In 2006, the Tripod Complex Fire burned more than 175,000 acres in north-central Washington. The fire, which was within the Okanogan-Wenatchee National Forest, was more than three times the size of Seattle. Yet while considered severe at the time, even larger wildfires in 2014, 2015 and 2021 have since dwarfed Tripod.

Past research shows that large and severe wildfires like these were much rarer in the western U.S. and Canada prior to the late 20th century.

“Fire exclusion policies for much of the 20th century yielded many dense forests with largely uniform composition,” said , a research scientist with the 91̽��School of Environmental and Forest Sciences. “By the turn of this century, we had mature and densely treed, multi-layered forests with high fuel content — and as a result, large, destructive wildfires can ignite and spread more easily. There’s simply more to burn across large landscapes.”

Prichard, along with colleagues from the U.S. Forest Service’s Pacific Northwest Research Station — , Nicholas Povak and Brion Salter — and consulting fire ecologist Robert Gray, have created a modeling tool that will allow managers and policymakers to imagine and realize a different future: one where large, severe wildfires like Tripod are once again rare events, even under climate change.

The tool, known as REBURN, can simulate large forest landscapes and wildfire dynamics over decades or centuries under different wildfire management strategies. The model can simulate the consequences of extinguishing all wildfires regardless of size, which was done for much of the 20th century, or of allowing certain fires to return to uninhabited areas. REBURN can also simulate conditions where more benign forest landscape dynamics have fully recovered in an area.

In a pair of papers published and in the journal Fire Ecology, the team applied REBURN to the region in north-central Washington where the 2006 Tripod Complex Fire burned. Simulations showed that setting and allowing smaller wildfires to burn can yield more varied and resilient forests over time. Such forests are made up of forest condition “patches” of different sizes and shapes, and all at different stages of recovery from their most recent fire. Patches that recently burned acted as “fences” to the flow of fire for at least the next 5 to 15 years, preventing wildfires from spreading widely. REBURN simulations showed that a forest landscape comprised of 35 to 50% “fence” areas had far fewer large-scale and damaging wildfires.

“Landscapes had tipped to more ‘benign’ burning conditions,” said Hessburg.

REBURN simulations showed that, when fence areas were less abundant across a region, larger and more severe wildfires tended to dominate how the landscape developed over time.

“The model allows us to simulate what can happen when different management scenarios are applied before the fact, including how small or medium-sized fires in uninhabited areas can reshape forest vulnerability to fires,” said Prichard. “We found that having a more complex forest environment — in terms of tree age, composition, density, fuel content — makes it harder for large fires to spread and become severe.”

“We also found that non-forest areas comprised of grasslands, shrublands, wet and dry meadows, and sparsely treed woodlands were key ingredients of wildfire-resilient forests,” said Hessburg. “REBURN showed us that our policy of extinguishing all wildfires created forests like those that exist today, with large, severe wildfires growing more prevalent. In addition to destroying homes and blanketing cities and towns with smoke, conflagrations like these displace wildlife, destroy habitats, and can burn large areas severely, sometimes making it difficult for forests to return.”

Short intervals between forest reburns can be especially harmful for long-term recovery by destroying young trees that have not yet produced cones, they added.

From 1940 to 2005 in Washington’s North Cascades, fire crews extinguished more than 300 fires in their early stages in the Tripod area — most triggered by lightning strikes. By the 1980s and 1990s, forests in the region had become high-density tinderboxes, loaded with older, dying trees and lots of dead wood and other fuel on the ground.

Research has shown that before large-scale European colonization of the area, smaller wildfires shaped forests in north-central Washington and elsewhere in the Pacific Northwest. The Methow people and other tribes in the region actively set fires through cultural burning practices. Aerial photos show that, as recently as the 1930s, forests in north-central Washington had a “patchwork quilt” structure that kept large wildfires from forming easily.

“Forests with more complex structure — including densely and lightly treed areas like meadows and grasslands, shrublands, and spare woodlands — also create a wider variety of habitats for wildlife,” Hessburg said. “Recently burned areas can develop into wet or dry meadows that can host deer or moose. Other, younger tree-dense areas can host lynx and snowshoe hares.”

REBURN can be adapted to other regions in the western U.S. and Canada. Prichard, Hessburg and their colleagues are currently adapting it to simulate forest development in the vast forests of southern British Columbia and northern California, including regions recently hit by wildfires and those culturally burned by Indigenous people.

But knowing when — or even whether — to allow a small fire to burn in an uninhabited region is no easy task, since fire managers must protect people, their homes and livelihoods. The team hopes ongoing research will help refine the model and the insight it can provide to modified forest management strategies.

“This is a new type of tool that couples forest and non-forest development models over time, fuel fall-down after fires, and a fire growth model,” said Hessburg.

“We hope that it will help people who make major decisions about our forests understand the long-term consequences of different practices and policies when it comes to wildfires,” said Prichard. “We hope it will make these conversations easier to have by grounding our predictions in sound forest science.”

The research was funded by the Joint Fire Science Program and the U.S. Forest Service Pacific Northwest Research Station.

