Friday, June 24, 2011

Agricultural consequences of the Black Death

The Black Death, caused (as DNA testing of victims has recently confirmed) by the bubonic plague, Yersina pestis, swept through Europe primarily in the years 1347-1351, with some recurring outbreaks thereafter. This plague not only brought great demographic changes to Europe, killing off probably about half of the population, but substantial changes to the economy and especially to the dominant sector of the economy then, agriculture. The Black Death provides a great empirical test of Malthusian theories of agricultural economies and it is very informative to look at what happened.

Under a naive reading of Malthusian theory, yield (the amount of food or fodder produced per unit area) should have improved after the Black Death: a lower population abandoned marginally productive lands and kept the better yielding ones. Furthermore, the increased ratio of livestock to arable acres should have improved fertilization of the fields, as more nutrients and especially nitrogen moved from wastes (wild lands) and pastures to the arable.

But while marginal lands were indeed abandoned (or at least converted from arable to pasture), and the livestock/arable ratio indeed increased, it's not the case that yield improved after the Black Death. In fact, the overall (average) yield of all arable probably declined slightly, and the yields of particular plots of land that were retained as arable usually declined quite substantially. Yields declined and for the most part stayed low for several centuries thereafter. Other factors must have been work, factors stronger than the abandonment of marginally productive lands and the influence of more livestock on nutrient movement.
Per capita agricultural output (vertical axis) vs. population density (horizontal axis) in England before, during, and after the Black Death and through the agricultural revolutions of the succeeding centuries.

The main such factor is that increasing yield without great technological improvement requires more intensive labor: extra weeding, extra transport of manures and soil conditioners, etc. Contrariwise, a less intensive use of land readily leads to falling yield. After the Black Death, labor was more expensive relative to land, so it made sense to engage in a far less intensive agriculture. The increase of pasture and livestock at the expense of the arable was a part of this. But letting the yield decline was another. What increased quite dramatically in the century after the Black Death was labor productivity and per capita standard of living (see first three points on the diagram, each covering an 80-year period from 1260 to 1499).

Indeed, the whole focus in the literature on improvements in "productivity" as yield in the agricultural revolution has been very misleading. The crucial part of the revolution, and the direct cause of the release of labor from the agricultural to the industrial and transport sectors, was an increase in farm labor productivity: more food grown with less labor. Over short timescales, that is without dramatic technological or institutional progress, farm labor productivity was inversely correlated with yield for the reasons stated. Higher labor productivity, certainly not higher yield, is what distinguished most of Europe for example from East and Southeast Asia, where under intensive rice cultivation, and abundant rain during warm summers, yield had long been far higher than in Europe. Per Malthus, however, population growth in these regions had kept pace with yield, resulting in a highly labor-intensive, low labor productivity style of agriculture, including much less use of draft animals for farm work and transport.

The bubonic plague was spread by rodents, who in turn fed primarily on grain stores. This also had a significant impact on agriculture, because grain-growing farmers and grain-eating populations were disproportionately killed and people fled areas that grew or stored grain for regions specializing in other kinds of agriculture. In coastal regions like Portugal there was a large move from grain farming to fishing. In Northern Europe there was a great move to pasture and livestock, and in particular a relative expansion of the unique stationary pastoralism that had started to develop there in the previous centuries, both due to the relative protection of pastoralists from the plague and the less labor-intensive nature of pastoralism after land had become cheaper relative to labor.

A final interesting effect is that the long trend from about the 11th to the 19th century in England of conversion of draft animals from oxen to horses halted temporarily in the century after the Black Death. The main reason for this was undoubtedly the reversion of arable to pasture or waste (wild lands). Oxen are, to use horse culture terminology, very "easy keepers". As ruminants they can convert cellulose to glucose for energy and horses can't. Oxen, therefore, became relatively cheaper than horses in an era with more wastes and less (or at least much less intensive use of) arable for growing fodder. This kind of effect occurred again much later on the American frontiers where there was a temporary, partial reversion from horses to oxen as draft animals given the abundance of wild lands relative to groomed pasture and arable for growing fodder. For example the famous wagon trains to California and Oregon were pulled primarily by oxen, which could be fed much better than horses in the wild grasslands and arid wastes encountered. However in England itself, the trend towards horses replacing oxen, fueled by the increasing growth of fodder crops, had resumed by 1500 and indeed accelerated in the 16th century, playing a central role in the transportation revolutions of the 15th through 19th centuries.

Saturday, June 11, 2011

Trotting ahead of Malthus

Progress in the Malthusian isocline in England from the 13th through 19th centuries, as, among many other factors, horses slowly replaced oxen for farm work and transport, the ratio of draft animals to people increased, and more arable land was devoted to fodder relative to food.(click to enlarge)

I have previously discussed Great Britain's unprecedented escape from the Malthusian trap. Such escapes require virtuous cycles, i.e. positive feedback loops that allow productive capital to accumulate faster than it is destroyed. There are a number of these in Britain in the era of escape from the Black Plague to the 19th century, but two of the biggest involved transportation.

One of these that I've identified was the fodder/horse/coal/lime cycle. More and better fodder led to more and stronger horses, which hauled (among other things) coal from the mines, initially little more than quarries, that had started opening up in northeastern England by the 13th century. Coal, like wood, was very costly to transport by land, but relatively cheap to ship by sea or navigable river. As fodder improved, horses came to replace oxen in the expensive step transporting goods, including coal, from mine, farm, or workshop to port and from port to site of consumption. Many other regions (e.g. in Belgium and China) had readily accessible coal, but none developed this virtuous cycle so extensively and early.

