At the edge of the papaya grove were ten low earthen mounds that the team had identified as human-made. Carbon dating indicated that they were constructed in about 1000 A.D. The archaeologists had begun opening up the largest of the mounds. Already they had discovered nine burials, one body placed in a big funerary urn, all apparently interred at the same time. Because the scientists were unlikely to have uncovered the area’s only concentration of human remains in their first, exploratory test pit, they believed that the entire mound was likely to be full of burials—hundreds of them. “That suggests thousands of people lived here,” Neves said. “In 1000 A.D., that’s a big place.”
Shoving back his baseball cap, Neves levered himself into the excavation site, a six-foot, rectangular hole with the right-angled corners and precisely vertical walls that are a hallmark of archaeological investigation. One of the visiting researchers passed down a Munsell soil-color chart. Resembling strips of paint-color samples, these are used by pedologists (soil scientists) to classify soils. Neves scraped the wall lightly, exposing fresh earth, and pinned the chart to the wall with a big-headed nail. From the top of the dig he dangled a measuring tape—alternating ten-centimeter strips of red, white, and green—to indicate depth. Digital cameras ratcheted and whined. It was a vest-pocket version of the inspection of Folsom by the graybeards.
Neves had a little trouble hanging the tape because he couldn’t find a place where it wouldn’t get snagged on the broken ceramics protruding from the walls. They bristled from the side of the dig in a profusion that reminded me of the Beni mounds, hundreds of miles upstream. Some of the pieces seemed to form horizontal layers. As in the Beni, the ceramics had apparently been smashed deliberately, perhaps to build up the surface.
I asked Petersen, a ceramics specialist, how many plates and bowls and cups were in the mounds. He pulled out a scrap of paper and a pen and scribbled some numbers. In a minute or two he looked up. “This is a rough, back-of-the-envelope-type estimate,” he warned, showing me the result: the single mound we were standing on might contain more than forty million potsherds. “Think of the industry required to produce that much pottery,” Neves said. “Then they just smash it. Look at the way they piled up this good soil [to make the burial mound]—it’s all wasteful behavior. I don’t think scarcity was a problem here.”
The ecological constraints on tropical soils are in large part due to the gravitational energy of raindrops. Rainfall, drumming down day in and day out, pounds the top few inches of earth into slurry from which nutrients are easily leached and which itself easily washes away. In uncut forest, the canopy intercepts precipitation, absorbing the physical impact of its fall from the clouds. The water eventually spills from the leaves, but it hits the ground less violently. When farmers or loggers clear the tree cover, droplets shoot at the ground with more than twice as much force.
Slash-and-burn minimizes the time in which the ground is unprotected. Intensive agriculture is much more productive but maximizes the land’s exposure. This painful trade-off is why ecologists argue that any attempt by tropical forest societies to grow beyond small villages has always been doomed to fail.
According to Charles R. Clement, an anthropological botanist at the Brazilian National Institute for Amazon Research (INPA) in Manaus, though, the first Amazonians did avoid the Dilemma of Rainfall Physics. Speaking broadly, their solution was not to clear the forest but to replace it with one adapted to human use. They set up shop on the bluffs that mark the edge of high water—close enough to the river to fish, far enough to avoid the flood. And then, rather than centering their agriculture on annual crops, they focused on the Amazon’s wildly diverse assortment of trees.
In his view, the Amazon’s first inhabitants laboriously cleared small plots with their stone axes. But rather than simply planting manioc and other annual crops in their gardens until the forest took them over, they planted selected tree crops along with the manioc and managed the transition. Of the 138 known domesticated plant species in the Amazon, more than half are trees. (Depending on the definition of “domesticated,” the figure could be as high as 80 percent.) Sapodilla, calabash, and tucumá; babaçu, açai, and wild pineapple; coco-palm, American-oil palm, and Panama-hat palm—the Amazon’s wealth of fruits, nuts, and palms is justly celebrated. “Visitors are always amazed that you can walk in the forest here and constantly pick fruit from trees,” Clement said. “That’s because people planted them. They’re walking through old orchards.”
