The effect of cables and leaves on the dynamic properties of red oak (Quercus rubra) with co-dominant stems

Abstract

In the United States, cabling is a common arboricultural practice intended to reduce the likelihood of failure of weakly attached or overextended branches, yet no studies have investigated whether this is true. We tested ten red oaks with and without (i) steel support cables and (ii) leaves using a conventional pull and release test. From acceleration time histories of freely swaying trees, we determined their natural frequency and damping ratio. Red oaks with cables had greater natural frequencies than trees without them because the cable increased trees’ stiffness. Red oaks had greater natural frequencies when they were leafless, since the overall mass of the tree without leaves was smaller. Red oaks had greater damping ratios when they were in-leaf—presumably because of aerodynamic drag, but installing a cable did not affect the damping ratio. The latter finding suggests that the cable only affected trees’ stiffness. Practitioners can use the findings to better understand the implications of installing support cables in trees, but additional work is needed to consider related variables such as the tension and height at which cables are installed.