- Author: Kara Manke
Reposted from Berkeley News
For nearly half a century, lightning-sparked blazes in Yosemite's Illilouette Creek Basin have rippled across the landscape — closely monitored, but largely unchecked. Their flames might explode into plumes of heat that burn whole hillsides at once, or sit smoldering in the underbrush for months.
The result is approximately 60 square miles of forest that look remarkably different from other parts of the Sierra Nevada: Instead of dense, wall-to-wall tree cover — the outcome of more than a century of fire suppression — the landscape is broken up by patches of grassland, shrubland and wet meadows filled with wildflowers more abundant than in other parts of the forest. These gaps in the canopy are often punctuated by the blackened husks of burned trunks or the fresh green of young pines.
“It really is a glimpse into what the Sierra Nevada was like 200 years ago,” said Scott Stephens, a professor of environmental science, policy and management at the University of California, Berkeley, and co-director of Berkeley Forests.
Stephens is the senior author of a new study that gathers together decades of research documenting how the return of wildfire has shaped the ecology of Yosemite National Park's Illilouette Creek Basin and Sequoia and Kings Canyon National Parks' Sugarloaf Creek Basin since the parks adopted policies for the basins — at Illilouette Creek in 1972 and Sugarloaf Creek in 1968 — to allow lightning-ignited fires to burn.
While the prospect of smoke over iconic Half Dome has worried politicians and tourists alike, the work of Stephens and his colleagues demonstrates that allowing frequent fires to burn in these basins has brought undeniable ecological benefits, including boosting plant and pollinator biodiversity, limiting the severity of wildfires and increasing the amount of water available during periods of drought. All these benefits are also likely to make the forest more resilient to the warmer, drier conditions brought by climate change, the research suggests.
“In many ways, fire has successfully been restored to Illilouette, and it has made for a complex mosaic of vegetation with cascading effects on things like water,” said study co-author Brandon Collins, who holds a joint appointment as a research scientist with Berkeley Forests and with the U.S. Forest Service. “In Illilouette, you can have patches of young, regenerating trees from a fire 15 years ago, or areas where a classic understory burn has resulted in big, old, widely-spaced trees. You can even have areas where fire has missed because there's more moisture, such as adjacent to a creek or on the edge of a meadow. All this complexity can happen in a really short amount of space.”
The study findings arrive in the middle of a critical fire season, when drought conditions throughout the western U.S. have already sparked numerous large wildfires, including the Dixie Fire, which, as of Aug. 8, was the second largest wildfire in California history. While climate change has played a role in increasing the severity of these fires, Stephens said, Illilouette Creek Basin serves as an example of how current forest conditions in the Sierra — largely shaped by decades of fire suppression — are also driving these massive blazes.
“I think climate change is no more than 20 to 25% responsible for our current fire problems in the state, and most of it is due to the way our forests are,” Stephens said. “Illilouette Basin is one of the few places in the state that actually provides that information, because there is no evidence of changes in fire size or in the severity of fires that burn in the area. So, even though the ecosystem is being impacted by climate change, its feedbacks are so profound that it's not changing the fire regime at all.”
Returning fire to Yosemite
For millennia, wildfires sparked by lightning, or lit by Native American tribes, regularly shaped the landscape of the western U.S., not only causing destruction, but also triggering necessary cycles of rebirth and regeneration. However, the arrival of European colonists in the late 1800s, followed by formation of the U.S. Forest Service in 1905, ushered in an era in which fire was viewed as the enemy of humans and forests alike, and the vast majority of wildfires were quickly extinguished.
By the 1940s and 1950s, a number of forest managers and ecologists had begun to question the wisdom of fire suppression, noting that the practice was eliminating valuable wildlife habitat and increasing the severity of fires by allowing decades of fuel buildup. These fire proponents included A. Starker Leopold, an acclaimed conservationist and professor of zoology and forestry at UC Berkeley, as well as Harold Biswell, a professor at UC Berkeley's School of Forestry.
In response to a foundational 1963 report led by Leopold, the U.S. National Park Service changed its policy in 1968 to allow lightning fires to burn within special fire management zones — usually remote regions at high elevations — where danger to human settlements was low. Sequoia and Kings Canyon National Parks established the first fire management zone in 1968, followed by Yosemite National Park in 1972.
“I think it was finally recognized that fire is an integral piece of these ecosystems, and there were a few key people who were willing to take the risk of letting these fires happen,” Collins said.
‘It isn't always clean, and it's not always nice'
Between 1973 and 2016, Illilouette Creek Basin experienced 21 fires larger than 40 hectares — approximately equal to 75 football fields — while Sugarloaf experienced 10 fires of that size. In Illilouette, the result today is a forest that may look a bit messy to the untrained eye, but it holds a lot of resilience.
