Root growth beneath sidewalks near trees of four genera

Abstract

Four genera of trees from four different plant families located in Cincinnati, Ohio, U.S., were examined: Gleditsia (honeylocust), Koelreuteria (goldenraintree), Quercus (oak), and Zelkova (zelkova). The trees were planted in tree lawns 3.5 m (11.5 ft) or less in tree lawn width. Approximately 1,100 sidewalk joints near the trees planted within the last 20 years were observed for the presence of a root. The incidence of one or more roots, 1cm (3/8 in.) in diameter or larger growing under the sidewalk at sidewalk joints within 1.8 m (6 ft) of the main stem was noted. The probability of finding a root growing underneath the sidewalk was modeled against the time since the tree was planted, trunk diameter, and tree lawn width. It was noted that the probability of finding a root approached 100% as trunk diameter approached 30 cm (12 in.), with some variation among genera. Gleditsia developed roots growing beneath the sidewalk at the smallest trunk diameter, followed by Zelkova, Koelreuteria, and Quercus. Time since planting and tree lawn width were less significant predictors of root presence than trunk diameter. Overall, Quercus produced the fewest roots of the four genera that were detected beneath the sidewalk.