Post-fire recovery is faster than expected in the forests of the western Cascades, SEFS-led study finds

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Photo by: Sofia Kruszka

New research published by the SEFS Harvey Lab looks at how forests west of the Cascade crest in Washington and northern Oregon are recovering from recent large and severe fires. The answer? Surprisingly fast, when compared to many interior dry forests elsewhere in the western US. When it comes to recovery, the age of the forest prior to the fire had an impact, with old-growth forests showing more abundant and diverse tree seedlings establishing after the fire compared to forests that were younger and simpler in structure before the fire. 

In other forests of western North America, post-fire tree regeneration has slowed or potentially stopped altogether in some cases due to increases in fire size, severity, or frequency in combination with warmer and drier post-fire conditions. However, even after recent large and severe fires, the burned forests on the west side of the Cascades are exhibiting rapid natural post-fire tree regeneration and forest recovery. 82% of stands where the fire was severe and killed all the pre-fire trees had post-fire regeneration rates that exceeded Washington state forest practice minimum density thresholds by 3-5 years post-fire, suggesting that, overall, naturally occurring tree regeneration is sufficient for meeting management objectives of forest recovery. Seedling density increased in areas with cooler and wetter conditions and with proximity to surviving live trees; but, surprisingly, tree seedlings were abundant at distances up to 400 meters from the nearest live tree. As lead author and PhD student Madison Laughlin put it “Seeing abundant post-fire tree seedlings at such far distances from live mature trees suggests we may be underestimating seed availability following severe fire in these forests. Seeds might be dispersing farther than previously thought, or some cones on trees that were killed by fire might persist, if not burned, and provide an on-site seed source. These are hypotheses we are currently testing in our ongoing research.”

Lead author and SEFS PhD student Madison Laughlin. Photo by: Brian Harvey

This research highlights the importance of old-growth forests and suggests that the complexity in older forests promotes forest resilience to severe, stand-replacing wildfires. Because these areas burn infrequently relative to other drier forest ecosystems in the western US, little research has been conducted on post-fire regeneration in the region. As warming continues due to climate change and wildfire potential increases in northwestern Cascadia, it will be critical to understand how forests are re-establishing with trees after severe fire. “Post-fire recovery of forest ecosystems is something that can play out over very long time scales, especially in forests that are characterized in part by infrequent and severe fires. These findings are encouraging signs for forest resilience to these kinds of fires in the northwestern Cascades, and our future re-measurements of these plots will help us track long-term recovery”, mentioned SEFS Professor Brian Harvey, senior author on the study. “We’re also measuring multiple complementary response variables in coordinated studies so we can track things like the entire post-fire plant community as well as the post-fire fuel profiles and potential for subsequent reburns in these areas. This collectively is helping us build understanding of how fire affects a wide diversity of ecosystem components, and with our partners, co-develop strategies for managing that diversity pre- and post-fire.” 

The study was published in the journal Forest Ecology and Management, led by SEFS PhD student Madison Laughlin with coauthors Jenna Morris, Liliana Rangel-Parra, and Brian Harvey from Professor Brian Harvey’s lab in SEFS, and Drs Dan Donato and Joshua Halofsky at the Washington Department of Natural Resources. It uncovers a critical piece in our understanding of forest resilience and managing post-fire landscapes. The findings suggest a high capacity for recovery from large and severe fires that are characteristic in forests west of the Cascades in Washington and northern Oregon—particularly in areas with old-growth forests.

This research was supported by a grant from the United States Geological Survey Northwest Climate Adaptation Science Center, the USDA Forest Service – PNW Research Station as part of the Westside Fire and Climate Adaptation Research Initiative, the Good Neighbor Authority between the USDA Forest Service and Washington Department of Natural Resources, the Jack Corkery and George Corkery Jr. Endowed Professorship in Forest Sciences, and support from Jerry Franklin.

SEFS researchers contribute to publications on smoke hazards from prescribed burns in California

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SEFS Research Associate Professor Ernesto Alvarado was a co-author on two recent publications that help forest managers assess risk from prescribed burns in California’s Central Sierra range. Co-author Joe Wilkins, Assistant Professor at Howard University, was a postdoc in Alvarado’s lab during the research. The team created a framework to help land managers assess the air quality implications of land management scenarios with varying levels of prescribed burning. Using models that estimate the smoke efforts on ecosystems and nearby communities, the researchers found that moderate amounts of burning would reduce overall smoke levels.

