California's drought of 2012-2016 killed millions of trees in the Sierra Nevada — mostly by way of a bark beetle epidemic — leaving a forest canopy full of dry needles. A study published from the University of California, Davis, and the U.S. Forest Service helps answer concerns about what effect dense, dead foliage could have on subsequent wildfires and their burn severity.
In the study, published in the journal Ecological Applications, scientists found that the presence of recently dead trees on the landscape was a driver of wildfire severity for two large fires that occurred toward the end of the drought: the 151,000-acre Rough Fire in 2015 and the 29,300-acre Cedar Fire in 2016.
The publication is the first field-based study to document the important role recently dead trees can play in exacerbating fire severity in California forests that are historically adapted to frequent, low-severity fire.
Climate change and forest management
The study highlights the importance of forest fuels, in addition to climate change, as a strong driver of fire severity in Sierra Nevada forests.
“We've long known that both fire weather and forest fuels can influence wildfires, but it was unclear whether recently dead trees would change conditions enough to alter fire severity,” said lead author Rebecca Wayman, an associate specialist of forest and fire ecology in the UC Davis Department of Environmental Science and Policy. “We found that the dead trees did increase fire severity, even though these fire-suppressed forests were already at risk of unnaturally severe wildfire prior to the drought.”
It wasn't drought alone that killed millions of trees, Wayman noted. A prolonged, hot drought hit forests that were overly dense and water-stressed due to more than a century of excluding wildfire and Indigenous fire from the landscape. This resulted in a bark beetle outbreak that was unprecedented in the Sierra Nevada.
Fortunately, the same strategies commonly used to reduce the risk of catastrophic wildfire — thinning and prescribed fire — also can reduce the severity of future bark beetle epidemics.
“It's a win-win to restore forests to healthier, less-dense conditions, especially as they face hotter and drier climate conditions that promote both wildfire and bark beetle attacks,” Wayman said.
Disturbance brings shifts
For the study, the researchers collected data on 180 plots within the Rough Fire and Cedar Fire footprints, located in the Sierra and Sequoia national forests, and the Giant Sequoia National Monument. It identified pre-fire tree mortality as influential on all measures of wildfire severity on the Cedar Fire, and on two of three measures on the Rough Fire. For the Rough Fire, it was the most important predictor of trees killed by fire. For the Cedar Fire, weather conditions during burning had the strongest influence on fire severity.
The dual disturbances also shifted the pine-dominated system of the Rough Fire study area to a cedar/pine/fir system, which is less well-adapted to wildfire. Dominant species remained unchanged in the area affected by the Cedar Fire, which was already dominated by fire-sensitive species.
Pre-fire tree mortality may have a greater influence on fire when weather conditions are mild compared to when high temperatures, low relative humidity and high winds can drive extreme wildfire behavior, the study indicated.
“The question of how two profound disturbances — drought and fire — interact to affect California forests is an important one,” said co-author Hugh Safford, regional ecologist for the USDA Forest Service's Pacific Southwest Region and an adjunct member of the research faculty at UC Davis. “Current and projected future trends suggest that this sort of double-whammy will become more and more common as the 21st century progresses and the climate continues to warm. Our study helps us better understand how California forests are impacted by two extreme events in close proximity in time and how we might change these impacts with proactive management.”
The study was funded by the USDA Forest Service Pacific Southwest Region.
Media contact(s)
Rebecca Wayman, Environmental Science and Policy, 530-401-0471, rbwayman@ucdavis.edu
Kat Kerlin, News and Media Relations, 530-752-7704, 530-750-9195, kekerlin@ucdavis.edu
Catastrophic wildfires are becoming more frequent, more intense and more destructive in California. They are burning in a variety of vegetation types — from high-elevation northern-Californian coniferous forests to southern-Californian chaparral ecosystems — and some (e.g. the Thomas [2017] and Tubbs, Sonoma County [2017]) have been fanned by unusually strong wind events. Despite these differences, however, there is broad consensus that a major part of the uptick in catastrophic fires is the state's failure to adequately manage fuel loading in range- and forested lands.
