Arid land: sheep may safely graze.
Very often goats are the last domesticated animals seen grazing on severely degraded, arid rangelands, like those covering so much of the African Sahel. Overgrazing by livestock--especially by the goats and sheep of subsistence herders --is often blamed for the desertification of these dry lands and the famine that follows (SN: 5/4/85, p. 282). But a new study calls into question this apparent cause-and-effect relationship.
Focusing on the Ngisonyoka people in northwest Kenya, a team of ecologists and anthropologists from Colorado State University in Ft. Collins and The State University of New York in Ginghamton studied how use of arid-land resources by nomadic subsistence herders affects the dry-range ecosystem they inhabit. And contrary to what had been assumed for decades by many authorities, the scientists found that traditional subsistence herding practices "may be cornerstones of [ecological] stability and sustainable [agricultural] productivity rather than prescriptions for degradation and famine.'
For roughly four years, the researchers studied 9,650 herders and their livestock: 85,200 sheep and goats, 9,800 cattle, 9,800 camels and 5,300 donkeys. Their goal was an "energy flow' analysis of the ecosystem: a quantitative picture of how much of the energy contained in native vegetation was being extracted--primarily through grazing animals--to feed and shelter the nomand community. An account of their findings appears in the Nov. 8 SCIENCE.
Milk--more than half of which came from camels--accounted for 80 percent of the nomads' livestock-derived diet; meat and blood each contributed another 9.5 percent. Livestock accounted for three-fourths of the total nomad diet, more than twice its percentage in the typical U.S. diet, according to Michael Coughenour of Colorado State. Most of the rest came from food purchased with livestock products.
The overall effect of this "flow' amongst the land, animals and nomads, the researchers conclude, was that subsistence herding did not degrade the ecosystem. One reason for this is that the primary human staple, camel's milk, is ultimately derived from the plentiful, hardy, woody plants.
Not only does this traditional subsistence pastoralism (livestock agriculture) apparently preserve the fragile arid ecosystem, the scientists found, but also "it appears that the negative effects of drought, including famine, could be lessened if development policies and procedures recognized the appropriateness of pastoral ecosystems in these environments.'
Research on subsistence pastoralism in Brazil and northern Peru by James Phister, a Texas Tech University range scientist based in Lubbock, shores up that conclusion. Since subsistence herders tend to be "in harmony with environmental fluctuations,' Phister says, it's unlikely their animals will overgraze--unless outside subsidies, such as water (for irrigation), fertilizer (for cultivation) or money (for food and animals), encourage the herders to settle in one place.