LET THEM EAT COLONIES - Dirt: The Erosion of Civilizations - David R. Montgomery

Dirt: The Erosion of Civilizations - David R. Montgomery (2007)


There is nothing new except what has been forgotten.


GUATEMALANS GROW SOME OF THE BEST COFFEE in the world, but most can't buy it at home. Neither can tourists. When I was there last I had to wake up on freeze-dried Mexican Nescafe, even though I can buy bags of freshly roasted Guatemalan coffee beans two blocks from my house in Seattle. Less well known than the story of how Europe carved out global empires is how the way Europeans treated their soil helped launch the exploration and history of the New World. Today's globalized agriculture that ships local produce overseas to wealthier markets reflects the legacy of colonial plantations established to help feed European cities.

Like many ancient agricultural societies, Europeans began working to improve their dirt once soil fertility and access to fresh land declined. But unlike the Mediterranean's intense spring and summer rains that promoted erosion from bare fields, western Europe's gentle summer rains and winter-spring snow pack limited erosion of even highly erodible loess soils when farmed. Moreover, by rediscovering soil husbandry western Europeans kept soil degradation and erosion at bay long enough to establish colonial empires that provided new land to exploit.

Farming spread from the Middle East into Greece and the Balkans between seven and eight thousand years ago. After moving into central Europe's easily worked loess, agriculture steadily advanced north and west, reaching Scandinavia about three thousand years ago. Consuming Europe's forest soils as it went, agriculture left a record of boom-and-bust cycles associated first with Neolithic and Bronze Age cultures, then Iron Age and Roman society, and most recently the medieval and modern periods when colonial empires began mining soil and sending both produce and profits back to feed Europe's increasingly urban populace-the Industrial Revolution's new class of landless peasants.

The first agricultural communities reached Europe's doorstep in southern Bulgaria around 5300 BC. At first farmers grew wheat and barley in small fields surrounding a few timber-framed buildings. Agricultural expansion into marginal land lasted about two thousand years before the agricultural potential of the region was fully exploited and persistent cultivation began to exhaust the soil. With no evidence of a climate shift, local populations grew and then declined as agricultural settlement swept through the area. Evidence for extensive late Neolithic soil erosion shows that agriculture spread from small areas of arable soils on the valley bottoms into highly erodible forest soils on steeper slopes. Eventually, the landscape filled in with small communities of several hundred people farming the area within about a mile of their village.

In these first European communities, population rose slowly before a rapid decline that emptied settlements out for five hundred to a thousand years, until the first traces of Bronze Age cultures then appeared. This pattern suggests a fundamental model of agricultural development in which prosperity increases the capacity of the land to support people, allowing the population to expand to use the available land. Then, having eroded soils from marginal land, the population contracts rapidly before soil rebuilds in a period of low population density.

This roller-coaster cycle characterizes the relation between population and food production in many cultures and contexts because the agricultural potential of the land is not a constant-both technology and the state of the soil influence food production. Improved agricultural practices can support more people with fewer farmers, but soil health eventually determines how many people the land can support. Floodplains continually receive nutrients from periodic flooding, but most other land cannot produce continuously high crop yields without intensive fertilization. So once a society comes to depend on upland farming it can cultivate a fraction of its land base at any one time, expand the area under cultivation, keep inventing new methods to counteract declining soil fertility, or face agricultural decline owing to degradation of soil fertility or gradual loss of the soil itself.

As agriculture spread north and west, people opened the first clearings in Europe's ancient forest to cultivate small plots for a few years at a time. Ash from burned vegetation fertilized newly cleared fields, helping to maintain initial crop yields until soil fertility declined enough to make it worth the hassle of moving on. The practice of abandoning worn-out fields periodically left fallow land to revegetate, first with grasses, then shrubs, and eventually back to forest. Ground cultivated for a few years then lay fallow for decades as the recolonizing forest gradually revived the soil, allowing clearing and planting again decades later.

Lake sediments, floodplain deposits, and soils record the postglacial evolution of the European landscape. From 7000 to 5500 BC stable environmental conditions left little evidence of human impact. Pollen preserved in lakebeds shows that Neolithic farmers opened clearings in dense forest as agriculture spread north from the Balkans. Cereal pollen shows up in soil profiles and sediment cores about 5500 BC in central Europe. Sediment cores from lakes provide the first incontrovertible evidence of substantial human impact on the central European landscape as massive amounts of charcoal and increased sedimentation-evidence for accelerated soil erosion-coincide with pollen evidence of extensive forest clearing and cereal cultivation around 4300 BC, when postglacial temperatures in Europe were at a maximum.

Farmers had arrived, but Europe was still wild. Lions and hippopotamuses lived along the Thames and Rhine rivers. While scattered bands of people foraged around Europe's lakes, rivers, and coast, a rich soil developed beneath huge oak, elm, and beech trees that stabilized loess-mantled slopes.

Germany's first farmers were drawn to the forest soil developed on silt dropped by glacial winds between the Rhine and Danube rivers. Several centuries later a second wave of related arrivals settled across northern Europe in a band stretching from Russia to France. Soon farmers grew wheat, barley, peas, and lentils on the region's fertile loess. Hunting and gathering thrived outside the loess belt.

Neolithic farmers kept livestock and lived in large longhouses near fields along rivers and streams. Houses were occupied for the several decades that the surrounding fields were kept under continuous cultivation. As isolated longhouses began coalescing into small hamlets, farming spread beyond the loess. More land was cleared and cultivated more continuously. By about 3400 Bc hunting for survival was history throughout central Europe.

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 culminated 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.

The soils at Frauenberg, a Neolithic site in southeastern Germany, record erosion of nearly the entire soil profile that began with early Bronze Age agriculture. Located on a hill that rises three hundred feet inside a bend in the Danube River, the site's combination of loess soils and a sweeping view of the surrounding country appealed to prehistoric farmers. Remnants of the original soil found in excavations at the site document three distinct periods of occupation corresponding to Bronze Age farming, a Roman fort, and a medieval monastery. Radiocarbon dating of charcoal pulled from soil horizons show that little erosion occurred as soil developed after deglaciation-until Bronze Age farming exposed clay-rich subsoil at the ground surface and eroded nearly the entire loess cover. Subsequent erosion slowed once the less erodible subsoil was exposed. Forest currently blankets the site, which still has limited agricultural potential.

Evidence from soils, floodplains, and lake sediments at sites across Germany shows that human impact has been the dominant influence on the landscape since the last glaciation. Erosion and human occupation occurred in tandem but not in regional pattern as expected for climate-driven events. Just as in ancient Greece and around the Mediterranean, central European cycles of agricultural clearing and erosion associated with population growth gave way to migration, population decline, and renewed soil formation.

Surveys of truncated hillslope soils at more than eight hundred sites along the Rhine River indicate that post-Roman agriculture stripped up to several feet of soil from hillslopes cleared of native forest. Erosion since AD 6oo has been about ten times the erosion rate before forest clearing through erosive runoff across bare, plowed fields. Similar soil surveys in Luxembourg report an average of twenty-two inches of lost soil and accelerated soil loss over more than 9o percent of the landscape. Despite the prevalence of Neolithic farming on central Europe's slopes, most of the region's modern agricultural land lies on valley-bottom deposits of reworked soil eroded off surrounding slopes.

