Ecology, Climate and Human Activities Conspire to Set the World on Fire

Article excerpt

Earth is a fire planet. Ever since the first plants appeared--and provided fuel--more than 420 million years ago, fire has flourished in Earth's oxygenated atmosphere. Some scientists even think that long before humans, fire carved out entire landscapes, clearing dense forests to make way for grasslands.

In recent years, the fingers of flame have extended their reach over more of the Earth's surface. Wildfires are occurring more often and becoming more severe, a perplexing change in fire patterns that threatens to transform ecosystems, reduce biodiversity and even alter climate. To stamp out the flames, researchers have to understand why fire is spreading and figure out how to fight fire with science.

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Fire has many faces. It helps some ecosystems thrive but destroys others. It helps people clear land but can also destroy homes and take lives. Sometimes useful, sometimes destructive, fire is always unpredictable--and that makes it a difficult subject. "Understanding fire is a science, and until now, the science of fire hasn't been properly recognized," says ecologist David Bowman of the University of Tasmania in Hobart, Australia.

But now, researchers from different disciplines are beginning to investigate the science of fire. Some ecologists monitor forest fires burning today, using satellite images to discern how much forest is aflame and how severe the fires are. Other scientists track how forests regenerate after fires. And geologists reach into the past, using remnants of long-cooled forest fires for clues about how fire shaped the ancient Earth.

"Everyone in their respective fields had some knowledge about fire. But now we've got to come together to map out the role of fire in the Earth system," Bowman says.

The "Earth system" is the sum of the planet's physical, chemical, biological and social parts, processes and interactions. Fire can shape landscapes, shift climate and even change processes such as the carbon cycle--blazes have impacted the planet for eons. But now, people could be shifting the balance in a new direction.

Bowman and other fire experts reviewed recent fire research in the April 24 Science. The latest work illuminates the complicated role that fire plays on Earth and highlights the interactions among climate, fire and humans.

People are playing more of a role in fire than ever before, the research reveals. In the tropics, fires are routinely started to clear forestland for agriculture or pastureland. And as more homes are built farther into the wilderness, on land where fire used to roam free, the natural patterns of fire are being suppressed.

"There's an emerging need to look at fire at the intersection between biology, ecology and society," Bowman said at a teleconference coinciding with the paper's online release.

New research suggests that, while fires may burn locally, their consequences spread globally. When forests blaze, carbon stored in vegetation escapes into the atmosphere as carbon dioxide, a greenhouse gas. Added up, the fires that burn all over the world could be a significant source of atmospheric carbon, even contributing to climate change.

At the same time, changes in climate could make landscapes more prone to burning. Droughts can set the stage for fires to burn in places where they never used to. And when the natural patterns of fire change, ecosystems change. Fire may kill but not completely destroy trees. "That means there's more fuel waiting for the next fire," says Eric Kasischke of the University of Maryland in College Park, an ecologist who studies fire and climate in boreal forest ecosystems.

Scientists don't have a complete understanding of fire in the Earth system yet. But as researchers pull together the threads of fire science, integrating different areas of research, a new appreciation of fire's global impacts is emerging.

Fire watch

Some ecosystems thrive on fire, such as arid savannas that burst into flame easily, burn often, but soon regenerate. …