Building density, not trees, drove home loss from Los Angeles firestorms, says new study
A scene of the destruction in the aftermath of the fire in Paradise, California in 2019. Cal Poly photo by Joe Johnston.
Findings suggest policymakers focus on home hardening over tree removal
– A new peer-reviewed study by researchers from California Polytechnic State University found that building density, not urban trees, was the strongest predictor of whether homes were destroyed during the Southern California firestorms of January 2025.
The research team examined 15,082 structures and 52,893 tree canopies within the Eaton and Palisades fire scars and evaluated the relative associations of urban canopy and structure density with structure damage.
“Our study shows that during extreme urban firestorms, houses become the primary fuel source,” said Reed Kenny, a biological sciences lecturer at the university and the study’s lead author. “Once fire enters a neighborhood, structure-to-structure spread matters far more than the presence of trees.”
The study, “Urban trees and structure loss in the 2025 Eaton and Palisades fires,” appeared online in April and is scheduled for print publication in July in the “Urban Forestry & Urban Greening” journal. The article was coauthored by scientists and faculty from the university and the Urban Forest Institute, a nonprofit organization focused on sustainable urban forest management.
Researchers examined the Eaton and Palisades fires, two of the most destructive urban-interface fires in California history. The study used CAL FIRE damage inspections, building footprint data, LiDAR mapping, satellite imagery, and wind modeling to evaluate factors influencing structure loss.
The researchers concluded that homes located in densely packed neighborhoods were significantly more likely to burn than homes in less dense areas.
Across both fires, each additional nearby structure per hectare increased the probability of structure destruction. Researchers found the influence of tree canopy was minor, inconsistent and, in some cases, associated with lower losses.
The Palisades and Eaton fires began Jan. 7 in Los Angeles County and burned areas including Pacific Palisades, the forested slopes between Santa Monica and Malibu, and the unincorporated community of Altadena.
Together, the fires killed 30 people and destroyed more than 16,000 homes and businesses, causing an estimated $76 billion to $131 billion in losses.
Key findings from the study included that building density was the strongest predictor of home loss in both fires, homes closer to neighboring buildings were more likely to be destroyed, tree canopy effects were minor and contradictory between the two fires, and simulating the removal of all tree canopy within two meters of homes produced only small reductions in predicted losses.
The study also examined implications for California’s Zone Zero defensible space regulations, which may require vegetation removal within the first 5 feet around structures to create ember-resistant zones.
Researchers said policymakers should be cautious about removing urban tree canopy without stronger evidence that trees are major drivers of home destruction in dense urban firestorms.
The study noted that urban trees provide shade, cooling, stormwater capture, cleaner air, and public health benefits. Researchers said large-scale canopy removal could create environmental and human costs while doing little to reduce losses in similar fires.
Instead, the study suggested communities may benefit more from focusing on fire-resistant building materials, ember-resistant vents and roofs, increased spacing between structures where possible, neighborhood-scale fire planning, and maintenance practices such as pruning and leaf litter removal.
Researchers concluded that future wildfire policy should prioritize home hardening and urban design while balancing the benefits urban trees provide to communities.
Read an abstract of the research here: https://www.sciencedirect.com/science/article/abs/pii/S1618866726002104.
Liberalism caused this disaster. Everyone who has followed this knows it. Cutbacks in funds for the fire department, disputes over vegetation, failure of governance, going to Ghana, two reserviors that remained dry. The article fails to address the root causes.
Liberalism caused this disaster. Everyone who has followed this knows it. Cutbacks in funds for the fire department, disputes over vegetation, failure of governance, going to Ghana, two reserviors that remained dry. The article fails to address the root causes.