How wildfire can create healthier forests

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Berkeley News writer Kara Manke discusses a new UC Berkeley report that shows how allowing lightning fires to burn in Yosemite's Illilouette Creek Basin recreated a lost — and more resilient — forest ecosystem. She spoke with Scott Stephens, a professor of environmental science, policy and management at Berkeley and co-director of Berkeley Forests. “We can't just allow wildfire to manage our landscapes,” Stephens told Manke. “If we don't change it in 10 or 20 years, the forest ecosystems are going to change right in front of our eyes, and we're just going to be passengers.”

Yosemite National Park's Illilouette Creek Basin in September 2018. (UC Berkeley photo by Emily Gonthier)

Read a transcript of Berkeley Voices episode #83: “How wildfire can create healthier forests.”

Intro: You're listening to Berkeley Voices. I'm Anne Brice.

[Music: “Calisson” by Blue Dot Sessions]

A lot of us might remember Smokey Bear. He was that serious cartoon bear wearing a pair of blue jeans with a belt buckle and a hat that read “Smokey.” He was in PSAs everywhere — on posters, on TV and the radio, saying his unforgettable slogan:

[Forest fires PSA from 1988: “Remember, only you can prevent forest fires.”]

Created by the U.S. Forest Service and the Ad Council in the 1940s, Smokey Bear was the symbol of responsibility. I remember when I was 8, I met someone dressed as Smokey Bear on a class field trip. And I left this meeting having learned something that would stick with me for a long time: that fire was the enemy — something that should be suppressed, extinguished — and definitely not allowed to run rampant through our precious forests.

But Smokey Bear, we now know, wasn't giving us the full picture.

A new report from UC Berkeley has shown that allowing certain wildfires to burn can have a lot of benefit to the ecology of a forest, and for the humans and wildlife that depend on forest resources.

[Music fades]

My colleague at Berkeley News, Kara Manke, spoke with the senior author of the report, Scott Stephens. He's a professor of environmental science, policy and management at UC Berkeley and co-director of Berkeley Forests.

Anne Brice: Hi Kara, welcome to Berkeley Voices.

Kara Manke: Hi Anne, it's great to be here.

Anne Brice: So, Kara, can you start by talking about this report and what Scott Stephens and his team found?

Kara Manke: Yeah, certainly. So, for many years now, Scott Stephens has been leading research in a watershed in Yosemite National Park called the Illilouette Creek Basin. And what makes Illilouette unique is that since the early 1970s, forest managers have had a policy of trying to let lightning fires burn pretty much as they naturally would: trying to keep a close eye on them, but not putting them out unless they absolutely have to.

And, as a result, they have created this patch of forest — it's about 60 square miles — that has become almost like a natural laboratory for forest ecologists who want to understand better the interaction between wildfire and forest ecosystems.

Scott Stephens is a professor of environmental science, policy and management at UC Berkeley and co-director of Berkeley Forests. (UC Berkeley photo)

Here's how Stephens describes the Illilouette Creek Basin today:

Scott Stephens: I mean, it really is a place that shows tremendous change, variability, tree death, tree regeneration, meadows, areas also with big trees  — there are a lot of big trees out there. So, I think it's really what the Sierra Nevada was 200 years ago.

Anne Brice: What were the forests like in the Sierra Nevada back then?

Kara Manke: We don't know exactly what the forests of the Sierra Nevada looked like 200 years ago, but we do know that there used to be a lot more fire. Lightning would regularly start fires that would burn parts of the forest, and also a number of Native American tribes would light fires to help with hunting and to encourage biodiversity.

However, with the arrival of European colonists in the late 1800s, fire really came to be seen as the enemy, and when the U.S. Forest Service was created in 1905, one of its main missions was fire suppression. And as a result, many of the forests in the Western U.S., including in the Sierra Nevada, are now very dense and have this almost wall-to-wall tree cover.

Scott Stephens: We look at forests with an eye that they all need to be green all the time, and they're all made with big trees. It turns out no forest can do that. You have to regenerate it. You have to get young trees and allow them to regenerate. So, Illilouette is doing that.

[Music: “Turning to You” by Blue Dot Sessions]

Anne Brice: We are in the middle of wildfire season. And we've already seen several catastrophic fires, like the month-old Dixie Fire in California, which is now the largest fire in the U.S. It has destroyed more than 1,000 homes and businesses and isn't close to being contained.

Many people are saying these fires are happening mostly because of climate change. But Stephens says it's more complicated than that — that it has more to do with the state of our forests. Can you explain what he means by that?

Kara Manke: Yeah, one of the most interesting things that Stephens said is that he thinks this hotter, drier weather that we're seeing as a result of climate change is only about 20 to 25% responsible for the recent increases in catastrophic wildfires in California.

