Mass tree die-offs lead to disaster, and a Cal Poly professor is looking for answers

An international study published by a Cal Poly forestry professor found that trees around the globe are dying faster due to prolonged exposure to drought and heat — and those deaths are creating prime conditions for the kinds of devastating wildfires and mudslides California has seen this year.

Richard Cobb, who is in his first year teaching in Cal Poly’s natural resources management and environmental sciences department, led a collaboration of 20 researchers across 17 countries that aimed to address the potentially deadly and destructive conditions resulting from future forest die-offs with the hopes of spurring better forest management.

The study comes at a critical time. Cobb said the Sonoma and Napa county wildfires in October — which destroyed more than 10,000 homes and killed 44 people — were “a real wake-up call” for researchers who have studied disease dynamics in Sonoma and Big Sur for more than a decade.

Tree Mortality still
Cal Poly assistant professor Richard Cobb recently published findings that show forests worldwide are dying at an accelerated rate in part because of prolonged exposure to drought and heat. David Middlecamp dmiddlecamp@thetribunenews.com

“It really laid bare that we need to understand how disease may affect the dynamics of wildfire,” said Cobb, an Arizona native who earned his PhD in ecology at UC Davis. “Understanding that can help us improve our emergency planning. My hope is that it could even help us with wildland vegetation management in order to protect us from these kind of catastrophic impacts.”

A worldwide effort

According to the study, researchers are finding that many of the forest disturbances seen around the globe — defined as a temporary change in environmental conditions that causes a pronounced change in ecosystem — are linked.

Just in recent months, Cobb said, Central Coast residents have experienced this connection firsthand.

The burn areas in Montecito left over from the nearly 282,000-acre Thomas Fire were particularly vulnerable to flash flooding, resulting in mud and debris flows that have killed at least 20 people.

Cobb’s research reaffirms that the large-scale die-offs seen with sudden oak death — a disease that’s killed millions of trees along the Northern California coast — and the bark beetle infestations in the Sierra Nevada that are turning huge swaths of pine trees brown, have been increasing in severity and frequency across the world.

Cobb and his colleagues studied forest mortality events in Africa, Australia, Europe, Central America, South America and North America. He authored the study and said his role was to bring the collected data together in a consistent way.

Though each ecosystem is different, the common link in mortality events is heat and drought, conditions expected to worsen in the coming decades and century.

“As precipitation patterns and temperature patterns change,” Cobb said, “with the overwhelming trend being increases in the length, frequency and severity of drought as well as increases in average temperature, we are seeing a lot more mortality.”

In the Sierra Nevada, trees stressed by drought are unable to create pitch to defend against the voracious beetles, and they can die suddenly in staggering numbers. That can turn once-healthy forests into veritable tinderboxes.

A count in December blamed bark beetles and years of drought for an estimated 129 million dead trees over 8.9 million acres in California, according to the Forest Service and Cal Fire.

This June 6, 2016, photo shows a tree stained blue by a fungus carried by the bark beetle, which diminishes trees’ value as lumber, near Cressman, California. California’s drought and a bark beetle epidemic have caused the largest die-off of Sierra Nevada forests in modern history. Scott Smith Associated Press

Lessons for government

A key goal of Cobb’s study was to develop a new set of research questions and a unified framework that would provide officials at the county, state and federal levels with a road map to deal with forest die-offs.

Cobb said one of the reasons the research paper is getting a lot of attention among the academic community is that the authors made a significant effort to identify things that had commonly gone wrong with management solutions.

Among the mortality events studied, Cobb said many of the same mistakes came up, particularly with agencies being unwilling to define their forest protection goals and pursue them through an experiment-based approach.

“It’s not a new idea, adaptive management, but it is one where we constantly have to remind the powers that be to do experiments,” Cobb said. “Collect good data, and when they don’t work out, don’t try to cover it up. Learn something from it.”

And when it comes to confronting the large and costly wildfires that have become more frequent with climate change, Cobb said government budgets don’t accurately reflect the cost of fully combating them.

In this June 6, 2016, firefighters with the California Department of Forestry and Fire Protection remove dead trees near Cressman. Years of drought and a bark beetle epidemic have killed more than 129 million trees as of December 2017. Scott Smith AP

“We have to throw all the resources we can at these things in order to protect lives and protect property,” Cobb said. “But the agencies have to borrow from their other funds in order to pay for that.

“It’s a self-fulfilling process.”

Cobb said elected policymakers carry some of the burden for not adequately funding fire and treatment separately, making the cycle worse.

That’s helped unify people working in plant pathology and schools of forestry to improve management strategies moving forward, he said.

“Everybody is confronting some sort of problem,” Cobb said. “They’re confronting a problem that causes pain in people’s lives — economic, famine, problems with a fire — and I think a lot of people in these fields are driven to improve those conditions, the conditions that are costly to people’s lives.”

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