“When some people visit Illilouette, they say, ‘Look at all these dead trees!'” Stephens said. “I think we have this idea that forests need to be green all the time and made up with only big trees. But it turns out that no forest can do that. It has to be able to grow young trees and regenerate. Illilouette is doing that, but it isn't always clean, and it's not always nice.”
In Illilouette, wildfire has created a more diverse array of habitats for animals like bees and bats, while allowing a variety of plant life to flourish. The detailed history of wildfires in Illilouette has also provided foresters with valuable information on how the impact of one wildfire on landscape and vegetation can influence the trajectory of the next wildfire.
“Since fires are generally allowed to burn freely in Illilouette, we could look at what happens when two fires have burned close to each other: When does the second fire burn into the area that was burned by the first fire, and when does it stop at the previous perimeter?” Collins said. “We found that it really depended on the amount of time that had passed since the first fire. If it had been nine years or under, fires almost never burned into a previous fire perimeter.”
Collins said that Illilouette has also given forest managers a unique opportunity to study how wildfire behaves under a variety of conditions, rather than only at its most dire.
“One of the things that's kind of perverse about the fire suppression policy is that we actually constrain fires to only burn under the worst conditions. If the fire is mellow, that's a good time to put it out, and, as a result, they only burn when we can't put them out,” Collins said. “But by letting these fires burn (in Illilouette), they're able to experience the full range of weather conditions. On bad days, some of these fires have really put up a pretty good plume. But on the flip side, they also get to burn under more moderate conditions, too, and it makes for really varied effects.”
Returning fire to Illilouette has also had the somewhat counterintuitive impact of increasing the availability of water in the basin, a key finding as California weathers yet another year of extreme drought.
Study co-author Gabrielle Boisramé, an assistant research professor at the Desert Research Institute in Nevada, began studying water in Illilouette as a Ph.D. student in environmental engineering at UC Berkeley. Her simulations and measurements indicate that small gaps in the tree canopy created by wildfires have allowed more water from snow and rainfall to reach the ground, while also reducing the number of trees competing for water resources. As a result, soil moisture in some locations in Illilouette increased as much as 30% between 1969 and 2012, which likely contributed to very low tree mortality in the basin during the drought years of 2014 and 2015.
Measurements also indicate that streamflow out of Illilouette Creek Basin has increased slightly since the managed wildfire program began, while streamflow out of other similar watersheds in the Sierras have all decreased. Boosting the amount of water that flows downstream is likely to benefit both the humans and the aquatic ecosystems that depend on this precious resource.
“There's more and more work being done that examines the effects of fire on hydrology, but most of the other research is looking at the effects of catastrophic fires that burned up an entire forest,” Boisramé said. “As far as we know, we're the only ones in the western U.S. studying a restored fire regime, where we're not just looking at one individual fire, but a number of fires of mixed severity that have occurred over natural intervals of time. There just aren't that many places to study the long-term effects of these repeated wildfires because Sugarloaf and Illilouette were the first areas in California — really the first western mountain watersheds — where they started allowing fires to burn most of the time.”
Fighting for fire
Most U.S. national parks now practice some form of fire use, rather than full fire suppression, and in 1974, the National Forest Service also changed its policy to also allow some fires to burn on its lands, although areas of fire use are rare in this agency. However, these federal fire use policies have struggled to gain a foothold, largely because of the inherent risks involved in managing wildfire.
Even in Sugarloaf Creek Basin, where many fires have been allowed to burn, there has also been significantly more fire suppression than in Illilouette, the study found. As a result, the ecological benefits in Sugarloaf are not as pronounced as those in Illilouette.
“I think one of the key things to recognize is that the landscape in Illilouette was already somewhat unique, partly because it is at slightly higher elevation than a lot of the forests we manage,” Collins said. “As a result, it already had a mix of vegetation with patches of meadows and rock, and I think maybe that gave managers a little more ease in letting fire happen there. It doesn't have the potential to really push off a giant megafire because it lacks the continuity that some of these other areas have.”
While both naturally-sparked fires and prescribed burns could help large swathes of the Sierra forest become more resilient to both drought and high severity fire, opposition to national “let it burn” policies in California remains strong, with state and local fire agencies often favoring the safety of fire suppression.
Collins and Stephens both acknowledge that the current fuel density in much of the Sierra, mixed with the hotter, drier conditions already triggered by climate change, has made managing wildfire even riskier than it was when forest managers started allowing fires to burn in Yosemite in 1972. However, they argue, fire suppression will never succeed in the long term, because the longer that forest fuel sources are allowed to build up, the more likely it becomes that wildfires will turn catastrophic when they are finally sparked.
