Factors affecting long-term mortality of residential shade trees: Evidence from Sacramento, California

Urban tree survival is essential to sustain the ecosystem services of urban forests and monitoring is needed to accurately assess benefits. While some urban forestry studies have reported street tree survival, little is known about the factors influencing residential yard tree survival, especially over the long-term. We assessed residential shade tree survival in Sacramento, California over 22 years. Tree survival data were collected through field surveys and aerial photointerpretation. Survival analysis was used to evaluate longitudinal tree survivorship. Multivariate logistic regression was used to identify factors associated with mortality at the property- and tree-level. Our results showed that 22-year survivorship was 42.4% with 96.2% annual survival rate and 3.82% annual mortality rate. Our observed mortality was substantially higher than initial projections that were used to estimate long-term energy saving performance of the Sacramento Shade program. We found that higher mortality during the establishment phase was associated with greater number of trees delivered and with planting in low and high net property value properties (compared to those with medium net property value). For the post-establishment phase, trees with small mature size those planted in backyards and those in properties with very unstable homeownership were more likely to die. This study has implications for the development of data-driven urban forestry programs and provides more realistic assumptions to accurately estimate the long-term benefits of tree planting initiatives.