Neolithic settlements in southern France are concentrated almost exclusively on limestone plateaus known today for bare white slopes sporting thin, rocky soil and sparse vegetation. When farmers arrived, these uplands were covered by thick brown soil that was far easier to plow than clay-rich valley bottoms. No longer suitable for cultivation, and considered something of a backwater, the limestone plateaus around Montpellier are used primarily for grazing. The harbor at nearby Marseille began filling with sediment soon after Greek colonists founded the city in 6oo BC. Sedimentation in the harbor increased thirtyfold after agricultural clearing spread up the steep slopes around the new town.

Early forest clearing in Britain led to extensive soil erosion long before the Roman invasion, as a growing population slowly cleared the forest to plow the slopes. High population density in Roman times exacerbated the loss, in part because better plows worked more of the landscape more often. The population fell dramatically as the empire collapsed, and took almost a thousand years to build back to the same level.

Floodplain sediments along Ripple Brook, a small tributary of the River Severn typical of lowland Britain, record a dramatic increase in deposition rates (and therefore hillslope soil erosion) in the late Bronze Age and early Iron Age. The relative abundance of tree pollen recovered from valley bottom sediments shows that between 2,900 and 2,500 years ago the heavily forested landscape was cleared and intensively farmed. A fivefold increase in floodplain sedimentation speaks to a dramatic increase in hillslope erosion.

Net soil loss averages between three and six inches since woodland clearance in England and Wales. Some watersheds have lost up to eight inches of topsoil. Although much of the loss occurred in the Bronze Age or Roman times, in some places substantial erosion occurred after medieval times. Just two hundred years after Nottinghamshire's famed Sherwood Forest was cleared for agriculture, the original forest soil has been reduced to a layer of thin brown sand over rock. Just as in Lebanon's ancient cedar forest, most of the topsoil is now gone from Robin Hood's woods.

Across the border in Scotland, radiocarbon dating of a sediment core recovered from a small lake west of Aberdeen provides a continuous record of erosion from the surrounding slopes for the past ten thousand years. Sediment deposition rates in the lake, and thus erosion rates on the surrounding slopes, were low for five thousand years under postglacial shrub land and birch forest. Following the arrival of agriculture, pollen from crops and weeds coincide with a threefold increase in the sediment deposition rate. After the Bronze and Iron Ages, erosion decreased dramatically for almost two thousand years as native plants regenerated across a largely abandoned landscape-until erosion accelerated again in the modern era.

Similar cores taken from small lakes in southern Sweden also record the transition from little preagricultural erosion to much higher rates after arrival of the plow. One from Lake Bussjosjo shows that forest stabilized the landscape from 7250 to 750 BC until erosion accelerated following forest clearing. Erosion increased further under intensified agriculture in the sixteenth and seventeenth centuries. A core pulled from Havgardssjon provides a 5,ooo-year record of vegetation and erosion. The archaeological record around the lake has no Bronze or Iron Age artifacts. Lakebed sediments piled up four to ten times faster after agricultural settlement began around AD iioo. All across the glaciated terrain of Scandinavia, Scotland, and Ireland, farmers could not make a living until enough ice-free time passed to build soil capable of sustaining cultivation.

Put simply, European prehistory involved the gradual migration of agricultural peoples, followed by accelerated soil erosion, and a subsequent period of low population density before either Roman or modern times. Just as in Greece and Rome, the story of central and western Europe is one of early clearing and farming that caused major erosion before the population declined, and eventually rebounded.

As the Roman Empire crumbled, the center of its civilization shifted north. Abandoning Rome as the capital, Diocletian moved his government to Milan in AD 300. When Theodoric established the Gothic kingdom of Italy on the ruins of the Roman Empire, he chose Verona as his new capital in the north. Even so, many of northern Italy's fields lay fallow for centuries until an eleventh-century program of land reclamation began returning them to cultivation. After several centuries of sustained effort, most of northern Italy's arable land was again under cultivation, supporting prosperous medieval cities that nurtured a renaissance of literature and art.

As northern Italy's population rebounded, intensive land use increased silt loads in the region's rivers enough to attract the attention of Leonardo da Vinci and revive the Roman art of river engineering and flood control. Intensive cultivation on hillside farms spread into the Alps, producing similar results on the Po River as Roman land use had on the Tiber River. Eventually, after eight centuries of renewed cultivation, even northern Italy's soil faltered. Mussolini's Fascist government spent about half a billion dollars on soil conservation in the 1930s.

Because Rome imported most of its grain from North Africa, Egypt, and the Middle East, it made fewer demands on the soils of the Po Valley, Gaul (France), Britain, and the Germanic provinces. Roman agriculture in its western European provinces was mostly confined to river valleys; for the most part hillslopes that had been farmed in the Bronze Age remained forested until medieval times. It is no coincidence that these northern provinces fed the western European civilization that centuries later rose from the ruins of the Roman Empire.

After the empire collapsed, many Roman fields north and west of the Alps reverted to forest or grass. In the eleventh century, farmers worked less than a fifth of England. With half in pasture and half in crops left fallow every other year, this meant that only about 5 percent of the land was plowed each year. Less than io percent of Germany, Holland, and Belgium were plowed annually in the Middle Ages. Even in the most densely populated parts of southern France, no more than 15 percent of the land was cultivated each year.

In early medieval times, townships controlled a given area of land held in common by all villagers. Each household received a share of land to cultivate each season, after which the fields reverted to communal use. The general rule was to plant a crop of wheat, followed by beans and then a fallow season. After the harvest, cattle wandered the fields turning crop stubble into meat, milk, and manure.

Columbia University professor Vladimir Simkhovitch saw the structure of medieval village communities as an adaptation to farming degraded soils. He noted that a similar pattern of land use and ownership characterized many old villages throughout Europe where the land holdings of individual peasants had not been fenced off and enclosed. Barns, stables, and vegetable gardens were always near homesteads, but fields were divided into a patchwork of land belonging to individual farmers. Each farmer might own ten or more parts of three different fields managed collectively for a crop of wheat or rye, then oats, barley, or beans, and finally fallow pasture.

Simkhovitch argued that an inconvenient arrangement in which a farmer had no say in the rotation or type of tillage used on his fieldswhich could be quite distant from each other-must have been adopted throughout the continent for good reason. He doubted that such arrangements were simply inherited from Roman villas or imposed under feudal ism. Simkhovitch hypothesized that an individual farmer could not keep enough cattle to maintain the fertility of his plot, but a village's livestock could collectively fertilize the commons enough to slow their degradation. Simkhovitch believed that the already degraded state of the land made cooperation the way to survive-a notion contrary to the "tragedy of the commons" in which collective farming was thought to have caused land degradation in the first place.

Figure to. Miniature from an early-sixteenth-century manuscript of the Middle English poem God Spede ye Plough (original held at the British Museum).