The state is currently in the process of finalizing a document, the California Vegetation Treatment Program (VTP), which will serve as an update to their 1980s document, “Vegetation Management Program.” This unwieldy document serves as the blueprint for how the state will strategically approach fuels management. Practices such as mechanical treatments (e.g. mowing, mastication), manual (e.g. weed-whacking, weed-pulling), herbicide application, and prescribed fire will be included in the VTP, as they were in the 1980s VMP. One remarkable new addition, however, will be the inclusion of grazing as an approved fuels management treatment. Accordingly, there is renewed effort around the state from the livestock and ranching communities to communicate how domestic livestock can be integrated into a responsible, long-term fuels management program.
Fundamentally, we need to think about two kinds of grazing: 1) what might be called “traditional” grazing, and 2) what might alternatively be named “targeted” grazing. Traditional grazing is how we have always thought about grazing: in California, cattle are managed in extensive rangeland pastures to produce meat. Alternatively, the ultimate purpose of targeted grazing is to have a particular species of livestock graze at a certain density for a specific period of time for the purpose of managing vegetation. In this model, the saleable product is not meat, milk, or fiber, but instead acres of biomass cleared, thinned, or removed.
Importantly, however, it should be noted that both kinds of grazing can and do manage fuel loading in range- and forested lands in California. This is a point the ranching community has worked hard to make in the popular press recently. See, for example, the recent video produced by the National Cattlemen's Beef Association featuring cow/calf producer Richard Atmore of Ventura, California, discussing how grazing on his ranch just outside the city limits reduced impact of the Thomas Fire on urban residents. (https://www.facebook.com/watch/?v=2365669617085882). My own experiences conducting soil and rangeland monitoring after the Thomas Fire confirm the same phenomenon. All five of the ranches I sampled had areas of grazed grassland that did not burn at all during the fire immediately next to shrubland areas that burned at a high intensity [see Figure x]. In this way, it is critical to recognize the good work that traditional grazing already does to reduce the sorts of fuels that might otherwise exacerbate fire in wildlands or on the wildland-urban interface.
But again, targeted grazing is different. It is an old idea (livestock grazing) applied in a novel manner. Increasingly, homeowners, private land owners, municipalities, public agencies, and utility companies across the state are using grazing animals where it's too steep to mow, too labor-intensive to hand-pull weeds or run a masticator, too challenging to execute a prescribed burn, or too expensive to apply herbicides.
It remains to be seen, however, how effective targeted grazing with cows, sheep, and/or goats will be on the Central Coast. While there is ample evidence that these livestock species will consume the naturalized annual grass species common in the area, there is less direct evidence of their ability to consume shrub and sub-shrub species common to our local chaparral and coastal sage scrub communities. Certainly, more work and experimentation will need to be done if and when targeted grazing for fuel load modification becomes more widespread. Animal genetics (insofar as it may impact an individual animal's preference for certain plant species) and augmenting the timing of use may both be important factors that will influence success. Research suggests that targeted grazing might be most effective 1) in the years after a wildfire, when large-diameter shrubs have been removed and begin to regrow; 2) as a follow-up to maintain other fuel treatments, like mastication; or 3) as a way to thin fuels — though not necessarily to remove them entirely — to reduce fire intensity and rate of spread.
It is important to recognize that targeted grazing is not exactly like running a traditional ranching operation, and targeted grazing operators face a unique set of challenges. They must be mobile (with their fencing, stock water, handling equipment, etc.), they must provide protection from livestock predators (if running sheep or goats), they must know how to effectively communicate with landowning clients and the general public, and they need to be certain they can provide forage for their livestock year-round (even if the paying jobs are seasonal). As new operators that may or may not have previous livestock experience increasingly offer their services, it will be important to provide resources to ensure their success.
