Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

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asters. Larger societies, with more diverse and extensive resources, can rush
aid to disaster victims. But the complexity that brings resilience may also
impede adaptation and change, producing social inertia that maintains
collectively destructive behavior. Consequently, large societies have difficulty
adapting to slow change and remain vulnerable to problems that eat
away their foundation, such as soil erosion. In contrast, small systems are
adaptable to shifting baselines but are acutely vulnerable to large perturbations.
But unlike the first farmer-hunter-gatherers who could move
around when their soil was used up, a global civilization cannot.
In considering possible scenarios for our future, the first issue we need
to consider is how much cultivatable land is available, and when we will
run out of unused land. Globally about one and a half billion hectares are
now in agricultural production. Feeding a doubled human population
without further increasing crop yields would require doubling the area
presently under cultivation. But we are already out of virgin land that
could be brought into long-term production. Such vast tracts of land could
be found only in tropical forests and subtropical grasslands—like the
Amazon and the Sahel. Experience shows that farming such marginal lands
will produce an initial return until the land quickly becomes degraded, and
then abandoned—if the population has somewhere to go. Look out the
plane window on a flight from New Orleans to Chicago, or Denver to
Cincinnati. Everything you see is already in agricultural production. This
huge expanse of naturally fertile ground literally feeds the world. The suburbs
growing around any city show that we are losing agricultural land
even as the human population continues to grow. With the land best suited
for agriculture already under cultivation, agricultural expansion into marginal
areas is more of a delaying tactic than a viable long-term strategy.
Second, we need to know how much soil it takes to support a person,
and how far we can reduce that amount. In contrast to the amount of
arable land, which has varied widely through time and across civilizations,
the amount of land needed to feed a person has gradually decreased over
recorded history. Hunting and gathering societies needed 20 to 100
hectares of land to support a person. The shifting pattern of cultivation
that characterized slash-and-burn agriculture took 2 to 10 hectares of land
to support a person. Later sedentary agricultural societies used about a
tenth as much land to support a person. An estimated 0.5 to 1.5 hectares of
floodplain fed a Mesopotamian.
Over time, human ingenuity increased food production on the most
intensively farmed and productive land so that today, with roughly 6 bil-
life span of civilizations