Extinguished Earth

Compared to a 2000 satellite map (left), the model (right) predicts a substantial increase in forest cover in the absence of fire.

The world's forests would cover twice the area they do today had there been no forest fires, a new mathematical model predicts. The model also suggests that fire may have a greater role than climate change in shaping global ecosystems. The findings, researchers say, could help experts respond better to landscape fires and a changing climate.

For the past 100 years, biologists have assumed that climate shapes the distribution of the world's vegetation: Forests grow in areas with high rainfall, while seasonally dry regions become grasslands. But in some parts of the world, there is a clear mismatch between climate and flora. Scientists cannot fully explain, for example, why there are only shrubs and grass in places that get enough rain to support forests.

Suspecting that fires may have once ravaged such areas, William Bond, an ecologist at the University of Cape Town, South Africa, and colleagues wondered how the world would look had there been no fires. Creating a simulation, they fed climate data, as well as factors like changes in carbon dioxide levels and soil composition over time, into a mathematical model. The model predicts that, in the absence of fire, global forest cover would more than double from about 27% to nearly 57% of vegetated land. Grasslands in large parts of South America and Central Africa, for example, would be forested, while savannas and shrublands would shrink by 48 and 60%, respectively, the researchers report in the current issue of New Phytologist.

Based on the results, Bond says, "we are hoping people will rewrite ecology textbooks" to include fire as a major player in the shaping of the world's vegetation. However, he notes that the model does not account for the impact of human activity on this process.

"It's an excellent, well-founded study with huge amounts of data to back it," says Jon Keeley, a research ecologist with the United States Geological Survey (USGS). "There have been countless studies showing the effects of fire on vegetation but they all seem to be geographically confined. This is the first time somebody has taken a step back to look at the global picture."

Related sites
The report
William Bond's home page
How wildfires work

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