California's decision to formally recognize grazing as an important fuels management practice in their forthcoming Vegetation Treatment Program should have a profound effect on the frequency and scale of use of both traditional and targeted grazing. It is an exciting opportunity for the livestock industry to meaningfully help address and provide solutions for the wildfire threat in our region.
Vista View at North Sonoma Mountain Regional Park // Detail of photo courtesy of harminder dhesi / flickr
When the Tubbs and Nuns wildfires exploded across Sonoma County in 2017, firefighters found they lacked critical information. Details on the vegetation, structures, and roads distributed across the landscape would have helped them better evacuate residents and allocate fire suppression resources.
It was only after the fires were extinguished that authorities realized much of that data was available—in the form of “veg maps.” Created by the Sonoma County Agricultural Preservation and Open Space District, Ag + Open Space as it's known locally, the maps deconstruct the terrain, depicting slope, aspect, soil type, hydrological qualities, buildings, roads and driveways—even the density of trees and brush—in exquisite detail.
Fine-scale vegetation map of Sonoma County // Image courtesy of Sonoma County Ag + Open Space
Such maps, officials realized, could be an immense asset when responding to wildfires. They could even serve a preventative purpose: helping “fireproof” undeveloped land by turning open space from a wildfire liability to a fire-prevention asset.
The maps are produced through LiDAR, or Light Detection and Ranging, which is kind of like radar, except it uses pulsed lasers emitted from aircraft or satellites instead of radio waves. The process yields precise 3-D maps of the earth's surface, detailing vegetation type and density. Researchers can look at a LiDAR map and evaluate “fuel ladders”—deadwood on the forest floor combined with the limbs and branches running from the ground to the tree tops—in any given stand of trees, down to resolutions of one centimeter.
“Using the maps for wildfire response wasn't our original intent,” says Karen Gaffney, a UC Berkeley alumna and the conservation planning manager for Ag + Open Space. Originally part of a project supported by the Sonoma County Water Agency and grants from NASA, the maps were created for land and wildlife conservation purposes. “But it just so happens much of that data is proving valuable for disaster planning.”
The maps are being used to flag the best fire evacuation routes and the sites most susceptible to contamination or erosion post-fire.
When it comes to wildfire, it's largely about fuel. While the forests of the West were once subject to regular low-intensity fires that produced large, well-spaced trees and light accumulations of deadwood, more than a century of overzealous wildfire suppression and rising temperatures from climate change have reversed this dynamic. Combine the current dense, thicket-like stands of trees and piles of dead branches with hot, dry autumn winds, and the result is wildfires of devastating ferocity—wildfires like the 2017 North Bay fires and the 2018 Camp Fire in the town of Paradise.
Like many areas, Sonoma County has been attempting to use “prescribed” fire and tree thinning to reduce fuel loads, says Gaffney. Shortly before the Nuns Fire ripped through Glen Ellen, an experimental prescribed burn conducted at a nearby ranch demonstrated the effectiveness of such efforts. The encroaching wildfire immolated nearby woodlands and structures, but dropped to low, flickering flames when it hit the prescribed burn zone. There simply wasn't the fuel to sustain it.
The message was clear to the county's disaster response planners: the more wildlands that can be burned under controlled conditions, the better.
The district's veg maps are now being used by county officials to identify candidate open spaces for thinning and prescribed fire, with prioritization going to the most vulnerable areas.
“In conjunction with our partners at Pepperwood Preserve and Tukman Geospatial, we've created fuel loading maps from our LiDAR data that identify areas where heavy ladder fuels are located close to structures,” says Gaffney, who declined to comment on specific sites. “And because we can map development footprints down to resolutions of one centimeter, we can even identify risks for individual buildings.”
Ladder fuels maps of Sonoma County // Image courtesy of Sonoma County Ag + Open Space
The maps are also being used to flag the best fire evacuation routes and the sites most susceptible to contamination or erosion post-fire.
