permaculture

["Lawrence F. London, Jr." <lflj@intrex.net>]

<http://www.geotimes.org/jan08/article.html?id=geomedia.html#BOOK>
Dirt: The Erosion of Civilizations
by David Montgomery.
University of California Press, 2007.
ISBN 0520248708.
Hardcover, $24.95.
Soil can bring down society, as detailed in Dirt
William Ruddiman

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
outright catastrophe.
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.