Dirt: The Erosion of Civilizations

I'm still on Christmas vacation, but have been reading dirt: The Erosion of Civilizations by David Montgomery as my idea of cheery relaxation reading. I wanted to offer a few comments as a mini-review (meaning I want to give my impressions without being held to any particular standard - I am still on vacation after all!)

Firstly, to state my prejudices on this issue - soil erosion is an issue that I've found difficult to form a clear opinion on (you can read as far as I'd gotten in the "Soil Loss" section of this Oil Drum piece. It's clearly important in the long term, it doesn't seem to be an acute crisis globally (though it's certainly serious in some places), and it's not easy to sort out the science and decide exactly how acute a problem it is. Conventional agriculture clearly discounts the problem and is focussed on short term profit over long-term health of the soil. On the other hand, there is clearly an over-alarmist wing of the environmental movement (epitomized by people like Lester Brown) that is prone to overstating the severity and immediacy of the issue. In between these extremes, I haven't really been able to figure out the situation to my satisfaction.


I'd like to understand the issue better, particularly since in one likely future of continued high oil prices, it seems probable that global civilization will try to greatly increase its take from the biosphere by making a lot of biofuels, which will presumably require using more fragile lands than we have used hitherto. In that scenario, soil erosion will become more important as a potential limitation on the growth and sustainability of civilization. Hence my picking up and reading dirt.

In terms of coverage, the book starts with a very short introduction to the natural processes of soil formation and erosion, and then almost immediately turns to an account of the role of soil problem in past civilizations, beginning with the Sumerians and the salinization of what is now Southern Iraq, then moves onto the role of the loss of soil in the demise of Greek and Roman civilization, the Mayans, neolithic Europe and various Pacific islands. There is also an extensive discussion of the history of soil problems in the early United States, and the modern era, beginning with the dust bowl, as well as problems in the Soviet Union and the Sahel of Africa.

I have pretty mixed feelings about the book. On the plus side, it's accessible - it's a clear and entertaining read that I had no difficulty finishing. It covers a lot of ground, and the author obviously knows a great deal about his field.

On the downside, if you've read books like Jared Diamond's Collapse, and Clive Ponting's New Green History of the World, a fair amount of this stuff is familiar ground. That's fair enough I guess - not all readers of dirt will have read those books and there's something to be said for being comprehensive. Still, it did mean that for me, the most interesting sections were the ones covering things I didn't know much or anything about. Like the evidence for boom-and-bust cycles associated with soil erosion in prehistoric Europe. For example, from pp85-86

German soils record periods of agriculturally induced soil erosion from hillsides followed by periods of soil formation lasting roughly five hundred to a thousand years. Soil profiles and alluvial sediments in southern Germany's Black Forest record several periods of rapid erosion associated with increased population. Neolithic artifacts in truncated soil profiles show that initial erosion after the arrival of agriculture about 4000 BC culminate in extensive soil loss by 2000 BC. Declining cereal pollen and a period of soil formation characterized a thousand years of lower population density until renewed erosion in Roman times peaked in the first centuries AD. A second cycle of agricultural decline, soil formation, and forest expansion followed until renewed population growth in the Middle Ages initiated a third, ongoing cycle.

I could have used a far longer exposition of the evidence for the collapse of neolithic agricultural societies in Europe.

A longer and fascinating-to-me account was the discussion of the neglect of soil conservation measures in the early post-revolutionary United States. Apparently, techniques of crop-rotation, fallowing, and manuring that were commonplace in Europe were all neglected in the US because it was cheaper to exhaust the soil and move west than it was to look after the soil properly. His hypothesis of the role of soil exhaustion in the start of the Civil War is particularly fascinating. For example, from p137:

