Arid Environment

Fires, droughts are changing Sonoma Valley’s trees

The burn-scarred landscape of Sugarloaf Ridge Regional Park is healing after a series of devastating fires, but returning to normal has been complicated during an extreme drought fueled by climate change.

It’s not just a matter of if a wild land grows back, but what replaces the vegetation of that area, which is affected by moisture in the climate that is sorely lacking in Sonoma Valley in recent years.

“As climate continues to warm and get less predictable, we have more variable precipitation regimes. That’s also going to impact what’s going to regrow after and what is going to flourish in the future,” said Scott Stephens, a professor at the UC Berkeley’s Department of Environmental Science, Policy and Management.

Sonoma Valley is in transition to a new, more arid climate, which could lead to a landscape which reflects a savanna more than a forest, Stephens said.

But it’s not just climate change at fault, Jason Wells said, a registered professional forester at the Sonoma Resource Conservation District.

For much of the past century, the US Forest Service had policies aimed at suppress fire wherever and whenever it occurred, Well said. But the policy led to the overgrowth of old trees which died, dried up and became kindling for the intense fires in Northern California in recent years.

Patches of the forest burned by the Nuns fire in 2017 are healing today, yet the next generation of saplings face an uncertain future.

“One of the biggest questions is how can these high severity forested areas…the oak woodlands and mixed evergreen forest, what’s going to happen to these places that are already sprouting since 2017?” Stephens said.

Climate change and challenges

While fires bring the nutrients of trees and vegetation into the soil, the seeds and saplings of oaks and other large trees need a moist climate to crack open to access those nutrients, said Chris Carson, Sonoma Valley Stewardship Program Manager for Sonoma Land Trust.

It’s why after a rainstorm on a fire scorched plain, it’s not uncommon to see super blooms of star lilies and whispering bells, otherwise known as “fire followers” ​​for their tendency to grow in fire scarred landscapes.

But all of Sonoma Valley is in an extreme drought, according to the US Drought Monitor, as is about 40% of California overall. Even for plants which have sprouted despite the limited rain may not be safe.

“Some plants will re-sprout, some might be too stressed because of the high-severity fires that come too frequently and they may succumb,” Stephens said. “And you might really have some winners and some losers in terms of species.”

But in addition to the prolonged drought, the rainy season of Northern California has also been shortened. According to one study, the rainy season is starting nearly a month later than it did in the 1960s.

“It’s getting warmer. Winters are more erratic in terms of rainfall patterns,” Stephens said. “We experienced that this year in a big way.”

In late October, parts of Sonoma County received more than 6 inches of rain within 24 hours, shattering some local records. Yet January and February 2022 — two months which typically see showers — were uncharacteristically dry.

These intense and short periods of rainfall complicate the return of oaks and other slow-growing trees, Stephens said, who need sustained moist climates in order to regrow after fires.

Instead, invasive species like Spanish and French Broom — which grow quickly and are often the starting point of wildfires near roadways — overtake swaths of wild land, stealing patches of sunlight and inhibiting the growth of indigenous plants, Wells said.

“(Broom) heavily occupy sites that have significant amounts of sunlight and disturbance,” Wells said. “Roadways are kind of a huge place where they’re found, and roadways are also a huge point of access for a fire start site.”

Sonoma Valley has turned into a precarious environment corresponding with intense weather events, Stephens said. And climate change is making the ecosystem “more vulnerable to high temperatures fire” due to heightened and moisture decreased in trees.

This perilous environment is caused by more than just climate change, it’s also a result of long standing policies regarding forest management, he added.

“But when you talk to indigenous communities, they really emphasize this idea of ​​stewardship,” Stephens said. “I don’t think we realize how much more vulnerable they are today than they once were, say, a thousand years ago.”

Disrupted life cycles

Burns are a natural part of any forest’s life cycle: clearing out canopies of trees for new generations, killing off sick and old plants and trees, and delivering the stored nutrients inside vegetation back into the soil.

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