TheImprovement ofTropical and Subtropical Rangelands

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The Nature ofTropical and
Subtropical Rangelands
This report focuses on areas of low and undependable precipitation
within the tropics and subtropics. 1 Much of the area is occupied
by savannahs and thom-bushlands, often characterized by a rich diversity
of grasses. The prominence of grasses in tropical rangelands
in many in8tances reflects the repeated use of fire in hunting or range
renewal (Sauer, 1962), as well as the coevolution of grasses and wild
herbivores (Harris, 1969). Substantial tracts of forest are associated
with tropical rangelands in some regions; in others, extensive swamps
created by the seasonal overbank flooding ofexotic rivers are features
of considerable regional importance.
Tropical rangelands differ greatly from rangelands in temperate
regions, and social adaptations to these differences are reflected in the
management of range resources. Differences of climate (Trewartha,
1964), soils (Sanchez, 1976), vegetation (Davy, 1938; French, 1957),
and other environmental factors are well documented and generally
well understood. The management of tropical rangelands is further
affected by the prevalence of livestock diseases. Rinderpest, footand-mouth
disease, contagious bovine pleura-pneumonia, anthrax,
east-coast fever, trypanosomiasis, and sheep pox have historically
taken heavy tolls in the tropics (Pratt and Gwynne, 1977). Strategies
to blunt the impact of disease include increasing livestock holdings to
levels that assure the survival of a breeding nucleus. The relatively
high levels of social, economic, and political differentiation within
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