Deep-rooted trees for urban environments: Selection and propagation

Abstract

Seedling liners of three tree species (Fraxinus uhdei, Pistacia chinensis, and Zelkova serrata) were planted in the field and grown for 18 months. Pneumatic air excavation followed by digital photography, three-dimensional modeling, and root analysis showed there were significant differences in root architecture among the three species and within each species' population. Among the three species, Pistacia chinensis had, on average, the deepest, most vertically oriented root systems and Fraxinus uhdei and Zelkova serrata the shallowest; however, there were shallow-rooted and deep-rooted genotypes in each species. Shallow-rooted and deep-rooted genotypes of Fraxinus and Zelkova selected from the seedling populations were propagated vegetatively by cuttings, planted in the field, and grown for 5 to 6 years. On excavation and three-dimensional model creation, the root architecture of the cutting-propagated clones was assessed using liminal angles and individual root angles. Cutting-propagated clones of shallow-rooted parents were shallow-rooted; thus, they maintained the parents' root architecture. Cutting-propagated clones of deep-rooted parents were also shallow-rooted; they did not maintain their parents' root architecture. Results are discussed in terms of genetic, physiological (e.g., auxin treatment, adventitious root formation), and environmental (e.g., soil moisture) factors that can affect tree root growth and development. ©2008 International Society of Arboriculture.