Simkhovitch argued that by failing to maintain their soil, ancient societies failed themselves. "Go to the ruins of ancient and rich civilizations in Asia Minor, Northern Africa or elsewhere. Look at the unpeopled valleys, at the dead and buried cities.... It is but the story of an abandoned farm on a gigantic scale. Depleted of humus by constant cropping, land could no longer reward labor and support life; so the people abandoned it."' The introduction of alfalfa and clover into European agriculture helped rebuild soil fertility, Simkhovitch insisted. Noting that there were no hay fields before the sixteenth and seventeenth centuries, he suggested that enclosure of common fields allowed converting enough land to pasture to raise the cattle and sheep needed to manure the land and thereby increase crop yields.

The conventional explanation for the low crop yields of medieval agriculture invoked a lack of enough pasture to supply cultivated land with the manure needed to sustain soil fertility. Until recently, historians generally considered this to reflect ignorance of the value of manure in maintaining soil fertility. It now seems as likely that medieval farmers knew that keep ing land in pasture restored soil fertility, but impatience and economics made the required investments unattractive to folks perpetually focused on maximizing this year's harvest.

After centuries when post-Roman agricultural methods and practices limited crop yields, population growth accelerated when an extended run of good weather increased crop yields during medieval times. As the population grew, the clearing of Europe's remaining forests began again in earnest as new heavy plows allowed farmers to work root-clogged lowlands and dense river valley clays. From the eleventh to the thirteenth century, the amount of cultivated land more than doubled throughout western Europe. Agricultural expansion fueled the growth of towns and cities that gradually replaced feudal estates and monasteries as the cornerstone of Western civilization. Europe's best soils had been cleared of forest by about AD 12oo. By the close of the thirteenth century, new settlements began plowing marginal lands with poor soils and steep terrain. Expansion of the area of planted fields allowed the population to keep growing. Doubling over a couple of centuries, by AD 1300 Europe's population reached eighty million.

Powerful city-states arose where the most land was plowed under, particularly in and near the fertile lowlands of Belgium and Holland. By the middle of the fourteenth century, farmers were plowing most of western Europe's loess to feed burgeoning societies and their new middle class. Already hemmed in by powerful neighbors, Flemish and Dutch farmers adopted crop rotations similar to those still used today.

The catastrophic European famine of 1315-17 provides a dramatic example of the effect of bad weather on a population near the limit of what its agricultural system could support. Every season of 1315 was wet. Waterlogged fields ruined the spring sowing. Crop yields were half of normal and what little hay grew was harvested wet and rotted in barns. Widespread food shortages in early 1316 compelled people to eat the next year's seed crop. When wet weather continued through the summer, the crops failed again, and wheat prices tripled. The poor could not afford food and those with money-even kings-could not always find it to buy. Bands of starving peasants turned to robbery. Some even reportedly resorted to cannibalism in famine-stricken areas.

Malnutrition and starvation began to haunt western Europe. The population of England and Wales had grown slowly but steadily after the Norman invasion until the Black Death of 1348. Major famines added to the toll. The population of England and Wales fell from about four million in the early 13006 to about two million by the early 1400s. Europe's population dropped by a quarter.

After the Black Death depopulated the countryside, landlords competed to retain tenant farmers by granting them lifelong or inheritable rights to the land they worked in exchange for modest rents. As the population rebounded, a final push of agricultural expansion filled out the landscape with farms in the early sixteenth century. Starting in the late 15005 landlords motivated by the promise of getting higher rents from leasing land at inflated rates began enclosing lands formerly grazed in common. Already out of land and surrounded by powerful neighbors, the Dutch started their ambitious campaign to take land from the sea.

John Fitzherbert's 1523 Book of Surveying, the first work on agriculture published in English, held that the way to increase the value of a township was to consolidate rights to common fields and pasture into single enclosed tracts next to each farmer's house. Over the next several centuries this idea of reorganizing the commons to give every farmer three acres and a cow evolved into transforming the English countryside into large estates, portions of which could be rented out profitably to tenant farmers. Except for the peasants working the land, most thought that privatizing the commons would injure none, and benefit all by increasing agricultural production.

In the tumultuous sixteenth and seventeenth centuries much of England's agricultural land changed hands in Henry VIII's war against the Catholic Church, the wars of succession, and the English Civil War. The insecurity of land tenure discouraged investing in land improvement. By the second half of the seventeenth century, some argued that England should adopt the Flemish custom of agricultural leases under which the owner would pay a specified sum to the tenant if four impartial persons, two selected by the landlord and two by the tenant, agreed that the soil had been improved at the end of the lease.

As Europe's climate slid from the medieval warm period into the Little Ice Age (which lasted from about AD 1430 to 1850), extended cold periods meant shorter growing seasons, reduced crop yields, and less arable land. Perennially living on the edge, the lower classes were vulnerable to severe food shortages after bad harvests. Governments monitored the price of bread to gauge the potential for social instability.

Desire for land reform among the peasantry, fueled by instability and shortages, would help trigger the Reformation. Land held by the Church had grown over the centuries far beyond the fields cleared by monks, because the Church seldom relinquished land bequeathed by the faithful. Instead, bishops and abbots rented out God's land to poor, land-hungry peasants. By the fifteenth century the Church, which owned as much as four-fifths of the land in some areas, overtook the nobility as Europe's largest landlord. Monarchs and their allies seeking to seize church lands harnessed widespread resentment among tenants. Popular support for the Reformation rested as much on desire for land as the promise of religious freedom.

An increasing demand for crops meant less pasture, little overwinter animal fodder, and not enough manure to sustain soil fertility. As the population kept rising, intensively cultivated land rapidly lost productive capacity-increasing the need to plant more marginal land. Shortage of vacant land to plow helped motivate the rediscovery of Roman agricultural practices such as crop rotations, manuring, and composting.

Renewed curiosity about the natural world also stimulated agricultural experimentation. In the sixteenth century, Bernard Palissy argued that plant ashes made good fertilizer because they consisted of material that the plants had pulled from the soil and could therefore reuse to fuel the growth of new plants. In the early 16oos Belgian philosopher Jan Baptista van Helmont tried to settle the question of whether plants were made of earth, air, fire, or water. He planted a seedling tree in two hundred pounds of soil, protected it from dust, and let it grow for five years, adding only water. Finding that the tree had grown by one hundred and seventy pounds, whereas the soil had lost an insignificant two ounces, van Helmont concluded that the tree had grown from water-the only thing added to the process. Given that the soil had lost but a minuscule fraction of the weight of the tree, he dismissed the potential for earth to have contributed to the tree's growth. I doubt that he ever seriously considered air as a major contributor to the mass of the tree. It took a few more centuries before people discovered carbon dioxide and came to understand photosynthesis.

In the meantime, agricultural "improvers" came to prominence in the seventeenth century once the landscape was fully cultivated. Most of the low hills and shallow valleys of the Netherlands are covered by quartz-rich sand ill suited for agriculture. Supporting a growing population on their naturally poor soils, the Dutch began mixing manure, leaves, and other organic waste into their dirt. Working relatively flat land where erosion was not a problem, over time they built up dark, organic-rich soils to as much as three feet thick. Lacking more land, they made soil. As the Dutch had, the Danes improved their sandy dirt enough to more than double their harvests by adopting crop rotations including legumes and manure. In other words, they readopted key elements of Roman agriculture.

