Adapting Western US Forests to Climate Change & Wildfires:

Forests in western North America are shaped by fire and -- for the past century or more -- by the absence of it. After more than a century of fire exclusion and under a rapidly changing climate, fire behavior has changed, and damage from wildfire is increasing. With more than a century of forest and fire science to build on, scientists, managers, and communities are refining management options for reducing risks to communities and ecosystems.

Wildfire is not only inevitable, it is an essential component of our environment. Restoring the once abundant influence of low- to moderate-severity fire increases the likelihood of conserving or restoring ecological processes and functions. In addition, as demonstrated by Indigenous fire practices around the globe and fuel reduction projects across the West, we can learn to live with fire and influence the way wildfires burn.

What -- if anything -- we can do to mitigate a worsening wildfire problem is hotly debated. However, strong evidence provides guidance for why and how to adapt western North American forests to climate change and future wildfires. A team of leading fire and forest scientists have summarized the consensus in the field on  10 common questions about fuel reduction  in seasonally dry, fire-prone forests.

• Q1: Are treatments unwarranted and even counterproductive?
• Q2: Is forest thinning alone sufficient to mitigate wildfire hazard?
• Q3: Can forest thinning and prescribed burning solve the problem?
• Q4: Should forest management be concentrated in the wildland urban interface (WUI)?
• Q5: Can wildfires on their own do the work of fuel treatments?
• Q6: Is the primary objective to assist firefighting response and containment?
• Q7: Do fuel treatments work under extreme fire weather?
• Q8: Is the scale of the problem too great -- can we ever catch up?
• Q9: Will planting more trees mitigate climate change?
• Q10: Is post-fire management needed or even ecologically justified?

First, let's define some terminology. Critical elements of climate- and wildfire-adaptation strategies are reduction of fuel loads and restoration of patchiness in forest and non-forest habitats. These objectives an be achieved through the use of managed fires, prescribed burns, or mechanical thinning followed by prescribed burning.

• Managed wildfires: are lightning or unintentional human-caused ignitions that are allowed to burn under weather and fuel conditions appropriate for achieving management objectives.
• Prescribed burns: are human-caused ignitions specifically designed to achieve management objectives.
• Thinning: refers to the use of machines or hand tools to cut or harvest pre-commercial or commercial trees. Unless surface fuels (organic materials on the forest floor that can fuel a fire) are also reduced, thinning alone can amplify, rather than diminish, fire behavior and severity.

Our focus is on the seasonally dry forests of interior Western North America. The broad ecoregions not grayed out on the map below give a rough indication of the extent of these forest types. Although mesic and coastal forests can also be seasonally dry and may have been affected by fire exclusion, particularly in the drier portions of their range and where Indigenous peoples commonly burned them, they are not the focus of this review. Source: The Nature Conservancy's Terrestrial EcoRegions and EPA's Ecoregions of North America.

Historically, lightning and Indigenous fire practitioners promoted fires that burned parts of the landscape every year. Low- to moderate-severity fires burned so often that dead vegetation, young trees, and shrubs could not build up across entire landscapes, as they have today. This limited high-severity fire and favored patchy, often open-canopy forest.

Frequent fire fostered a widespread distribution of trees of all ages, including mature and old trees. These conditions increased the resistance and resilience of forest and non-forest ecosystems to severe drought, wildfire, and insect or pathogen activity. That's why we call them "fire-dependent" landscapes.

Fire exclusion has radically altered the way fire-dependent landscapes look and function, including how they burn. This process began with the suppression of cultural burning practices mastered through millennia of  living with fire . Subsequently, the grazing of huge herds of sheep, cattle, or horses and the addition of railroads and roads limited fire spread. Along with the suppression of fire to favor timber production, these actions all contributed to an unprecedented era of fire exclusion. More than a century later, forests have gotten much denser, and they have expanded at the expense of non-forest habitats.

As live and dead fuels accumulate, the risk of high-intensity fire increases. Until about 1900, ponderosa pine-dominated forests (like those shown below) burned frequently at low- to moderate-severity. Abundant dead fuels on the ground (surface fuels) and live fuels in the understory (ladder fuels) contributed to the high-severity Reading Fire in 2012. Location: Lassen Volcanic National Park in northeastern California. Source: 1923: A.E. Weislander, 1993-2013: Alan H. Taylor.

