1. Archer S.: 1993, in: Varra M., W. Laycock and R. Pieper (eds),Ecological implications of livestock herbivory in the West, Society for Range Management (in press).
2. Bailey, R.G.: 1989,Environmental Conservation 16, 307?309.
3. Cramer, W.P. and Solomon, A.M.: 1993,Climatic Research (in review).
4. Dregne, H., Kassas, M. and Rosanov, B.: 1991,Desertification Control Bulletin 20, 6?18. United Nations Environment Programme, P.O. Box 30552, Nairobi, Kenya.
5. Edwards, G., and Walker, G.: 1983,C 3,C 4:Mechanisms, and Cellular and Environmental Regulation, of Photosynthesis. 542 p. Blackwell, Oxford.