EUGENE, Ore.–While the hundreds of fires blazing in the western United States may be seen as acute natural disasters, threatening lives, homes and forests, they are also completely natural, according to Cathy Whitlock, a University of Oregon geography professor who studies long-term patterns of fires.

Natural, she explains, means they occur regularly when considered within a larger historical and biological context of ever-changing climatic conditions.

"So, when I hear people blame large fires on fire suppression policies or hear them say the fires we see now result from forest management practices, I am unconvinced," she says. "The forces at work are much larger. Western forests are diverse and have evolved in the face of fire."

Low-elevation forests have historically burned every decade or so, and may show the effects of 50 years of fire suppression, she adds, but the higher elevation forests–many of which are now in flames–probably do not.

Whitlock is a paleoecologist. She studies changes in ancient environments over periods of thousands of years to discover the patterns that become apparent only when taking the long-term view. She and her graduate student colleagues study the historical record of fires in the American west–areas such as Oregon, California and the Bitterroot Mountains of western Montana, the site of many devastating fires in recent weeks.

"The impression that you get over and over again in studying forests over long periods of time is just how dynamic they really are," she says. "Forests are constantly changing and are exquisitely sensitive to climate variations."

This sensitivity to climate changes will likely result in huge changes to western forests in the coming decades. Current climate projections suggest a future of warm, dry summers in the northwestern United States as a result of the build up of greenhouse gases in the atmosphere. It is thus likely that fires will become more frequent and perhaps more severe than they are at present–and the effort to suppress them will become increasingly difficult and costly.

Smoldering cigarettes and lightning strikes might be the immediate causes of a blazing forest, Whitlock says, but, in a larger sense, responsibility lies with climate.

Climate is a powerful force of change, reshaping the face of the land. As a climate changes, it can create cooler, wetter weather patterns that are less likely to result in fires or the hot and dry conditions needed for large-scale fires. These fires then act as a fiercely efficient tool by which the make-up of an area’s vegetation can be rapidly obliterated, allowing for other species to take over.

"It is important to keep in mind that forests are always changing and fire is a major way that they change. A big fire isn’t necessarily a natural disaster, but rather part of a natural process to which forests are adapted and by which they evolve," she explains.

Of course there are huge dangers and costs sometimes associated with forest fires, and people are naturally concerned, Whitlock notes.

"If we fully understand how forests evolve and the natural role that fire plays in that evolution, we can incorporate that knowledge into human activities, such as our decisions about where to build our houses and how we respond to dry years and fires," she says.

The history Whitlock and her colleagues seek to discover is recorded in the sediments at the bottom of lakes. The researchers extract tube-shaped sediment cores–two inches in diameter and up to a hundred feet in length–from the bottom of lakes. They then bring their information-laden sediment cores back to their laboratory at the UO for careful analysis. As the researchers examine successively deeper layers of the sediments, they discover information about the environment as it was farther and farther back in time.

"We are trying to retrieve and interpret an extraordinarily subtle record that exists in nature," Whitlock explains.

What do they find?

Changes over time in the number and kinds of pollen in the sample tell the story of changes in vegetation. Tiny chunks of charcoal tell the story of fires just as ash tells of a volcanic eruption. Each observation a researcher makes is a piece of the puzzle that the team puts together to create an understanding of how the environment evolved thousands of years ago.

Combining careful laboratory analyses and powerful radiocarbon dating techniques, the researchers piece together a very accurate history of a specific location dating as far back as the last Ice Age, approximately 20,000 years ago.

During the past 2,000—3,000 years, much of the northwestern United States was relatively cool and wet, reducing the likelihood of fires in any given year. In contrast, about 8,000 years ago, the climate was warmer and drier than today; fires occurred frequently. Whitlock has found, for instance, that in Yellowstone during this period, large fires occurred about every 75—100 years.

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