The Killing Fields

Kent Julin remembers the day in 1998 when he first realized something truly unusual was happening in Marin County.

He was driving near his home in Woodacre when he saw a completely brown coast live oak tree. Julin, a battalion chief with the Marin County Fire Department and a native of Marin, had heard of a strange new tree killer known as Sudden Oak Death, but most people at the time thought it was a bug problem confined to a limited area.

When he saw the dead oak, though, he did a double take. “It was like a librarian walking by a bookshelf and there’s a book missing,” says Julin, who is also a professional forester and has done everything from vegetation management and archaeological studies to environmental research in Alaska. “I thought, ‘Something is wrong here.’”

It was the beginning of a decade-long battle against a disease that began in Marin and has leaped from one coastal city to the next all the way to Oregon, laying waste to the signature tree that graces California’s golden hills.

Julin can now see dozens of dead and dying oak trees as he drives through the picturesque countryside of West Marin. “See that hillside?” he asks, pointing to a grass-covered slope covered partly by green oak woodlands. “In the next ten years most of those coast live oaks will be dead.”

So far, Sudden Oak Death exists in forests and wildlands only in 14 California and Oregon counties, but the potential—indeed, the likelihood—of its spread is real. The pathogen behind the disease has been detected in nurseries and garden stores in 21 U.S. states, in British Columbia and throughout Europe. It has also been found in natural areas in the United Kingdom, the Netherlands, Germany and Ireland.

Sudden Oak Death is now known to have 107 susceptible host plants, including such common garden ornamentals as camellias and rhododendrons. In some woodland areas, virtually every tree—oak, bay, madrone—is infected. Most hosts survive, but do suffer some form of wilting. In redwood trees, for instance, the disease causes some sprouts at the base of the tree to turn brown.
Tan oak, coast live oak and black oak trees are clearly the most susceptible (white oaks are not). Tens of thousands of oaks have already died in Marin and neighboring counties; more than a million trees have died overall.


Efforts to develop vaccines, step up inspections of ornamental plants and convince hikers to clean their boots have helped manage the disease, but the number of infected trees and plants went up in 2006, according to findings released at this year’s Sudden Oak Death Science Symposium in Santa Rosa.

“It’s somewhat like a tsunami,” says Julin. “It’s not a good thing, but it helps to know when it is coming.” There are more than 10 million acres of oak trees along 1,500 miles of the California and Oregon coasts. Live oaks, with their elegant shape and structure, are an integral part of the Marin landscape. Hundreds of animal species—including spotted owls, red-legged frogs and tiger salamanders—live off them.

Julin believes Marin residents are at the epicenter of a vast ecological shift that is transforming California’s woodlands. County supervisors need only look out the windows of the Civic Center and see large patches of brown in the nearby San Pedro Mountains to grasp the seriousness of the problem.

It all started in 1995 when a Mill Valley homeowner complained about dying tan oak trees on his property. Nobody knew it at the time, but it is now believed that rhododendrons delivered from a nursery infected the trees.

The killer microbe apparently made its way to America on ornamental plants from some far-off land, most likely in Southeast Asia, scientists say. Native oaks were particularly susceptible to the invader.

Julin began working with David Rizzo, a UC Davis professor of plant pathology, and Matteo Garbelotto, a UC Berkeley forest pathologist, in an attempt to figure out what was going on.

The telltale sign of the disease, they discovered, was an oozing wine-colored canker on the trunk of an infected tree. This so-called “bleeding” was followed by an infestation of ambrosia beetles and the appearance of black tarlike bubbles called hypoxylon. Quick death followed (thus the name Sudden Oak Death).

Rizzo and Garbelotto finally isolated the microscopic culprit in 2000. It was a funguslike organism called Phytophthora ramorum, the same kind of pathogen that caused the Irish potato famine from 1845 to 1850. Phytophthora means “plant killer” and ramorum means “branched,” which refers to shape of the microbe when seen under a microscope, Julin says.

The pathogen thrives in cool, wet conditions, where it produces thousands of offspring that enter oak trees through the bark and limbs. The spores have two tails that allow them to swim swiftly through water. Scientists theorize that unusually wet El Niño conditions have helped spread the disease.

