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Arboriculture & Urban Forestry Online
Volume 48, Issue 4 — July 2022

Quantitative Tools for the Prediction of Pavement Damages Associated with Urban Trees

Louis S.H. Lee

Abstract: Background: Tree pits are urban green infrastructures in paved areas. But tree roots and flares, especially of larger trees, may come into conflict with pavement, resulting in tree health decline and repair costs. This study aimed to (1) establish allometric relationships between diameter at breast height (DBH) and trunk flare diameter (TFD) of common urban tree species, and (2) identify factors affecting the presence and magnitude of protruding roots and flares. Methods: The terms “protruding roots” and “protruding flares” were strictly defined as roots and flares reaching or exceeding the border between the open soil and the adjacent paving material. The study surveyed 1,100 trees of 14 species planted in tree pits in Chai Wan, Hong Kong. Results: DBH was a significant predictor of TFD but was less significant when trees with protruding roots or flares were considered separately. In most logistic models, DBH was significantly and positively related to the odds ratio of the occurrence of protruding roots and flares. Overall, a centimetre increase in DBH brought 1.049 to 1.114 times higher likelihood of protruding roots and flares. Multiple regression suggested that for every square-metre increase in the open soil area in tree pits, the maximum length of protruding roots and flares increased by 0.154 to 0.172 m. This relationship could be attributed to the underlying association between DBH and open soil area. Species-specific regression results were tabulated to allow more accurate estimation of protruding roots and flares. Conclusion: For urban planners and pavement engineers, the approach recommended in this study could be adopted to optimise urban greening and pavement design.

Keywords: Pavement Damage; Protruding Roots; Tree Care; Tree Pit; Trunk Flare; Urban Green Infrastructure.

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