Stewardship matters: Case studies in establishment success of urban trees

Abstract

Urban tree planting initiatives aim to provide ecosystem services that materialize decades after planting, therefore understanding tree survival and growth is essential to evaluating planting program performance. Tree mortality is relatively high during the establishment phase, the first few years after planting. Qualitative assessments of programs with particularly high establishment survival can indicate best management practices for other programs to emulate. We present two case studies of high survival for young urban trees, from planting projects in East Palo Alto, CA and Philadelphia, PA, with the nonprofit organizations Canopy and University City Green, respectively. The Philadelphia case consists of two neighborhood planting projects: Kingsessing and Powelton. These trees were located mostly in streetside soil strips and sidewalk cut-outs. We used longitudinal tree survival and growth data, combined with detailed information about planting project characteristics and tree care practices, to make inferences about the underlying causes of establishment success. Annual survival during approximately six years after planting was 99.4% in East Palo Alto, 98.4% in the Kingsessing and 95.4% in Powelton. The East Palo Alto and Kingsessing outcomes are among the highest establishment survival ever reported. Our results indicate that planting and maintenance practices, program management and site characteristics contributed to establishment success. Stewardship was essential, both in terms of specific tree care activities and program processes to support those activities. These planting projects were implemented by small nonprofits which enhanced their staffing capacity through intensive volunteer and youth internship programs. Experienced volunteers, including professional arborists and landscape architects, served as leaders and trainers for other volunteers and interns. Climate-appropriate species selection and site conditions may have also played a role in East Palo Alto's exceptionally high survival. The survival and growth observed in these planting projects can be considered best case scenarios for neighborhood tree planting.