Yosemite National Park - Fire History (U.S. National Park Service)

Indians and Fire
For over 4,000 years, people have relied on Yosemite Valley's meadows and oak woodlands to provide food, medicine, and materials for baskets, string, and shelter. Yosemite's early inhabitants periodically set fires to promote the growth milkweed, dogbane, sedge root, and bunch grass. Research on mud cored from Yosemite Valley showed a marked increase in ash deposits after people began living in Yosemite Valley. When Euro-Americans began living in Yosemite Valley in the 1850s, traditional burning practices were stopped and fire suppression became official policy until the 1970s.

Fire History
Yosemite has also always experienced low-intensity surface fires naturally ignited by lightning. However, open and park-like forests captured in historic photos have been replaced with denser, altered forests as a result of fire supression. The lack of natural fire has led to overgrown and unhealthy forests.

In the left image, Yosemite Valley as it looked in 1899, with large expanses of open meadow and few incense-cedar and pine trees. On the right, Yosemite Valley today, where as much as 75 to 90 percent of meadows have been lost to tree encroachment.

As a result of fire supression, smaller forest openings allow for less understory growth (grasses and shrubs) and wildlife habitat. Small trees have been encroaching on meadows that once would have been maintained by frequent fires. There are now larger accummulations of built-up woody debris in the forest and more smaller trees, creating the potential for a catastrophic crown fire. All of these conditions combined have increased the potential for larger, more dangerous fires. For the past two decades, the National Park Service has restored fire to much of Yosemite, though the present program has not been able to meet the needs of the whole park. Prior to fire suppression, it is estimated that an average of 16,000 of Yosemite’s 747,000 acres may have burned under natural conditions in the park each year.

In Yosemite, fire records date back to 1930 and information is also available for about another decade of documented fire history. Therefore, fire managers at Yosemite have 80 years of records on fire and fire suppression activities on which to rely. In addition, tree ring studies provide a history of fire frequency dating back hundreds and thousands of years. This historical information has been of great importance in creating the goals and objectives for Yosemite's Fire Management Program and current Fire Management Plan.