|
William Catton's
landmark book, Overshoot:
The Ecological Basis
of Revolutionary Change was published in 1980. The
premise of his thesis is that any species - including man - can
be too successful in exploiting ecological niches and their
accompanying resources.
As an
explanation, David Delaney describes a 3-phase
process
in Overshoot in a Nutshell:
-
The
creation of
stocks is due to ongoing
geological and biological activity. A resource stock forms
when
a part of the daily production of a resource, a flow,
accumulates slowly without being exploited, perhaps over millions
of years. An enormous stock of a resource may accumulate before
it encounters a species that can exploit it easily. After such an
encounter, only predation and disease limit reproduction of the
species.
Without
significant predation or disease, and
while large amounts of the stock remain easily available, the
population of a species can grow to a size hundreds of times that
which can be supported by the flows that created the stock. The
daily production of a resource is a mere trickle compared to the
flood available from a stored accumulation.
-
After a long
period during which more of the
stock is consumed each day by the growing population than was
consumed on the preceding day, the stock starts to exhaust.
Deposits of the stock become harder to find. Less can be obtained
from the stock each day than the day before.
-
The time now
remaining before complete
exhaustion of the stock may be much shorter than the time that
elapsed between encounter with the stock and the first signs of
approaching scarcity. Soon, individuals begin to compete
desperately for the remaining stock. To stay alive, they
resort
to alternative resources of lower and lower quality. By consuming
the sources of flow, they destroy the capacity of their
environment to produce the original flow. They also destroy the
capacity of their environment to produce flows of alternative
resources. Most of the population dies.
|
Paul Harrison,
in
Chapter 17
of The Third Revolution,
delineates a
comparable 3-phase sequence:
-
In
the beginning
is abundance. Resources are
vast in comparison with human numbers. Population density is low.
There is plenty for everyone: all people need to do is to collect
what is there. This is the gathering phase.
-
Gradually
numbers
multiply and exert increasing
pressure on resources. Yet at first people continue with the
technologies and attitudes of the gathering phase. The resource
is depleted. This is the mining phase. In some
cases, when
fuelled by windfall profits, as in tropical forests, it reaches a
paroxysm in pillaging.
-
What follows is
the crisis phase.
Potentially renewable living resources are not renewed, but
depleted below the level at which they can renew themselves.
Scarcities develop - hunted species disappear one by one, soil
yields fall, firewood and water have to be sought further and
further away. Depletion reaches the level at which it becomes
visible, even painful.
|
Consider
the following examples:
 A
recent "natural
experiment" was the
ecological suicide of a population of reindeer that exhausted
their resource base when they became free of the usual factors
regulating their numbers. In 1944, twenty-nine reindeer were
introduced to St. Matthew Island in the Bering Sea. Reindeer are
normally subject to predators, and reindeer on continents use
migration as a safety valve to leave an area and allow its
vegetation to recover. But St. Matthew Island lacked predators,
and migration was impossible, while the animals ate and bred
unchecked. Since the animals had nowhere to migrate, the
slow-growing lichens which the reindeer depended on for food had
no chance to recover from reindeer grazing. By 1963 the reindeer
had multiplied to six thousand. When a harsh winter struck in
1963-64, all except forty-one females and one sterile male
starved to death, leaving a doomed population on an island
littered with thousands of skeletons.
-
 A dramatic example of
preindustrial collapse involves one of the most advanced Indian
civilizations of North America, the abandoned pueblos of the U.S.
Southwest.
When Spanish
explorers reached the U.S.
Southwest, they found
immense multistory dwellings - pueblos - standing uninhabited in
the middle of treeless desert. Pueblo Bonita at Chaco Canyon was
the largest building erected in North America prior to the
construction of skyscrapers in the late 19th century. Navajo
Indians in the region knew of the vanished builders only as
"Anasazi," meaning "the Ancient Ones."
Why did the
Anasazi
erect a city in a barren
wasteland? Where
did they obtain their firewood, or sixteen-foot-long wooden beams
that supported the roofs? Why did they abandon the city that they
had built at such enormous effort?
Archaeologists and
paleobotanists were able to
reconstruct the
following course of events. When the Chaco pueblos were erected,
they were not surrounded by barren desert, but by pinyon-juniper
woodland, with ponderosa pine forest nearby. As occupation
continued at Chaco, however, the woodland and forest were cleared
until the environment was renderd into the treeless wasteland
that it remains today. The Indians then had to travel over ten
miles for firewood, and over twenty-five miles for pine logs.
After the pine forest was cleared, they built an elaborate road
system to haul spruce an fir logs from mountain slopes over fifty
miles away, relying on little more than human muscle power.
In addition,
the Anasazi had solved the
problem of agriculture
in a dry environment by building irrigation systems to concentrate
available water into valley bottoms. As deforestation caused
progressively increasing erosion and water runoff, and as
irrigation channels gradually dug gullies into the ground, the
water table may finally have dropped below the level of the
Anasazi fields, making irrigation without pumps impossible.
Although drought may have been a precipitating factor, the
Anasazi abandoment of Chaco Canyon probably resulted from a
self-inflicted ecological disaster.
|
A
population that grows in
response to abundant but finite resources - like the reindeer
of
St. Matthew Island - tends to exhaust its resources. By the
time
that remaining resources will not be adequate for the next
generation, the next generation has already been born. In their
effort to survive and thrive, they use up every scrap, so that
little remains to sustain even a small population. A human
population can exhaust finite resources in the same manner as the
reindeer of St. Matthew Island. The Anasazi of Chaco Canyon offer
a dramatic (although geographically less isolated) historical
example.
Is Drawdown
» Overshoot
» Collapse relevant
to our contemporary global human population?
|
