Terraces and Raised Beds

In grad school down at UT, we read quite a bit about various agricultural adaptations in the Pre-Colombian Americas. Public knowledge about the sophistication of indigenous civilizations is improving (do elementary schools still teach, as they did when I attended mine, that all Indians were essentially hunter-gatherers?), but my sense is that people still do not appreciate the scale of development, especially in Central and South America. It was the article The Lost City of Z, published four or five years ago in the New Yorker, that opened my eyes. David Grann, an magician of an author who turned the piece into a book, highlighted archaeological finds in the Amazon that are consistent with an account by a Spanish conquistador, Francisco de Orellana, of vast settlements. After Orellana passed through, smallpox and other diseases ravaged the population, and since inhabitants relied on mud and wood as construction materials, decay erased the built record to all but the most astute eyes.

In the Andes, the Incas were only the last of several empires that flourished. One of their predecessors, based at Tiwanaku near the south shore of Lake Titicaca, developed into a city of 15-30,000 people, with hundreds of thousands more tilling the shores around the lake. Since Lake Titicaca sits high on the Altiplano, at 12,500 feet, well above the Andean treeline, these people had to develop incredibly sophisticated methods of farming to survive in the harsh alpine climate. And yet, they not only scratched out their existence but thrived, making Tiwanaku the seat of an empire that stretched up and down the Pacific coast for hundreds of miles and reached east into the lowland jungle.

When I took the bus to Copacabana, a touristy little town on Lake Titicaca just east of the border with Peru, I had ample opportunity to scrutinize the hillsides. At one point, we had to get off the bus to cross a small strait (the bus rides in one rickety wooden boat, the passengers on another due to an unfortunate capsizing a few years back). Above the dock, the hillside climbed several hundred feet, every inch of it covered in crumbling terraces. Nowadays, people only till the flat lands closest to the lake (though they don’t seem to have any mechanized system of irrigation). The amount of labor it took to carve the hillsides into terraces is mind-boggling: people must have swarmed across these hillsides like ants, once.

Proximity to the lake affords a major advantage for farmers, as the massive body of water acts as a heat sink, extending the growing season considerably by warding off destructive frosts. The locals further developed this system in miniature, in what is known as suka kollu or raised bed agriculture.

On the floodplain adjacent to the lake, farmers created a series of long, relatively narrow (several meters wide) beds, interspersed with channels fed by lake water. Again, the water served as a local heat sink, extending the growing season and, at times, mitigating the effect of the harsh Andean sun. Irrigation was easy, and when soil on the beds grew exhausted, farmers could reach to the bottom of adjacent channels and scoop up mud rich with nutrients from decaying plant matter. While crops such as potatoes were rich in carbohydrates, waterfowl and fish in the channel provided a convenient source of protein.

Contemporary farmers in the region have lost the knowledge to cultivate these fields, but a few experiments by social scientists have found that the raised bed system can yield ten times as much produce as conventional methods and one and half times as much as conventional methods supplemented with artificial fertilizers and pesticides. It is not easy to convince the local population to adopt unfamiliar methods of farming, however.

Back near the capital city, Andrew, Tom and I went for a walk along a ridge west of La Paz. Our perch had tremendous views of Illimani, a giant 6,000 meter peak that looms over La Paz, as well as the agriculture along the valley walls. Innumerable fields, most long abandoned, were visible. Since the climate is so dry, it takes centuries for wild plants to recolonize tilled soil.

The population pressure to cultivate such seemingly marginal landscapes must have been intense. That people did so and were able to build a thriving civilization seems to convincingly refute the Malthusian thesis.