TheImprovement ofTropical and Subtropical Rangelands

OVERVIEW 3
associated with the extensive UIe of spar88, IIC&ttered, and often seasonal
or ephemeral natural vegetation. Moat ofthe world's estimated
3 billion head ofdomesticated livestock are reared on tropical or subtropical
rangelands, rather than on highly productive pastures or in
feedlots. Most of the red meat consumed by humans is produced
on rangelands. Some 135 million people, about 20 percent of the
world's population, base their economies and societies on rangeland
resources.
The pastoralists' systems of livestock production characteristically
require movement of herds and herders over large areas, on
either a seasonal basis (transhumant pastoralism) or a basis of perpetual
migration (nomadic pastoralism). Pastoral socioeconomic systems
can be further distinguished by combinations of other activities
with those of herding. Herding, along with some agricultural
crop production is a frequent combination, creating what are known
as agro-pastoral systems; herding and tree-crop production creates
silvo-pastoralism. Important economic activities ofother pastoralists
involve conducting, supporting, or controlling long-distance overland
trade routes.
Reduced vegetative cover is often the result of overstocking, uncontrolled
or concentrated grazing, removing woody plants for fuel
or shelter, and clearing natural vegetation. Destructive management
practices are often related to colonial-period modifications of indigenous
management systems: for example, highly regulated land-use
systems, such as the "eMma system of Masina, were widely converted
to open-aceese systems with the imposition of the European
law of public domain; the ecological integrity of indigenous pastoral
systems was frequently destroyed through the imposition of international
boundaries; cattle-based livestock systems were promoted in
marginal drylands at the expense of 8U8tainable indigenous systems
based on better-adapted forms of livestock; wells projects encouraged
concentrated gruing around water supplies; and the new economic
order stimulated herd increase and its attendant economic rewards.
Population growth in pastoral societies, approximately 1.5-2.0 percent
annually (National Research Council, 1983b), is regulated by the
observance of restrictive mores and other mechanisms. Hence, internally
generated population growth is seldom a problem in pastoral
zones. Indeed, declining population, with a corresponding inability
to manage large herds, is often a serious problem. Further, the higher
annual rates of growth in agricultural societies, characteristically on
the order of 2.5-3.0 percent, encourages agricultural expansion into