“For example, we can determine if a [burned] structure that contained toxic materials is at significant risk of contaminating a nearby stream,” Gaffney says. “While the maps first responders and firefighters typically use show all the major and secondary roads, our data let us create maps that show the much smaller routes that could also be used for evacuation.”
The veg map approach to wildfire response and planning is gaining fans beyond the borders of Sonoma County.
“Marin County and San Mateo County have acquired LiDAR technology and are creating their own veg maps,” says Allison Schichtel, the conservation GIS coordinator for Ag + Open Space, “and Monterey and Santa Cruz Counties are looking into it. I did a presentation at a forestry and GIS workshop, and there were folks from [far] northern California and southern Oregon who wanted to know all about it. Interest is growing—kind of like an amoeba.”
The humble rake has been in the spotlight in recent weeks, and its role as a forest management tool ridiculed and scorned. However, most fire professionals believe rakes are a necessary part of saving California's forests.
Those who are familiar with fire are undoubtedly familiar with the McLeod, which is a standard firefighting tool and … it is essentially a rake (one side is a rake with coarse tines and the other side has a flat sharpened hoe). The McLeod was created in 1905 by a U.S. Forest Service ranger who wanted a single tool that could rake fire lines (with the teeth) and cut branches and roots (with the sharpened hoe edge). The McCleod is used to scrape fuels off of a fire line, preventing fire spread. The use of hand tools like the McLeod continues to be one of the standard ways that wildfires are stopped (although often aided by the rake's bigger and more powerful cousin: the bulldozer).
While the McLeod is a fire-fighting tool, it is also an essential fire-managing tool. When conducting controlled burns (i.e., purposeful fire), the fire is contained within desired areas by diligent raking with McLeods and other hand tools. These tools are necessary for conducting controlled burns.
While it isn't feasible to reduce fire risk by raking the forest with hand tools, if you hold a drip torch in the other hand, you could get the work done.
A drip torch consists of a canister for holding fuel that comes out of a spout (with a loop to prevent fire from entering the fuel canister) and a wick from which flaming fuel is dropped to the ground when the wick is ignited. The drip torch is the most common tool for lighting prescribed burns, which can be used to remove excess fuel buildup in the forest.
In a forest setting, these two tools — the rake and the torch — must be used together. Without a rake, the fire is not easily contained. And without a drip torch, the fuel that was raked cannot burn. Of course, prescribed burns rely on a number of other pre-specified factors (the prescription), including wind, temperature and humidity.
Using fire in a controlled manner drastically reduces the impacts of wildfire in a forest. Typically flames are kept low and most or all of the trees survive the fire, while much of the dead material on the forest floor (the “fuel”) is consumed. This reduces the risk of the forest burning at high severity in the future, thereby protecting nearby homes and towns. It also reintroduces fire as an important ecosystem process, which improves the health and biodiversity of forests and maintains the ecosystem services they provide, including wildlife habitat, water filtration and carbon sequestration.
Use of a rake and a drip torch together could make a great difference for reducing the impacts of wildfire in California and the West. The National Interagency Fire Center reported that during 2017, only half a million acres were treated with prescribed fire in the West, while 7.4 million acres (almost 15 times more) burned in wildfires. In the Southeastern U.S., where there is a long-standing tradition of prescribed burning, only 2 million acres burned in wildfires while over 5.5 million were burned using prescribed fire.
This was not always the case. Use of prescribed fire, or ‘light burning,' was once common in California until it was outlawed by federal and state policy in 1924. Although the merits of expanding its use are widely known and appreciated, it has been very difficult to do because of concerns about air quality, liability and lack of skilled burners. One of the biggest constraints is that we have very few people who have experience with ‘good fire' and very few qualified people who know how to safely burn.
