Mature Trees May Be Protecting Homes From Wildfire. Fire Defense Guidelines Haven’t Caught Up.

One of the earliest and most visible consequences of climate change in the western United States is the rise of destructive wildfires. California has become the emblem of this crisis, but Oregon and Washington are increasingly affected as well. Homes and communities located in or near forests appear especially vulnerable. It seems intuitive to assume that forests—and the trees within them—ignite homes. Yet a growing body of post‑fire observations from landscape architects, fire‑adapted communities, and residents who have lived through recent disasters suggests a more complicated picture. These accounts indicate that mature trees may not be the threat we assume, but part of the protection we need.

What Defensible Space Means

Government agencies emphasize two main strategies for reducing wildfire risk : “home hardening,” which involves fire‑resistant construction measures, and the creation of “defensible space,” the landscape zones around a home that help slow fire spread.

While guidelines vary by region, defensible space creation generally includes:

• Zone 0 (0–5 feet): A non‑combustible area immediately around the structure

• Zone 1 (5–30 feet): Limited, well‑maintained vegetation

• Zone 2 (30–100 feet): Reduced vegetation and fuel loads

These guidelines are broadly sound. But as currently written, they do not distinguish between young, fire‑prone vegetation and mature, healthy trees that may actually help protect homes.

Evidence That Mature Trees Can Buffer Fire

In an article for the American Society of Landscape Architects, Ronnie Siegel raises concerns about removing large trees near homes. Drawing on field observations, mapping, and eyewitness accounts from the Eaton Fire in Los Angeles County, Siegel reports that the most combustible elements in the landscape were homes, cars, and other structures—not the surrounding vegetation.

The Eaton Fire followed the hottest summer on record, with minimal rainfall and strong Santa Ana winds that carried embers long distances. Yet post‑fire surveys revealed a striking pattern: houses were reduced to foundations while many trees, shrubs, and even lawns remained intact. Even species often labeled as highly flammable, such as pines and deodars, retained green needles despite scorched bark. Several homes that lacked adequate “home hardening” survived because they were shielded by mature native oaks.

Moisture appears to be the key factor. Plants that retain water—especially native species adapted to dry summers—are far less likely to ignite. Even non‑native species, when irrigated, can serve as effective ember buffers.

Other practitioners have noted similar patterns. In a webinar on fire‑resistant native landscaping, horticulturist Gregory Rubin emphasized that plant moisture—not species identity alone—largely determines whether vegetation ignites. Well‑irrigated native shrubs and trees, he explains, can slow or redirect fire movement. Likewise, in a presentation on post‑fire rebuilding, UC Berkeley professor Kristina Hill describes how an irrigated park with mature trees in Paradise, California, became an informal refuge during the Camp Fire because the trees offered more protection than the surrounding built environment.

These accounts do not constitute formal scientific studies, but they share a consistent theme: healthy, hydrated vegetation behaves very differently from the dry, stressed fuels that drive severe wildfire behavior.

Mature Trees in the Pacific Northwest

Working in western Oregon and Washington, I frequently encounter properties with mature Douglas firs and mixed conifer forests. Research on wildfire behavior in Pacific Northwest forests shows that mature forest patches rarely contribute significantly to fire spread. Even Douglas firs—often labeled as highly flammable due to their resin content—become more fire‑resistant with age.

Several characteristics make mature trees more resilient:

• Thick bark that insulates against heat

• High canopies that reduce the likelihood of fire reaching the crown

• Open crowns that limit crown‑fire potential

• Deeper root systems that help access moisture during dry periods.

• Wind buffering, which reduces ember travel

In short, mature trees are often less flammable than younger ones and can act as windbreaks that slow ember movement. Because they take decades to develop these protective traits, removing them carries long‑term consequences.

Moisture, Health, and Climate Stress

Of course, not every tree is an asset. Drought‑stressed, diseased, or poorly maintained trees can become hazards, especially after long dry spells. And no amount of vegetation management can substitute for home hardening—fire‑resistant roofs, ember‑proof vents, and non‑combustible materials remain essential.

But the emerging evidence suggests that defensible space guidelines, as currently written, may be too blunt. A five‑foot non‑combustible zone around a home makes sense. Removing ladder fuels makes sense. Removing young, dense, or unhealthy trees makes sense. Yet the removal of mature, healthy trees—especially in regions where they naturally occur—may be counterproductive.

An ongoing Case Study: My Own Property

I’ve taken this evolving understanding to heart on my own property in western Oregon. My home is surrounded by mature coastal redwoods, Douglas firs, cedars, and native hardwoods. Early on, I considered removing several large conifers near the house. Instead, I only removed smaller and less healthy trees to give the larger ones more space to grow vigorously. I also installed irrigation to keep both native and non-native species hydrated during the dry season, pruned trees to raise their crowns, removed ladder fuels, and maintained a five-foot non-combustible perimeter. The results are visible: my large mature trees thrive with the removal of competing smaller trees and the additional water they receive during dry months. My trees remain healthier and greener through late summer than nearby unirrigated stands.

Removing unhealthy trees and limbing up trees on my own property to increase fire safety.

Updating Guidelines for a Changing Climate

As climate change accelerates, we need defensible space guidelines that reflect the complexity of real landscapes. That means investing in systematic research on how mature trees influence ember travel, wind patterns, and fire intensity around homes. It means distinguishing between healthy and unhealthy vegetation. And it means recognizing that the built environment, not the forest, is often the most dangerous fuel in a fire.

Before we cut down trees that have taken a century to grow, we should be absolutely certain they are the problem. Right now, the evidence suggests they may be part of the solution.

Sources:

Siegel, Ronnie, April 2025: With a Landscape Approach, We Can Reduce the Risk of the Next Wildfire Disaster Published online at the ASLA (American Association of Landscape Architects) website. Last accessed January 2026.

Climate Forests Mature Trees are Fire Resistant , last accessed January 2026

Webinar:  Rubin, Greory “Fire-resistant Native Landscaping”, viewed October 2025

Webinar: Hill, Kristina Phd “Rebuilding For Fire Safety”  attended life , August,14, 2025