Trees typically begin dying about two years after a particularly wet year. This summer, which follows two extremely wet years, could be particularly bad, Julin says.
Sudden Oak Death is epidemic in Marin, Sonoma, Santa Cruz and Monterey counties—every tan oak tree in some canyons of Big Sur has been killed. Marin is ground zero. Researchers estimate that as much as 80 percent of the forest canopy at China Camp is infected. The watershed lands on Mount Tamalpais, Blithedale Canyon and the forests around Kent Lake have all been hit hard. Trees have been steadily dying as well in Tamalpais Valley, Tiburon, San Rafael, Nicasio and Inverness.

“If you drive through Samuel P. Taylor State Park, go up on the north side of Bolinas Ridge or go to the Mountain Theater, you will see the same thing,” Julin says. “It’s creeping up slowly in our woods, but to me it is really dramatic. We have front-row seats to evolution.”

Driving through Woodacre, Julin points out a withered California bay tree, the host scientists say is the primary culprit in the spread of the pathogen. The bay is not killed like the oak. Instead, it dies back and then resprouts, allowing spores to continually use it as a jumping-off point.

A bit farther, Julin spots three live oak trees next to a home on Oak Grove Avenue. Each has a dark red bleeding stain on the trunk. He pulls off a chunk of bark. It smells like the cork from a bottle of red wine, another signature of the disease.
“These are doomed; there’s no stopping this,” he says of the trees. Then he sweeps his arm around to indicate several other oaks across the street. “All these trees are being exposed. They are just getting it at different stages.”

The death of so many trees could cause soil erosion, degrade watershed land and drive deer and other wildlife that depend on oak acorns onto private property. Live oak trees also add as much as $30,000 to property values. And trees killed by the disease can cost property owners thousands of dollars each to remove.



Die-offs have happened before. Dutch Elm Disease and the Chestnut Blight ravaged entire tree species on the East Coast during the last century. The American chestnut tree, which grew 80 to 100 feet tall, was the king of the eastern forest until the 20th century. It was said that a squirrel could travel from Michigan to Georgia without ever leaving the chestnut canopy. Then, around the turn of the century, a fungus imported to America on Asian chestnut seedlings spread through the native species range. Within a few decades, entire forests—more than 3.5 billion trees—had been wiped out.

“Sudden Oak Death is like the Chestnut Blight,” Julin says. “What’s disturbing about it is that, unlike Dutch Elm and the Chestnut Blight, which attacked one species, a lot of our native species are affected. They don’t all die, but they are carriers.”
Oak trees are normally fire resistant, but those killed by Sudden Oak Death litter the hills with bone-dry wood. “What this means for a firefighter is you have an enormous amount of standing wood that is dead,” Julin says. “It creates a fire ladder of fuel that allows a fire to climb to the tops, creating a crown fire. Those are the most difficult fires to stop.”

Amid this bleak picture, there is some hope, says Julin.   In 2003, the first major breakthrough in the treatment of the tree disease was approved for use on oaks. The phosphate product, developed by the Australian company Agrichem, protects endangered oaks from infection and helps infected trees fight off the disease, according to UC Berkeley scientists. The state approved two versions of the compound—a spray and an injection—for use by professional arborists and foresters.

Also, a new diagnostic test gives arborists, growers and inspectors a tool to quickly determine if a tree is infected with Phytophthora ramorum. Scientists are also trying to isolate oak strains that are resistant to the disease so they can be cultivated and replanted. Mountain bikers and hikers are being encouraged to clean their tires and boots before they leave an infected area so that they do not carry the pathogen to other places.

“But these practices are only going to slow the spread of the pathogen,” Julin says. “We’re not going to stop it. There is nothing that is going to stop it.”

Julin says the dispersal of Sudden Oak Death and other pathogens is assured by the thriving world market for ornamental plants. Inspectors cannot check every nursery plant, and infected plants often slip past.

In 2004, a Southern California nursery shipped plants carrying Sudden Oak Death to stores in at least five states. As a result, 15 states imposed partial or full bans on California nursery stock, damaging the state’s $13 billion plant-growing industry.

Even if the disease could be controlled by chemicals, it can still live for years in hosts like the bay tree and infect future generations of oaks. Julin thinks residents of Marin should prepare themselves to live with “huge changes” in the landscape.

“I think that’s what we’re in for,” he says. “Homeowners need to be aware that these trees can fall and plan for the future by planting trees that are not susceptible. If we just sit back and do nothing, we are only going to be the victims of what happens.”

Image 2:  Marin County Fire Department forester Kent Julin with a dying live oak
Image 3:  An infected oak: leafless branches, already discolored