Why Climate Change Could Mean More Explosive Southern California Fires

Southern California is home to some of the most diverse plant communities in the world, from coastal sage scrub and oak woodlands to conifer forests and inland chaparral.

But where biologists see ecological niches, fire officials see fuel sources for wildfire.

Many climate models predict that greenhouse gases will create a hotter, drier future for California over the next century. And that will likely amp up the potential for big blazes on these varying landscapes, creating new challenges for firefighters.

One plant community already feeling the heat is the high-elevation pine woodlands in places like Mount Baldy, Idyllwild and Big Bear.

"Here we have a lot of Jeffrey pines and a lot of white firs," Paris Krause pointed out on a recent hike through the piney peaks of the San Bernardino Mountains.

She's a contract botanist with the U.S. Forest Service, hired to study the aftermath of 2015's Lake Fire near Big Bear.

Thanks to extremely dry conditions, that fire quickly spread across 48 miles, reducing entire hillsides of pines to charred trunks.

"There are a few needles left on trees. Like this tree in front of us has four needles at the very peak," she said.

Even with the needles, that tree and scores around it are dead. Krause said the fire was so intense it likely baked any seeds resting in the ground, making it hard for new trees to come back.

That opens the door for another plant community to move in.

"Right here this is a white thorn or a Ceanothus," Krause says, pointing to a small green cluster of leaves. "And right over there, that is a baby Manzanita."

These are both common chaparral species that are now thriving in the wake of the Lake Fire.

"That’s actually a pattern that is quite familiar to us in California," said James Thorne, a researcher with UC Davis.

He says chaparral often comes into piney areas right after a fire, but it doesn’t typically stick around as new saplings grow through it. But that could change.

Thorne and his team of researchers modeled future climate conditions in the state and found that if we don’t significantly curb greenhouse gases, it’s likely that areas now dominated by conifer forests may not be able to sustain them.

"It’ll become more suitable for the chaparral," Thorne said.

That means in a hotter, drier future we may permanently lose our conifers to chaparral. For firefighters, that would mean a shift in approach.

http://i.imgur.com/JVCkGPP.gif
This GIF depicts areas of pine forests from 1981 to 2099. Blue areas show suitable conditions for these forests to thrive. Red areas show unsuitable conditions triggered by climate change. (Source: UC Davis)

"The problem with chaparral, and as we see an increase in it, is that it burns very hot and very rapidly," said Mike Mohler from Cal Fire.

He says chaparral fires grow fast and out of control. Since so many Southern Californians live near chaparral, he says these are the fires that often destroy homes.

The recent Sand Fire was a textbook example: It torched more than 40,000 acres, claimed one life and burned nearly 20 structures.

Mohler says fires in pine forests are hard to fight up close, because there are often few roads and lots of trees. Instead, crews make fire breaks and back-burn to take away fuel as the fire advances.

Chaparral fires, on the other hand, are easier to attack head-on with hoses and hand crews, but that puts firefighters in more danger, he said.

http://imgur.com/vXLadxr
This GIF depicts areas of chaparral from 1981 to 2099. Blue areas show suitable conditions for chaparral. Red areas show unsuitable conditions because of climate change. (Source: UC Davis)

Still, even as chaparral threatens to take over pine forests, chaparral itself is at risk of being replaced by an even more flammable plant community, according to Rick Halsey.

Halsey runs the nonprofit Chaparral Institute, and he is full of facts on the benefits of this ever-present ecosystem. For instance, he says chaparral plants prevent erosion, help rainwater absorb deeper into soils and provide habitat for many animals.

Halsey said most people, though, just see chaparral as a fire waiting to happen.

"And so as a consequence they look at these areas as a place of fear and danger rather than an important part of California’s ecology," he said.

Chaparral systems actually need fire every couple of decades to help certain plants germinate and to weed out others. But he adds that too many fires in too short a time means even these plants can disappear.

That happened on a hillside of the Del Dios Highlands Preserve in San Diego County where a fire struck in 1997 and another one hit 10 years later.

Now the hillside is covered in non-native, weedy grasses.

"The point is there’s no shrubs, and they were here before. The frequency between the two fires eliminated the shrubs and allowed different species to come in."

Halsey says the non-native grasses that are choking out the chaparral dry out easily and burn even faster than the native shrubs that were here before.

Grasslands aren’t new to California, says Cal Fire’s Mohler, but they may be the most dangerous of all the plant types because of how quickly a fire can shift.

"[The fire] can turn in a moment’s notice with just a minor wind shift, and come back against fire personnel, and cause massive burns," Mohler said.

He said firefighters have to be on high alert when dealing with grass fires, but luckily they respond well to attacks from above with water- and retardant-dropping planes.

Mohler says firefighters and forest managers can work together to mitigate new fire risks from changing plant communities, but a lot of the changes expected from global warming can't be stopped.

He and others worry that as these effects strengthen, explosive fires will be the new normal for every ecosystem in Southern California.

This story is part of Forever Fire Season, KPCC’s in-depth coverage of the new reality of year-round fire season in Southern California. Over the next few weeks we’ll cover those affected by the summer’s destructive wildfires and efforts to develop better firefighting tools and reduce the risk of property damage.

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