Their findings were published in Nature Sustainability and Environmental Research Letters in December 2023, and January 2024 respectively.

While wildfire increases, SEFS-led research on historical fire regimes shows the Pacific Northwest is in a fire deficit

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Prof Brian Harvey’s Lab conducted research of the Norse Fire from 2017 in the Snoqualmie National Forest.

Despite increasing wildfire activity over the last few decades, contemporary fire years burn less than a quarter of the area burned on average historically. A recent study led by SEFS affiliate faculty members and Washington Department of Natural Resources forest ecologists Dan Donato and Josh Halofsky, and SEFS associate professor Brian Harvey, compared fire activity between 1985 and 2020 to historical fire amounts and severities. SEFS affiliate assistant professors Alina Cansler, Derek Churchill, and Ryan Haugo were co-authors on the paper, published in the journal Forest Ecology and Management.

Prior to the 20th century, the drier, inland forests of eastern Washington and Oregon experienced active fire regimes, both from lightning ignitions as well as Indigenous cultural burning practices. The frequent fire activity played an important role in the ecosystem, removing grasses, shrubs, small trees, and dead leaves that act as fuel for fires, and maintaining forest health by promoting fire-resilient species across the landscape. Fire suppression practices, which became common in the 1900s, dramatically lowered the amount of fire activity at all severity levels. Combined with other land-use impacts, the resulting denser, simpler makeup of modern forests is less resilient to climate change and ecological disturbances.

Now, the forests of eastern Washington and Oregon exist in a fire deficit, with less area burned in all severity types than occurred historically. The biggest deficits of area burned compared to historical rates are for low- and moderate-severity fire, but even high-severity area burned is below historical rates for most years in most forest zones.

Understanding the context of fire in this region may reframe how we view wildfire in relation to forest heath and re-evaluate what constitutes a ‘good’ or ‘bad’ wildfire year. Even in large wildfires, much of the area burned is likely contributing to forest restoration objectives. The “work” that low- to moderate-severity fire can do – thinning the forest to reduce stand densities to favor larger fire-resistant trees, and breaking up the homogenous, dense stands of modern forests – often aligns with the goals of restoration efforts on a larger and more effective scale.

“Often, fire years get cast as ‘bad’ mainly based on area. This analysis shows that that’s too simplistic, and maybe even just incorrect. On average, more than half of that fire is doing beneficial work of some kind,” said Donato.

Large wildfires carry clear risks and negative impacts to communities, such as loss of life and property, burning municipal watersheds, or affecting resources of value. But classifying fires based on area alone fails to recognize the benefits that can also occur. “It’s complex, because within the total area burned by wildfires there is a broad diversity of outcomes,” said Harvey. Small fire years lower certain risks but also further exacerbate the fire deficit, and consequently, lessen the landscape’s resilience. A more comprehensive method of assessing fire impacts, the authors suggest, would consider both the negative impacts and the “work” accomplished by wildfires.

The study highlights the need for restoring fire-dependent forests through a combination of forest thinning, prescribed burning, and managed wildfires. “Forest restoration is expensive and difficult. Managed wildfire, and the good work that some fires do, is a really important tool in the toolbox that can expand the area of our effective restoration treatment,” said Donato.

Credit: University of Washington

The study does not suggest a return to historical fire regimes, given the vast increases in infrastructure and human populations, but provides critical context for recent trends and future expectations in wildfire activity.

“This changes what our baseline expectations for a fire year should be. It’s useful to think about what this means for the additional impacts of fires as well, whether it be smoke or impacts on ecosystems and wildlife. Our baseline for all of those things, for our lifespans, is probably anomalously or artificially low,” said Harvey.

As annual area burned increases due to warming temperatures and increased drought, the relationship between high-severity and low- to moderate-severity wildfires may change in surprising ways, the authors noted. But harnessing the work of wildfire in appropriate places and under safe conditions, while minimizing negative impacts is an important mechanism for restoring resilient forests.

SEFS and U.S. Forest Service researchers develop wildfire modeling tool for the Pacific Northwest and beyond

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SEFS research scientist Susan Prichard, alongside colleagues from the U.S. Forest Service’s Pacific Northwest Research Station — Paul Hessburg, Nicholas Povak and Brion Salter — and consulting fire ecologist Robert Gray, have developed a tool for modeling wildfires that could help managers and policymakers better understand long-term consequences of different fire management practices and policies.

