全球智库信息集成服务系统(G2TT): Managed Fires Can Help Mitigate the Risks Posed by Increasing Frequency of Wildfires

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Managed Fires Can Help Mitigate the Risks Posed by Increasing Frequency of Wildfires 智库博客

时间：2022-04-04 作者： Ann Bartuska;Matthew Wibbenmeyer 来源：Resources for the Future (United States)

As damages from wildfires mount, mitigation is becoming ever more important to stanch increases in wildfire activity. Given the scale of need for effective forest management, managed wildfires—employed with care and consideration—can be a viable option.

As damage from wildfires mounts, mitigation is becoming ever more important to stanch increases in wildfire activity. Several factors—including climate change and increased development in high-wildfire-hazard areas—underly the recent upward trends in wildfire damages. While these factors may not be easily addressed in the short or medium term, policymakers can improve on forest management practices—which to date have contributed to the increase in fire activity—through the use of targeted prescribed fires and managed wildfires. Managed fires are not without risk; however, not employing managed fires comes with its own risks. Given the scale of need for effective forest management, managed wildfires—implemented with care and consideration—can serve as a viable option.

In combination with climate change, which has increased fuel aridity and the length of fire season, many western forests are now primed for an increase in wildfire activity. Over the past several decades—and especially over the past several years—the western United States has seen a dramatic increase in wildfire activity and the costs those wildfires engender, including property destruction and health consequences of smoke emissions. Wildfires have increased in part due to nearly a century of forest management policies that took aggressive action in minimizing fires. In 1935, the US Forest Service set a goal of suppressing all fires by 10:00 a.m. the morning after ignition. Though the negative ecological consequences of this policy came to be understood by mid-century, and the so-called “10 a.m. policy” was rescinded by the 1970s, tolerance for wildfires remains quite low even today. As a result, many western forests have become dense with vegetation. These forests are at increased risk of insect and disease outbreaks, and wildfires that are not quickly contained in these areas have greater potential to become intense and dangerous.

Science and practice clearly have demonstrated that methods of forest fuel treatments such as thinning forest stands, combined with prescribed and managed fires, reduce wildfire intensity and rate of spread.

Science and practice clearly have demonstrated that methods of forest fuel treatments such as thinning forest stands, combined with prescribed and managed fires, reduce wildfire intensity and rate of spread. Thinning forest stands can reduce intensity and rate of spread by reducing understory brush and saplings that create “ladder fuels,” which facilitate the spread of fires from the forest floor up into the forest canopy. Thinning thus makes fires easier for firefighters to contain and can be especially effective when combined with prescribed burns to further reduce the fuel load.

However, the extent of forest management needs is substantial. According to modeling by the US Forest Service, fuel treatments are needed on approximately 51 million acres of federal, state, tribal, and private lands. At an average cost of $1,000 per acre (based on US Forest Service data), treating 51 million acres would cost $5 billion–$6 billion per year over ten years. Even the significant boost in wildfire mitigation spending provided by the 2021 Infrastructure Investment and Jobs Act does not approach the amount of funding that’s necessary to make a dent in forest management: the bill provides a total of $3.3 billion in funding for wildfire management, and that funding is spread over several years.

Where risks to life, property, and natural resources are low, wildfires can be approached opportunistically to accomplish fuel reduction at relatively low cost. This concept is at the heart of the new 10-year strategy developed by the US Forest Service, a plan known as “Confronting the Wildfire Crisis: A Strategy for Protecting Communities and Improving Resilience in America’s Forests.”

So-called “managed wildfires” are unintentional and unplanned fires, which are allowed to burn naturally in areas where fires would present relatively lower threat. For example, in the Eagle Cap Wilderness in northeast Oregon’s Wallowa Mountains, forest managers occasionally have allowed fires ignited by lightning to burn under careful supervision without suppression. In 2019, the Granite Gulch Fire was discovered deep in the wilderness in late July. Because the year had been wetter than normal, the fire was far enough away from populated communities, and the fire was discovered late in the fire season, close to season-ending rains, managers determined that allowing the fire to burn could achieve ecological restoration goals and constitute an acceptable risk. By burning and hence thinning fuels under relatively safe conditions, managed fires like the Granite Gulch Fire can reduce threats from potentially more hazardous wildfires in the future.

Nevertheless, such strategies are not possible everywhere. One example is the Angeles National Forest in southern California. Its high population density, difficult access, and high number of fire ignitions probably means that a prudent management approach involves aggressively extinguishing fires as soon as possible. In places like the Angeles National Forest, fuels management necessarily relies on a combination of forest thinning and the careful use of prescribed fire.

Managers then must weigh the potential risks against the potential benefits of “letting it burn”—bearing in mind forest health and the reduced risk of future fires.

In determining where and when to suppress wildfires—and when to allow managed wildfires themselves to help thin forests—managers are charged with implementing a risk-based approach that must consider the likelihood of fire escape and spread, fire intensity, and potential consequences for infrastructure. In assessing risks, managers draw on sophisticated fire-simulation models, which integrate data on topography, vegetation, and a range of potential weather scenarios. Managers then must weigh the potential risks against the potential benefits of “letting it burn”—bearing in mind forest health and the reduced risk of future fires.

It’s frequently difficult to find this balance, given that managed fires are not without risks—but not employing managed fires has its own risks. Given the scale of current needs for forest management, and increasing risks due to climate change, the opportunistic use of wildfires to avoid even more catastrophic losses can be a feasible and useful option.