permaculture

["Lawrence F. London, Jr." <lflj@bellsouth.net>]

Ancient farming method may help conserve savannahs
Aleida Rueda

26 April 2012 | EN | ES


The study found slash-and-burn may not be the most effective method for 
managing savannahs
Flickr/Ben Sutherland

A fire-free farming method practiced by early inhabitants of the 
Amazonian savannahs could help inform efforts to conserve and 
rehabilitate these important ecosystems around the world, a study has found.
The research provides greater historic context forfindings presented at 
a conference earlier this year (26 January), which suggested that 
slash-and-burn — in which trees are felled, left to dry and then burned 
to prepare land for farming — provides better growing conditions for 
valuable trees such as mahogany.
This latest study, published in Proceedings of the National Academy of 
Sciences (9 April), found that 800 years ago, prior to European 
settlement of Latin America, indigenous farmers had developed a 
technique known as 'raised-field' farming to manage land sustainably 
without using fire.
The method involved constructing small agricultural 'mounds' which 
promoted drainage, soil aeration and moisture retention. It conserved 
soil nutrients and organic matter, and preserved soil structure.
The ancient technique was studied by researchers, who have created the 
first detailed picture of land use by documenting the very low 
frequencies of charcoal particles — an indicator of fire — in the 
savannahs of French Guyana.
"Modern indigenous groups living in savannah environments regularly burn 
the savannahs. From there paleoecologists extrapolated that all 
savannahs have been burned regularly in the past. But this was not the 
case," José Iriarte, researcher at the University of Exeter, United 
Kingdom, and leader of the study, told SciDev.Net.
"Building small mounds was the only way that they could cultivate these 
seasonally flooded savannahs. They were creating an elevated, dry, 
fertile platform," Iriarte said.
The researchers say that the study gives a unique perspective on 
land-use before as well as after the first Europeans arrived, and 
reveals that the high fire incidence in Amazonian savannas was a 
post-settlement phenomenon.
Iriarte says raised-field and slash-and-burn are techniques developed to 
suit different environments, but commented that burning resulted in the 
long-term depletion of soil nutrients. "In the long run, if [land] is 
not left fallow for a long period [of up to 20 years, it] is 
impoverished," he said.
The authors say their findings suggest that raised-field agriculture 
could also provide better water infiltration and storage in soil and 
crop roots, and promote crop growth. They also say their findings may 
apply in flooded savannah settings elsewhere in the world.
"We think that raised-field agriculture, which would require careful 
management of organic matter, could be applicable in all seasonally 
flooded savannas," said Doyle McKey, professor at the Université de 
Montpellier II, in France, who also participated in the study.
Link to full article in PNAS