Where may it burn this year in the North Bay? Experts say even recent wildfire areas at risk

Editor's Note: This story, originally published May 16, included a Press Democrat map showing the fire history in the region. No part has been more impacted than Lake County, which has been hit by major fires every year since nearly 2015.

Four years after it roared into Santa Rosa, the Tubbs fire remains a menacing presence in Fountaingrove, where it consumed nearly 1,600 homes and a new fire station in the fall of 2017.

Dead trees and regrown Scotch broom — both highly flammable — now abound in the canyons and drainages of Fountaingrove, where the windblown wildfire ripped through oak and conifer woodlands that hadn’t seen a major fire in more than a half century.

Residents are jolted by the sound of limbs crashing to the ground and avoid entering the forest of skeletal trees.

And it’s by no means an isolated concern as the drought-stricken North Bay heads into a foreboding fire season with a legacy of 23 major blazes totaling nearly 1.5 million acres — the equivalent of 130% of Sonoma County — from 2015 through 2020.

The names of those fires are seared into the region’s memory, and their footprints now abut across a burned landscape stretching from the Mendocino National Forest to Interstate 80 outside Vacaville and from the Russian River near Guerneville to Blue Ridge overlooking Lake Berryessa and the Central Valley.

Interactive Press Democrat map showing the major wildfires that have burned in Sonoma, Napa, Lake and Mendocino counties since 2015. (The Press Democrat)

Much of that landscape could burn again this year, say fire ecologists and firefighters. That includes areas scorched by Sonoma County’s five worst wildfires — the Tubbs and Nuns in 2017, Kincade in 2019 and last year’s Walbridge and Glass fires.

“Fire is a natural occurrence on the landscape, and as such California ecosystems have evolved to survive and, in some cases, thrive when impacted by fire,” said Cal Fire Division Chief Ben Nicholls, who oversees Sonoma County operations.

The risk has been amplified by drought and by the kind of fuels that big, fast-moving wildfires can leave behind or promote in their wake. As a result, most areas within the footprints of the recent blazes have “enough available vegetation” to burn again, Nicholls said, allowing that reduced fuel will diminish their intensity.

The ultimate consideration is wind, which “overrides all other factors,” Nicholls said, noting the North Bay’s catastrophic infernos were pushed by winds hitting as much as 60 to 70 mph.

Nature’s resilience helped restore the hazard in Fountaingrove, where the loss of tree canopies let in sunlight that promoted heavy regrowth of Scotch broom, creating conditions that could be worse than in 2017, said Paul Lowenthal, Santa Rosa’s assistant fire marshal.

The fire season is off to an ominous, early start with a red flag warning from May 7-11 amid a run of near-record-breaking heat in the region and winds clocked at up to 64 mph over Mount St. Helena. Cal Fire said that by Friday more than 2,000 wildfires this year have charred nearly 14,000 acres — a head start even over last year, when 4.2 million acres burned in the state’s worst-ever year for wildfires.

The Santa Rosa Fire Department declared Monday as the official start of fire season in the city, saying it comes considerably earlier than normal “due to severe drought conditions locally and throughout the state.”

The U.S. Drought Monitor listed about 60% of California in extreme drought — the second highest category — including all of the Bay Area. A year ago, just 3% of the state was in that condition.

Citing the potential for a “long and significant fire season,” Fire Chief Scott Westrope said, “I ask that the community please take the appropriate measures to protect your home and your property this season.”

Based on the movement of past wildfires — including the Hanly fire of 1964 and the Tubbs, Kincade and Glass fires — Santa Rosa is bracing for the greatest fire threat coming from the north, Lowenthal said.

The city is intent on clearing fuel from the Fountaingrove, Mark West and Riebli areas and the north side of Rincon Valley, and is preparing an application for a Cal Fire fire prevention grant that could cover 75% of the cost to property owners for the work, he said.

The state is expected to allocate more than $200 million to the program to pay for cleanup work that could begin this year, said Paul Berlant, Cal Fire assistant deputy director.

But what the North Bay’s fire-prone history portends for this year remains a “nuanced question,” said Sasha Berleman, fire ecologist at Audubon Canyon Ranch and a federal firefighter.

Sonoma County is a “mosaic of ecosystems” that can be more or less flammable after a wildfire, she said.

In Armstrong Redwoods State Natural Reserve near Guerneville, the low-intensity Walbridge fire left the green canopies of the redwoods and Douglas firs intact while consuming dead wood and natural litter on the ground, preserving the shade that keeps the forest cool and damp, she said.

That’s exactly what controlled burns are intended to do as intentionally set ground-level fires create defensive buffers around and between developed areas and establish strategic fire breaks in increasingly fire-prone regions like the Mark West Creek corridor north of Santa Rosa.

The carefully staged burns, widely used at Pepperwood Preserve in the Mayacamas Mountains northeast of Santa Rosa, are a modern revival of the fires set by native people for millennia to clear out cluttered forests, promote plant growth and flush game.

But when intense wildfires rush into woodlands crowded with small trees and accumulated litter — so-called ladder fuels — flames ascend to the canopy with deadly consequences for the mature trees.

When the main stem of a tree burns severely enough that it will inevitably die, it can resprout from the base and grow in a big, brushy mass that can push 6 feet high, said Berleman, who has a doctorate in wildland fire science from UC Berkeley.

Combined with fire-cured logs, these masses become the “perfect scenario” for a another high-severity fire.

“That’s where I get really concerned,” she said.

Berleman has seen that development at Audubon Canyon Ranch’s 535-acre Bouverie Preserve and other places along the east side of Sonoma Valley in the Nuns, Tubbs, Kincade and Glass fire footprints.

The map created by The Press Democrat of the region’s recent major wildfires shows little overlap between the blazes, and last year’s Glass fire was noteworthy for shooting the gap between the Nuns and Tubbs fires.

Nicholls recalled the Glass fire burned into the Nuns fire footprint where it crossed Adobe Canyon Road into an area with a lighter fuel load, enabling firefighters to stop the Glass fire along its southern edge.

Pepperwood Preserve, a 3,200-acre tract devoted to conservation science and education, is in a unique position to quantify the impact of wildfires after the Tubbs swept over 95% of the terrain followed by the Kincade fire scorching 60% two years later in 2019. The Glass fire came within 5 miles last year.

The first blaze killed 50% of saplings and 30% of mature trees in research plots that include 4,000 oaks, firs and madrones, said Lisa Micheli, a watershed scientist and the nonprofit’s CEO.

Now assessing the loss from the Kincade fire, Pepperwood’s staff is intrigued by the collapse of oak, bay and fir trees that appeared to survive both fires in what Micheli called “delayed mortality.”

“We don’t know what grows back,” she said, speculating the future landscape may sustain more shrubs, which burn and come back, and fewer trees.

Douglas firs have been hit hardest, but Micheli said they are a native invasive species that multiplied during the era of fire suppression and are “not a big loss.”

The preserve’s Douglas fir trail has been renamed the Kanamota Trail, after the Wappo name for Mount St. Helena.

Pepperwood’s rebuilt structures are fire-hardened, and an evacuation plan is in place.

Asked if the preserve could burn again this year, Micheli said: “I believe so.”

You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.