The Decline of Yosemite

Eric Michael Johnson writes in Scientific American, the belief in the myth of pristine wilderness by naturalist John Muir has had a negative impact on the biodiversity and the ability to prevent catastrophic fire damage in Yosemite National Park.

The results of this analysis were statistically significant (p < 0.01) and revealed that shade-tolerant species such as White fir and incense cedar had increased to such an extent that Yosemite Valley was now two times more densely packed than it had been in the nineteenth century. These smaller and more flammable trees had pushed out the shade-intolerant species, such as oak or pine, and reduced their numbers by half. After a century of fire suppression in the Yosemite Valley biodiversity had actually declined, trees were now 20 percent smaller, and the forest was more vulnerable to catastrophic fires than it had been before the U.S. Army and armed vigilantes expelled the native population.

In other words, the native population of Yosemite managed the forest far better than the park service and conservationists that came after them.

It wasn’t only Muir who was struck by the ordered beauty of Yosemite Valley. Lafayette Bunnell, the New York physician who accompanied Savage on his exploits in 1851, recalled that “the valley at the time of discovery presented the appearance of a well kept park.” Likewise, Galen Clark who was the state guardian of the Yosemite Grant after it was ceded to California, remembered similar conditions when he first visited in 1855. “At the time,” Clark wrote, “there was no undergrowth of young trees to obstruct clear open views in any part of the valley from one side of the Merced River across to the base of the opposite wall.”

However, these conditions didn’t stay that way for long. Forty years later Clark found that Yosemite’s open meadowland had all but disappeared, estimating that it had been “at least four times as large as at the present time.” The reason for this, known in the nineteenth century but little appreciated until recently, were the many ways that Yosemite’s first inhabitants had transformed their environment over hundreds, if not thousands, of years. Chief among these was the strategic use of fire.

“Native Americans’ uses of fire pervaded their everyday lives,” explains University of California, Davis, ecologist M. Kat Anderson, whose research appears in the edited volume Fire in California’s Ecosystems. The approach centered on setting fires to keep the land open and aid in travel, a wildlife management tool to burn off detritus and increase pasturage for deer, as well as for fire prevention purposes.

“Native Americans thoroughly understood the necessity of ‘fighting fire with fire,’” Anderson says. “Their deliberately set fires were often designed to preclude the kinds of catastrophic fires that regularly devastate large areas today.”

These fires may also have played an important role in promoting biodiversity. In 1996 Anderson wrote the Sierra Nevada Ecosystem Project’s final report to U.S. Congress (pdf here), co-authored with Californa State University, Fresno, archaeologist Michael Moratto. In their report the authors state that most plants useful to the tribes of the Sierra Nevada were shade-intolerant varieties that required regular burning in order to thrive. These species included deer grass for use in basketry, edible native grasses, as well as a variety bulb, corm, and tuber species. By setting intentional fires throughout the forest “gaps or grassy openings were created, maintained, or enlarged within diverse plant communities,” the authors wrote. “The result was that plant diversity was maximized.”


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