Soil improvement theories spread to England where population growth motivated innovation to increase crop yields. Seventeenth-century agriculturalists broadened the range of fodder crops, developed more complex crop rotations, used legumes to improve soil fertility, and used more manure to maintain soil fertility. In addition, introduction of the Flemish practice of growing clover and turnips as ground cover and winter fodder changed the ratio of animals to land, increasing the availability of manure. Improvers promoted clover as a way to rejuvenate fields and regain high crop yields: clover increased soil nitrogen directly through the action of nitrogen-fixing bacteria in nodules on the plant roots and, as feed for cattle, also produced manure.

Despite cold winters, wet summers, and shorter growing seasons, English agriculture increased its yields per acre from 1550 to 1700, in what has been called the "yeoman's agricultural revolution." At the start of the seventeenth century, between a third and half of English agricultural land was held by yeomen-small freehold farmers and those with long-term leases. In the early 16oos farmers obsessed with fertilization began plowing into their fields lime, dung, and almost any other organic waste that could be obtained. Farmers also began shifting away from fixed grain lands and pasture and began planting fields for three or four years, and then putting them to pasture for four or five years before plowing them up once again. This new practice of "convertible husbandry" resulted in much higher crop yields, making it attractive to plow up pastures formerly held in common.

The new breed of land improvers also pioneered systems to drain and farm wetlands. They experimented with plow design and with ways to improve soil fertility. Upper-class landowners advocated enclosing pasturelands and growing fodder crops (especially turnips) to provide winter feed for cattle and increase the supply of manure. Adopting the premise that communal land use degraded the land, an idea now called the "tragedy of the commons," agricultural improvers argued that enclosing the commons into large estates was necessary to increase agricultural output. A Parliament of property owners and lawyers passed laws to fence off fields that had been worked in common for centuries. Land enclosures increased crop yields and created tremendous wealth for large landowners, but the peasants thus fenced out-whose parents ate meat, cheese, and vegetables raised by their own efforts-were reduced to a diet of bread and potatoes.

Soil husbandry began to be seen as the key to productive, profitable farming. Gervase Markham, one of the first agricultural writers to write in English instead of Latin, described soils as various mixtures of clay, sand, and gravel. What made good soil depended on the local climate, the character and condition of the soil, and the local plants (crops). "Simple Clays, Sands, or Gravels together; may be all good, and all fit to bring forth increase, or all ... barren." Understanding the soil was the key to understanding what would grow best, and essential to keeping a farm productive. "Thus having a true knowledge of the Nature and Condition of your ground.... it may not only be purged and clensed ... but also so much bettered and refined." 2

Prescribing steps to improve British farms, Markham recommended using the right type of plow for the ground. He advised mixing river sand and crushed burned limestone into the soil, to be followed by the best manure to be had-preferably ox, cow, or horse dung. In describing procedures for improving barren soils, Markham advocated growing wheat or rye for two years in a field, and then letting sheep graze and manure it for a year. After the sheep, several crops of barley were to be followed in the seventh year by peas or beans, and then several more years as pasture. After this cycle the ground would be much improved for growing grain. The key to sustaining soil fertility was to alternate livestock and crops on the same piece of ground.

Equally important, although it received less attention, was preventing erosion of the soil itself. Markham advised plowing carefully to avoid collecting water into erosive gullies. Good soil was the key to a good farm, and keeping soil on the farm required special effort even on England's gentle rolling hills.

Almost half a century later, on April 29, 1675, John Evelyn presented a "Discourse on Earth, Mould and Soil" to England's Royal Society for the Improvement of Natural Knowledge. In addressing what he feared could be considered a topic unworthy of the assembled luminaries he invited the society's fellows to descend from contemplating the origin of heavenly bodies and focus instead on the ground beneath their feet. He implored them to consider both how soil formed and how the nation's long-term prosperity depended on improving the kingdom's dirt.

Evelyn described how distinct layers of topsoil and subsoil developed from the underlying rock. "The most beneficial sort of Mould or Earth, appearing on the surface ... is the natural (as I beg leave to call it) underturf-Earth and the rest which commonly succeeds it, in Strata's or layers, 'till we arrive to the barren, and impenetrable Rock." Of the eight or nine basic types of soil, the best was the rich topsoil where mineral soil mixed with vegetation.

I begin with what commonly first presents it self under the removed Turf, and which, for having never been violated by the Spade, or received any foreign mixture, we will call the Virgin Earth; ... we find it lying about a foot deep, more or less, in our Fields, before you come to any manifest alteration of colour or perfection. This surface-Mold is the best, and sweetest, being enriched with all that the Air, Dews, Showers, and Celestial Influences can contribute to it.

The ideal topsoil was a rich mixture of mineral and organic matter introduced by "the perpetual and successive rotting of the Grass, Plants, Leaves, Branches, [and] Moss ... growing upon it."3

Regaling his audience with the works of Roman agriculturalists, Evelyn described how to improve soil with manure, cover crops, and crop rotations. Like the Romans, Evelyn used odor, taste (sweet or bitter), touch (slippery or gritty), and sight (color) to evaluate a soil. He described different types of manure and their effects on soil fertility, as well as the virtues of growing legumes to improve the soil.

Echoing Xenophon, Evelyn held that to know the soil was to know what to plant. One could read what would grow best by observing what grew naturally on a site. "Plants we know, are nourished by things of like affinity with the constitution of the Soil which produces them; and therefore 'tis of singular importance, to be well read in the Alphabet of Earths and Composts." Because soil thickened as organic material supplied from above mixed with the rotting rocks below, sustaining good harvests required maintaining the organic-rich topsoil ideal for crops. Mineral subsoil was less productive, but Evelyn believed that nitrous salts could resuscitate even the most exhausted land. "I firmly believe, that were Salt Peter ... to be obtain'd in Plenty, we should need but little other Composts to meliorate our Ground."4 Well ahead of his time, Evelyn anticipated the value of chemical fertilizers for propping up-and pumping up-agricultural production.

By the start of the eighteenth century, improving farmland was seen as possible only through enclosing under private ownership enough pasture to keep livestock capable of fertilizing the plowed fields. Simply letting the family cow poop on the commons would not do. The need for manure imposed an inherent scale to productive farms. Too small a farm was a recipe for degrading soil fertility through continuous cropping. Although very large farms turned out to mine the soil itself, this was not yet apparent-and Roman experience in this regard was long forgotten. To the individual farmer, enclosure was seen as the way to ensure a return on investing to improve soil fertility from well-manured ground.

Figure ii. Title page to The Whole Art of Husbandry, published in 1708.

Agricultural writers maintained that the key to good crop yields was to keep an adequate supply of manure on hand-to keep the right ratio of pasture to field on each farm, or estate as the case increasingly became. "The Arable-land must be proportioned to the quantity of Dung that is raised in the Pasture, because proper Manure is the chief Advantage of Arable-ground."5 The key to increasing agricultural productivity was seen to lie in bringing stock raising and cereal production into proximity and returning manure to the fields.

Still, not all land was the same; improvements needed to be tailored to the nature of the soil. British farmland consisted of three basic types: uplands lying high enough not to flood, lowlands along rivers and wetlands, and land susceptible to inundation by the sea. These lands had different vulnerabilities.