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.

The researchers applied REBURN to a region in north-central Washington, and found that setting prescribed burns and allowing smaller wildfires to burn can yield more varied and resilient forests over time.

As wildfire activity increases in forests, SEFS-led research helps predict wildfire severity based on fire size

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When wildfires cross a landscape, the severity of the burn isn’t uniform over the area impacted. Areas where most or all trees are killed by fire are considered “high severity burns.” The shape and size of high severity burned patches within fires play an important role in forest resilience and fire regimes, and have been difficult to predict.

person in a orange vest laughing in a forest
Michele Buonanduci and students from Prof Brian Harvey’s Lab conduct research of the Norse Fire from 2017 in the Snoqualmie National Forest

New research led by recent SEFS alumna Michele S. Buonanduci, a member of SEFS Associate Professor Brian Harvey’s lab, identifies a method to predict burn severity for future fires by looking at the relationship between fire size and patterns of burn severity. The researchers used data from over 1600 fires occurring in the Northwest US between 1985 and 2020 to see how relationships between fire size and severity vary across space and time, and found that the larger the fire, the higher the likelihood of large, contiguous, simple patches of high severity burned area. This relationship was consistent across the Northwest US and throughout the 35-year satellite record used in the study. Published in Ecology Letters, these findings provide a way to predict fire severity and impact based on projected fire sizes for near-term fires.

“It’s really difficult to plan for future fire activity if we don’t have a sense of what these fire severity patterns might look like,” said Buonanduci.

Given the complexity of the factors that influence fire severity, including topography, vegetation type, and weather, projecting future burn impacts is challenging. “A really wide range of severity levels and patterns are possible at any given landscape and just might depend on the weather at the time of burning,” said Buonanduci.

With collaborators from the Washington Department of Natural Resources, Buonanduci and her co-authors sought to anticipate the types of spatial patterns we might see in future fires, given projections for fire size.

Fire severity directly affects post-fire seed availability and dispersal, rates of forest regeneration, carbon uptake, and landscape change to non-forest. When you have large, contiguous high severity burn areas, forests are more likely to transition to non-forest vegetation as it’s more difficult for the remaining unburnt seed sources to reach the interior of the burn area than it would be in smaller, patchy burn areas.

“Those high severity patches are often where management intervention is most needed in terms of replanting with tree seedlings following fire. So having a sense of the range of ecological effects we might expect is going to be really important for forest managers working in a variety of contexts,” said Buonanduci.

aerial view of a burned forest
Students from Prof Brian Harvey’s Lab conduct research of the Norse Fire from 2017 in the Snoqualmie National Forest

Already, the results of this work are in use to better prepare land managers and communities for future fires. Buonanduci and her collaborators are using their findings to make projections for potential ecological effects of fire in western Washington and northwestern Oregon in the near future.

Co-authors on the study included Daniel Donato and Joshua Halofsky, SEFS affiliate assistant professors with the Washington State Department of Natural Resources, and SEFS alumna Maureen Kennedy, associate professor of quantitative wildfire ecology at the School of Interdisciplinary Arts and Sciences at UW Tacoma.

This work was funded by a US Geological Survey Northwest Climate Adaptation Science Center award and a Graduate Research Innovation award from the Joint Fire Science Program.

SEFS wildfire and forest management research highlighted in publications and presentations

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SEFS Professor Brian Harvey and students in his lab recently published papers on wildfire and forest management, including how fire potential and carbon storage after beetle outbreaks can be changed by forest management decades prior (Ecosystems), how forest resilience is affected by the combination of wildfire severity and post-fire climate conditions across the western US (Proceedings of the National Academy of Sciences), and how wildfire severity in areas experiencing more than one fire in recent decades are reshaping forest landscapes and forest resilience across the northwest US (Global Ecology and Biogeography). Harvey and students, as well as SEFS Assistant Professor Brittany Johnson, also presented at the Oregon Post-fire Research and Monitoring Symposium in February, including the following recorded talks:

RAPID Response: Brian Harvey to Study Re-Burned Yellowstone Forests

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by Karl Wirsing/SEFS

In 1988, wildfires burned about a third of Yellowstone National Park’s forests. Most of those wooded areas hadn’t burned in 100 to 300 years, largely within the average burn cycle for those forests, and they bounced back really well from the disturbance. But what happens when the next fire comes far sooner than the average? With shorter-interval burns and changing climate conditions, will the younger trees and forest be as resilient to a severe fire? Along with collaborators at the University of Wisconsin, Professor Brian Harvey will try to answer those questions, among others, this summer as part of a new National Science Foundation grant for Rapid Response Research (RAPID).