For more information, contact Prichard at 509-341-4493 and sprich@uw.edu and Hessburg at 509-423-6738 and paul.hessburg@usda.gov.

All forest fire smoke is bad for people, but not all fires in forests are bad.

This is the conundrum faced by experts in forest management and public health: Climate change and decades of fire suppression that have increased fuels are contributing to larger and more intense wildfires and, in order to improve forest health and reduce these explosive fires, prescribed and managed fire is necessary.

These intentional fires — some deliberately set and others unintended but allowed to burn under control — will reduce the intensity of wildfire smoke in the long run, but they are still creating health-impacting smoke, often hitting populations least protected from exposure to smoke.

To find consensus on how to deal with the impacts of all fires on dry Western forests, the 91̽�� and The Nature Conservancy led a series of conversations involving roughly 60 experts charged with keeping forests and people healthy. The led the organization of these discussions.

On May 2, more than two dozen of those participants that is part review of current scientific understanding of the issues and health impacts and part consensus report on how to deal with them.

“It started as a conversation between experts who think about fire from really different angles in order to find how we can address fire through an interdisciplinary lens,” said lead author , a postdoctoral fellow in UW’s Department of Environmental & Occupational Health Sciences. “It took a little bit to get to the fact that it was really smoke that brought us all together. We kind of had to set a baseline for what peoples’ starting points were — all smoke is bad smoke from a public health perspective, but we can’t do fire management without more fire.”

That working group — comprised of scientists, practitioners and managers who specialize in areas of forest and fire ecology, fire safety, air quality, health care and public health — agreed on six statements and recommendations as part of its “interdisciplinary approach” to the issues.

“The Nature Conservancy is dedicated to an evidence-based approach to forest and fire management practices that supports the health of both nature and people. These consensus statements aim to serve as guideposts for forest health and public health professionals to work together to promote healthy and resilient forests and communities,” said , co-author and director of conservation science for The Nature Conservancy in Oregon.

The first consensus statement addresses the issue of the long-running effort to suppress all forest fires versus the historic practices of Indigenous peoples:

“We recognize the need to listen to and integrate a diversity of perspectives, in particular those embodied by Indigenous peoples who have successfully used fire as an ecological tool for thousands of years,” the authors wrote.

“I’ve often heard from Tribal leaders how controlled burns were one of many tools they employed historically to steward healthy ecosystems,” said , co-author and executive director of the Tribal Healthy Homes Network. “This Tribal knowledge has been overlooked, perilously, during decades of European colonization, and federal land management practices. It is only in recent years, as forest ecosystems decline in health, that Western science has begun to recognize and learn from the innate sensibility and sustainability of traditional Tribal burning practices.”

Here are the other five consensus statements:

• Prescribed fires in addition to managed fires for resource benefit are both necessary management techniques to keep forests resilient and to lessen the negative ecological and public health impacts of wildfires.
• Certain regions of the Western U.S. will experience more smoke days with heightened use of prescribed and managed fire; however, we expect the impacts of smoke exposure to be reduced over the long term in comparison with untreated land burned by wildfires. With these techniques, exposure in affected communities can be planned and lessened.
• No degree of smoke exposure is without risk. However, additional investment in advance preparation for affected populations can lower associated health risks. A smoke-resilient community is resilient to smoke from any type of fire.
• We must work to promote both equity in process (e.g., who has a say in decision-making) and equity in outcomes (e.g., who gets exposed to the smoke) within those communities and populations experiencing disproportionate impacts from smoke.
• We are missing opportunities for positive impact by working as separate disciplines. We recommend that further and intentional integration of forest/fire and health disciplines (including the practitioners, tools and resources) needs to occur to lessen the human health effects of smoke exposure due to prescribed and managed fires.

In their conclusion, the authors point out that when all stakeholders work together to “combat this climate and public health crisis,” communities will be more able to meet these goals, both during and outside of wildfire season.

“Extra attention must be given to people who have more smoke exposure, are more likely to experience health problems from smoke, and who don’t have enough support to anticipate, adapt, respond or recover from smoke,” added , senior author and associate professor of environmental and occupational health sciences in the 91̽��School of Public Health. “These disproportionately affected populations must be included in decision-making to address inequities in smoke health impacts.”

D’Evelyn hopes the paper will inspire more interagency and cross-disciplinary efforts and funding for research and preparation.

“There are really wonderful community organizations working to make sure that people have access to clean air. And, there are really wonderful organizations working to do as much prescribed burning as they’re allowed to lessen the smoke or lessen the severity of wildfires when they come through,” D’Evelyn said. “But there are gaps where communities, organizations and researchers could be collaborating to have an even bigger impact on preparedness.”

Other co-authors are Jihoon Jung, Ernesto Alvarado, Jill Baumgartner, Pete Caligiuri, R. Keala Hagmann, Sarah Henderson, Paul Hessburg, Sean Hopkins, Edward Kasner, Meg Krawchuk, Jennifer Krenz, Jamie Lydersen, Miriam E. Marlier, Yuta J. Masuda, Kerry Metlen, Susan Prichard, Claire Schollaert, Edward Smith, Jens Stevens, Christopher Tessum, Carolyn Reeb-Whitaker, Joseph Wilkins, Nicholas Wolff, Leah Wood.