Among the early uses of coal was for heating, fuel for certain industrial processes that required heat (e.g. in brewing beer), and, most interestingly, for burning lime. Burned lime, slaked with water, could unlike the limestone it came from be easily ground into a fine powder. This great increase in the surface area of this chemical base, which let it de-acidify the soils on which it was applied. The soils of Britain tend to be rather acidic, which allows poisonous minerals, such as aluminum, to absorb into plants and blocks the absorption of needed nutrients (especially NPK -- nitrogen, phosphorous, and potassium). The application of lime thus increased the productivity of fields for growing both food and fodder, completing the virtuous cycle. This cycle operated most strongly during the period of the consistent progress in the English Malthusian isocline from the 15th through 19th centuries.

Another, related, but even more important cycle was the horse/transport and institutions/markets/specialization cycle. More and better horses improved the transport of goods generally, including agricultural goods. John Langdon [1] estimates that a team of horses could transport a wagon of goods twice as fast as a team of oxen, which suggests a factor of four increase in market area. Add to this the Western European innovations in sailing during the 15th century (especially the trading vessels and colliers that added lateen sails(s) to the traditional square sails, allowing them to sail closer into the wind), and market regions in much of Western Europe and especially Great Britain were greatly expanded in the 15th and 16th centuries.

Expanded markets in turn allowed a great elaboration of the division of labor. Adam Smith famously described how division of labor and specialization greatly improved the productivity of industry, but to some extent this also operated in British agriculture. Eric Kerridge [2] eloquently described the agricultural regions of Britain, each specializing in different crops and breeds of livestock. Some were even named after their most famous specializations: "Butter Country", "Cheese Country", "Cheshire Cheese Country", "Saltings Country", etc. These undoubtedly emerged during the 15th through 19th centuries, as prior to that time European agriculture had been dominated by largely self-sufficient manors. And closing the cycle, there emerged several localities that specialized in breeding a variety of horses. Most spectacularly different British regions during this period bred no less than three kinds of large draft horses: the Shire Horse, the Suffolk Punch (in that eastern English county) and the Clydesdale (in that Scottish county).

Institutions such as advertising and commercial law emerged or evolved to allow lower transaction cost dealings between strangers. This was probably by far the most non-obvious and difficult aspect of the problem of expanding markets. Greatly aiding in this evolution was the growth of literacy due to spread in Europe of the inexpensive books produced by printing especially in the 16th and later centuries. Where in the Middle Ages literacy had been the privilege of a religious elite, with very few on a manor literate beyond the steward, after the 15th century an ever increasing population could read advertisements, order goods remotely, read and even draft contracts.

Another effect of longer-distance transportation was to open up more remote lands, which had been too marginal to support self-sufficient agricultural, to reclamation for use in specialized, trade-dependent agriculture. The ability to lime soils that were otherwise too acidic also often contributed to reclamation.

There were many other improvements to English agriculture and transportation during these crucial centuries, but the above cycles were probably the most important up to the 19th century. Here I'll mention three important transportation improvements later in this period that in many ways show the culmination of the underlying trend: the development of the turnpike (private toll) roads in the 18th century and the associated development of scheduled transportation services, (2) a great expansion in the use of horse-drawn rail cars in coal and other mines, and (3) the development of river navigations largely in the 17th and 18th centuries, and canals largely in the 18th and early 19th centuries, again almost entirely through private investment and ownership.

As coal mines were dug deeper, they were increasingly flooded with water. Long before the steam engine, these mines were pumped by horse-powered gins. Here horses on a gin power an axle (bent through a Hooke universal joint) and belt, in this case powering an 18th century farmyard innovation, the threshing machine. The horses know to not step on the rapidly spinning axle. I'm going to guess that the horse gin was the inspiration for the merry-go-round:

Horse-drawn wagons on rails took coal from mines to docks on navigable rivers and (no small matter) pulled the empty wagons back uphill. Coal and other ores were hauled by horses over these wagonways over distances of a few kilometers. They were almost exclusively used for mines, quarries, clay pits, and the like, running from mine mouth to navigable water. Here's a horse pulling coal on a wagonway:

More horses pulling coal on rails:

Now the only thing left of horse-drawn rail are tourist relics:

Even in 1903 the London streets were still powered by horses (see if you can spot the two still-rare horseless carriages):

And now for a taste of the British river navigations and canals:

The Trent and Mersey canal, built in the late 18th century, could take you from one side of England to the other:

Where Romans had used aqueducts to move water, the British used them in their canal system to move goods where their canals needed to span valleys. A large number of aqueducts were built from stone in Britain during its canal boom in the 18th century. This was the original Barton Aqueduct on the Bridgewater Canal (1760s):

In the late 18th century the smelting of iron using coal instead of wood was perfected. Soon thereafter iron became cheap enough to use for constructing bridges and aqueducts. One result was the spectacular Pontcysyllte Aqueduct in Wales. What in the early 19th century was a towpath for horses is now a sidewalk for tourists. Careful, it's a long way down!


Eric Kerridge, The Farmers of Old England

John Langdon, Horses, Oxen, and Technological Innovation