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 thorn-bushlands, often characterized by a rich
diversity of grasses. The prominence of grasses in tropical rangelands in many
instances reflects the repeated use of fire in hunting or range renewal (Sauer,
1952), 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
of exotic 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, 1954), soils
(Sanchez, 1975), 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, foot-and-mouth disease, contagious bovine pleuro-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 the tropics similarly affect the exploitation
and management of range