For author affiliations, please see the publication.

This research was funded by Science for Nature and People Partnerships, The Nature Conservancy and CDC’s National Institute for Occupational Safety and Health.

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For more information, contact D’Evelyn at sdevelyn@uw.edu.

Exceptionally hot and dry weather this summer has fueled dozens of wildfires across the western U.S., spewing smoke across the country and threatening to register yet another record-breaking year. More than a century of fire exclusion has created dense forests packed with excess trees and brush that ignite and spread fires quickly under increasingly warm and dry conditions.

Scientists largely agree that reducing these fuels is needed to make our forests and surrounding communities more resilient to wildfires and climate change. But policy and action have not kept pace with the problem and suppressing fires is still the norm, even as megafires become more common and destructive.

Seeing the urgent need for change, a team of scientists from leading research universities, conservation organizations and government laboratories across the West has produced a that clearly lays out the established science and strength of evidence on climate change, wildfire and forest management for seasonally dry forests. The goal is to give land managers and others across the West access to a unified resource that summarizes the best-available science so they can make decisions about how to manage their landscapes.

“Based on our extensive review of the literature and the weight of the evidence, the science of adaptive management is strong and justifies a range of time- and research-tested approaches to adapt forests to climate change and wildfires,” said co-lead author Susan Prichard, a research scientist in the 91̽��’s School of Environmental and Forest Sciences.

These approaches include some thinning of dense forests in fire-excluded areas, prescribed burning, reducing fuels on the ground, allowing some wildfires to burn in backcountry settings under favorable fuel and weather conditions, and revitalizing Indigenous fire stewardship practices. The were published Aug. 2 as an invited three-paper feature in the journal Ecological Applications.

The authors studied and reviewed over 1,000 published papers to synthesize more than a century of research and observations across a wide geographic range of western North American forests. The analysis didn’t include rainforests in the Pacific Northwest or other wet forests where thinning and prescribed burning wouldn’t be advised.

“The substantial changes associated with more than a century of fire exclusion jeopardize forest diversity and keystone processes as well as numerous other social and ecological values including quantity and quality of water, stability of carbon stores, air quality, and culturally important resources and food security,” said co-lead author and 91̽��researcher .

This ambitious set of articles was inspired by the reality that under current forest and wildfire management, massive wildfires and drought are now by far the dominant change agents of western North American forests. There is an urgent need to apply ecologically and scientifically credible approaches to forest and fire management at a pace and scale that matches the scope of the problem, the authors say.

Part of the solution involves addressing ongoing confusion over how to rectify the effects of more than a century of fire exclusion as the climate continues to warm. Land managers and policymakers recognize that the number and size of severe fires are rapidly increasing with climate change, but agreement and funding to support climate and wildfire adaptation are lagging.

To that end, these papers review the strength of the science on the benefits of adapting fire-excluded forests to a rapidly warming climate. The authors address 10 common questions, including whether management is needed after a wildfire, or whether fuel treatments (thinning, prescribed burning) work under extreme fire weather. They also discuss the need to integrate western fire science with traditional ecological knowledge and Indigenous fire uses that managed western landscapes for thousands of years.

Although climate change brings with it many uncertainties, the evidence supporting intentional forest adaptation is strong and broad based. The authors clearly demonstrate that lingering uncertainties about the future should no longer paralyze actions that can be taken today to adapt forests and communities to a warming climate and more fire.

“This collection represents a blending of scientific voices across the entire disciplinary domain,” said co-lead author , a research ecologist with the U.S. Forest Service and affiliate professor at the UW. “After reviewing the evidence, it is clear that the changes to forest conditions and fire regimes across the West are significant. The opportunity ahead is to adapt forests to rapidly changing climatic and wildfire regimes using a wide range of available, time-tested management tools.”

Co-authors on this special report are from University of Arizona, University of British Columbia, University of California, Berkeley, University of California, Merced, University of Idaho, University of Montana, University of New Mexico, Northern Arizona University, Oregon State University, The Pennsylvania State University, Utah State University, U.S. Forest Service research stations (Pacific Northwest, Pacific Southwest, Rocky Mountain), U.S. Forest Service, Pacific Southwest Region, Washington State Department of Natural Resources, California Department of Forestry and Fire Protection, U.S. Fish and Wildlife Service, U.S. Geological Survey, The Nature Conservancy, R.W. Gray Consulting, Rocky Mountain Tree-Ring Research and Spatial Informatics Group.

This research was funded by U.S. Fish and Wildlife Service, The Wilderness Society, The Nature Conservancy of Oregon, Conservation Northwest, The Ecological Restoration Institute, Washington State Department of Natural Resources, U.S. Forest Service (Pacific Northwest and Pacific Southwest Research Stations), and the California Department of Forestry and Fire Protection.

For more information, contact Prichard at sprich@uw.edu, Hessburg at paul.hessburg@usda.gov and Hagmann at hokulea@uw.edu