The fire record her team built for the Western U.S. for the past 3,000 years shows "that fires during the 20th century generally are actually fewer and smaller than ever before given current climate conditions," said Marlon, who emphasized the role of climate on wildfire.
"The general trend from high fire in the 1800s to very low fire in the 1900s is strong and clear from three independent datasets," she said. "Open park-like conditions may have indeed occurred after the 'peak' in burning during the mid-1800s."
Baker and Williams contend that past studies of forest structure and fires were not so much wrong as "incomplete" because that they placed too much emphasis on anecdotal references, sampled too small of areas and often concentrated on old-growth stands more resistant to fire.
One of the earliest references to the open nature of the forests is found in a 1943 study by Harold Weaver, a forester from Oregon State who characterized forests in Oregon's eastern Cascades as "like a park, with clean-boled trees and grassy forest floor."
An updated view was summarized in the 2012 spring edition of California Forests: "Human fire suppression activity during the past 100 years have created dense, more crowded forests and shifted the fire regime in Sierran mixed conifer forests from one of frequent, low-level fire to one where high intensity wildfires are more common," wrote John Battles, chairman of ecosystem sciences in Department of Environmental Science, Policy and Management at the University of California, Berkeley
Williams said the Wyoming studies have significant implications for wildlife that depends on post-fire habitat, such as the black-backed woodpecker, which has survived for millions of years by eating beetle larvae in burned trees.
Four conservation groups filed a petition with the U.S. Interior Department in May seeking Endangered Species Act protection for the bird in the Sierra Nevada, Oregon's Eastern Cascades and the Black Hills of eastern Wyoming and western South Dakota.
The new studies provide the first "real, direct data'" showing that more forests burned historically, creating more post-fire forest habitat, said Chad Hanson, a forest ecologist and director of the John Muir Project who is helping lead the listing effort and suing the Forest Service to block post-fire logging in woodpecker habitat near Lake Tahoe.
"It indicates the woodpeckers had more habitat historically than they do now,'" Hanson said.
Williams said when he started the study he had "the same general ideas most people have — that the forests were less dense and there were frequent, less severe fires to maintain that structure."
Now, he believes thinning and post-fire salvage operations should be re-examined and emphasis placed on maintaining high-density stands in certain circumstances that would not threaten people or homes.
"We shouldn't be managing just for low-density forests," he said. "We should not be unhappy with — or perhaps even manage for — higher severity fires in the forests."
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