Muir Woods' scarred trees reveal history of wildfires

More than a million visitors a year come from all over the world to marvel at the magnificent redwoods at Muir Woods National Monument, an untouched old forest only a dozen miles from the Golden Gate Bridge.

People wandering through Muir Woods cannot help but notice an ominous sight: dozens of trees bearing the blackened scars of old fires. The flames burned into the heart of the trees, and some of the scars are deep enough and tall enough so that two or three people can stand inside the living tree. The scars, some of them hundreds of years old, show that wildfire is not new to this part of the world. These scarred trees are part of our past — and our future. Fire is as much a part of California as the summer sun and the winter rain.

The oldest trees in Muir Woods date to the 13th century, when Genghis Khan invaded China and the English barons forced King John to sign the Magna Carta. Even then fire stalked the forest.

One of the old-growth trees in Muir Woods was cut down after a localized fire about 10 years ago — and scientists found history inside. “There were very many scars,” said National Park Service scientist Alison Forrestel. Some of the more recent scars dated from about 1820, others from the period 1835 to 1841. The biggest was in 1822, the most recent in 1863. The scars seem to indicate that wildfires swept through Muir Woods fairly regularly and they were intense enough to blacken tall redwoods.

And redwoods, Forrestel said, “are very resistant to fire,” with thick bark and wood that is tough to burn. That is one reason redwood is so valuable as lumber and led to the logging of most of California’s huge forests. Old-growth redwoods survived to tell the fire tale in only a few places, including Muir Woods.

The scars in Muir Woods are evidence of wider wildfires. If that old forest burned, it is logical to conclude almost all the wooded areas of California had major fires over the centuries.

But the West Coast fire story goes back thousands of years more — and involves major human impact on the land.

“The Native Americans used fire as a tool for 15,000 years,” said Jared Childress, a fire specialist with the Audubon Canyon Ranch in Marin County.

The native people relied on acorns as a food source, and often burned the early crop of acorns to eliminate insects. “The second crop would then be better,” Childress said. They also used fire to clear brush and drive and snare game animals.

“They also knew when to burn and how to burn,” he said. In that way, the native people could control the fire. The fires, however, changed the ecology of what became California, he said. Because the fires affected the soils and composition of the forests, “there were more trees like the bay tree and Douglas fir as a result,” he said.

Of course, natural causes — like lightning storms — also produce fires. And often fires got out of hand, because once they started, there was no way to put them out. Early European explorers sailing on the coast reported big fires on shore, and in the Spanish and Mexican periods there were times when the Bay Area was choked with smoke, much as it has been in recent days.

But there is a big difference between those times and now. Best estimates put the pre-European population at about 300,000— fewer people than modern Placer County. Now there are 39 million Californians.

To protect those people, almost all fires have been vigorously suppressed. The result has been both an increase in population and in the fuel in the state’s wooded areas.

The major problem is in what foresters call the forest understory — brush, dead trees, snags. “It’s not the big trees that are the problem,” Childress said. “It’s the small ones.”

And fires are increasing in number and size: the Santa Barbara fires of 1990, the East Bay hills fires of 1991, the blazes near Yosemite, the deadly Wine Country fires last year. And the Carr and Camp fires this year.

“We know strong winds that drive fires are not new to the region,” Childress said. “And neither are dry periods. But now we add climate change with warmer summers, drier winters, a big fuel buildup — a combination of all those things.”

Childress advocates controlled burns under carefully monitored conditions to ease the threat. But that’s not easy to do. The last major controlled burns on Mount Tamalpais near Muir Woods were more than 20 years ago. There were a lot of complaints about smoke and health.

And in 2000, a poorly planned “prescribed burn” set by the National Park Service got out of control and blackened 80 square miles and 400 houses near Los Alamos, N.M. That made it very difficult to use large controlled burns. Conditions have to be nearly perfect.

But Childress continues to advocate controlled burns. “California is going to burn,” he said. “The question is how, when and where we want it to burn.”

Carl Nolte is a San Francisco Chronicle columnist. His column appears every Sunday. E-mail: cnolte@sfchronicle.com Twitter: @carlnoltesf

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