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Study erodes image of pre-Columbian farmers.

Traditional farming in central Mexico, first implemented around 3,500 years ago, caused at least as much soil erosion as plows, livestock raising, and other techniques introduced by the Spanish in the 16th century A.D., according to a new study,

And a return to traditional farming methods in order to make more efficient use of agricultural land, now under consideration in Mexico, probably will not produce the desired results, geographer Sarah L. O'Hara of the University of Sheffield in England and her colleagues assert in the March 4 NATURE.

"[The researchers] have provided a landmark study which shatters the myth of pre-Columbian America as an Eden in which people were 'transparent in the landscape'," writes Karl W Butzer, a geographer at the University of Texas at Austin, in a commentary accompanying the new report.

O'Hara and her co-workers obtained 21 sediment cores, ranging in length from about 4 feet to more than 8 feet, from the floor of Lake Patzcuaro, which lies more than a mile above sea level in central Mexico. Archaeological evidence for human settlements in the highlands surrounding Lake Patzcuaro dates back about 4,000 years.

Soil erosion into the lake, indicated by a predominance of clay and minerals associated with nearby agricultural land rather than natural lake sediments, first appears in core segments carbon-14 dated from around 3,600 to 2,900 years ago, the scientists say, These dates correspond to the rise of maize cultivation in central Mexico, they maintain.

A more intensive period of soil erosion extended from about 2,500 to 1,200 years ago, O'Hara's group reports. Sediment built up most rapidly in the lake's north basin, they note. The regions inhabitants, whose identity remains uncertain, apparently preferred to settle just north of Lake Patzcuaro and farm the steep slopes jutting down to its waters, the investigators say,

Comparable soil erosion occurred again between 850 and 350 years ago, reflecting extensive forest clearing by the Tarascan people, who dominated the region at the time of the Spanish conquest in 1521 A.D., O'Hara's group holds.

Soil erosion into Lake Patzcuaro following the introduction of Spanish agricultural methods falls at or below previous levels, they point out.

The environmental damage produced by pre-Columbian agriculture around Lake Patzcuaro equals that generated by ancient Maya "slash and burn" farming techniques in Central American forests more than 1;000 years ago, according to the scientists.

Native Americans exploited the land and other natural resources to support their large population centers, Butzer notes. O'Hara's study indicates that they did not operate "in harmony with nature" and possessed no panaceas that would improve modern land use, he contends.

Some rural areas may reap benefits by incorporating small-scale traditional farming methods into an overall subsistence strategy that includes livestock raising, Butzer asserts.
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Title Annotation:evidence of extensive soil erosion from 2,500 to 1,200 years ago into Lake Patzcuaro, central Mexico
Author:Bower, Bruce
Publication:Science News
Article Type:Brief Article
Date:Mar 6, 1993
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