“In order to actually allow this to happen, political and public institutions need to be willing to accommodate risk, because there will be some unpredictability. There are going to be fires that get larger, and more severe burning in places that have had very little fire for a century or more,” Stephens said. “We can't guarantee that Illilouette is going to be the new outcome, because it started when climate change was not nearly as severe. So, political institutions will have to accommodate that, or the first fire that doesn't do exactly what we hope will shut down the whole program.”
Collins and Stephens also advocate for more aggressive prescribed burning and restoration thinning throughout the Sierra to help get the forests to a place where lightning-sparked fires can be allowed to burn more safely.
Stephens credits strong, early leadership at Yosemite — including that of study co-author Jan W. van Wagtendok, who received a Ph.D. from UC Berkeley in 1972 and went on to serve as a research scientist at Yosemite for most of his career — for taking the huge risk of launching the program and allowing early fires to burn in the park.
“It's been 50 years now, but I think what we've learned helps us understand what is possible,” Stephens said. “We have 10 to 20 years to actually change the trajectory of the forest ecosystems in our state, and if we don't change them 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. That's why it's so important to continue this work.”
Previous funding from the U.S. Joint Fire Science Program, UC ANR Competitive Grants Program, and the National Science Foundation's Critical Zone Collaborate Network (award number 2011346) supported the research in this paper.
Study co-authors also include Sally Thompson of the University of Western Australia; Lauren C. Ponisio of the University of Oregon, Eugene; Ekaterina Rakhmatulina, Jens Stevens and Zachary L. Steel of UC Berkeley; and Kate Wilkin of San Jose State University.
- Author: Robert Sanders
Reposted from UC Berkeley News
An unprecedented 40-year experiment in a 40,000-acre valley of Yosemite National Park strongly supports the idea that managing fire, rather than suppressing it, makes wilderness areas more resilient to fire, with the added benefit of increased water availability and resistance to drought.
After a three-year, on-the-ground assessment of the park's Illilouette Creek basin, UC Berkeley researchers concluded that a strategy dating to 1973 of managing wildfires with minimal suppression and almost no preemptive, so-called prescribed burns has created a landscape more resistant to catastrophic fire, with more diverse vegetation and forest structure and increased water storage, mostly in the form of meadows in areas cleared by fires.
“When fire is not suppressed, you get all these benefits: increased stream flow, increased downstream water availability, increased soil moisture, which improves habitat for the plants within the watershed. And it increases the drought resistance of the remaining trees and also increases the fire resilience because you have created these natural firebreaks,” said Gabrielle Boisramé, a graduate student in UC Berkeley's Department of Civil and Environmental Engineering and first author of the study.
Boisramé and co-author Sally Thompson, a UC Berkeley ecohydrologist and assistant professor of civil and environmental engineering, found that even in the drought years covered by the study, the basin retained more water than similar areas outside the park. That translated into more runoff into the Upper Merced River, which flows through Yosemite Valley, at a time when other rivers in the surrounding areas without a restored fire regime showed the same or decreased flow.
“We know that forests are deep-rooted and that they have a large leaf area, which means they are both thirsty and able to get to water resources,” Thompson said. “So if fire removes 20 percent of that demand from the landscape, that frees up some of the water to do different things, from recharging groundwater resources to supporting different kinds of vegetation, and it could start to move into the surface water supplies as stream flow.”
The study is published in the current issue of the journal Ecosystems.
If the results are confirmed from other studies, including the UC Berkeley team's new project analyzing the Sugarloaf Creek Basin in Sequoia and Kings Canyon national parks, they could alter the way the federal government as well as water districts deal with fire, benefiting not only the forest environment but potentially also agriculture and cities because of more runoff into streams and reservoirs.
“I think it has the potential to change the conversation about wildfire management,” said co-author Scott Stephens, a fire expert and UC Berkeley professor of environmental science, policy and management who has studied the Illilouette basin since 2002.
This “wildfire management” strategy is counter to the federal government's 110-year-old Smokey Bear policy, which is followed throughout the West and emphasizes suppressing fires wherever they occur for fear they will get out of control. With persistent drought and a warming climate, the U.S. Forest Service budget is increasingly going to firefighting. On most federal land, only forest thinning and human-initiated prescribed burns are allowed as a way to manage the trees and underbrush.
Stephens noted, however, that these agencies have recognized the folly of total suppression — thanks in part to his own studies throughout the Sierra Nevada over several decades — and current draft wildland management policies for three of the state's national forests allow active wildfire management in up to 60 percent of the forests.
