- Author: Kara Manke
Reposted from the UC Berkeley News
A team of collaborators including the citizen science project SOD Blitz have detected the first cases of the infectious tree-killing pathogen Phytophthora ramorum in California's Del Norte county.
The pathogen, a fungus-like water mold that causes sudden oak death, has ravaged millions of native oaks and tanoaks along California's central and northern coasts since it was first introduced in the United States in the late-1980s.
The discovery in Del Norte marks the first time that sudden oak death has been found in a new county since the its emergence in nearby Trinity county in 2014, and brings the total number of affected California counties to 16.
“Now every California coastal county between Oregon's Curry County and the very southern border of Monterey County are infested, although the extent and distribution of infested areas within each county is extremely variable” said Matteo Garbelotto, an adjunct professor of environmental science, policy and management at the University of California, Berkeley, and founder and director of the SOD Blitz program.
“If the infestation in Del Norte were to expand, not only it would affect local resources, but it would also provide a bridge connecting the genetically distinct Oregon and California infestations, possibly further facilitating the adaptation of the pathogen to West Coast coastal forests,” said Garbelotto, who also serves as cooperative extension specialist for University of California Agriculture and Natural Resources. “It's a good thing that we detected it, because the sooner we know, the more options are available to minimize the impact of the disease.”
Each year, the University of California, Berkeley-led SOD Blitz project has employed volunteers from around the state to scour their local forests for signs of new outbreaks of the pathogen. Del Norte County has been monitored for these signs since 2004 by collaborators from UC Cooperative Extension, UC Berkeley, UC Davis, and Cal Fire. This year, the SOD Blitz brought additional sampling infrastructure and diagnostic expertise to the effort.
Hundreds of tree samples from uninfested San Luis Obispo county were also tested as part of this year's SOD Blitzes, but no cases were found.
The strain identified in Del Norte is the one called NA1, which is commonly found in California, rather than the emergent and potentially deadlier EU1 strain common in Europe and recently detected in Oregon.
The new finding has been reported to the California Department of Food and Agriculture (CDFA), and has no regulatory implications until the results are officially confirmed by the CDFA.
A new threat in Del Norte
The two infected trees in Del Norte county are located in Jedediah State Park about five miles east of Crescent City, reports Chris Lee, a forest pathologist with Cal Fire who organized this year's SOD Blitzes in Humboldt and Del Norte counties.
“The tanoak trees are located among old-growth redwoods, pretty far from the existing infestations we know of in Oregon and in northern Humboldt County,” Lee said. “Fortunately, past experiences indicate that redwoods suffer only minor damage from this pathogen. Little to almost no mortality of other tanoaks can be observed in the immediate surroundings at this site so far.”
The researchers also conducted follow-up testing on surrounding trees in the area but no additional cases of the pathogen were found.
“We have been monitoring this county for years and I had been hopeful that it would be spared from the disease,” said Yana Valachovic, forest advisor and county director for the UC. Cooperative Extension office in Del Norte and Humboldt Counties and co-sponsor of the Humboldt-Del Norte SOD Blitz. “A round of secondary sampling in nearby trees did not yield the pathogen making it difficult to speculate how the disease may have arrived and the extent of the infestation. Over the coming months we will be working with the landowners and managers of the region to help them assess the situation.”
More than a decade of Blitzes
Since Garbelotto launched the SOD Blitzes in 2007, thousands of volunteers have combed through California's coastal forests in search of signs of Phytophthora ramorum, the pathogen, which causes oozing cankers, browning leaves, and eventual death in infected oak and tanoak trees.
“The Blitzes started because we were and still are facing the necessity of precisely defining the extent of the SOD infestation over a gigantic range, and it was basically impossible for us to hire enough people to actually survey they entire coast of California,” Garbelotto said.
For each Blitz, Garbelotto partners with local organizations to recruit and organize volunteers. After a short training session, participants, many of whom are private landowners, survey a designated area for hints of the pathogen, which is often spread through infected bay laurel leaves and tanoak twigs.
Suspicious-looking leaves and twigs, along with details about the location, are sent to Garbelotto's lab at UC Berkeley, where they undergo a rigorous analysis and DNA testing to confirm the presence of the pathogen.
Every fall, their findings are combined with data from researchers as well as state and federal government agencies and made publicly available on the web (www.SODmap.org).
“Everybody who attends the SOD Blitzes is great, they are really interested and want to protect their trees,” said Kim Corella, a forest pest specialist at CalFire who has been organizing the SOD Blitzes in San Luis Obispo county since 2013.
In 2019, there were 22 local SOD Blitzes ranging from San Luis Obispo county in the south to Del Norte in the north. A total of 455 volunteers participated, 16227 trees were surveyed and 9000 leaves from 1732 trees were sampled and tested at UC Berkeley.
Though the SOD Blitzes have identified a number of new outbreaks, this is the first time that the project has uncovered infections in a new county.
“Our citizen science program run by UC Berkeley has been successful thanks to many collaborators, including UC Cooperative Extension, Cal Fire, the California Native Plant Society and the San Francisco Public Utilities Commission, just to name a few,” Garbelotto said. “Our project is providing key research findings to protect California Natural resources, highlighting the relevance Citizen Science has in the modern world.”
