"Savanna and forest are definitely not locally compatible," she said. "There is a risk of losing plants and animals endemic to one or the other, which would affect the people who depend on those species.
"Savannas, for instance, are useful to people as cattle rangeland," she said. "When forests encroach, the grass productivity decreases dramatically and the land becomes much less useful. In terms of livelihood, that would have a huge impact."
The team's work provides among the first experimental evidence that fire feedback -- the ecological effect of fires -- is the dominant force in maintaining the division between forests and savannas, and that it can determine where the habitats flourish. The researchers used satellite data of fire distributions -- combined with climate and soil data, as well as satellite data of tree cover -- to survey the tropical and subtropical regions of Africa, Australia and South America.
The researchers found that the frequency of fires determines whether forest or savanna will dominate an area more than other factors such as rainfall, seasons and soil texture, especially in areas with moderate precipitation. Regular fires prevent trees from establishing and savannas from turning into forest. A lack of fires allows a forest to develop, which in turn excludes future fires.
Human alterations to the climate and landscape, however, may disrupt the natural spread of fire in many areas and lead to very rapid changes in biome distribution, the Princeton researchers suggest. Direct actions such as building roads and deploying methods such as controlled burning that prevent the natural spread of wildfires could break up savannas, altering wildfires and allowing forests to take root. At the sam
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