Article

Fire: an elusive enemy

Christina Scott

Kelley Crews

American geographer Kelley Crews, who has been based in the southern African nation of Botswana for three years, says fire is a tricky thing to capture by satellite.

The inland floodplain known as the Okavanga Delta, where she works, "is one of the most fragmented landscapes I’ve ever worked in – wet versus dry, reserve versus open access and so on," says Professor Crews.

"We have very frequent fires but they’re relatively small compared to other African savannahs; a lot of the landscape burns but not all at the same time. And the landscape has a very quick recovery: even two weeks later, there can be enough biomass that it can move the satellite signal."

Crews’ research – part of a larger two decade effort by an international research team to investigate the varied sources of land disturbance – was thus "very complicated."

Interviews with 250 people revealed that nobody had ever seen a lightning strike trigger a fire, she says, although three interviewees said they had heard of it.

So lightning has been ruled out as a significant cause of fires, she told delegates at the International GeoScience and Remote Sensing Symposium held this year for the first time in Africa, at South Africa's University of Cape Town.

Professional hunters regularly use controlled fires to improve viewing and hunting opportunities for their section of the tourist market, she said.

Poachers also find it easier to track game in charred soil. "Perhaps the biggest cause of fires is poaching and poachers are also the biggest cause of fires that get out of control."

"Land can be disturbed by climate change; it is also disturbed by the human impact of ranching and poaching. We have good ways of tracking climate change. We also have good ways of tracking human management of land. What we don’t have is something that does both – and the problem is that they both happen at the same time."

A Danish ecological geographer, Rasmus Fensholt, spoke at the same session at the International Geoscience and Remote Sensing Symposium on decades of satellite data covering the Sahel region just south of the Sahara desert.

Zooming in to show differences between rangeland and agriculture, the University of Copenhagen geography researcher and former water consultant to the Senegalese government said the maps showed the impact of humanity rather than climate change, as "rainfall cannot explain these different patterns."

While it might be possible to use earth observation trend maps effectively to manage the true Sahel, further south other human-driven factors such as cutting down woody vegetation and farming that depleted soil nutrients meant that researchers should be "careful," Fensholt warned.

More information:

Environmental Science Institute

University of Copenhagen geography department University of Copenhagen geography department

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