A Plague of Sheep

Elinor Melville’s book, A Plague of Sheep, is a scary story about the Valle del Mezquital, a valley north of Mexico City.  Spanish colonists arrived there in 1521.  Melville describes the tragedy that occurred between then and 1600.  The valley is located at high elevation in a tropical region.  It has a cool and arid climate.  Valle del Mezquital means “a valley where mesquite grows.”  It got this name late in the seventeenth century, after it had been transformed into a barren land by an ecological revolution — a plague of sheep.

For the first hundred years of Spanish occupation, epidemics repeatedly blasted the natives, who had no immunity.  Between 1519 and 1620, the population of Mexico fell by 90 to 95 percent.  The Aztec and Inca civilizations were overwhelmed.  When the Spanish arrived, the densely populated Valle del Mezquital was home to the Otomi people, descendants of the once mighty Toltecs.  They were farmers who grew maize, beans, squash, chilies, tomatoes, amaranth, sage, and other crops.  The surrounding slopes were a mix of grass and forest.  Vegetation cover kept the soil moist, and there were a number of flowing springs.  This water was used to irrigate the fields.

As the native population was reduced by disease, cropland was abandoned, and became available for grazing.  The Spanish brought livestock which exploded in number because there was abundant vegetation and they had no competition from indigenous grazing animals.  Overgrazing radically altered the existing plant community, leading to irreversible changes.

The valley experienced an ungulate irruption, in which abundant vegetation is converted into abundant livestock that zoom past carrying capacity and then crash.  Eventually, some form of equilibrium is reached.  In many ways, it’s similar to the primate irruption that we’re experiencing today.  The cattle and horses could not be convinced to leave crops alone, so the herding eventually majored in sheep.

A severe epidemic from 1576 to 1581 sharply reduced the Indian population, which brought an end to their dominance in the valley.  Herding profits made sheep more valuable than Indian farmers.  Sheep rapidly grew in number.  While loggers cut trees for the mining industry, thousands and thousands of sheep stripped the land of grasses and young trees.  The hills were eventually deforested.  Some locations were stripped to bare soil, resulting in sheet erosion and gullies.  The land dried out, and the springs stopped flowing, which limited irrigation.  By 1600, “the valley was a homogenous mesquite-dominated desert.”

This is not a story of paradise transformed into parking lots, because the land was not a paradise in 1521.  Indians had lived there for thousands of years, and agriculture had not improved the land.  It encouraged erosion and other problems.  Without manure from livestock herds, soil nutrients were depleted.  The megafauna extinctions of the Pleistocene eliminated most species of large animals that may have been suitable for domestication in the Americas.  The Incas had llamas.  On the plus side, by not having livestock herds, Native Americans suffered little from infectious diseases until the Europeans arrived.

I got curious about the diet of the Indians.  It must have been similar to what the Aztecs ate in Mexico City, south of the valley.  Wikipedia informed me that Aztecs ate a number of wild animals, including fish, fowl, gophers, iguanas, salamanders, deer, crayfish, grasshoppers, ants, larvae, and insect eggs.  They also raised three domesticated animals for meat: turkeys, ducks, and dogs.

With the introduction of sheep, and the intensive overgrazing, the vitality of the Valle del Mezquital was sharply degraded.  The Spanish had no experience with grazing in this ecosystem.  Their culture was market driven, and maximizing the production of commodities was the path to prosperity and respect.  They lived as they were taught to live.

Garrett Hardin’s essay, The Tragedy of the Commons, declares that common lands are typically degraded by selfish careless use, while private property is lovingly nurtured by owners, because they have self interest in the long term productivity of the land.  But in the Valle del Mezquital, most of the overgrazing was done on private lands.  The owners were not illuminated with perfect knowledge, and they blatantly disregarded local limits on herd sizes.  Melville asserts that what happened in the valley was nothing more than the result of good old fashioned ignorance.  They didn’t know what they were doing, so they could not foresee the long term consequences.

I fell out of my chair.  Ignorance!  It’s so trendy to blame our woes on capitalism and mobs of insanely ambitious greed heads.  But our culture strongly encourages us to pursue wealth and status, by any means necessary, to the best of our ability, till the end of our days — Donald Trump is the ideal.  Our culture disastrously fails to provide everyone with a competent understanding of ecology and environmental history.  Imagine what this world would be like if we ever produced just one well-educated generation.  Our bizarre planet-wrecking mania would be cured.  Yippee!

Today, the Valle del Mezquital has enjoyed much progress, and is home to impressive refineries, cement factories, and nuclear power plants.  It has become a thriving center for the production of vegetable crops.  Irrigation now uses surface water (“black water”), which flows downstream from Mexico City, highly enriched with untreated human and chemical wastes.  Crops grow like crazy in raw sewage.  But salinization of the soil is increasing, which will eventually ruin the cropland.

The book has six chapters.  Five discuss the Valle del Mezquital, where grazing was introduced into an agricultural region.  One chapter discusses Australia, where sheep were introduced to a wild ecosystem.  Herders and herds exploded in number.  Indigenous vermin, kangaroos, were aggressively exterminated.  By 1838, much of New South Wales was “a naked surface without any perceptible pasture upon it for the numerous half-starved flocks.”  Grasslands were rubbished in 7 to 20 years.  The land dried out, erosion increased, and floods became more frequent.

Do you notice a pattern here?  Now it’s the twenty-first century, and the civilized world is raging with a devastating pandemic of get-rich-quick fever.  Almost all of our graduating scholars are nearly as ignorant as the Spanish settlers about ecological sustainability.  All our grads are tirelessly trained to believe that status seeking, via working and hoarding, is the purpose of life — a plague of shoppers.

Melville, Elinor, A Plague of Sheep, Cambridge University Press, New York, 1994.