Allometry of urban trees in subtropical Hong Kong and effects of habitat types

Abstract

Context: Quantitative information regarding tree species-specific size is an essential tool for landscape planning. It reflects tree-environment and human–environment interactions in the urban landscape. The effects of habitat types on tree allometry have seldom been evaluated. Objectives: Firstly, to derive size-related information of common urban tree species in Hong Kong. Secondly, to evaluate the effects of habitat types on tree allometry. Methods: A database of 28,622 trees was established by a field assessment. The allometric relationships (DBH-height and DBH-crown width relationships), by both OLS regression and quantile regression, and maximum size of 30 common urban tree species, and the effects of five main habitat types on tree allometry were determined. Species were assigned to groups according to dimensional traits by cluster analysis. Results: In general, the allometric relationships of height and crown width to DBH were significant and varied among species. The wide prediction intervals of the OLS regression indicated the high uncertainty of allometric relationships in our region. The 99th percentile crown width of most species reached 10 m, hinting the general failure of most habitats to meet the planting space requirement. Only two large-stature species have narrow crowns. Habitat types posed significant but small species-specific effects on tree allometry. Roadside tree pit was a particularly stressful environment. Conclusions: Our findings can act as a reference for landscape planning and management in Hong Kong and nearby cities, including species growth space requirement and habitat limitations. However, prediction of height or crown width from DBH must be carefully interpreted in our city.