Stability of four urban trees species in engineered and regular urban soil blends

Abstract

Urban trees face a litany of challenges from heat and air pollution through to undesirable soil conditions that hinder root development and negatively impact on overall growth and stability. Engineered soils have been designed to improve root colonisation zones and enhance soil volumes for trees with limited rooting space. In this study, force was applied to determine trunk resistance using a pulley and winch under regular and heavily irrigated soils to understand the stability of four tree species (Peltophorum pterocarpum, Samanea saman, Pouteria obovata and Calophyllum inophyllum) growing in different soil blends after 5 years of growth. Previous research has confirmed that these soils are beneficial to growth. Trees grown in skeletal soils (stone and gravel soil blends) were significantly more stable than trees planted in structural cells and compacted soils. Less force was required to deflect trees in near-saturated soils as compared to those in soils with less moisture. Samanea saman was found to be most stable across the various species and was especially so in the skeletal blends. The relationship between tree stability and engineered blends has received limited scientific scrutiny and the conclusions here provide evidence that some species are more susceptible to uprooting because of limited rooting space and that stability might be enhanced using engineered blends.