By Lara A. Roman and Frederick N. Scatena
Philadelphia, PA (November 2011) – Low street tree survival rates and the resulting short life spans are frequently discussed but inadequately quantified in urban forestry literature. This study is an analysis of previously published survival rates to determine the typical street tree annual mortality rate, and from there, to estimate lifespan. The research also includes a case study assessment of street trees in Philadelphia 2–10 years after planting.
Reported survivorship rates from 16 previous studies were compiled. Estimated annual survival rates for individual past studies were mostly above 91.0%. Based on the meta-analysis, researchers estimated that street tree annual survival rates ranged from 94.9 to 96.5%, and street tree population half-life ranged from 13 to 20 years.
Estimated mean life expectancy ranged from 19 to 28 years, which is considerably longer than the 7- or 13-year street tree average lifespan reported in previous studies. Estimated annual survival rates and lifespan metrics were similar in the Philadelphia case study.
Urban forest researchers are encouraged to use demographic concepts and analyses in the study of tree survival and mortality, and to monitor tree survival at repeated time intervals every few years.
NOTE: Lara A. Roman is currently finishing multi-year field studies of urban tree mortality. A project in West Oakland will shed light on the balance of planting and mortality rates in a street tree population, and a project in Sacramento will evaluate mortality, health, and growth during the establishment phase for yard trees.