[permaculture] REPOST: Dirt: The Erosion of Civilizations
Lawrence F. London, Jr.
lflj at intrex.net
Mon Jun 2 01:13:06 EDT 2008
Dirt: The Erosion of Civilizations
by David Montgomery.
University of California Press, 2007.
Soil can bring down society, as detailed in Dirt
In Dirt: The Erosion of Civilizations, David Montgomery provides a comprehensive and readable summary of how
civilizations have depended on the half-meter of life-generating topsoil that mantles our continents, and why that
dependence has failed locally in the past and may do so again across larger scales in the future. The book focuses on
agricultural plowing that has, over millennia, stripped away much of Earth’s soil and degraded much of what remains. The
primary driver in this enormous transformation of Earth’s surface has been short-term self interest, combined with
ignorance of the long-term consequences of our actions.
Most of the book covers case studies of soil use and misuse: in early Mesopotamia and Bronze-Age China, classical Greece
and Rome, Central American Maya, pre-Industrial Europe and European pioneers in the United States. Later chapters cover
modern issues such as the role of agribusiness and the impact of genetic engineering.
Montgomery notes at least one civilization that kept the land fertile for millennia — the native Amazonian people who
composted charcoal, manure, bones and other debris and created rich terra prieta soils. Another example of long-range
fertility — the Nile River Valley — owes little to human action and much to the river’s annual gift of both nutrients
and freshwater to flush away salts.
Montgomery adds his voice to centuries-old historical debates among historians about why civilizations declined. The
list includes: wars, changes in trade patterns, centralization of power and resulting societal rigidity, and
environmental factors. In Climate: Past, Present and Future, Hubert Lamb argues that climate played a major role, but
historians have largely dismissed his examples of “climatic determinism,” which focused on high latitudes and altitudes
of Europe where few people actually lived. More persuasive examples can be found in the arid Eurasian subtropics where
intervals of extreme drought brought an end to early empires, such as the Akkadian people of northern Mesopotamia.
Montgomery views resource depletion as more critical than climate, based on examples such as the salt buildup that
curtailed agriculture in early Mesopotamia, and the total depletion of trees and soils on Easter Island. He suggests
that soil degradation played a strong role in many other societal declines, but he astutely avoids over-exaggeration.
One chapter introduces a philosophical debate that began in pre-Industrial Europe about the interplay among population
growth, food production and innovation. In the pessimistic view of Thomas Malthus, Montgomery writes, population growth
leads to food shortages and then famine. Over pre-Industrial time, however, famine was not the major cause of human
mortality. The European famine of 1313 to 1317 is often cited as the type example of such a catastrophe, but within only
a decade, the stricken populations had already rebounded to pre-famine levels. By far the major killers of
pre-Industrial humans were the three great pandemics that killed tens of millions of people during the late Roman era,
the Medieval Black Death and the European entry into the Americas.
Montgomery contrasts Malthus with William Godwin, who optimistically suggests that food shortages lead to innovations
that increase food production. In support of his view, new plows and uses of manure increased food productivity in the
Netherlands and England during the Middle Ages despite large population growth.
These two contradictory views are still evident today in many opposing trends. Malnutrition still affects more than a
billion people each year, but the percentage of adequately fed humans has been rising for decades. For more than a
century, industrial plows have caused unprecedented rates of soil erosion, but “no-till” and other soil-conserving
measures are now spreading rapidly. No unexplored virgin lands are left for humans to convert to agriculture, but more
than 1.5 million square kilometers of well-watered land at middle and high northern latitudes has reverted to forest in
the last few decades and is available for renewed farming. Global population doubled twice in the 1900s, but it will
barely double once more before approaching a quasi-stable level soon after 2050 (because wealth allows people to have
fewer children). Global warming and the end of cheap oil are new threats, but genetic engineering is a new opportunity.
Montgomery takes note of these opposing factors, and he expresses serious concern about the ongoing loss and degradation
of soils and the negative implications for future agriculture. But wisely, he stops short of alarmist projections of
Ruddiman is a professor emeritus of environmental sciences at the University of Virginia and author of Earth's Climate
and Plows, Plagues and Petroleum, among other books.
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