Peach palms—the trees through which I looked at the Amazon from Painted Rock Cave—are Clement’s favorite example. Giddily tall and straight, they have up to a dozen stalks, with a protective mat of spikes wrapped around the bottom of the tree. The protection is little needed; peach palm wood is hard enough that in the Beni it was used for saw blades. Bundles of orange or red fruit hang like clusters of bocce balls from the base of the fronds. The fruit is soaked with oil and rich in beta-carotene, vitamin C, and, surprisingly, protein. When dried, the white or pink pulp makes flour for thin, tortilla-like cakes; when boiled and smoked, it becomes hors d’oeuvres; when cooked and fermented, it makes beer. (The sap also makes a kind of wine.) Two crops a year are not uncommon; in terms of yield per acre, peach palms are typically much more productive than rice, beans, or maize. Trees begin producing fruit after three to five years and can continue for another seventy years. Like strawberries, peach palm throws out adventitious shoots. With a little care, these can be harvested for heart-of-palm—very tasty heart-of-palm, in my experience. Bactris gasipaes, as scientists call it, has more than two hundred common names: pupunha, cahipay, tembe, pejibaye, chontaduro, pijuayo. To Clement, the proliferation of names suggests the plant was used for many purposes by many cultures.
In the 1980s and early 1990s Clement measured peach palms throughout the Amazon basin. He learned that several physical characteristics, including fruit size, lay on a gradient with those apparently closest to the wild state in western Amazonia, near the Beni; the implication was that the tree might first have been cultivated there. Using a different method, Jorge Mora-Urpí, one of Clement’s collaborators, concluded that Indians might have bred the modern peach palm by hybridizing palms from several areas, including the Peruvian Amazon. Whatever the origin, people domesticated the species thousands of years ago and then spread it rapidly, first through Amazonia and then up into the Caribbean and Central America. Bactris gasipaes was in Costa Rica 1,700 to 2,300 years ago and probably earlier. By the time of Columbus, one seventeenth-century observer wrote, Native Americans valued it so highly “that only their wives and children were held in higher regard.”
Unlike maize or manioc, peach palm can thrive with no human attention. Tragically, this quality has proven to be enormously useful. In the seventeenth and eighteenth centuries many Amazonian Indians, the Yanomamo among them, abandoned their farm villages, which had made them sitting ducks for European diseases and slave trading. They hid out in the forest, preserving their freedom by moving from place to place; in what Balée calls “agricultural regression,” these hunted peoples necessarily gave up farming and kept body and soul together by foraging. The “Stone Age tribespeople in the Amazon wilderness” that captured so many European imaginations were in large part a European creation and a historical novelty; they survived because the “wilderness” was largely composed of their ancestors’ orchards. “These old forests, called fallows, have traditionally been classified as high forest (pristine forest on well-drained ground) by Western researchers,” Balée wrote in 2003. But they “would not exist” without “human agricultural activities.” Indeed, Amazonians typically do not make the distinction between “cultivated” and “wild” landscapes common in the West; instead they simply classify landscapes into scores of varieties, depending on the types of species in each.
After we had spoken for a while Clement took me out of his office and into INPA’s experimental forest. To my untrained eye, it looked much the same as the forests around the lodges outsid
e Manaus that attract ecotourists, except that INPA staffers kept down the undergrowth. There was the same cool green light from the canopy, the same refulgent smell, the same awe-inspiring sense of variety. The air vibrated with the same inharmonic racket of squealing, burbling, croaking, and cheeping birds. Dribbling down some of the tree trunks were little runnels that looked like dried sap. On a previous visit to the Amazon I had seen runnels just like these on a rubber tree in an abandoned plantation. Thinking it was a drip of latex sap, I plucked at one. It was the cover for a termite superhighway. Termites boiled out of the little tunnel and all over my hand. Termites bite. Flapping my hand wildly, I leapt back from the tree. My sandaled foot landed on a ground-wasp nest. In this way I learned why some Amazonians have a jaundiced view of biodiversity. On Clement’s tour I kept my hands to myself.
