort Collins CO 80526 USA