On hillslopes, the thin layer of a foot or so of topsoil was essential to good farming. Such lands were naturally prone to erosion and vulnerable to poor farming practices. On lowlands, the soil was replenished by upland erosion that produced fine deposits downslope. "As to Lands lying near Rivers, the great Improvement of them is their over-flowing, which brings the Soil of the Uplands upon them, so as that they need no other mending though constantly mowed."6

Working land too hard for too long would reduce soil fertility. Sloping land was particularly vulnerable. "Where Lands lie upon the sides of Hills ... great care must be taken not to plow them out of heart." 7 Recognizing such connections, most landlords obliged their tenants to fallow fields every third year, and every other year if manure was unavailable. Reviving worn-out fields proved highly profitable-when enough land was enclosed. Under the banner of agricultural improvement, Parliament repeatedly authorized land enclosures that created large estates at the expense of common land, enriching the landed gentry and turning peasants into paupers.

English farmers gradually increased per-acre grain yields to well above medieval crop yields of twice the seeded amount, which were no greater than early Egyptian crop yields. Traditionally, historians attributed increased yields between the Middle Ages and the Industrial Revolution to the introduction of clover and other nitrogen-fixing plants into crop rotations in the eighteenth and early nineteenth centuries. Crop yields at the start of the eighteenth century were not all that much greater than medieval levels, implying that increased agricultural production came largely from expanding the area cultivated rather than improved agricultural methods. Wheat yields had risen by just a bushel and a half over medieval yields of ten to twelve bushels per acre. Yet by i8io yields had almost doubled. By i86o they had reached twenty-five to twenty-eight bushels an acre.

Increasing labor needed to harvest an acre of crops implies that crop yields rose over time. The number of person days required to harvest an acre of wheat increased from about two around 16oo to two and a half by the early 170os, and then to just over three in i86o. Overall crop yields increased by two and a half times in the six hundred years from I2oo to i8oo. So despite increasing yields, the tenfold population increase primarily reflected expansion of the area under cultivation.

During the same period about a quarter of England's cultivated land was transformed from open, common fields to fenced estates. By the end of the eighteenth century, common fields had almost disappeared from the English landscape. Loss of the common lands meant the difference between independence and destitution for rural households that had always kept a cow on the commons. Dispossessed, landless peasants with no work depended on public relief for food. Seeing the economic effects of the transformation of the English countryside, Board of Agriculture secretary Arthur Young came to see land enclosure as a dangerous trend destroying rural self-sufficiency. But enclosing and privatizing the last vestiges of communal property conveniently pushed a new class of landless peasants to seek jobs just as laborers were needed in Britain's industrializing cities.

By the early nineteenth century, British farms had developed into a mixed system of fields and pastures. A roughly equal emphasis on cultivation and animal husbandry provided for constant enrichment of the soil with large quantities of manure, and cover crops of clover and legumes.

English population growth mirrored increases in agricultural production from after the Black Death to the Industrial Revolution. Between 1750 and 1850, England's cereal production and population both doubled. Did a growing human population drive up demand for agricultural products? Or did increased agricultural production enable faster population growth? Regardless of how we view the causality, the two rose in tandem.

Nonetheless, as the population grew, the European diet declined. With almost all of the available land in cultivation, Europeans increasingly sur vived on vegetables, gruel, and bread. Without surplus grain to feed animals through the winter, and later without access to the commons to graze cattle, eating meat became an upper-class privilege. An anonymous pamphlet published in London in 1688 attributed massive unemployment to Europe's being "too full of people" and advised wholesale emigration to America. At the start of the nineteenth century, most Europeans survived on 2,ooo calories a day or less, about the average for modern India and below the average for Latin America and North Africa. European peasants toiling in their fields ate less than Kalahari Desert bushmen who worked just three days a week.

Despite increased agricultural production, food prices rose dramatically in both England and France during the sixteenth and seventeenth centuries. Persistent famine between 169o and 1710 stalked a population larger than could be reliably fed. While enlightened Europe lived on the edge of starvation, Britain largely escaped the peasant unrest that sparked the French Revolution by importing lots of food from Ireland.

Real hunger, as much as the hunger for empire or religious freedom, helped launch Europe toward the New World. Beginning with Spain, the thickly settled and most continuously cultivated parts of western Europe most aggressively colonized the New World. Before the Romans, the Phoenicians and Greeks had settled Spain's eastern coast, but Iberian agriculture remained primitive until aggressive Roman cultivation. The Moors introduced intensive irrigation to Spain a few centuries after the fall of Rome. More than five hundred years of Moorish agriculture further degraded Spanish soils. By the fifteenth century, the fertile soils of the New World looked good to anyone working Spain's eroded and exhausted soil. Within a few generations, Spanish and Portuguese farmers replaced gold-seeking conquistadors as the primary emigrants to Central and South America.

By contrast, it took more than a century after Columbus for northern European farmers to begin heading west for religious and political freedom-and tillable land. English and French peasants were still clearing and improving land in their own countries. German peasants were busy plowing up newly acquired church land. Germany did not even begin to establish overseas colonies until the 185os. The northern European rush to America did not kick into full gear until the late nineteenth century. Relatively few people from northwestern Europe migrated to America while there was still fertile land at home.

As continental Europe filled in with farms, peasants moving up into the hills set the stage for crisis once eroding slopes could no longer support a hungry population. When eighteenth-century farmers began clearing steep lands bordering the French Alps, they triggered landslides that carried off soils and buried valley bottom fields under sand and gravel. By the late eighteenth century, the disastrous effects of soil erosion following deforestation of steep lands had depopulated portions of the Alps. Nineteenth-century geographer Jean-Jacques-Elisee Reclus estimated that the French Alps lost a third to more than half their cultivated ground to erosion between the time Columbus discovered America and the French Revolution. By then people crowding into cities in search of work could neither grow nor pay for food.

Figure i2. Mid-eighteenth-century agricultural landscape (Diderot's Encyclopedie, Paris, 175i-8o).

A decade of persistent hunger laid the groundwork for revolution as the homeless population of Paris tripled. According to the bishop of Chartres, conditions were no better in the countryside, where "men were eating grass like sheep, and dying like flies." Revolutionary fervor fed on long lines at bakeries selling bitter bread full of clay at exorbitant prices. Anger over the price of the little available for sale and the belief that food was being withheld from the market spurred on the mobs during key episodes of the French Revolution.

Dissolution of the nobility's large estates freed peasants to grab still forested uplands. Clearing steep slopes triggered debris torrents that scoured uplands and buried floodplain fields under sand and gravel. Large areas of upper Provence were virtually abandoned. Between 1842 and 1852 the area of cultivated land in the lower Alps fell by a quarter from the ravages of landslides and soil erosion.