It was July—winter in the Amazon, the worst time of the year for fruit. Nevertheless, Clement was able to find yellow bacuri and purple açai. He plucked what looked like a four-foot version of a string bean from a branch, split it lengthwise, and showed me flattened, shiny seeds arrayed along its length like teeth in a jaw. Each seed was the size of a thumb bone and nestled in a fluffy white coating. “Try this,” he said. “It’s the ice-cream bean.” I put a seed in my mouth and sucked on it. The coating did taste quite like vanilla ice cream, and was just as refreshing. Three or four more fruits followed, each equally strange to me. (This is what people like about biodiversity.) Peach palm was not in season, but he found another member of the same genus. The fruit, when peeled, was unappetizing—quite like soggy cardboard in color, texture, and flavor. Clement squeezed some pulp. Oil dribbled from his fingers to the ground. “This’ll put some calories into you,” he said.
Planting their orchards for millennia, the first Amazonians slowly transformed large swaths of the river basin into something more pleasing to human beings. In the country inhabited by the Ka’apor, on the mainland southeast of Marajó, centuries of tinkering have profoundly changed the forest community. In Ka’apor-managed forests, according to Balée’s plant inventories, almost half of the ecologically important species are those used by humans for food. In similar forests that have not recently been managed, the figure is only 20 percent. Balée cautiously estimated, in a widely cited article published in 1989, that at least 11.8 percent, about an eighth, of the nonflooded Amazon forest was “anthropogenic”—directly or indirectly created by humans.
Some researchers today regard this figure as conservative. “I basically think it’s all human created,” Clement told me. So does Erickson, the University of Pennsylvania archaeologist who told me in Bolivia that the lowland tropical forests of South America are among the finest works of art on the planet. “Some of my colleagues would say that’s pretty radical,” he said. According to Peter Stahl, an anthropologist at the State University of New York in Binghamton, “lots” of researchers believe that “what the eco-imagery would like to picture as a pristine, untouched Urwelt [primeval world] in fact has been managed by people for millennia.” The phrase “built environment,” Erickson argued, “applies to most, if not all, Neotropical landscapes.”
GIFT FROM THE PAST
“Landscape,” in this case, is meant exactly—Amazonian Indians literally created the ground beneath their feet. According to Susanna Hecht, a geographer at the University of California at Los Angeles, researchers into upland Amazonia took most of their soil samples along the region’s highways, which indeed passed through areas with awful soil—some regions were so saturated with toxic aluminum that they are now being mined for bauxite. A few scientists, though, found patches of something better. “In part because of the empty-Amazon model,” Hecht told me, these were “seen as anomalous and insignificant.” But in the 1990s researchers began studying these unusual regions of terra preta do Índio—rich, fertile “Indian dark earth” that anthropologists believe was made by human beings.
Throughout Amazonia, farmers prize terra preta for its great productivity; some have worked it for years with minimal fertilization. Among them are the owners of the papaya orchard I visited, who have happily grown crops on their terra preta for two decades. More surprising still, the ceramics in the farm’s terra preta indicate that the soil has retained its nutrients for as much as a millennium. On a local level, terra preta is valuable enough for locals to dig it up and sell as potting soil, an activity that, alas, has already destroyed countless artifacts. To the consternation of archaeologists, long planters full of ancient terra preta, complete with pre-Columbian potsherds, greet visitors to the Santarém airport. Because terra preta is subject to the same punishing conditions as the surrounding bad soils, “its existence is very surprising,” according to Bruno Glaser, a chemist at the Institute of Soil Science and Soil Geography at the University of Bayreuth, Germany. “If you read the textbooks, it shouldn’t be there.”*25
Because careful surveys of Amazon soils have never been taken, nobody knows the amount and distribution of terra preta. Woods has guessed that terra preta might represent as much as 10 percent of the Amazon basin, an area the size of France. A recent, much more conservative estimate is that it covers .1 to .3 percent of the basin, a few thousand square miles. The big difference between these numbers matters less than one might expect: a few thousand square miles of farmland was enough to feed the millions in the Maya heartland.
