UW News

August 2, 2021

New report: State of the science on western wildfires, forests and climate change

UW News

wildfire in washington's methow valley

The Cedar Creek fire burns in Washington’s Methow Valley in late July 2021. Lucky Jim Bluff, near Mazama, is seen behind.Jessica Kelley

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 synthesis of the scientific literature 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.

two photos show the change over time in tree cover under fire exclusion policies

These two images show the same landscape in Washington state – the top taken in 1936 and the bottom in 2012. The top photo shows a landscape with less tree cover, maintained naturally through frequent historical wildfires. The bottom photo shows how forest cover has densified and expanded in the same area under policies of fire exclusion.John Marshall Photography

“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 University of Washington’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 findings were published Aug. 2 as an invited three-paper feature in the journal Ecological Applications.

A low-intensity prescribed burn to reduce fuels in a forest accustomed to wildfires.

A low-intensity prescribed burn to reduce fuels in a forest accustomed to wildfires.John Marshall Photography

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 UW researcher Keala Hagmann.

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.

This collection of photos shows the same forest with different treatments, clockwise from top left: No thinning (untreated); after thinning; spring after prescribed burning; summer after burning.John Marshall Photography

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.

untreated vs. treated forestland

An aerial photo showing untreated forestland (left) near Winthrop, Washington, across the road from an area that has been thinned (right).John Marshall Photography

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 Paul Hessburg, 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