UC Davis

Internal wood deterioration is a leading cause of structural failure in urban trees, threatening the ecosystem services and public safety benefits that street trees provide, yet its prevalence and underlying drivers remain poorly understood across cities and species. To address this gap, we used resistance drilling (Resistograph) to assess internal deterioration in 323 street trees spanning seven species across three cities in the United States, Sacramento, California; Raleigh, North Carolina; and New Orleans, Louisiana. Approximately one in three trees showed evidence of deterioration in at least one drilling profile, indicating that internal deterioration is a common condition in urban tree populations, despite the absence of outward signs of damage. Using AICbased model comparison, we found that city of origin was the strongest predictor of deterioration prevalence, with trees in New Orleans showing higher deterioration probability than those in Sacramento. We attribute this pattern to New Orleans' warmer and wetter climate, recurring hurricane damage, and chronically waterlogged soils. These findings highlight the utility of resistance drilling as a valuable complementary tool for urban tree risk assessment and underscore that the urgency of deploying such assessments is not uniform across cities, municipalities facing warmer temperatures, higher precipitation, or recurrent storm damage may need to prioritize internal deterioration assessment more systematically.