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| Earth on Sep 21, 2011

Human influence takes the wild out of some wildfires

A study shows that humans have historically increased wildfire activity – and decreased it. A scientist says, “Fire is a defining feature of humans.”

As people in some areas of the southern United States battled record-breaking wildfires in 2011, an international team of 18 scientists was trying to define how, historically, humans have influenced wildfires – both by setting fires and by putting them out.

According to the study – published in the Journal of Biogeography in September 2011 – a region’s background level of wildfire activity is difficult to assess and understand. To study past levels of wildfire activity, scientists use a variety of tools including remote sensing, tree ring analyses, charcoal deposits and historical written records. From a review of these types of analyses, the researchers found that, while humans have often increased wildfire activity in many areas around the world, they have also decreased it.

A firefighter extingushes a small debris fire that grew out of control. Image Credit: U.S. Army.

For example, wildfires were rare in tropical rainforests before human settlement but are more common now, because of the practice of slash-and-burn agriculture.

Alternatively, the researchers found that wildfires once were common natural occurrences in tropical savannas during the dry season. But fire levels decreased once humans introduced livestock that grazed down the flammable grasses.

The study also notes that it is plausible that humans are now influencing wildfire activity via less direct pathways – such as through urbanization and droughts induced by climate change. But, these researchers caution, such effects are difficult to disentangle from natural background activity in any given area.

The red-cockaded woodpecker is dependent on fire-adapted longleaf pine ecosystems for its survival. Image Credit: Michael McCloy, U.S. Fish & Wildlife.

According to these scientists, humans have a long and varied relationship with fire. Archeological evidence suggests that humans were using fire, likely to cook with, as early as 690,000 to 790,000 years ago. Today, humans use fire for many reasons – to produce electricity, to clear land for agriculture and to manage wildlife species. For example, the red-cockaded woodpecker, pictured at right, is dependent on fire-adapted ecosystems for its survival.

The researchers mention that human ingenuity has also progressed to the point where people now use fire for fire suppression. This involves starting small, controlled fires to reduce fuel levels in forests – to prevent larger, more catastrophic fires from occurring at a later time.

In a press release, David Bowman, lead author and professor at the School of Plant Science, University of Tasmania, commented:

Fire is such a defining feature of humans, and we are the only animals that use fire. We could have been called Homo igniteus as much as Homo sapiens.

Unfortunately, humans also have a tendency to misuse fire, as is the case in arson and the carelessness that allows campfires and debris fires to burn out of control.

The team published their results on September 14, 2011, in an early online edition of the Journal of Biogeography, saying their goal was to provide a framework that would aid in the design of more sustainable fire management practices that will help protect human health, property and ecosystems as this century progresses. The study is titled “The human dimension of fire regimes on Earth” and was coordinated by the University of California’s National Center for Ecological Analysis and Synthesis (NCEAS). It is freely available as an open access paper (pdf) at the Journal of Biogeography.

Bottom line: An international study conducted by 18 scientists concludes that humans influence wildfire activity and that people largely do so through creating or reducing ignition sources, and by increasing or decreasing the flammability of landscapes. The researchers said they hope that the historical framework they provide will help inform others about their attempts to design more sustainable fire management practices.

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