As foresters and educators for the University of California Cooperative Extension, we are working to expand the use of prescribed fire on private forest and grasslands in California. Central to our efforts are educational events that give people an opportunity to experience prescribed fire first-hand. In the last two years, we have hosted workshops throughout northern California, and many of our workshops have included a live-fire component where landowners and other community members can try their hand at prescribed burning, under the direction and guidance of more experienced burners.
Our efforts in California are inspired by approaches in other parts of the country, including “Learn and Burn” events in the Southeast, prescribed burn associations in the Great Plains, and prescribed fire training exchanges (TREXs), an innovative training model developed by The Nature Conservancy's Fire Learning Network. All of these efforts have a focus on reconnecting people with fire, and they give participants the skills and experience needed to put fire back in the management toolbox.
We hope that by empowering people to pick up the drip torch (and the rake) on their own properties, we can help them educe the risk of wildfire and improve the health of their forest and range lands. There is no time to waste.
The world certainly seems more flammable these days. Thousands of homes were lost last year in Sonoma County alone, and wildfires have raged across California all summer. And not just in California: Records from the federal National Interagency Fire Center show that U.S. acreage burned in wildfires leaped from 1.8 million in 1995 to 10 million in 2017.
But even as the burned acreage has jumped exponentially, the number of fires—or “ignitions” in wildfire-speak—dropped significantly, from 82,234 in 1995 to 71,499 in 2017. Why the discrepancy? Put simply, fires are getting harder to control, so they're getting bigger. To blame are the build-up of forest fuels from decades of aggressive fire suppression as well as drier, hotter, and windier conditions caused in large part by climate change.
That's only part of the problem, though. The fires are getting costlier, both in terms of human life and property loss. And a major—perhaps the major—driver to this trend is the “expanding bull's eye” of high-risk development, specifically the rapid growth of Wildland-Urban Interface (WUI).
Conceptual model of the “expanding bull's-eye effect” with increasing development spreading from an urban core over time. // Ashley et al. 2014
“Interface” is that transitional zone between suburbs or cities and forested areas. From a firefighter's perspective, WUI combines the worst of both realms: Interface areas are not only cheek-to-jowl with fuel-rich forests, they're also often characterized by dense housing tracts landscaped with lush, highly flammable vegetation. Today's wildfires, in short, are not your grandpa's wildfires; they're usually hybrid, human-started fires, involving both structures and forests, which greatly complicates the task for wildfire fighters and escalates the cost in life and property.
A recent study shows that WUI, primarily from suburban and recreational development, is the fastest-growing land-use category in the lower 48 states. And home losses from wildfire correspond directly to the expansion of interface.
Anu Kramer, a postdoctoral research associate at the University of Wisconsin who took her PhD in environmental science, policy and management at Cal, co-authored the paper in the Proceedings of the National Academy of Sciences that examined WUI changes from 1990 to 2010.
“We found that there was a 33 percent increase in WUI for the period and a 41 percent increase in new homes built in WUI areas—from 30.8 million to 43.4 million,” Kramer said—meaning there are more and more zones where development abuts wildland. “Basically, this translates as greatly increased fire risk.”
Kramer and her colleagues confirmed that post-fire construction tends to concentrate in areas of equal or higher fire risk than those that had last burned.
Those statistics suggest that neither policy makers nor home owners have grasped the profound risks implied by building in pleasant, leafy—and highly combustible—environs, particularly in the West.
“The main takeaway from our most recent research is that these interface areas need to be targeted for outreach—education for home owners on creating defensible spaces, and regulations, and funding that would result in such things as fuel breaks, more sensible zoning, and mandates on fire resistant construction materials.”
Instead, there seems to be a kind of collective determination to repeat the mistakes of the past.
“I'm involved in some research on rebuilding trends after wildfires, looking at where new homes are going in,” said Kramer. “On average, 94 percent of buildings [in a burn zone] have been rebuilt after 25 years.”
