Kylie Kowalske | Mustang News Credit: Kylie Kowalske | Mustang News

Fifty million — about the number of kangaroos in Australia, people in South Korea and Facebook users whose information was breached in September. Fifty million is also about how many trees are estimated to have been killed by Sudden Oak Death on the West Coast alone. That number is rising every day.

Forestry and natural resources senior Raymond Lee is determined to stop this trend from ever reaching San Luis Obispo County.

Lee is spending his final quarter at Cal Poly predicting where Sudden Oak Death’s pathogen would affect San Luis Obispo County. By creating a risk map of where it would likely exist, Lee said he hopes to be proactive in treating the deadly disease.

Plants get pathogens just like people; some are killed, and some are not. Sudden Oak Death, caused by the plant pathogen Phytophthora ramorum, affects more than 100 species but only kills a certain few. Lee is focusing on California bay laurel — a plant native to the golden state — because it is phenomenal at spreading Sudden Oak Death spores, but does not die from it.

Though officials believe the pathogen has not yet made it to the county, it teeters on the San Luis Obispo County and Monterey County line, according to CAL FIRE Forest Health Specialist Kim Corella.

“Once it’s here, there’s nothing we can really do,” Corella said. “It’s here to stay.”

Sudden Oak Death acts differently in each species, but in tanoaks, coast live oaks, Shreve’s oaks, California black oaks and canyon live oaks, the disease typically lies dormant for years before showing signs of infection. It then kills the tree in a matter of weeks, according to the California Oak Mortality Task Force.

For these species, the disease enters through the trunk — or the leaves, in the case of tanoaks — and causes red or brown cankers that ooze black or red sap before killing the tree altogether.

Because trees have circulatory systems that are far different from that of humans, antibiotics would not work to treat them, according to forestry and natural resources professor Richard Cobb. Even if they did, it would be impossible to treat 5 billion oaks and tanoaks in coastal California, he said.

“There’s no cure and people don’t want to hear that,” Cobb said.

Though the disease is not necessarily curable, Cobb and Lee said they hope knowing at-risk regions in the county can help officials change their surveillance. Cobb described the pathogen as the most important biological source of tree mortality in the coastal range.

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Cobb, who is mentoring Lee through his senior project, said Sudden Oak Death is a serious threat to landowners and land managers throughout the county. He said Lee’s project is something county and state officials have been requesting for some time now.

Corella explained that the culmination of drought and high temperatures have put incredible stress on trees in California. Because of this, Sudden Oak Death is killing trees that would have otherwise survived these conditions. Oaks are some of the most drought-tolerant trees, but climate change and extreme temperature patterns are devastating decades of growth that are hard to get back.

Because the county is so biologically diverse, Corella said they are unsure how devastating the pathogen will be once it gets here. What they do know is that it will have a huge financial impact, because it is expensive to maintain and move trees or provide prescribed burns, which are currently the only options for treatment, according to Cobb.

More importantly, the death of mass amounts of oaks will cause the loss of the keystone species coast live oak, Lee said.

“Imagine going out to some park or reserve and there are just no oak trees,” Lee said. “You’d have a hillside that’s just bushes. And if you don’t have trees, it’s like, ‘Where am I gonna get my shade?’”

Cobb said the areas that would most likely be affected would be parts of Poly Canyon, oak forests on Bishop Peak and some oak forests on Cuesta Ridge, all of which he considers “places that are pretty paramount to the community’s access to natural lands.”

Greater than aesthetic and recreational value, the loss of oak forests would have devastating effects on the ecosystem. According to Cobb, we rely on forests for water quantity and quality, as well as for fire dynamics of the area, and food and shelter for different wildlife species.

Cobb said he believes Sudden Oak Death could have been a factor in the 2008 Basin Complex Fire near Big Sur, as well as the 2017 Sonoma County fires. He said he sees that as his department’s responsibility — to anticipate problems as they come up and to then help local agencies come up with solutions.

“That’s why I was paying attention in [San Luis Obispo] County with this risk map,” Cobb said. “I said, ‘Yes, you do [need one].’ Step one.”

The project

The beginnings of Lee’s project were humble — they started with failure.

In a geographic information system (GIS) class, Applied GIS (NR 418), during Fall 2017, Lee’s group was assigned to work on the very project he is working on now. However, the first time around, the group’s compilation of jumbled data only led them wayward. He said they went in the wrong direction and used all of the wrong methods for weeks. He stayed through Thanksgiving break and missed his brother’s birthday.

“That was a very difficult quarter. Straight up, that is one of the three classes I broke down in and was like, ‘I straight up can’t do this right now.’ That was hard. It was worth it, though,” Lee said.

Lee went to Cobb after the quarter ended and decided he would try again with their data for his senior project.

The team — Lee, enthusiastic to get on his bike and get some fresh air, and curly-haired Cobb, also a cyclist and one who prefers to be shoeless — are a spirited duo. The team said they were excited to get started on something that could be realistically applied to the county.

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From there, Lee spent six months sitting in front of a computer screen searching maps and databases for the likelihood of bay laurels and modeling data, and two months out in the field on his bike collecting data.

The two displayed their research at the California Forest Pest Council Meeting at University of California, Davis on Nov. 13-14. They said they hope once they translate their research into more digestible information, they can make their maps public and their methodology can be used in other counties as a more efficient, inexpensive way to map risk.

Lee graduated in December and hopes to do something with GIS or some form of research post-graduation. Ideally, he said, he would be able to be somewhere where he can spend time on his bike exploring the landscape.

His greatest takeaway from the project: the uncertainty of it all. The first-hand research experience gave him a healthy glimpse of that.

“That’s science: we’re mostly sure this is the right answer,” Lee laughed.


Corella suggested hikers and bikers need to be diligent about cleaning their shoes after going out to prevent the spread of Sudden Oak Death. Because the pathogen’s spores can drop off and stay in the ground for years, if hikers go out in Monterey or Humboldt Counties, where the pathogen has killed millions of trees,  there is a good chance it can be spread to San Luis Obispo if shoes are not cleaned. She also suggested not moving firewood.

Students can stay educated by visiting and participating in the county’s SOD Blitz in May 2019, where volunteers will be educated on the pathogen before being sent into the county to collect samples of trees that may be affected by the disease to be lab-tested.

Corella invites curious community members to call their county agricultural commissioner or send her an email at for more information.

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