But this still doesn't explain the vitriolic southern opposition to Lincoln's proposed territorial limitation on the spread of slavery. After all, slavery in the South was not itself directly at issue in the the election of 1860. Consider that slaves moved west along with their owners. At the time of the first national census in 1790, Maryland, Virginia, and the Carolinas held 92% of all the slaves in the South. Two decades later, after a ban on importing more slaves, the coastal states still held 75 percent of the South's slaves. By the 1830s and 1840s many of the slaveholders in the Atlantic states were breeding slaves for western markets. For plantation owners who stayed behind to work exhausted fields, the slave trade became an economic lifeboat. In 1836, more than one hundred thousand slaves were shipped out of Virginia. One contemporary source estimated that in the late 1850s slave breeding was the largest source of prosperity in Georgia. Census data for 1860 suggest that the value of slaves directly accounted for almost half the value of all personal property in the South, including land. By the start of the Civil War, almost 70 percent of the slaves in the South toiled west of Georgia.

Whether Missouri, Texas, and California would become slave states was a make-or-break issue for plantation owners moving west. The labor-intensive plantation economy of the South required conscripted labor. And for all practical purposes, the rapid soil erosion and soil exhaustion produced by slave-based agriculture condemned the institution of slavery to continuous expansion or collapse. So if slavery was banned in the West, slaves would lose their value - wiping out half of the South's wealth. Lincoln's election threatened slave owners with financial ruin.

It's certainly a compelling and plausible narrative!

But this brings me to my greatest problem with the book - I can't figure out how much of it to believe. Most of the book is structured as narrative exposition, with relatively light attention to detailed evidentiary discussion, and minimal guidance to the reader as to where the author is advancing ideas that are far from a scholarly consensus (a critique I would strongly make of Clive Ponting's books also).

For example, Montgomery discusses the role of soil exhaustion in weakening Rome prior to it's final collapse. He doesn't claim it's the only factor, but he does claim it's an important one. But what he doesn't give his reader much clue about is the fact that mainstream historians don't by and large believe this. For example, if you read something like Peter Heather's The Fall of the Roman Empire : A New History of Rome and the Barbarians you'll find internal Roman environmental problems largely dismissed as irrelevant, and instead a focus on the expansion of the Persian and Hunnic empires placing excessive stress on a Roman empire which had long-standing vulnerabilities due to the need to have more than a single emperor to cover an empire that was large compared to contemporary travel distances.

Where does the truth lie? I don't know, but Montgomery didn't give me much compelling reason to accept his account over that of others. Similarly, in his discussion of more current issues, I found more than a hint of an author who had accepted relocalist ideology without enough critical thinking (p243)

Similarly, as oil becomes more expensive it will make less sense to ship food halfway around the world: the unglobalization of agriculture will become increasingly attractive and cost effective. The average piece of organic produce sold in American supermarkets travels some 1500 miles between where it is grown and where it is consumed. Over the long run, when we consider the effect on the soil and on a post-oil world, markets for food may work better (although not necessarily more cheaply) if they are smaller and less integrated into a global economy, with local markets selling local food. As it becomes increasingly expensive to get food produced elsewhere to the people, it will become increasingly attractive to take food production to the people -- into the cities.

While this sounds superficially plausible, the whole idea that "food miles" is a useful measure of the environmental impact of producing and distributing food, or even the amount of oil required, doesn't really stand up to much quantitative analysis. And the idea that producing food in the city is ever going to happen at much scale sounds implausible to me: the whole point of cities is to concentrate all the non-food-producing trade-and-manufacture functions of society in a small area where they can happen more easily and efficiently. This has been true since Uruk was the largest city in the world, was true all through the era when society had no petroleum at all to power transport, and I'm sure will be true in the future: land in the city is too expensive to use very much of it for food production.  We're a long way from soil science here, and I think the fact that the author hasn't actually thought this through very deeply is showing.

So at the end of the day, although I'm glad I read it, I found myself unsatisfied by the book. It's enjoyable and interesting, but I'm looking forward to the beefier more thorough book that I hope Montgomery will write in ten years after he's thought harder about all the issues, engaged more thoroughly with opposing points of view and gained a deeper understanding of disciplines outside of his own that bear strongly on the points he's trying to make.