TheImprovement ofTropical and Subtropical Rangelands

36 IMPROVEMENT OF TROPIOAL AND SUBTROPIOAL RANGELANDS
of radiation, temperature, aaturation deficit, and wind apeed, weighted for
altitude and latitude. They are calculated on the buis of Thomthwaite'a concept
of moisture induea (1948), combined with Penman'a eatimate of evaporation
(1948).
3. In many areas of the tropics, a liveatock unit is taken to be a mature
Hbu cow with calf at foot (averacinl about 300 kl liveweilht and having a
daily dry matter requirement of 6.5 to 8.5 kl)'
4. In an ecological context, information is aimply organised or patterned
energy or material that tells the obaerver IOmething about the put, present,
or probable future atate of an ecoeyatem or ita componenta. Human responae
to environmental information is unique compared with that of other organism.
becauae it occurs largely at the cognitive level where cultural conditioning
affecta both perception and the aelection of appropriate reaponaea.
REfERENCES
Davy, J. B. 1938. The classification of tropical woody vegetation types. Paper,
01 tIN OommonwcaltJa ForuCry IrvCitutc 13:1-85.
French, M. H. 1957. Nutritional value of tropical grasses and fodders. HaW
Abmuctl 27:1-9.
Harris, D. R. 1969. Agricultural syatems, ecosystema and the origins of agriculture.
In The DomCltietJlion and EsploWaion 01 Planll and Animall. P. J. Ucko
and G. W. Dimbleby, eda. Aldine-Atherton, Chicago, Dlinois; USA.
Johnaon, D. L. 1969. The Nalut'e 01 NomtUlirm: A Oompcrativc Stwlv 01 PtJItorol
Migrutioru in SoutJatoeltem Alia and Nortlalm Africa. Department of Geography
Reaearch Paper No. 118, University of Chicago, Chicago, Illinois, USA.
National Reaearch Council. 1981. Environmental DCf"ldation in MClUJ"ittJflia.
Board on Science and TechnolOC for International Development. National
Academy Press, Washington D.C., USA.
National Reaearch Council. 19831.. Alf'OloruCry in tIN Welt Africon SaheL Board on
Science and Technology for International Development. National Academy
Pre.., Washington D.C., USA.
National Reaearch Council. 1983b. Environmental OIaangc in tIN Welt AfrWm
Sahel. National Academy Press, Washington D.C., USA.
Penman, H. L. 1948. Natural evaporation from open water, bare loil and gr.....
Proceeding, 01 tIN Rollal Sociq. Series A, 193:120-145.
Pratt, D. J. 1968. Ranleland development in Kenya. AI'II'ICIlI 01 Arid Zone 7:177­
208.
Pratt, D. J. and M. D. Gwynne, eds. 1977. Rangeland MClMfcment and EcoI09II
in ECIIt Africa. Hodder and Stoulhton, London, England.
Rambo, A. T. and P. E. Sajise. 1984. An Introduction to Humo.n EIlO109ll Be,careh
on Agricultural Svlte"" in SoutJacut Alia. University of the Philippines at Lol
BanOl, College, Laguna, Philippines.
Sanchel, P. A. 1975. Propcme, and Managcment 01 Soill in tIN 7h>pic,. John Wiley
and Sons, New York, New York, USA.
Sauer, C. O. 1952. Agricultural Originl andDilpcr,alI. Bowman Memorial Lectures,
aer. 2. American Geographical Society, New York, New York, USA.
Schmidt-Niellen, K. 1964. De,ert Animall: Phllliological ProNe"" 01 HIlCIt and
Water. Oxford University Press, Oxford, England.