1. Barber, M. C. (ed.): 1994, Environmental Monitoring and Assessment Program: Indicator Development Strategy, EPA/620/R-94/022, Athens, Georgia, U.S. Environmental Protection Agency, Office of Research and Development, Environmental Research Laboratory.
2. Bender, G. L. (ed.): 1982, Reference Handbook on the Deserts of North America, Westport, CT: Greenwood Press.
3. Box, T. W.: 1989, ?Rangelands?, in: Sampson, R. N. and Hair, D. H. (eds.), Natural Resources for the 21st Century, Washington, DC: American Forestry Association, Island Press, pp. 101?120.
4. Brown, D. E., Lowe, C. H, and Pase, C. P.: 1979, ?A Digitized Classification System for the Biotic Communities of North America, with Community (Series) and Association Examples for the Southwest?, J. Arizona-Nevada Academy of Science 14, (1).
5. Grover, H. D. and Musick, H. B.: 1990, ?Shrubland Encroachment in Southern New Mexico, USA: An Analysis of Desertification Processes in the American Southwest?, Climatic Change 17, 305?330.