French highway engineer Alexandre Surell worked on devising responses to the landslides in the Upper Alps (Hautes-Alpes) in the early 1840s. He noted the disastrous consequences that followed when cultivation pushed into the mountains. Torrents cascading off denuded slopes buried fields, villages, and their inhabitants. Everywhere the forests had been cut there were landslides; there were no landslides where the forest remained. Connecting the dots, Surell concluded that trees held soil on steep slopes. "When the trees became established upon the soil, their roots consolidate and hold it by a thousand fibres; their branches protect the soil like a tent against the shock of sudden storms."8

Recognizing the connections between deforestation and the destructive torrents, Surell advocated an aggressive program of reforestation as the way to a secure livelihood for the region's residents. Plowing steep land was an inherently short-term proposition. "In the first few years following a clearing made in the mountains, excellent crops are produced because of the humus coat the forest has left. But this precious compost, as mobile as it is fecund, lingers not for long upon the slopes; a few sudden showers dissipate it; the bare soil quickly comes to light and disappears in its turn."9 Measures to protect the forest and the soil were often unsuccessful because it was more immediately profitable to clear and plant, even though deforested slopes could not be farmed for long.

While Surell fretted about how to restore upland forests, George Perkins Marsh toured France during his service as American ambassador in Italy. Witnessing the long-term effects of forest clearing on both steep land and valley fields, Marsh saw that bare, eroded mountain slopes unfit for habitation no longer absorbed rainfall but rapidly shed runoff that picked up sediment and dumped it on valley fields.

An observant tourist, Marsh feared the New World was repeating Old World mistakes.

The historical evidence is conclusive as to the destructive changes occasioned by the agency of man upon the flanks of the Alps, the Apennines, the Pyrenees, and other mountain ranges in Central and Southern Europe, and the progress of physical deterioration has been so rapid that, in some localities, a single generation has witnessed the beginning and the end of the melancholy revolution.... It is certain that a desolation, like that which has overwhelmed many once beautiful and fertile regions of Europe, awaits an important part of the territory of the United States, and of other comparatively new countries over which European civilization is now extending its sway.10

Marsh compared what he saw in Europe to New York State, where the upper Hudson River was filling with sediment as farmers plowed up the forest. He held that gentle slopes in areas where rainfall was evenly distributed throughout the seasons could be reasonably farmed on a permanent basis. Ireland, England, and the vast Mississippi basin fit this definition. In contrast, steep terrain could not be plowed for long without triggering severe erosion, especially in regions with torrential rains or parching droughts.

French deforestation peaked in the early i8oos. In i86o the marquis de Mirabeau estimated that half of France's forest had been cleared in the previous century. Inspector of Forests Jonsse de Fontaniere echoed Surell's stark assessment of the prospects of the High Alps. "The cultivators of the land ... will be compelled ... to abandon the places which were inhabited by their forefathers; and this solely in consequence of the destruction of the soil, which, after having supported so many generations, is giving place little by little, to sterile rocks."1 i

French authorities began passing laws to protect and restore public and private woodlands in 1859. Clearing of European forests accelerated briefly, though, when twenty-eight thousand walnut trees were cut to supply European manufacturers with gunstocks during the American Civil War. Despite such profiteering, by 1868 almost two hundred thousand acres of the High Alps had been replanted with trees or restored to meadow.

Touring southern France before the Second World War, Walter Lowdermilk found intensive farming practiced on both steep slopes and valley floors. Some farmers maintained hillslope terraces like those built by the ancient Phoenicians. Lowdermilk marveled over how in eastern France, where terracing was uncommon, farmers would collect soil from the lowest furrow on a field, load it into a cart, haul it back up the slope, and dump it into the uppermost furrow. Centuries ago when this practice began, peasant farmers knew that they had upset the balance between soil production and erosion, and that people living on the land would inherit the consequences. They probably did not appreciate how far they were ahead of Europe's gentlemen scientists in understanding the nature of soils.

At the May 5, 1887, meeting of the Edinburgh Geological Society, vice president James Melvin read from an unpublished manuscript by James Hutton, the Scottish founder of modern geology. The rediscovered work revealed the formative geologic insights Hutton had gained from farming the land, observing and thinking about relationships among vegetation, soil, and the underlying rocks. In particular, Melvin appreciated the parallels between Hutton's century-old musings and Darwin's newly published book on worms.

Hutton saw soil as the source of all life where worms mix dead animals with fallen leaves and mineral soil to build fertility. He thought that hillslope soils came from the underlying rock, whereas valley bottom soils developed on dirt reworked from somewhere upstream. Soil was a mix of broken rock from below and organic matter from above, producing dirt unique to each pairing of rocks and plant communities. Forests generally produced fine soils. "[A forest] maintains a multitude of animals which die and are returned to the soil; secondly, it sheds an annual crop of leaves, which contribute in some measure to the fertility of the soil; and lastly, the soil thus enriched with animal and vegetable bodies feeds the worms ... which penetrate the soil, and introduce fertility as they Multiply. 1112 Anticipating Darwin in recognizing the role of worms in maintaining soil fertility, Hutton also understood the role of vegetation in establishing soil characteristics. The visionary geologist saw soil as the living bridge between rock and life maintained by returning organic matter to the soil.

At the close of the eighteenth century-long before Melvin rediscovered Hutton's lost manuscript-Hutton argued with Swiss emigre Jean Andre de Luc over the role of erosion in shaping landscapes. De Luc held that ero sion stopped once vegetation covered the land, freezing the landscape in time. At issue was whether topography was the ultimate fossil, left over from Noah's flood. Hutton questioned de Luc's view, pointing to the turbid waters of flooding rivers as evidence of erosion endlessly working to lower mountains. "Look at the rivers in a flood;-if these run clear, this philosopher [de Luc] has reasoned right, and I have lost my argument. Our clearest streams run muddy in a flood. The great causes, therefore, for the degradation of mountains never stop as long as there is water to run; although as the heights of mountains diminish, the progress of their diminution may be more and more retarded."13 In other words, steeper slopes eroded faster, but all land eroded.

Figure 13. French farmers loading soil from their lowest furrow into a cart to be hauled back uphill in the late 1930s (Lowdermilk 1953, 22, fig. 12).

A few years later Hutton's disciple, geologist and mathematician John Playfair, described how weathering created new soil at about the rate that erosion removed it. He saw topography as the product of an ongoing war between water and rock. "Water appears as the most active enemy of hard and solid bodies; and, in every state, from transparent vapour to solid ice, from the smallest rill to the greatest river, it attacks whatever has emerged above the level of the sea, and labours incessantly to restore it to the deep."14

Adopting Hutton's radical concept of geologic time, Playfair saw how erosion worked gradually to destroy land that dared rise above sea level. Yet the land remained covered by soil despite this eternal battle.

The soil, therefore, is augmented from other causes, ... and this augmentation evidently can proceed from nothing but the constant and slow disintegration of the rocks. In the permanence, therefore, of a coat of vegetable mould on the surface of the earth, we have a demonstrative proof of the continual destruction of the rocks; and cannot but admire the skill, with which the powers of the many chemical and mechanical agents employed in this complicated work, are so adjusted, as to make the supply and the waste of the soil exactly equal to one another.15

The soil maintained a uniform thickness over time even as erosion continuously reshaped the land.

About the time Hutton and Playfair were trying to convince Europe's learned societies of the dynamic nature of soil over geologic time, parallel arguments about the controls on the size and stability of human populations were brewing. Europeans began questioning the proposition that greater population led to greater prosperity. On an increasingly crowded continent, limits to human population growth were becoming less abstract.

