Along the California coast, millions of oaks are bleeding to death, and researchers say there’s nothing we can do to stop it.

There’s little exaggeration there. Several species of oaks native to central and northern California are succumbing to “Sudden Oak Death,” a disease that causes the trees to break out in cankers that literally bleed sap. The pathogen responsible, Phytophthora ramorum, infects oaks through their trunks, and it is unforgiving.

Bleeding trunk cankers on a tanoak. Cankers can be caused by P. ramorum, though such cankers can also be caused by many other diseases. (Photo Credit: Photo by Brendan Twieg, UCCE Humboldt and Del Norte Counties)

Bleeding trunk cankers on a tanoak. Cankers can be caused by P. ramorum, though such cankers can also be caused by many other diseases. (Photo Credit: Brendan Twieg, UCCE Humboldt and Del Norte Counties)

Not every tree infected with this disease will die, but tanoaks, coast live oaks, Shreve’s oaks, California black oaks, canyon live oaks, will often fall apart as they rot from the inside out.

Scientists are still unsure where P. ramorum came from, but it was probably brought to California sometime in the nineties. It wasn’t identified until much later, and much too late.

“[S]lowing the spread of P. ramorum is now not possible, and has been impossible for a number of years,” reads the latest study on the epidemic, led by Nik Cunniffe of the University of Cambridge, in collaboration with researchers from the University of California, Davis and North Carolina State University, and published in the May 2016 issue of PNAS.

Cunniffe and his colleagues claim that, despite extensive and long-range transmission of P. ramorum along the West Coast, “effective exclusion of the pathogen could, in principle, have been possible,” if California had taken action 14 years ago. That window has closed, and the oaks will die.

The severity of this epidemic cannot be overstated. At this point, the pathogen cannot be stopped from killing California’s oak trees. And the epidemic is spreading. One county in southwestern Oregon has also been infected, as has part of England. In England, however, it isn’t oak that is being killed but larch trees – a completely unrelated tree to the oak.

Both oak and larch have major commercial significance to the timber industry, to say nothing of the ecological roles they play in controlling regional climates. By 2030, some 14,000 square kilometers of California forest will be afflicted with Sudden Oak Death, and all that dead wood will assuredly increase the threat of wildfires in a state ravaged by drought.

How did it get to this point? How did state officials not notice or not act in time?

The fact is, we did this to ourselves.

Dirty Boots, Foreign Bugs and the Curse of Globalization

Despite its parasitic nature, P. ramorum is not a fungus. It is in fact an oomycetes, a eukaryotic microorganism closely related to some algae. It is the same class of organism that caused the Irish potato blight.

That it shares DNA with one of the most notorious agricultural disasters in history might clue you in to P. ramorum’s nastiness, and lead you to think that scientists and/or farmers were keeping their eyes peeled for similar pathogens. But no one’s quite sure how P. ramorum got to California, or England.

“We still don’t know where it came from,” Dr. Tom Kimmerer, Chief Scientist at Venerable Trees, Inc., told Planet Experts. “In the case of the emerald ash borer, we know that it came from China, we know that it arrived in packing material, we know that it travels around when people move firewood. But in the case of Phytophthora ramorum, it seemed to show up simultaneously in California and Europe.”

California oak woodland on the east flank of Sonoma Mountain, Sonoma County, CA. (Photo via WikiMedia Commons)

California oak woodland on the east flank of Sonoma Mountain, Sonoma County, CA. (Photo via WikiMedia Commons)

A Fulbright Scholar, Dr. Kimmerer holds a PhD in Forestry and Botany from the University of Wisconsin and has made it his life’s work to preserve the ancient trees in the Bluegrass Region of Kentucky.

“We here in Kentucky are terrified of this disease,” he added, “because it kills red oaks, and red oaks are an important part of our timber industry. If our red oaks got infected, we’d be in big trouble, economically and ecologically.”

Yet despite the importation of P. ramorum-infected rhododendrons, there have been no reported infections in the region. “We haven’t a clue why,” he said, both amused and frustrated. “We don’t know how this organism makes its living.”

But scientists do have a fairly clear idea of how it gets from place to place.

“In California, bay laurel can get infected, but just the leaf tips die and it doesn’t really harm the tree that much. But then the spores can drip off onto tan oaks and red oaks. This oomycetes is extremely efficient at hopping around the landscape from one plant to another and not killing most of them.”

Symptoms of infestation. (Photo Credit: Photo by Brendan Twieg, UCCE Humboldt and Del Norte Counties)

Symptoms of P. ramorum infestation. (Photo Credit: Brendan Twieg, UCCE Humboldt and Del Norte Counties)

Then visitors to the forest do the rest of the work.

“People go hiking up Mount Tam [located in Marin County, California] where the disease is prevalent, and two weeks later they go hiking in another part of California where the disease is not prevalent. But they’re not going to clean their boots in between,” said Kimmerer.

That it took decades for the general public to notice the problem makes more sense when considering the size and nature of California’s forests.

“A period of probably 10 years went by between the time the disease was first seen and the time we actually started doing something about it. And that’s very typical,” Kimmerer explained. “Somebody goes hiking and they see some dead tanoak, they’re not going to immediately run to the nearest ranger station and report it, they’re going to go, ‘Oh, there’s some dead tanoaks.’

