South America's Amazonis the largest tropical rainforestand river system on Earth.But the Amazon is disappearing at the rate ofabout eight hundred thousand hectares a year.This deforestation is caused by an increasein agriculture and cattle ranchingand the building of roads and dams.Another cause is the illegal cutting of treesfor logging companies.Now, a new study saysancient Amazonian farming methodscould offer valuable lessons for today.The study looks at the pre-Columbian period.Christopher Columbus and other European explorersbegan arriving in the Americasin the late fourteen hundreds.The researchers studied a coastal wetland areawhere ancient farm beds and canals remain unchanged.The site is in French Guyana.A widely held belief is that pre-Columbian farmersused a great deal of fire to manage Amazonian ecosystems.But the scientists say their studycalls this idea into question.It shows that raised-field farmers limited their burningto improve agricultural production.Jose Iriarte from the University of Exeter in Englandwas lead author of the study.Mr. Iriarte says fire results in the loss ofimportant nutrients for crops.When land is not being used for farming,periods without fire are most effectivein rebuilding soil organic matterand preserving soil structure."So in this sense," he says,"we interpreted that they were limiting firesbecause it was better to grow cropsin these raised field systems."He says this fire-free methodby the pre-Columbian farmershelped change the seasonally flooded savanna,or grassland, into productive cropland.Raised fields provide better drainage and soil aerationand also hold moisture during the dry season.This fire-free method of agriculturewould have been labor intensive.It ended when up to ninety-five percent ofthe native people died from diseasesbrought by the Europeans.Mitchell Power is curator of the Natural History Museumat the University of Utah.MITCHELL POWER: "Once the Columbian encounter happens,we don't see that type of agriculture any more.We start to see increased burningand a shift towards dry-land farming.So people were then clearing forestsand making their raised beds in the forests.And so, what we think is happening is thatthere was a huge demographic collapse in this region."The European colonizers broughtslash-and-burn methods of agriculturethat remain a threat to the rainforest.Experts say at current rates,more than half of the Amazon's tropical rainforestcould be gone by twenty-thirty.The study is in the Proceedings ofthe National Academy of Sciences.You can find a link at 51voa.com.And that's the VOA Special English Agriculture Report.