How PG&E monitors tree death from the sky

While hovering over villas with Greek-like columns or horses walking next to grapevines, PG&E contractors scrutinized the landscape for any trees that could catch flame if sparked by power lines.

Dead and dying trees are of high concern because of their likelihood to “spread more rapidly in these already dry, hot and drought-stricken conditions,” according to CalFire. In response, PG&E launched a program in 2014 that performs additional inspections of high-risk fire areas that are likely to see an increase in tree mortality due to successive years of drought, according to experts.

PG&E’s aerial reconnaissance of trees has become even more important in recent years, not only because of the megafires provoked by power lines throughout Northern California, but also furthered by California’s drought, which has caused worsening disease and infestations in local tree populations.

In six of the last nine years, Sonoma Valley has received lower-than-average precipitation, according to National Weather Service data.

“Persistent and severe drought conditions are worsening already widespread forest health issues and resulting in new insect and disease outbreaks,” stated an article published by the Sonoma County Farm Bureau. Michael I. Jones, the author of the article and forest advisor for Mendocino, Lake and Sonoma County, observed what he believed to be an emergent infestation of western pine beetles.

“It would seem we are at the initial stages of a western pine beetle outbreak, and I would suspect we will see a significant increase in pine mortality throughout the summer and into the next year,” Jones wrote.

Likewise, Sudden Oak Death affects 163,000 acres in Sonoma County, according to USDA Forest Service aerial surveys — more than any other county in California. Data collected from a program at the University of California, Berkeley called SOD Blitz “showed a nine-fold increase in estimated true infection rate of trees in some areas of Sonoma County from 2015-17 and new outbreaks continued to appear in 2018.“

The proliferation of dead and dying trees pose a potentially grave threat when mixed with the 81,000 miles of distribution lines operated by PG&E in Sonoma County, long enough to go from San Francisco to New York and back more than 15 times.

“A tree that isn't getting the nutrients it needs is more susceptible to pathogens and insects,” said Devon Sharp, a vegetation program manager on the aerial team for PG&E. “When flying up in the air, we’ll identify a tree near a power line that looks like... it's dead or dying, potentially, from the sky and then we take down the coordinates from the air.”

Sharp said the high-risk patrols are axing approximately 1,000 trees a year in Sonoma County alone.

After another disappointing year for rainfall this winter, he said “we need to treat every year now as we need to be on high alert, essentially.”

“We're going into this fire season just as we've done in the historic drought years, which is inspecting more lines, inspecting the trees more frequently, and trying to be better prepared,” Sharp said.

On Thursday, June 30, PG&E contractors tracked power lines through Sonoma Valley. Two foresters sat on the same side of the helicopter to keep eyes on the power line they were tracking, while the pilot operated the helicopter like a hummingbird down the ends of lines and back.

After the aerial crew identifies which trees may be of concern, a ground team is sent in to observe the health of the tree and, ultimately, decide if it will get the axe, Sharp said.

While he oversees the end of many thousands of trees, he’s also born witness to the new beginnings in these fire-scarred landscapes.

“It's really encouraging to see wildlife spring back up after a fire,” Sharp said. “Even in response to the Glass fire in the Sonoma Valley, I've seen greenery reappear.”

Contact Chase Hunter at and follow @Chase_HunterB on Twitter.

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