The Reverend Thomas Malthus infamously proposed that a boom-andbust cycle characterizes human populations in his 1798 Essay on the Principle of Population. A professor of political economy at Haileybury College, Malthus argued that exponentially growing populations increase faster than their food supply. He held that population growth locks humanity in an endless cycle in which population outstrips the capacity of the land to feed people. Famine and disease then restore the balance. British economist David Ricardo modified Malthus's ideas to argue that populations rise until they are in equilibrium with food production, settling at a level governed by the amount of available land and the technology of the day. Others like the marquis de Condorcet argued that necessity motivates innovation, and that agriculture could keep up with population growth through technological advances.

Malthus's provocative essay overlooked how innovation can increase crop yields and how greater food production leads to even more mouths to feed. These shortcomings led many to discredit Malthus because he treated food production and food demand as independent factors. He also neglected to consider the time required for agriculturally accelerated erosion to strip topsoil off a landscape or for intensive cultivation to deplete soil fertility. Although his views seemed increasingly naive as England's population kept growing, political interests seeking to rationalize exploitation of Europe's new working class embraced them.

Malthus's ideas challenged prevalent views of human impact on nature in general and on the soil in particular. In Political justice, published five years before Malthus's essay, William Godwin captured the fashionable view of the inevitable progress of human dominion over nature. "Threefourths of the habitable globe are now uncultivated. The improvements to be made in cultivation, and the augmentations the earth is capable of receiving in the article of productiveness, cannot, as yet, be reduced to any limits of calculation. Myriads of centuries of still increasing population may pass away, and the earth be yet found sufficient for the support of its inhabitants." 16 In Godwin's view, scientific progress promised endless prosperity and ongoing advances in material well-being. The basic perspectives of Malthusian pessimism and Godwinian optimism still frame debates about the relationships between human populations, agricultural technology, and political systems.

Published early in the Industrial Revolution, Malthus's ideas were adopted by those wanting to explain poverty as the fault of the poor themselves, rather than an undesirable side effect of land enclosure and industrial development. Taken at face value, Malthus's ideas absolved those at the top of the economic ladder from responsibility for those at the bottom. In contrast, Godwin's ideas of material progress became associated with the movement to abolish private property rights. Naturally, Malthus would have more appeal for a Parliament of wealthy landowners.

As intellectuals debated the earth's capacity to provide sustenance, the working classes continued to live on the verge of starvation. Vulnerability to bad harvests continued well into the nineteenth century as European agriculture could barely keep up with the rapidly growing cities. High grain prices during the Napoleonic Wars further accelerated land enclosures across Britain. Then in 1815, after the eruption of Indonesia's Tomboro volcano, the coldest summer on record produced catastrophic crop failures. Food riots in England and France spread across the continent when hungry workers faced skyrocketing bread prices. The price of a loaf of bread remained a central point of working-class protest as the discontent of the urban poor bred radicals and revolutionaries.

A potato blight that arrived from America in 1844-45 showed just how insecure food production had become. When Phytophthora infestans wiped out the Irish potato harvest in the summer of 1845 and the next year's crop failed too, it left the poor-who could not afford to buy food at market rates from the indifferent British government-with literally nothing to eat. Completely dependent on potatoes, the Irish population crashed. About a million people died from starvation or associated diseases. Another million emigrated during the famine. Three million more left the country over the next fifty years, many bound for America. By 1900 the population of Ireland was a little more than half of what it had been in the 1840s. Why had the Irish become so dependent on a single crop, particularly one introduced from South America only a century before?

At first glance the answer appears to support Malthus. Between 1500 and 1846 the Irish population increased tenfold to eight and a half million. As the population grew, the average land holding dwindled to about o.2 hectares (half an acre), enough to feed a family only by growing potatoes. By 1840 half the population ate little besides potatoes. More than a century of intensive potato cultivation on nearly all the available land had reduced the Irish to living on the verge of starvation in good years. But a closer look at this story reveals more than a simple tale of population outpacing the ability to grow potatoes.

The potato grew in importance as a staple while Irish agriculture increasingly exported everything else to Britain and its Caribbean colonies. In 1649 Oliver Cromwell had led an invasion to carve Ireland into plantations to pay off with land the speculators who bankrolled Parliament in the English Civil War. Ireland's new landlords saw lucrative opportunities provisioning Caribbean sugar and tobacco plantations. Later, increasing demand for food in Britain's industrializing cities directed Irish exports to closer markets. In 1760 hardly any Irish beef went to Britain. By i8oo four out of five Irish cows sent to market ended up on British tables. The growth of Britain's urban population created substantial demand for food Irish landlords were happy to supply. Even after the official union of Ireland and England in i8oi, Ireland was run as an agricultural colony.

The potato increasingly fed rural Ireland as land was diverted to raise exports. In order to devote the best land to commercial crops, landlords pushed peasants onto marginal lands where they could grow little other than potatoes. Adam Smith advocated the potato as a means to improve landlords' profits in The Wealth ofNations because tenants could survive on smaller plots if they grew nothing but potatoes. By 1805 the Irish ate little meat. With most of the country's beef, pork, and produce shipped off to Britain, the poor had nothing to eat when the potato crop failed.

There was no relief effort during the famine. On the contrary, Irish exports to England increased. The British Army helped enforce contracts as landlords shipped almost half a million Irish pigs to England at the peak of the famine in 1846. This policy of expedience was not unusual. More food was available during many European famines than was accessible to peasants who had no backup when their crops failed. Poor subsistence farmers could not buy food on the open market. As the ranks of the urban poor grew, they too could not afford food at the higher prices famines produced. And without land they could not feed themselves. Food riots swept across Europe in 1848 in the wake of the potato blight and a poor grain harvest on the continent.

Agricultural economics began to shape radical thought. In the early 1840s, before he met Karl Marx, Friedrich Engels took issue with Malthus and argued that labor and science increased as fast as population and therefore agricultural innovation could keep pace with a growing population. Marx, by contrast, saw commercialized agriculture as degrading to both society and the soil. "All progress in capitalistic agriculture is a progress in the art, not only of robbing the worker, but of robbing the soil; all progress in increasing the fertility of the soil for a given time is a progress towards ruining the more long-lasting sources of that fertility."17 (Ironically, in the decade before the 1917 Russian Revolution, Czar Nicholas II passed land reforms that began giving peasants title to their land. Unlike the urban poor who rallied to Lenin's promise of "bread, peace, and land," rural peasants were slow to embrace the revolution Marx anticipated they would lead.)

Governments continued to export grain during famines well into the twentieth century. Soviet peasants starved in the 1930s when the central government appropriated their harvest to feed the cities and sell to foreign markets for cash to fund industrialization. In most famines, social institutions or food distribution inequities cause as much hunger as absolute shortages of food.

The initial response to rising population in postmedieval Europe was to bring progressively more marginal land into agricultural production. Yields may have been lower than from traditional farmlands, but the food produced from these lands helped sustain population growth. Starting in the eighteenth century, European powers harnessed the agricultural potential of their colonies around the world to provide cheap imported food. European agricultural self-reliance ended when imports shifted from lux uries such as sugar, coffee, and tea to basic foodstuffs like grains, meat, and dairy products. By the end of the nineteenth century, many European nations depended on imported food to feed their populations.