The value of forest clearings
Wildfire management, as opposed to suppression, comes with major changes in the way the forest looks, Stephens and Thompson said. Unlike the dense stands of pine and fir most people associate with Yosemite and similar mid-elevation Sierra Nevada and Rocky Mountain forests, the Illilouette Creek basin has thinner forests and more clearings with dead trees.
“There is much more dramatic structural change in this forest than most people would probably feel comfortable with,” he said. “You are talking about low-density forests and gaps of 4 or 5 acres, up to maybe 100 acres. These are the result of major fires about every decade or so, large enough to cause tree scarring and affecting as much as one-quarter of the basin.”
These fire-caused clearings, however, act as natural fire breaks and make the area resistant to catastrophic fires such as the 2013 Rim Fire in the western part of the park, which burned 250,000 acres and left patches up to 20,000 acres in which not a single conifer tree survived. These areas could take a century to recover, Stephens said.
“In the Illilouette basin we lost about 20 percent of the forest cover, but there was a 200 percent increase in wetland vegetation: meadows starting to reemerge from forests that have probably encroached on historical locations,” Thompson said. “That sets us up to think that this new regime should be leakier as far as water goes — leaky in the way that suits us as a society.”
Even if these wildfire management techniques don't produce more runoff, Thompson added, “I think it is a fabulous result in terms of forest management if you end up with a healthier forest with some better intact aquatic habitat, even if you don't see a drop of water further downstream. It is still the right thing to do from an ecological point of view.
“Bottom line, this strategy might be a triple win-win-win for water, forest structure and fire risk,” she said.
The ‘jewel' of Yosemite National Park
The findings are the culmination of a 14-year study led by Stephens and his UC Berkeley colleagues to learn how monitoring natural, lightning-caused fires with a bias toward letting them burn affects the landscape, the vegetation and the groundwater. Only four areas in the western U.S., including two in California — the Illilouette Creek basin and the Sugarloaf Creek basin — have allowed lightning fires to burn in large areas for decades.
Most studies of different ways to manage wildland fires have been limited to a few hundred acres, and it's hard to extrapolate from such limited experiments to an entire forest. Luckily, Yosemite National Park started its experiment in 1973 — spurred by a 1963 report authored by the late UC Berkeley forester Starker Leopold — to let nature take its course in the Illilouette Creek watershed, stepping in only when fires in the basin threatened to get out of control or sent too much smoke into Yosemite Valley two miles to the northwest.
“This is the first study that looks at fire regime restoration on a watershed scale with empirical data,” he said. “Others do smaller areas or modeling, but this is 40,000 acres — a big place — over many years.”
One reason the basin was chosen was that it was surrounded by granite walls, which naturally prevented fires from spreading outside the basin. It had not been burned by the indigenous tribes of the region, which often set fires to increase acorn production, and had no history of prescribed burns. In fact, it saw only natural, lightning-caused fires except for an interval of nearly a century — 1875 to 1972 — when the park suppressed all fires.
While Stephens and his many students documented the changes in fire over the past 400 years, Boisramé and Thompson analyzed aerial photos to document vegetation change. Then, with the help of installed sensors and more than 3,000 soil moisture measurements throughout the basin, the team was able to estimate the amount of water in the landscape today versus in the past. They found similar or marginally drier conditions where forests had been replaced with shrubs, but these were balanced by much wetter conditions in small areas where meadows expanded.
They observed more snow reaching the ground because of the clearings, and more snow remaining during the spring, delaying runoff. And in recent drought years, when surrounding basins saw more trees die, there was almost no tree mortality in the Illilouette basin.
“In order to really understand whether this approach should be part of our management toolkit, I would recommend that we give it a crack in a few other places,” Thompson said. “This appears to be a promising management strategy without significant harm and with several very strongly quantifiable benefits and several very suggestive outcomes.”
Boisramé, who spent the past four summers sampling and camping in the Illilouette Creek basin, emphasized that this is not a strategy that would work everywhere. But in wilderness areas where wildfire management is being considered because of its safety benefits — to reduce underbrush and eliminate fuel for out-of-control and catastrophic fires that risk lives and property — the ecological and hydrological benefits are a big bonus. Areas with similar elevation and climatic conditions to the Illilouette basin, and thus perhaps suitable for managed wildfire, comprise about 18 percent of the Sierra Nevada, though the strategy may work at lower elevations as well.
“The whole ecosystem will be better off if we let the natural fire process back in,” she said.
The research was supported by a grant from the federal Joint Fire Science Program.