A lodgepole forest in Yellowstone that naturally reseeded after the 1988 fires.

RAPID grants are a special category for funding research that needs to be carried out immediately. They provide a one-year pulse of money for time-critical projects that can’t wait for the usual funding cycle. In this case, more than 10 thousand hectares of forest in Yellowstone did in fact re-burn last summer—only 28 years after the 1988 fires—so this summer will be the first and best opportunity to observe how these forests respond to the short-interval disturbance. “This grant provides an awesome opportunity to get there as soon as the forest is likely to show signs of resilience, or if it is not going to be as resilient,” says Brian. “This is the key time and place to be testing these questions.”

Natural disturbances, of course, are integral to forests worldwide, but conifer forests in western North America are facing warmer temperatures and larger, more severe wildfires than at any time in recorded history. Changing climates—with hotter, drier summers—are increasing disturbance frequency in some areas, and disrupting long-established patterns of forest regrowth and succession. In Yellowstone’s forests, the dominant species is lodgepole pine, which has closed, serotinous cones that release their seeds only in response to fire. Nearly all of the seedlings then establish one year after a fire; historically, they’ve then had many decades to grow and start producing cones (and seeds) of their own before the next burn. But instead of a fire interval of 150 to 300 years, these Yellowstone forests could start seeing new fires within a matter of a few decades. “Some systems are used short-interval fires,” says Brian. “But throughout much of Yellowstone, that’s a novel thing.”

The ecological consequences of these changing fire regimes are unclear and could be profound in the next century. The results of this study, in turn, could be widely relevant for understanding abrupt changes in forest ecosystems across the globe.

“This project is a unique opportunity to test what’s going on at the leading edge of climate change and changing fire regimes in these areas,” says Brian. “We’re really seeing the start of conditions in Yellowstone that may be heading outside the range we’ve seen in the paleo-ecological record. No matter what we find, it’s going to be extremely exciting, and very important. On one hand, these ecosystems can always surprise us in their resilience. On the other hand, as many times as we’ve been surprised by their resilience, we may be heading toward a state where things could be changing pretty rapidly.”

Similar to the sites Brian will be studying this summer, this lodgepole pine forest—originally burned in the 1988 fire—was re-burned in 2012 (with this photo taken in 2015).

Starting this July, Brian will head out to the burned sites in Yellowstone with his incoming master’s student, Saba Saberi, along with an undergrad field intern. They will meet up with a team from the University of Wisconsin, and together they’ll be investigating and measuring a number of factors for how the shortened fire interval is affecting the forest, including burn severity, post-fire tree seedling establishment and carbon storage.

A major component of this research, which Brian’s master’s student will be leading, involves studying how well satellites can measure burn severity in forests that are still very young since the last severe fire. “We have well-developed satellite indices to measure burn severity in forests, but most of these indices have really only been tested on older forests with much greater live biomass,” says Brian. “However, when fire burns through a dense stand of 25-year-old trees, we don’t know how accurately the satellite can detect burn severity. This is a big part of what Saba will be testing in her master’s research at SEFS. “Calibrating these satellite indices will allow us to investigate spatial patterns of burn severity over much broader scales, and gain insight into how fire regimes may be changing right before our eyes.”

The RAPID grant provides a total of $200,000 in funding, with just under $60,000 coming to Brian for his role in the project, and the rest supporting his collaborators at the University of Wisconsin.

Also joining the crew in the field will be a freelance writer from the New York Times to spend a weekend a write a store about the project. The Discovery Channel will be sending a team, as well, as part of documentary about the research on climate change and fire. Brian and his collaborators plan to produce a series of mini-documentaries (5-8 minutes in length), in English and Spanish, to explain effects of increased fire activity and climate warming on western forests to a wide audience.

It’s going to be a packed July for Brian and his partners, and we look forward to hearing reports from the field!

Photos © Brian Harvey.