More trees also means more competition for water, more vulnerability to drought, and less water flowing downslope to meadows and aquatic ecosystems.

With climate change, annual droughts are becoming more severe, and fire seasons are getting longer, hotter, and drier, increasing the vulnerability of fire-excluded forests and embedded non-forest ecosystems. To learn more about climate change impacts on forests, check out the Northwest Climate Adaptation Science Center's "Changing Wildfire, Changing Forests" storymap, linked below:

Ongoing evaluation of implementation and effectiveness is essential for any credible management strategy.  For more than a century, especially over the past 30 years , great effort and expense has been invested in evaluating the advisability of restoring abundant low- to moderate-severity fire, particularly as the climate warms.

While it is common to hear that the goal of fuel reduction treatments is to prevent wildfires, this is an oversimplification. Treatments do not prevent fires from starting, and they aren't necessarily intended to stop wildfires from spreading. In fact, the goal of ecologically based fuel reduction treatments is to restore the role of abundant low- to moderate-severity fire in fire-dependent ecosystems to reduce the risk of extensive high-intensity wildfires. Reducing fuel loads lowers the heat generated, lowers flame lengths, and lowers the likelihood that fire will carry into the treetops.

"Treatments do not prevent fires from starting, and they aren't necessarily intended to stop wildfires from spreading. In fact, the goal of ecologically based fuel reduction treatments is to restore the role of abundant low- to moderate-severity fire in fire-dependent ecosystems to reduce the risk of extensive high-intensity wildfires."

One way to reduce fuels is through thinning, which is the practice of reducing the number of trees in the forest by hand or with machines. Thinning, sometimes also referred to as fuel reduction, focuses on removing small trees and vegetation that could carry fire from the ground into the canopy, reducing the risk of high-severity fires.

Ideally, thinning is followed by prescribed burning, which removes surface fuels. This combination is generally the most effective for reducing fire hazards and promoting biodiversity.

Effective fuel reduction treatments protect large, old trees that tend to be naturally fire-resistant and have significant ecological and cultural value. The focus in fuel reduction treatments is on thinning younger trees that would have been killed by frequent fire historically, and which now create a risk to the older and larger legacy trees. Because of this focus on smaller trees, harvest-based fuel treatments rarely generate much revenue. When commercially valuable trees are removed, often larger trees, the funds may cover part of the cost of conducting prescribed burns, monitoring, and other forms of management.

Restoring the once abundant influence of low- and moderate-severity fire also offers other social and ecosystem benefits. Thinning and burning in partnership with local Indigenous knowledge supports cultural values, economies, livelihoods, and food and medicine security. Reducing forest density can increase resilience to drought, insects, diseases, and restore habitat for species dependent on open forests. For a deep dive on restoring prescribed fire, check out the video at the link below:

While thinning and burning are critical tools, they do not solve all of the problems associated with wildfires today. Locally-adapted, collaborative solutions must also include strategies that address fire-adapted communities such as:

• Home hardening
• Defensible space
• Managed wildfire
• Enhanced prevention
• Suppression planning

Case Study: Active forest restoration treatment (pictured below) at Sinlahekin Wildlife Refuge, Washington Department of Fish and Wildlife. Credit: John F. Marshall.

Success stories like  saving South Lake Tahoe from the Caldor Fire  in the summer of 2021 have demonstrated that placing fuel treatments around at-risk homes and communities can limit fire growth. The video to the left is a deep dive in how fuel treatments helped save homes in the Caldor Fire. Source: US Forest Service.

Focusing on the WUI alone is not effective. If fuels continue to accumulate across the landscape, the intensity of the eventual wildfire can overwhelm more localized treatments. Under these conditions, it is preferable to strategically place treatments across the landscape to dampen fire severity, reduce ember production, and give firefighters additional opportunities to intervene.

Fuel treatments are not just about protecting communities. They also enhance the health of fire-dependent ecosystems, stabilize carbon storage, and protect old-growth trees and forests and water supplies for communities.

