Environmental Engineering Reference
In-Depth Information
intermittent and extensive use of land, with orderly
patterns (herds following seasonal rains, or planting the
same sequences of crops in fixed cycles) imprinted on
changing locations and over large areas. Shifting agricul-
ture was a part of the evolutionary continuum from
foraging to permanent cropping in forest and woodland
environments. Pastoralism, a form of resource conser-
vation, was an adaptation to exploit arid regions or a re-
sponse to desiccation using domesticated animals to
convert scarce, and seasonally nearly absent, grassy phy-
tomass into food in the form of milk, blood, and meat.
Not surprisingly, the sustainable population densities
of many nomadic pastoralists were not any higher than
those of less widely roaming foragers. In suitable envi-
ronments even the moderately productive forms of shift-
ing cropping with long regeneration cycles could support
populations 1 OM larger than the settled foraging com-
munities, but commonly 1 OM smaller than that sus-
tained by permanent field farming. For millennia these
ways of life dominated huge areas of all continents (ex-
cept Australia). Not infrequently, especially in Africa,
they blended into mixtures of seminomadic agropastoral-
ism, sometimes with a significant bit of foraging. Their
rapid twentieth-century retreat is attributable to rising
population densities, which lead, among pastoralists, to
unsustainably large herds (helped by better water supply
and control of animal disease vectors) and to overgraz-
ing; and, among shifting farmers, to drastically shortened
soil regeneration cycles, greater soil erosion, nutrient de-
cline, and eventual loss of many sites.
Animal husbandry is a form of prey conservation, a
strategy of deferred harvests whose opportunity costs are
greater for larger animals (Alvard and Kuznar 2001).
However, the smaller species (sheep, goats) were domes-
ticated first because of their higher growth rates. There
have been many social studies of pastoral societies in
transition (Helland 1980; Galaty and Salzman 1981;
Khazanov 2001) as well as descriptions of the traditional
pastoralist way of life (Irons and Dyson-Hudson 1972;
Monod 1975; Salzman 1981; Khazanov 1984; Rigby
1985; Evangelou 1984; Salzman 2004), but accounts
of pastoral energetics are rare, and only human energy
inputs are easy to approximate. Traditional pastoralists
did nothing to improve the pastures, and their labor was
confined to herding the animals, guarding them against
predators, watering them, helping with difficult deliv-
eries, milking them regularly, butchering them infre-
quently, and building temporary enclosures.
These tasks usually required only light to moderate ex-
ertion for 2-6 h a day, and many of them were done by
children. Evangelou (1984) showed that 92% of all herd-
ing and 42% of boma (enclosure) livestock work among
Kenyan Maasai were done by children. A single East Af-
rican herder managed up to 100 camels or 200 cattle and
400 sheep and goats (Helland 1980). Khazanov (1984)
lists similarly high rates in Asia: two mounted shepherds
for 2,000 sheep in Mongolia, an adult shepherd and a
boy for 400-800 Turkmen cattle. Herding, even with
additional labor (digging wells), was not labor-intensive,
and this fact was one of the key reasons for the reluctance
to convert to farming.
Given the enormous variety of natural settings, a nu-
merical analysis of the relation of livestock to grazing has
little significance unless one specifies a host of local fac-
tors determining the grazing potential (Monod 1975).
Grazing intensity also depends on the kinds and mixtures
of animals and on their metabolism, water requirements,
and vulnerability to parasites (Glossina, tse-tse fly, has al-
ways excluded many areas from grazing). Animal resil-
ience is a matter of large interspecific differences. In cool
