Mann, Charles (2002) Real Dirt on Rainforest Fertility

Mann, Charles (2002) Real Dirt on Rainforest Fertility -...

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65 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 9 AUGUST 2002 VOL 297 SCIENCE 920 IRANDUBA,AMAZÔNAS STATE ,BRAZIL— Above a pit dug by a team of archaeologists here is a papaya orchard filled with unusual- ly vigorous trees bearing great clusters of plump green fruit. Below the surface lies a different sort of bounty: hundreds, perhaps thousands, of burial urns and millions of pieces of broken ceramics, all from an al- most unknown people who flourished here before the conquistadors. But surprisingly, what might be most important about this central Amazonian site is not the vibrant or- chard or the extraordinary outpouring of ce- ramics but the dirt under the trees and around the ceramics. A rich, black soil known locally as terra preta do Indio (Indian dark earth), it sustained large settlements on these lands for 2 millennia, according to the Brazilian-American archaeological team working here (see sidebar). Throughout Amazonia, farmers prize terra preta for its great productivity—some farmers have worked it for years with minimal fertilization. Such long- lasting fertility is an anomaly in the tropics. Despite the exuberant growth of rainforests, their red and yellow soils are notoriously poor: weathered, highly acidic, and low in organic matter and es- sential nutrients. In these oxisols, as they are known, most carbon and nutrients are stored not in the soil, as in temperate regions, but in the vegeta- tion that covers it. When loggers, ranchers, or farmers clear the vegetation, the intense sun and rain quickly decompose the remaining or- ganic matter in the soil, making the land al- most incapable of sustaining life—one reason ecologists frequently refer to the tropical for- est as a “wet desert.” Because terra preta is subject to the same punishing conditions as the surrounding oxisols, “its exis- tence is very surprising,” says Bruno Glaser, a chemist at the In- stitute of Soil Science and Soil Ge- ography at the University of Bayreuth, Germany. “If you read the textbooks, it shouldn’t be there.” Yet according to William I. Woods, a geographer at Southern Illinois University, Edwardsville, terra preta might cover as much as 10% of Amazonia, an area the size of France. More remarkable still, terra preta appears to be the prod- uct of intensive habitation by pre- contact Amerindian populations. “They practiced agriculture here for centuries,” Glaser says. “But instead of de- stroying the soil, they improved it—and that is something we don’t know how to do today.” In the past few years, a small but growing group of rsearchers—geographers, archaeol- ogists, soil scientists, ecologists, and anthro- pologists—has been investigating this “gift from the past,” as terra preta is called by one member of the Iranduba team, James B. Petersen of the University of Ver- mont, Burlington. By
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This note was uploaded on 10/22/2010 for the course ASB 326 taught by Professor Falconer during the Fall '08 term at ASU.

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Mann, Charles (2002) Real Dirt on Rainforest Fertility -...

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