Most big terra preta sites are on low bluffs at the edge of the floodplain. Typically, they cover five to fifteen acres, but some encompass seven hundred or more. The layer of black soil is generally one to two feet deep but can reach more than six feet. According to a recent study led by Dirse Kern, of the Museu Goeldi in Belém, terra preta is “not associated with a particular parent soil type or environmental condition,” suggesting that it was not produced by natural processes. Another clue to its human origin is the broken ceramics with which it is usually mixed. “They practiced agriculture here for centuries,” Glaser told me. “But instead of destroying the soil, they improved it, and that is something we don’t know how to do today” in tropical soils.
As a rule, terra preta has more “plant-available” phosphorus, calcium, sulfur, and nitrogen than is common in the rain forest; it also has much more organic matter, better retains moisture and nutrients, and is not rapidly exhausted by agricultural use when managed well. The key to terra preta’s long-term fertility, Glaser says, is charcoal: terra preta contains up to sixty-four times more of it than surrounding red earth. Organic matter “sticks” to charcoal, rather than being washed away or attaching to other, nonavailable compounds. “Over time, it partly oxidizes, which keeps providing sites for nutrients to bind to.” But simply mixing charcoal into the ground is not enough to create terra preta. Because charcoal contains few nutrients, Glaser argued, “high-nutrient inputs—excrement and waste such as turtle, fish, and animal bones—are necessary.” Special soil microorganisms are also likely to play a role in its persistent fertility, in the view of Janice Thies, a soil ecologist who is part of a Cornell University team studying terra preta. “There are indications that microbial biomass is higher in terra preta than in other forest soils,” she told me, which raises the possibility that scientists might be able to create a “package” of charcoal, nutrients, and microfauna that could be used to transform bad tropical soil into terra preta.
Despite the charcoal, terra preta is not a by-product of slash-and-burn agriculture. To begin with, slash-and-burn simply does not produce enough charcoal to make terra preta—the carbon mostly goes into the air in the form of carbon dioxide. Instead, Indians apparently made terra preta by a process that Christoph Steiner, a University of Bayreuth soil scientist, has dubbed “slash-and-char.” Instead of completely burning organic matter to ash, ancient farmers burned it incompletely to make charcoal, then stirred the charcoal into the soil. In addition to its benefits to the soil, slash-and-char releases much less carbon into the air than slash-and-burn, which has large potential implications for climate change. Trees store vast amounts
of carbon in their trunks, branches, and leaves. When they die or people cut them down, the carbon is usually released into the atmosphere, driving global warming. Experiments by Makoto Ogawa of the Kansai Environmental Engineering Center, near Kyoto, Japan, demonstrated that charcoal retains its carbon in the soil for up to fifty thousand years. “Slash-and-char is very clever,” Ogawa told me. “Nobody in Europe or Asia that I know of ever understood the properties of charcoal in soil.”
Indians are still making terra preta in this way, according to Hecht, the UCLA geographer. Hecht spent years with the Kayapó, in central Amazonia, watching them create “low-biomass” fires “cool enough to walk through” of pulled-up weeds, cooking waste, crop debris, palm fronds, and termite mounds. Burning, she wrote, is constant: “To live among the Kayapó is to live in a place where parts of the landscape smolder.” Hecht regards Indian fire as an essential part of the Amazonian landscape, as it was in the forests of eastern North America. “We’ve got to get over this whole Bambi syndrome,” she told me, referring to the movie’s forest-fire scene, which has taught generations of children that burning wildlands is evil. “Let the Kayapó burn the rainforest—they know what they’re doing.”
In a preliminary test run at creating terra preta, Steiner, Wenceslau Teixeira of the Brazilian Agricultural Research Enterprise, and Wolfang Zech of the University of Bayreuth applied a variety of treatments involving charcoal and fertilizers for three years to rice and sorghum plots outside Manaus. In the first year, there was little difference among the treatments (except for the control plots, in which almost nothing grew). By the second year, Steiner said, “the charcoal was really making a difference.” Plots with charcoal alone grew little, but those treated with a combination of charcoal and fertilizer yielded as much as 880 percent more than plots with fertilizer alone. His “terra preta” was this productive, Steiner told me, despite making no attempt to re-create the ancient microbial balance.
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