Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

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than one hundred days in northern Senegal; in bad years it rains fewer than
fifty. Studies of ancient lake levels show that long droughts occurred repeatedly
over the past several thousand years. Tree ring studies from the Atlas
Mountains just north of the Sahel reveal at least six droughts lasting twenty
to fifty years between ad 1100 and 1850. The next run of dry years proved
catastrophic after almost a half million square miles of West African forest
were cleared in under a century.
The 1973 West African famine killed more than a hundred thousand
people and left seven million dependent on donated food. Triggered by
drought, the roots of the crisis lay in the changing relationship of the people
to the land. Extensive removal of ground-protecting vegetation triggered
severe soil erosion and a humanitarian disaster during the next run
of drier than average years.
The nomads and sedentary farmers of the Sahel traditionally practiced a
symbiotic arrangement in which the nomads’ cattle would graze on crop
stubble, manuring farmers’ fields after the harvest. When the rains came
the herds would head north following the growth of new grass. Continuing
north until the grass was no longer greener ahead of them, the nomads
would turn back south, their cattle grazing on the grass that grew up
behind them after they passed through on their way north. They would
arrive back in the south in time to graze and manure the farmers’ harvested
fields. In addition, Sahelian farmers grew a variety of crops and let land lie
fallow for decades between episodes of cultivation. The division of the
Sahel into separate states disrupted this arrangement.
Rapid expansion of French colonial authority across the Sahel in the late
nineteenth century altered the social conventions that had prevented overgrazing
and kept fields manured. Colonial authorities set up merchants in
new administrative centers to stimulate material wants. Poll and animal
taxes compelled subsistence farmers and nomads alike to produce goods
for French markets. Held to new political boundaries, nomadic tribesmen
who had moved their herds across the landscape for centuries increased
their livestock density to pay taxes. Farmers moved north into marginal
lands to plant crops for export to Europe. Pastoralists expanded south into
areas where lack of reliable water and insecurity had previously limited the
number of cattle and sheep. Large concentrations of animals around new
wells destroyed pastures and left the soil vulnerable to erosive runoff and
high winds during violent summer storms.
The Sahel became more evenly and continuously used for increasingly
intensive grazing and farming. Between 1930 and 1970, the number of
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