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Fewer fires in Africa these days

How flames spread, not how frequently people start them, controls burning on the continent

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5:23pm, December 19, 2011
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Africa, whose iconic savanna landscapes were shaped by fire, actually has fewer burns today than thousands of years ago, a new study suggests.

“There’s less wildfire in Africa than there has been in the last 4,000 to 40,000 years,” says Sally Archibald, an ecologist at the Council for Scientific and Industrial Research in Pretoria, South Africa who led the team that did the research. The work appears online December 19 in the Proceedings of the National Academy of Sciences.

The research also suggests that small changes in the landscape, such as how many roads cut across a grassland, can have big effects on how fire behaves.

The new study is “the first to systematically analyze the different ways in which humans would have altered ancient fire regimes,” says William Bond, an ecologist at the University of Cape Town in South Africa.

Park officials in sub-Saharan Africa have long debated how to best set and extinguish fires to control fire risk and maintain biodiversity. To tackle the question, Archibald and her colleagues looked at three ways people can affect fires: by changing how often they are ignited, the time of year in which they occur or the connectedness of the landscapes in which they occur (such as by cultivating land, creating pastures or building roads).

Then the scientists looked at remote-sensing data on how often fires burn today, and archaeological data in the form of charcoal dug from across the continent. By simulating how fire spread both now and in the past, Archibald’s team pieced together a picture of how fires changed as Homo sapiens appeared and spread across Africa.

Surprisingly, some factors — such as how often people lit fires — turned out to be not very important in dictating how fire spread. Far more significant, Archibald says, is how pastures or roads break the countryside up. Such landscape changes have kept fires from spreading as much as they did in the past; the amount of land burned in Africa probably peaked thousands of years ago, Archibald says.

The really big thing is that fire spread shows these threshold behaviors,” she says. “Small changes in one parameter can have a big change on the system.

Based on feedback from rangers, South African park managers have already been talking about changing some practices that don’t seem to work, such as getting rid of early-season burning — a change supported by the new research, Archibald says.

Other scientists could expand the same approach — combining studies of human technological innovation with models of fire spread — to continents such as Australia.

“Such information is vital to understanding the future trajectory of fire and the degree to which it can be managed to sustain ecosystems, protect human infrastructure and mitigate further changes to the atmosphere,” says Ross Bradstock, a fire expert at the University of Wollongong in Australia.

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