An Integrated Vegetation Management (IVM) Approach for Shaded Fuel Breaks
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Shaded fuel breaks are areas of thinned trees and cleared undergrowth, designed to slow an advancing fire. These areas are not completely free of vegetation, but ideally are maintained to encourage growth of desirable, native vegetation that helps keep soil stable and naturally reduces populations of ladder fuel species. In many parts of the western U.S., integrated vegetation management (IVM), including use of selective herbicides, is making it easier to create and maintain shaded fuel breaks that can help protect lives and property in wildfire events. A silviculture manager in Oregon shares his experience creating shaded fuel breaks in a recent project.
According to the National Interagency Fire Center, 8.8 million acres of U.S. land burned in wildfires in 2024, putting the year at 127% above the 10-year average. If that sounds high, consider that by January 15 of this year, 30,000 acres had already burned — a rate six times higher than the average.1 With wildfire threats worsening, shaded fuel breaks can be a vital risk-management practice. In many parts of the western U.S., using integrated vegetation management (IVM) is making it easier to create and maintain shaded fuel breaks that can help protect lives and property in wildfire events.
Reducing ladder fuels
Ladder fuels is a term describing vegetation that allows a low-burning fire to climb vertically into a tree canopy, creating a crown fire. Typically comprising woody species and brush, ladder fuels contribute to fire intensity and speed.
Mark Gourley recently retired as the Silviculture Director for Cascade Timber Consulting, Inc. in Oregon. In that role, he managed a team of foresters in breeding, planting and harvesting trees. He’s also been on the front lines of wildfires as a firefighter and has witnessed the swift and devastating effects of ladder fuels.
“I’ve seen 100-year-old trees full of lichen and moss with rhododendron [ladder fuel] growing alongside,” Gourley described. “It will catch these old-growth trees on fire, explode the top of that tree, and then catch the one right next to it. All of the sudden, you’ve got five or six Roman candles. You can’t get in there to fight that fire. It’s too dangerous.”
A similar effect happens when ladder fuels ignite near utility lines. These fires can quickly get out of control, and infrastructure interruptions to communities can be both dangerous and costly. Gourley has seen forest fires in high winds spin life-threatening fire devils and grow hot enough to melt concrete.
A fire needs three ingredients to ignite and keep burning: oxygen, heat and fuel. This is known as the fire triangle. In the Willamette Valley where Gourley is located, there is always a dry season, and it’s usually accompanied by high winds. Hundreds of years ago, the native populations living in the area appreciated that with these conditions, fires were inevitable. They would conduct planned burns to limit the one side of the fire triangle they could control — fuel. Today, foresters and land managers use a similar technique in the form of shaded fuel breaks.
Fires need three things to ignite and continue burning: oxygen, heat and fuel. Shaded fuel breaks aim to limit the fuel side of the triangle.
Why shaded fuel breaks?
Shaded fuel breaks are areas of thinned trees and cleared undergrowth, designed to slow an advancing fire. These areas are not completely free of vegetation, but ideally are maintained to encourage growth of desirable, native vegetation that helps keep soil stable and naturally reduces populations of ladder fuel species. Shaded fuel breaks provide precious time for people to evacuate, and they create defensible areas where firefighters can do their work. Where less ladder fuel is present, fires also remain closer to the ground longer. “If we can keep flames knee high or lower, we can fight the fire more easily with firetrucks, hoses and foam, before they get up into the crown of the tree,” Gourley said.
An aerial view of a shaded fuel break. In these areas, trees are thinned out and woody ladder fuel vegetation is removed. Shaded fuel breaks provide areas for escape and fire defense.
Using IVM to maintain shaded fuel breaks
Creating a shaded fuel break begins with selective logging to create wide spaces between trees. As part of an IVM approach, cuttings are cleared away and the area can be treated with herbicides to control small trees and undergrowth. This can be done before tree removal using a broadcast approach. After removal, follow-up treatment with a hack-and-squirt method can help control specific plants.
Another option is to put the cleared vegetation through a chipper. In this method, herbicides are not used. Instead, chipping serves to move the flammable ladder fuel closer to the ground. It also creates a layer of mulch that can guard against soil erosion. However, chipping can be expensive. It also contributes to resprouting of unwanted vegetation, which can lead to more intensive maintenance in the future.
When using herbicides in an IVM approach for shaded fuel breaks, selectivity is important so that the area remains hospitable to native vegetation. Native species that grow lower to the ground can displace ladder fuels, helping to create a naturally resilient landscape over time.
In 2022, Corteva Agriscience studied combinations of selective herbicides in an IVM approach for shaded fuel breaks in California. The results showed good to excellent overall control of woody plant species one year after treatment. Additionally, herbaceous cover was not reduced during this time compared to non-treated areas.2
Shaded fuel breaks in Cascade-managed forests: A case study in IVM
After seeing the way shaded fuel breaks were working for a similar timber organization in California, Gourley brought the idea back to the team at Cascade Timber Consulting, Inc. Through consultation and partnership with local researchers and Corteva Agriscience, Cascade developed a plan for creating shaded fuel breaks to serve as defensible ridges in case a fire breaks out. The fuel breaks were established around existing logging roads, helping to protect escape routes for personnel and access for firefighters.
The Cascade project, initiated in 2023, utilized a broadcast treatment of Cleantraxx® herbicide (64 oz.) and Oust® Extra herbicide (4 oz.). Vastlan® herbicide was then used in a hack-and-squirt method to control rhododendron, vine maple and other hardwood ladder fuel species.
Gourley said herbicide treatments are more affordable than using a chipper and he feels confident in the environmental profiles of the herbicide options available. “We have these new chemistries that we know have less impact on soil and insects.”
The untreated image (L) shows a significant amount of woody and brush vegetation, such as rhododendron, which can grow up to 20 feet tall and act as ladder fuel in a fire. After commercial thinning and treatment with Cleantraxx, Oust Extra and Vastlan herbicides (R), ladder fuels have been greatly reduced, but low-growing native vegetation remains. This can help slow an advancing fire.
Choosing selective herbicides was also important for achieving one of the other goals for the fuel breaks: encouraging growth of local huckleberry. Generations ago, the native population noticed improved huckleberry growth after controlled burns. “We decided, let’s put something back that the wildlife can use,” Gourley said.
The huckleberries will be appealing to bears and birds, and perhaps one day, people can harvest them from the roadsides.
Huckleberries were planted in the fall of 2024, so observations are just beginning. The Cascade team is monitoring the growth of both the native vegetation and ladder fuels, plus checking for any compatibility issues with the herbicides and huckleberries. “If needed, we’ll shield the berries during later treatments,” Gourley said.
Gourley has been sharing his shaded fuel break methods with the U.S. Forest Service and other stakeholders in the area. He’s hoping the idea will catch on, including incorporating herbicides into the approach. “I know shaded fuel breaks can work,” Gourley said. With ongoing observations and research, the hope is that more organizations will gain confidence in using herbicides to help maintain them.
1 “North American Seasonal Fire Assessment and Outlook: Outlook Period January 2025 through March 2025,” National Interagency Fire Center, Natural Resources Canada and Servicio Meteorológico Nacional, January 16, 2025, https://www.nifc.gov/sites/default/files/NICC/2-Predictive%20Services/Outlooks/NSWF%20-%20Potential%20Outlook%20-%20Archive/2024/January%20%28JFMA%29/202401-JFMA.zip.
2 Corteva Agriscience data on file.
Cleantraxx® and Vastlan® are not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product labels for details. Always read and follow label directions.
Oust® is a registered trademark of Bayer.
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