He thinks the rest is actually due to the structure of our forests, basically the way that more than a century of fire suppression and past practices of timber harvesting has allowed so much excess fuel to build up. Illilouette provides evidence of this, he says, because even though the region has also been affected by climate change, just like everywhere else in the Sierras, the severity of the fires that they are seeing in Illilouette have stayed the same.

Anne Brice: Do they know why wildfires haven't been getting any more severe in Illilouette?

Kara Manke: Yeah, so one reason for this fire resilience might be that patches of grassland and wet meadow that are created by recent burns can actually form natural barriers that prevent the spread of future fires.

Another really interesting discovery that they have made is that, perhaps counterintuitively, frequent fire actually increased the amount of water that is available in the forest and may have also helped trees survive during recent droughts.

Scott Stephens: The thing that just sparked my interest was the Hoover Fire, a 2001 burn, and that was a pretty big one. So, we had actually had some plots in an area previous to the Hoover Fire. So, we went out afterwards to find them and just do some measurements. And I remember walking in that place. I had walked out there before. It's a very typical lodgepole pine forest, you know, kind of big trees, very little understory, dry ground.

But when I walked out there after the Hoover Fire, probably around 2003 or something like that, all of a sudden I'm walking in six inches of water, and I'm going, “What the heck happened here? This is really remarkable.”

Anne Brice: So, what the heck did happen? How could wildfire create water?

Kara Manke: Stephens actually enlisted the help of a number of hydrologists, including many at UC Berkeley, and what they found from a combination of measurements on the ground in Illilouette and also hydrological simulations, is there are likely two major factors at play.

[Music: “Headlights-Mountain Road” by Blue Dot Sessions]

The first is that, with fewer trees, there is simply less demand for water. And the second is that these small gaps in the forest canopy that are created by wildfires actually allow more rain and snow to reach the ground and be absorbed by the soil.

Anne Brice: So, Kara, it sounds like there are a lot of benefits to letting wildfires burn in forests. Are we trying to do this outside of Illilouette?

Kara Manke: Yeah, I think there is a growing recognition that reintroducing fire to these forest ecosystems is more important than ever. But, in a lot of ways, we've also now created a situation in which it's riskier than ever, as well.

With the increase in heat waves and droughts that we've seen, paired with these dense forests that are full of fuel, it's now even more difficult to control these fires once they start, which is what we're now seeing with these massive fires like the Dixie Fire.

And in early August, because of some of these concerns, the U.S. Forest Service actually changed its guidelines, now telling firefighters that, for now, they must put out every fire as quickly as possible. Stephens said that they will evaluate this new policy next year.

Anne Brice: Are there other less risky ways to help our forests be more resilient to fire without letting fires burn? Is there anything we can do beforehand to kind of prep them in some way?

Kara Manke: Yeah. Luckily, letting these natural lightning fires burn isn't the only tool we have for shaping our forest ecosystems.

Stephens advocates for more aggressive prescribed burning, which is basically going in and deliberately lighting fires during low-risk times. So, this is often in the late fall, winter or spring, and letting those fires clear out some of this underbrush and built-up fuel.

A similar option is restoration thinning, and that's where you go in with machines instead of fire to take out some of the underbrush and some of these extra trees, focusing on the vegetation that you want to keep. These types of modifications on their own can really help the ecology of the forest, and they can also serve as tools to help make the forest safer to allow more natural lightning fires to burn, as well.

Scott Stephens: You know, it's been 50 years. What we've learned there I think helps us understand what is possible. We can't just allow wildfire to manage our landscapes. That's crazy. I think we have 10 to 20 years to actually change the trajectory of forest ecosystems in the state. If we don't change it in 10 or 20 years, the forest ecosystems are going to change right in front of our eyes, and we're just going to be passengers. So, that's why it's so important in earnest to start to do work like this.

[Music fades]

Anne Brice: You also talked with Stephens about a project he and his team started this summer working with the Amah Mutsun Tribal Band in the Santa Cruz Mountains. They're working with the tribe to restore their cultural fire regimes. Can you talk about what this partnership looks like and what they're hoping to accomplish with it?

Kara Manke: Yeah. There is a growing recognition that the cultural burning practices of the Indigenous people of California really had a lot of benefit to forest ecosystems. So, when it comes to land management, it is important not just to implement the prescribed burning and restoration thinning that researchers are exploring, but also to work with Indigenous people so that they can resume some of these important cultural practices that involve fire.

Anne Brice: Incredible. Kara, thanks so much for joining me on Berkeley Voices.

Kara Manke: Of course, thanks for having me.

Anne Brice: Kara Manke is a science and health writer for Berkeley News in the Office of Communications and Public Affairs at UC Berkeley.

Read Manke's story, “How wildfire restored a Yosemite watershed.”