When the Palisades and Eaton fires ignited on January 7, 2025, across Los Angeles County, they would become two of the most destructive urban-interface fires in California history—together killing 30 people and destroying more than 16,000 homes and businesses. As researchers from Cal Poly and the Urban Forest Institute combed through the wreckage, they discovered something counterintuitive: the trees that many blamed for the devastation were not the primary culprit. Instead, it was how close the houses stood to one another.
The study, published in Urban Forestry & Urban Greening, examined 15,082 structures and 52,893 tree canopies within the Eaton and Palisades fire scars. Using CAL FIRE damage inspections, building footprint data, LiDAR mapping, satellite imagery, and wind modeling, the team evaluated what actually predicted whether homes would survive. The findings were clear: building density was the strongest predictor of home loss in both fires.
"Our study shows that during extreme urban firestorms, houses become the primary fuel source," said Reed Kenny, a Cal Poly biological sciences lecturer and the study's lead author. "Once fire enters a neighborhood, structure-to-structure spread matters far more than the presence of trees." Homes closer to neighboring buildings were dramatically more likely to be destroyed. Each additional nearby structure per hectare significantly increased the probability of destruction—a pattern that held consistently across both fires.
By contrast, tree canopy effects were minor and contradictory. In some cases, trees were actually associated with lower losses. When researchers simulated removing all tree canopy within two meters of homes, the reduction in predicted losses was only small. The finding matters deeply because California is now implementing Zone Zero defensible space rules that may require removing vegetation within five feet of structures. The new research suggests policymakers should pause before scaling up such removals.
Urban trees are not a luxury in warming cities. They provide shade and cooling, capture stormwater, clean the air, and deliver documented public health benefits—amenities that become more valuable as climate extremes intensify. Large-scale canopy removal to address fire risk alone could create new environmental and human costs while doing relatively little to reduce losses in the kind of dense urban firestorms that destroyed Los Angeles neighborhoods in January 2025.
Instead, the Cal Poly team argues that communities may gain more meaningful protection by focusing on what actually stops fire from jumping between homes: 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. The reframing matters. As wildfire disasters increasingly move from forests into suburbs and cities, the question shifts from "Are trees the real problem?" to "Are vulnerable building characteristics the larger risk?"
The research offers policymakers a path forward: future wildfire policy should prioritize home hardening and thoughtful urban design while preserving the trees that communities depend on for livability and health. In dense urban areas facing extreme fire, it turns out, good neighbors—ones with some space between them and resilient exteriors—matter more than shade.