Fuel treatments prioritize suppression resources where they are most needed and present an opportunity to reintroduce the benefits of frequent low- to moderate-severity fire. In many forests, the wrong kind of fire is an ecological concern.

The intensity of the 2021 Bootleg Fire exceeded fire suppression capacity for several weeks. The wildfire killed nearly all trees in its path over extensive areas (shown in red on the map above). Including old trees that took centuries to grow and that survived numerous fires during extreme droughts.

"Even at more than 400,000 acres, it is not the size of the fire that's uncharacteristic; it is the size of the patches of dead trees."

Even at more than 400,000 acres, it is not the size of the fire that's uncharacteristic, it is the size of the patches of dead trees. More than three-quarters of the forest that burned was ponderosa pine. Prior to fire exclusion, fires burned so frequently through the landscape that fuel conditions supported low- to moderate-severity fire effects.

For example,  in 1918, fires covering hundreds of thousands of acres burned on the same landscape,  also during extreme drought. After those fires, patchy open-canopy forest and old-growth trees survived on nearly all the areas burned. The old-growth trees killed in the Bootleg Fire had survived the 1918 and earlier fires precisely because frequent fires kept fuel loads low.

After more than a century of fire exclusion, some of the largest patches of live trees in the area burned by the Bootleg Fire were in fuel reduction projects.  The Black Hill Restoration Project , marked by the Klamath Tribes and treated with prescribed fire by the Forest Service after mechanical thinning, helped protect old-growth ponderosa pine.

Expanding opportunities to manage fire under milder weather conditions holds promise. Some land managers -- including those managing national parks and wilderness areas -- have allowed fires to burn under moderate fire weather and fuel conditions for the past few decades in remote areas. These managed wildfires have restored more characteristic fire regimes and landscape patterns. Fires are typically smaller, lower in intensity and severity, and more variable than the wildfires that make headlines. However, the dominant approach across most public lands is still to suppress fire.

Wildfire is a highly effective but blunt tool that is best paired with strategic fuel treatments in areas of high ecological, cultural, or social value. For example, a fire burning hot enough to reduce tree density may jeopardize legacy fire and drought-tolerant trees, even though conservation of those legacy trees might be a primary management objective. Strategic fuel treatments add more options for fire managers, making it easier to say "yes" to managed fire when the conditions are right.

Fuel treatments can help firefighters in several ways. Areas with reduced fuel loads can give firefighters a chance to stop a wildfire's progress. They can also be used as a base to start operations to remove fuel ahead of a wildfire.

However, this is not the primary goal. In fact, this approach would be counterproductive, since more effective fire exclusion only leads to increased fuel loads and more severe, uncontrollable fires. Increased use of managed wildfire to safely reduce fuels over large areas during mild weather will more effectively assist firefighting response and containment.

There is strong scientific evidence that even under extreme weather conditions, fuel treatments can be effective at lowering fire severity. For optimal results, treatments need to be carefully designed and situated, of adequate size, and followed with maintenance treatments such as prescribed burning or managed wildfire. Some critics have noted that treatments don't stop large fires. That is true, but that is not the purpose of fuel reduction treatments. The goal is to moderate fire behavior and reduce the negative impacts of more than a century of fire exclusion on ecosystems and society. Large fires have always been a part of fire-prone forests. Even in today's climate, fuel treatments can result in fire effects that preserve ecological and cultural values on the landscape, including biodiversity, water quality, timber and other forest products, climate adaptation, and community safety.

The current pace and scale of fuel reduction is insufficient, particularly given the increasing likelihood of large fires due to climate change. Most wildfires do not encounter treated areas which represent a mere ~1% of the area burned by wildfires.

While treating the entire landscape is not the goal, increasing the treated area is. Strategically placed fuel reductions across the landscape can maximize benefits, all while treating a relatively small portion of the landscape. Strategic placement of fuel treatments will be informed by knowledge of Indigenous burning practices, weather, ignition patterns, vegetation, topography, and threat to communities.

Across the West, collaborative partnerships involving tribes, environmental groups, landowners, resource managers, industry representatives, and local communities have helped identify where treatments will provide the most benefit for a broad range of objectives and make the best use of limited resources.