As Western empires spread around the globe, colonial economics displaced locally adapted agricultural systems. Typically, introduction of European methods replaced a diversity of crops with a focus on export crops like coffee, sugar, bananas, tobacco, or tea. In many regions, sustained cultivation of a single crop rapidly reduced soil fertility. In addition, northern European farming methods developed for flat-lying fields shielded under snow in winter and watered by gentle summer rains led to severe erosion on steep slopes subject to intense tropical rainfall.

Europe solved its perennial hunger problem by importing food and exporting people. About fifty million people left Europe during the great wave of emigration between 1820 and 1930; many European peoples now have more descendants in former colonies than live in the motherlands. Colonial economics and policies that favored plantation agriculture unofficially encouraged soil degradation and perpetual hunger for fresh land. Paradoxically, the drive to establish colonies was itself driven by European land hunger fueled by degradation of upland regions and enclosure of communal farmland into large estates.

Europeans emerged from under the cloud of malnutrition and constant threat of starvation because their colonial empires produced lots of cheap food. Europeans outsourced food production as they built industrial economies. Between 1875 and 1885, a million acres of English wheat fields were converted to other uses. With a growing industrial economy and a shrinking agricultural land base, Britain increasingly ate imports. By i9oo Britain imported four-fifths of its grain, three-quarters of its dairy products, and almost half its meat. Imported food pouring into Europe mined soil fertility on distant continents to further the growth of industrializing economies.

After Europe's colonial empires dissolved at the end of the Second World War, Josue de Castro, chairman of the executive council of the United Nations Food and Agriculture Organization, argued that hunger not only prepared the ground for history's great epidemics but had been one of the most common causes of war throughout history. He viewed the success of the Chinese Revolution as driven by the strong desire for land reform among tenant farmers forced to surrender half their harvest from microscopic fields to owners of huge estates. Mao Ze-dong's strongest ally was the fear of famine. The chairman's most fervent partisans were the fifty million peasants he promised land.

Agitation for land reform in the third world colored the postcolonial geopolitical landscape of the twentieth century. In particular, subsistence farmers in newly independent countries wanted access to the large land holdings used to grow export crops. Since then, however, land reform has been resisted by Western governments and former colonies, who instead stressed increasing agricultural output through technological means. Generally, this meant favoring large-scale production of export crops over subsistence farming. Sometimes it meant changing a government.

In June 1954 a U.S.-backed coup overthrew the president of Guatemala. Elected in 1952 with 63 percent of the vote, Jacobo Arbenz had formed a coalition government that included four Communists in the fifty-sixmember Chamber of Deputies. An alarmed United Fruit Company, which held long-term leases to much of the coastal lowlands, launched a propaganda campaign pushing the view that the new Guatemalan government was under Russian control. It's unlikely that the few Communist party members in the government had that much clout; United Fruit's real fear was land reform.

In the late nineteenth century, the Guatemalan government had appropriated communal Indian lands to facilitate the spread of commercial coffee plantations throughout the highlands. At the same time, U.S. banana companies began acquiring extensive lowland tracts and building railways to ship produce to the coast. Export plantations rapidly appropriated the most fertile land and the indigenous population was increasingly pushed into cultivating steep lands. By the 1950s, many peasant families had little or no land even though companies like United Fruit cultivated less than a fifth of their vast holdings.

Soon after coming to power, Arbenz sought to expropriate uncultivated land from large plantations and promote subsistence farming by giving both land and credit to peasant farmers. Contrary to United Fruit's claims, Arbenz did not seek to abolish private property. However, he did want to redistribute more than ioo,ooo hectares of company-leased land to small farmers and promote microcapitalism. Unfortunately for Arbenz, U.S. Secretary of State John Foster Dulles had personally drafted the banana company's generous ninety-nine-year lease in 1936. With Dulles on United Fruit's side, even the pretense of Communist influence was enough to motivate a CIA-engineered coup in the opening years of the cold war.

Subsequent foreign investment opened more land for cash crops and cattle. International aid and loans from development banks promoted large projects focused on export markets. Between 1956 and i98o, large-scale monoculture projects received four-fifths of all agricultural credit. Land devoted to cotton and grazing grew more than twentyfold. Land planted in sugar quadrupled. Coffee plantations grew by more than half. Forced from the most fertile land, Guatemalan peasants were pushed up hillsides and into the jungle. Four decades after the 1954 coup, fewer than two out of every hundred landowners controlled two-thirds of Guatemalan farmland. As the size of agricultural plantations increased, the average farm size fell to under a hectare, less than needed to support a family.

This was the story of Ireland all over again, with a Latin American twist-Guatemala is a steep country in the rain-drenched tropics. But like Irish meat, Guatemalan coffee is sold elsewhere. And like its coffee, Guatemala's soil is also leaving as adoption of European agricultural methods to tropical hillslopes ensures a legacy of major erosion. The combination of cash crop monoculture and intensive subsistence farming on inherently marginal lands increased soil erosion in Guatemala dramatically, sometimes enough to be obvious to even the casual observer.

In the last week of October 1998, Hurricane Mitch dumped a year's worth of rain onto Central America. Landslides and floods killed more than ten thousand people, left three million displaced or homeless, and caused more than $5 billion in damage to the region's agricultural economy. Despite all the rain, the disaster was not entirely natural.

Mitch was not the first storm to dump that much rain on Central America, but it was the first to fall on the region's steep slopes after the rainforest had been converted into open fields. As the population tripled after the Second World War, unbroken forest surrounding a few cleared fields was replaced by continuously farmed fields. Now, most of the four-fifths of the rural population farm tiny plots on sloping terrain practicing a small-scale version of conventional agriculture. While accelerated erosion from farming Central America's steep slopes has long been recognized as a problem, Hurricane Mitch ended any uncertainty as to its importance.

After the storm, a few relatively undamaged farms stood out like islands in a sea of devastation. When reconnaissance surveys suggested that farms practicing alternative agriculture better survived the hurricane than did conventional farms, a coalition of forty nongovernmental agencies started an intensive study of more than eighteen hundred farms in Guatemala, Honduras, and Nicaragua. Pairing otherwise comparable farms that prac ticed conventional and so-called sustainable agricultural practices, teams inspected each farm for soil condition, evidence of soil erosion, and crop losses. Across the region, farms operated with sustainable methods such as polyculture, hillside terracing, and biological pest control had two to three times less soil erosion and crop damage than conventional farms under chemical-intensive monoculture. Gullies were less pronounced and landslides were two to three times less abundant on sustainable farms than on conventional farms. Sustainable farms had less economic damage as well. Perhaps the most telling result of the study was that more than nine out of ten of the conventional farmers whose farms were inspected expressed a desire to adopt their neighbors' more resilient practices.

Central America was but one of many regions where the growth of large, export-oriented plantations after the Second World War turned former colonies into agricultural colonies serving global markets. Commercial monocultures also displaced subsistence farmers into marginal lands across Asia, Africa, and South America. In the new global economy, former political colonies continued to serve the interests of wealthier nations-only now trading soil for cash. But this is not all that new: the United States was in the same position before its own revolution.