Determinants of establishment survival for residential trees in Sacramento County, CA

Urban forests can provide ecosystem services that motivate tree planting campaigns, and tree survival is a key element of program success and projected benefits. We studied survival in a shade tree give-away program in Sacramento, CA, monitoring a cohort of young trees for five years on single-family residential properties. We used conditional inference trees to identify the most important risk factors at different life history stages, and survival analysis to evaluate post-planting survivorship. Our analysis included socioeconomic, biophysical, and maintenance characteristics. In addition to field observations of tree planting status, survival, and maintenance, we also collected property ownership information through the Multiple Listing Service and neighborhood socioeconomic characteristics from the U.S. Census. We found that 84.9% of trees were planted, with 70.9% survivorship at five years post-planting. Overall, 58.9% of delivered trees survived to five years, which the local program calls survivability. Planting rates were higher in neighborhoods with higher educational attainment, and on owner-occupied properties with stable residential ownership. Five-year survival was also higher for properties with stable homeownership, as well as for tree species with low water use demand. When we incorporated maintenance characteristics from the first year of field observations, factors related to tree care were important to survival. Many residents did not adhere to recommended maintenance practices. Our results illustrate the critical role of tree care and consistent homeownership to young tree mortality on residential properties, and suggest that survival assumptions in urban forest ecosystem services models may be overly optimistic.