For example, the Rogue Basin Partners created the  Rogue Basin Strategy  to guide large-scale forest restoration projects throughout SW Oregon, one of the highest risk areas in the state of Oregon. The Rogue Basin Strategy was developed through a collaborative process that was informed by a rigorous scientific review and incorporated important community priorities, such as habitat protection, fire resilience, and economics. Creating a strategy helps shorten the planning time because objectives, priorities, modeling, and assessment of important resources to be protected has already been done.

Mechanical thinning, prescribed burning, and managed wildfire are the tools we have to reduce fuels. Each has its limitations, and each is needed in the right place. While we need to be realistic about the scale of the challenge, we can't use that to justify inaction.

Not necessarily. In fire-dependent, seasonally dry forests, dense forests and conifer plantations are highly susceptible to wildfires and drought. If the goal is to increase carbon storage to mitigate climate change, plantations are not a safe bet: when fire burns through dense young plantations, the result is often 100% tree mortality. A promising alternative approach to retaining and sequestering carbon in these forests is to thin them and retain the larger more fire-resistant trees. Thinning increases both the productivity of the remaining trees and their chances of survival from drought, insects and disease, and wildfires.

Even widely-spaced, fire-resistant trees like old-growth ponderosa pine are vulnerable to wildfires when surface fuel loads are high. Although most of the carbon in large fire-resistant trees remains on site even after being killed by fire, these trees will now decay, and, unless the fuels that accumulated under fire exclusion are reduced, the carbon they contain may be released in the next fire. In contrast, before fire exclusion these old-growth ponderosa pine trees survived numerous fires and continued sequestering and storing carbon.

In patches of high tree mortality, accumulated wood from downed trees can create conditions for high-intensity reburn events that can kill young regenerating forests and delay forest recovery. Even where wildfire effects are variable, post-fire fuels reduction may be required to increase resilience of the remaining forest to disturbance and climate change and protect valued cultural resources.

Commercial salvage logging, however, is rarely designed to maximize ecological outcomes or address fire risk. For example, while mature and old fire-resistant dead trees are often targeted for removal, they are important wildlife habitat and represent a relatively low fire risk compared to fine fuels and smaller trees.

Large patches of high-severity fire present additional challenges. High-severity fire in the right proportion can be ecologically beneficial. In forests with tree species that don't readily repopulate vast areas after disturbance, large patches may convert to shrub or grasslands after fire. If the goal is forest regeneration, it may be beneficial to reduce woody debris and flammable shrubs, while strategically planting seedlings in the sites most likely to support regenerating forest in the current climate.

Frequent low-severity fire historically maintained ponderosa pine forests and woodlands. After more than 100 years of excluding most fires, today's wildfires that burn a century of accumulated fuels during hot, dry weather can cause extensive tree mortality and severe soil damage, as in the Las Conchas Fire (pictured above) in 2011 in northern New Mexico. Recovery of forest ecosystems after such an uncharacteristically severe fire is challenging under current climate conditions, even on sites where mature trees thrived prior to the fire.

Fire is not only inevitable, it’s essential for maintaining these ecosystems and their functions. Restoring fire-excluded forests provides many social and ecological benefits, including stabilizing forest carbon, improving air quality, and increasing water availability. We can begin to recapture the influence of low- and moderate-severity fire by allowing more fires to burn during less extreme weather conditions when they’re easiest to extinguish and manage. Adaptation can be supported through strategically planned mechanical reduction of fuels, e.g., pre-commercial or commercial thinning, particularly when followed by prescribed burning or managed wildfire.

Despite calls to restore fire as a cultural and ecological process (e.g.,  The U.S. National Wildland Fire Cohesive Strategy ), the dominant approach to wildfire management continues to be aggressive suppression. Attempting to suppress all or most fires is a highly consequential active management prescription. Continued forest infilling and fuel accumulation predisposes forests to high-severity fire when fire inevitably returns, and leaves them vulnerable to increasing drought stress under a rapidly warming climate. 

As with any adaptive management approach, active monitoring and integration of lessons learned are critical, as is an honest assessment of the inherent risks of alternative actions or inaction. We cannot return landscapes to any historical condition or fire regime, nor is that a particularly useful goal at this point in time. Instead, it is urgent to use ecologically-informed strategies to adapt to a rapidly evolving future climate.