“It’s not until you get enough observations across a large enough area that professionals then get involved, do some diagnoses and try to figure out what it is.”

In this case, the issue is compounded by the fact that P. ramorum is an organism new to science. “I think that further delayed the response,” said Kimmerer. “What the heck is this?”

It is likely that, whatever the heck it is, the pathogen has already traveled around the world via the international trade of commercial plants – like rhododendrons.

A similar thing happened with the emerald ash borer, an Asian beetle largely responsible for wiping out ash trees in North America.

Emerald ash borer (Agrilus planipennis). (Photo Credit: USGS Bee Monitoring and Lab)

Emerald ash borer (Agrilus planipennis). (Photo Credit: USGS Bee Monitoring and Lab)

The eastern United States is beset by the beetle, which was first discovered in southern Michigan outside Detroit. “The insect was discovered about 2005,” said Kimmerer, “but going back people realized it had been here since about 1990.” Like P. ramorum, it took a decade before the beetle’s impact was understood, and by that time it was widespread.

Once a pest or pathogen is introduced to a foreign environment, it is extremely difficult to wipe out unless identified and exterminated early. Richard Cobb, a postdoc at the University of California, Davis, who worked with Cuniffe on the latest P. ramorum study, told The Washington Post that “[i]t would have taken unprecedented cooperation, and an unprecedented amount of funding” to stop the pathogen prior to 2002. That was the last year it might have made a difference.

“This would have been extremely difficult and there would be some tough questions about whether it would be worth, even then, such a huge investment,” he added, suggesting the cost could have been as high as $60 million per year.

“Once these things are established,” said Kimmerer, “there’s a lag between it happening and people noticing. Then there’s another lag before people say there’s something we should do about this. Meanwhile, commerce is moving plant material all over the world all the time.” This, he said, is “basically a recipe for disaster.”

Emerald ash borer. (Photo Credit: U.S. Department of Agriculture)

Emerald ash borer. (Photo Credit: U.S. Department of Agriculture)

So What Happens Now?

The oaks will die. Most of them, anyway.

And that will change the way the forest works, it will change the food chain. Tanoaks increase biodiversity in old-growth redwood forests by forming a valuable “second canopy” that provides food and shelter to animals. The acorns of the tanoak are a staple of acorn woodpeckers, Stellar’s jays and at least four species of squirrels. It is also a traditional food of local Native American communities.

Fewer trees will mean less moisture in the air, and fewer trees plus more dead trees will increase the likelihood of forest fires. It will also exacerbate the California drought, now approaching its fifth year.

In Brazil, the effects of deforestation are already evident, and insidious. Unchecked logging operations have choked off the region’s “flying rivers,” a term that describes how water vapor produced by the Amazon forest travels to the Andes and up to Argentina. The Amazon absorbs and releases billions of liters of water in the form of humidity, and cutting down its trees may have contributed to the worst drought in Sao Paulo in the last 84 years.

Aerial photograph of Sao Paulo Brazil, 2010 (Image: WikiMedia Commons)

Aerial photograph of Sao Paulo Brazil, 2010 (Image: WikiMedia Commons)

California’s climate will undoubtedly change to some degree, but the ecosystem will endure. It’s happened before.

In the first half of the 20th century, chestnut blight killed approximately four billion chestnut trees on more than 200 million acres in eastern North America. Before that disaster, the American chestnut was a major cash crop: Its wood “was used to build everything from homes to furniture to fences, railroad ties, and barrels”; its tannin was used in the manufacture of leather and the dying of silk; its blossoms produced honey; its nuts were highly nutritious.

Today, fewer than 20 large chestnut trees are known to have survived blight for longer than 10 years. Chestnut trees don’t grow anymore, not in any healthy way.

Yet the forests around the heart of traditional chestnut ranges are no less rich. “You wouldn’t notice the loss of chestnut in Kentucky,” said Tom Kimmerer. Other trees filled the niche. “Chestnut was one of our most abundant trees, and it is basically gone now as a species in our forest. You just don’t find it. But what happened was that all the other trees took advantage of the loss of the chestnut and they expanded.”

The same will happen with California’s oaks.

“The situation is bad, it’s a shame to lose these trees, but the natural world has a way of taking care of itself,” said Kimmerer.

But the loss of biodiversity will affect the ecosystem, and when a pest or pathogen wipes out another species of tree, there will be fewer species to take its place. The planet, overall, becomes a little less robust, a little less rich. “Other trees will take over,” said Kimmerer, “but it does dramatically reduce the diversity of our forest. And we’re doing this constantly, so we’re whittling away at our forests. We lost chestnut, we pretty much lost American elm. Now we’re losing ash. I don’t really see an end to that. Even if we only had one new pest or pathogen every 50 years, we would still lose a lot of diversity in our forests.”

And it will hurt the economy. Oak, ash, larches, these species are commercially significant. “White ash is a profound blow to the timber industry in the eastern United States,” Kimmerer explained. “Who knows what we’ll make baseball bats out of in the future, because they won’t be made out of white ash.”

It is not possible to stop the spread of Sudden Oak Death in California. The best we can do is become better monitors of pathogens, to set better standards for international trade, enforce those standards, and require the strictest control in treating wood and packing materials for international shipment.

The worst we can do is apologize. It is 14 years too late to say, “Sorry.”

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One Response

  1. Mikolaj Miazio says:

    Great article. Thank you.

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