Kramer and her colleagues created a computer model, which confirmed that post-fire construction tends to concentrate in areas of equal or higher fire risk than those that had last burned.
“Miranda Mockrin [a researcher with the U.S. Forest Service] has done a lot of work in Colorado on the social science aspects of wildfire,” Kramer said. “She looked at zoning changes after fires and found that yes, sometimes zoning gets stricter and people may be encouraged to build with materials that are more fire-safe, but in the majority of cases there were no changes, and in some instances restrictions were actually reduced. The potential for learning and adaptation after fires just isn't being fulfilled.”
Local governments are incentivized to rebuild as quickly as possible to recoup lost tax revenues and bring civic and economic life back to comfortable baselines.
That dynamic seems in play in the North Bay, observed Kramer, where homes currently are being rebuilt in the exclusive Fountaingrove area. This enclave of expensive houses was located along a ridge on the margins of Santa Rosa. Just under a year ago on the evening of October 8 th , the Tubbs Fire roared through the neighborhoods, consuming most of the homes and killing several people. The steep slopes and canyons of the ridge acted as chimneys, concentrating the full fury of the wind-driven flames onto the ridge top development.
It was a horrific event, but it was hardly an outlier. In fact, it had been predicted. In 1964, the Hanley Fire tracked virtually the same route as the Tubbs Fire, including the area now occupied by Fountaingrove. But in 1964, Fountaingrove didn't exist, and the Hanley Fire destroyed relatively few structures. When construction on Fountaingrove started in the 1990s, many residents protested to Santa Rosa regulators, citing the Hanley blaze.
So why rebuild in high-risk areas? As Kramer explains, local governments are incentivized to rebuild as quickly as possible to recoup lost tax revenues and bring civic and economic life back to comfortable baselines. Unfortunately, environmental and geophysical changes—more frequent high wind events, longer and more frequent droughts, higher summertime temperatures and milder winters—mean that an increasing number of communities, even those outside of wildland interfaces, are considered high-risk for catastrophic wildfire.
The past few fire-ravaged years have made it clear that we have reached a tipping point. Epic wildfires seem certain to gain in frequency and destructive power in coming decades.
The Tubbs Fire, for example, didn't just burn Fountaingrove, a development with a significant WUI. It also flattened 1,200 homes in Coffey Park, an older middle-class development in a thoroughly suburban area located west of Highway 101 and far from anything that could be construed as a “wildland.” Extremely high winds drove masses of embers across 101, where they ignited structures and landscaping in Coffey Park and surrounding business complexes. Such winds were once considered anomalous by fire scientists. Not anymore. If ferocious wildfire-associated winds aren't the new normal, they're on their way. Winds reaching 143 mph destroyed scores of homes in the recent Carr Fire in Redding, during which a literal fire tornado killed two firefighters.
“[The Tubbs and Carr Fires] demonstrate how these strong winds can influence where a fire goes and what it does,” said Kramer. “They also show we need better models for predicting impacts and assessing risks. The models currently used by Cal Fire [California's state wildfire fighting agency] have a pretty basic wind component that doesn't account for the kind of high wind events we've begun seeing. So Max Mortiz [the head of the Mortiz Fire Regimes and Ecosystems Management Lab at Cal] is working with Cal Fire to bring their models up to date.”
The past few fire-ravaged years have made it clear that we have reached a tipping point. Epic wildfires are no longer rare, and they seem certain to gain in frequency and destructive power in coming decades. Moreover, the number of communities at dire risk is much higher than has been assumed. As Kramer's work reveals, wildfire losses seem proportional to the growth of WUI. We can't eliminate wildfire, but we can certainly reduce the impacts.
Paradoxically, that involves introducing more fire—controlled fire—into our wildlands to consume heavy fuel concentrations. It also entails moderating the dizzying expansion of WUI. Left unregulated, the trends in housing growth will simply perpetuate the destruction.