1. The use of the herb layer by grazing ungulates in the Serengeti;Bell,1970
2. The use of resources;Blaxter;Anim. Prod.,1976
3. How China uses organic farming methods;Blobaum;Org. Grower Farmer,1975
4. Alternative Methods of Agriculture,1980
5. The nutrient cycles of an ecosystem;Boerman;Sci. Am.,1970