The project is supported by the US Forest Service, State and Private Forestry as well as the National Science Foundation, the Gordon and Betty Moore Foundation and the Pg&E Foundation.
- Author: Sarah Yang
Efforts to predict the emergence and spread of sudden oak death, an infectious tree-killing disease, have gotten a big boost from the work of grassroots volunteers.
A joint study reveals the power of citizen science in SOD Blitz, a survey project in which volunteers are trained to identify symptoms of sudden oak death. Led by Matteo Garbelotto at UC Berkeley and Ross Meentemeyer at North Carolina State University, the study was published today (Friday, May 1) in the journal Frontiers in Ecology and the Environment.
Sudden oak death is a fungus-like disease that has felled hundreds of thousands of trees in California. Crowdsourcing the survey and sampling work allowed researchers to gather information that would otherwise be too impractical and cost-prohibitive to obtain. Researchers then used the data to create a model that predicts the presence of the sudden oak death pathogen, Phytophthora ramorum, based upon such variables as rainfall and density of host trees.
Study authors compared the model based upon crowdsourced data gathered from the 2008-2013 blitzes with models using “pre-Blitz” research observations collected from 2000 to 2007. They found the SOD Blitz model to be more powerful, correctly predicting the presence of the pathogen 74 percent of the time, compared with models based on other sources of data.
“This paper shows that volunteers are as proficient as professionals in collecting data after they get some initial training,” said study principal investigator Garbelotto, an adjunct professor and cooperative extension specialist at UC Berkeley's Department of Environmental Science, Policy and Management. “The data we got from SOD Blitz resulted in the formulation of the best predictive model yet about the spread of sudden oak death in California. Additionally, we were able to identify new infestations and identify trees that needed to be removed. In one case, in Atherton, tree removal resulted in the only successful eradication of the pathogen in North America.”
The SOD Blitz model also revealed novel findings about the spread of the disease, finding that average population density and average maximum temperature were negatively correlated with the presence of the sudden oak death pathogen.
“The population density finding is important because of the debate about the role of humans in spreading sudden oak death disease,” said Garbelotto. “From this work we can say that humans are not currently spreading the disease, and that the pathogen is doing well spreading on its own.”
Beginning the Blitz
Jean Morrell, a retired biologist living on the Santa Lucia Preserve in Monterey County, learned about sudden oak death in 2007 through an on-site presentation and subsequent hike with Garbelotto that was organized for the homeowners on the preserve. The event provided the seeds for the idea of the SOD Blitz as a way to get more people – particularly other homeowners on the preserve – engaged. For Morrell, the idea kicked off a round of phone calls and personal outreach to her neighbors.
Garbelotto launched SOD Blitz the next year, in 2008, and it has since grown into one of the largest citizen science projects in the country, incorporating 21 coastal communities in California. Each spring researchers reach out to participants through news stories, radio announcements, community groups and other recruitment methods.
Participants go through mandatory, on-the-ground training by professionals to learn how to detect and sample infected trees. Training workshops last about an hour, and then volunteers are provided with symptom detection guides, a mobile mapping tool and packets for storing leaf samples.
“When it comes to predictive models, the more data the better,” said study lead author Meentemeyer, a professor of forestry and environmental resources and director of the Center for Geospatial Analytics at North Carolina State University. “This is especially true in less-studied urban ecosystems and people's backyards, where research scientists typically have little to no data. But the data need to be good, otherwise researchers are left dealing with a lot of noise. Motivated people, given a minimal amount of training, are clearly able to provide information that researchers need.”
‘People want to protect their trees'
In any one year, the return rate of participants ranges from 15 percent to as high as 40 percent, Garbelotto noted.
“From that first Blitz, we developed a core group of workers that have continued their interest and have followed up year to year,” said Morrell. “Sudden oak death is in all of our backyards, and it will have an effect on our neighborhoods. This is why we can engage people in the program. It not only allows participants to monitor their own space, but also, if they so desire, they can tromp out into the woods and do work in more remote areas. One only has to give up some ‘sweat equity' to participate, and the results are available to everyone at no cost. It's a win- win.”
Many participants are attracted to SOD Blitz by a shared love of the environment.
“I am an environmentalist, and my passion is trees. I believe they are the lungs of the Earth,” said Debbie Mendelson, who recruits SOD Blitz volunteers as a member of the Woodside Sustainability and Conservation Committee. “I think first and foremost, people want to protect their trees. Then there are folks who want to do something for the good of their community.”
Mendelson noted that SOD Blitz has also provided an opportunity to engage students in science. She has given presentations at local high schools about sudden oak death and citizen science. “I think it is a fantastic opportunity for students who have an interest in science to hear a scientist speak in an understandable and warm manner,” she said.
This year's SOD Blitz recruitment has already begun. Community meetings will be held at various locations through early June for those interested in learning more.
Once verified, data from SOD Blitz is uploaded and freely available online.
The National Science Foundation, U.S. Forest Service, Gordon and Betty Moore Foundation and PG&E Foundation helped support this work.
- Citizen Science Helps Predict Risk of Emerging Infectious Disease (Link to Frontiers in Ecology and the Environment study)
- SOD Blitz Project
- Citizen Scientists Key to Halting Sudden Oak Death (LiveScience op-ed)
- UC Berkeley a pioneer in citizen science